A SUMMARY OF PhD PROJECTS 2004

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A summary of PhD Projects 2003/2004

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Department of Electrical Power Engineering Faculty of Information Technology, Mathematics and Electrical Engineering

Norwegian University of Science and Technology This annual report gives an overview of current dr.ing research projects at the Department of Electrical Power Engineering. The folder contains a short status report of each project. Currently 29 students are registered in our PhD program, of which approximately 4 present dissertation each year. The department has 10 professors, 3 associate professors and 4 assistant professors. In addition to the scientific and administrative staff, the department house a mechanical workshop and an electrotechnical laboratory employing 6 people. The following three fields mainly cover the Research activity at the Department:

• Power Systems • Electrotechnical Materials and Installations • Energy Conversion

The PhD projects presented here are based on topics from all these areas. The research projects are both theoretical and practical and based on extensive use of our computer and laboratory resources. The projects are also influenced by our collaboration with industry and our co-operating institution SINTEF Energy Research AS. Since the PhD projects represent an important part of the department research this folder also gives a description of the department and the professors’ research activity. The nominal duration of PhD program is 3 years for full- time researchers of which half a year normally is devoted to post graduate courses. However, a typical PhD study last for 4 years, and during the additional year the researchers are involved in university/educational duties. For further information about the research projects presented, please contact the individual student given by name in this folder. For more information on previous projects, please contact the Department. NTNU, February 2, 2004 Robert Nilssen Professor

CONTENTS

PhD student: Supervisor: Title: p

Adhikary, Brijesh Holen, Arne T Electronic load controller and WAR compensator design for a micro grid system

2

Andreassen, Pål Undeland, Tore M. Power Electronics in Distributed Generation of Electrical Energy

4

Belsnes, Michael Fosso, Olav B Optimal utilization of the hydropower system 6

Bjerkan, Eilert Høidalen, Hans Kr. High frequency modelling of Power Transformers - Con-dition monitoring and fault detection

8

Catrinu, Maria Holen, Arne T. Multicriteria optimization of local energy systems 10

Di Marzio, Giuseppe Fosso, Olav B. Integration of Large Scale Wind Power 12

Ericson, Torgeir Finden, Per End-user flexibility by efficient use of ICT 14

Hansen, Oddbjørn Hansen Eilif H. System solutions for electrical installations in buildings 16

Hellesø, Svein Magne Runde, Magne Mechanical and thermal monitoring of overhead power lines using fibre optical sensors

18

Hoff, Erik Norum, Lars E. Control and monitoring for distributed power supply 20

Høyer-Hansen, Martin Nysveen, Arne Electric pipe heating - secular effects 22

Johansen, Børre Solvang, Eivind Cost efficient restoration - information and methods 24

Korpås, Magnus Holen, Arne T. Distributed Energy Systems with Wind Power and Energy Storage

26

Kristiansen, Tarjei Wangensteen, Ivar Risk Management in Electricity Markets 28

Krøvel, Øystein Nilssen, Robert Design and Construction of Large Electric Permanent Magnet Machines

30

Lund, Richard Nilsen, Roy Multilevel Power Electronic Converters for High Power Drives

32

Løken, Espen Holen, Arne T. Multi-criteria Decision Methods for Planning and Opera-tion of Energy Distribution Systems

34

Maribu, Karl Magnus Wangensteen, Ivar Distributed Generation in Liberalised Electricity Markets 36

Mauseth, Frank Nysveen, Arne Hybrid Electrical Insulation Systems 38

Næss, Bjarne Idsøe Undeland, Tore M. Utilization of Power Electronics in Wind Farms 40

Opdal, Knut Hansen, Eilif H Hollow light guides for general illumination of office buildings

42

Pedersen, Atle Ildstad, Erling Principle of electrocoalescence in crude oil 44

Skaar, Stev E. Nilssen, Robert Optimal Design of Permanent Magnet Generators for Distributed Power Generation

46

Tomta, Gjermund Nilsen, Roy High power high voltage electronic dc-dc converter 48

Trætteberg, Sidsel Ildstad, Erling Polymer insulation of HVDC cable 50

Vogstad, Klaus-Ole Faanes, Hans H. A system dynamics analysis of the Nordic Power market 52

Øvrebø, Sigurd Nilsen, Roy Sensorless control of Permanent Magnet Synchronous Machines

54

Previous projects from 1990 56

PhD student: Supervisor: Title: p

Electronic load controller and VAR compensator design for a micro grid system

Brijesh Adhikary 2004/01/20

Introduction: A micro grid is an electrically isolated system which can generate energy from various sources such as diesel generator sets, small hydropower, photovoltaic, wind turbines, fuel cells and so on. Induction motor is used as an induction generator when electricity is generated from micro hydel units (fig. 1) or from wind turbines. Induction generators have many advantages over synchronous generator such as ruggedness, less maintenance requirements, absence of dc excitation and inherent short circuit protection when working as a stand alone low cost energy conversion schemes. On the other hand an induction generator has some drawbacks, as it requires reactive power to improve the voltage regulation. In addition to this induction generator used in micro hydel scheme, converts all available mechanical energy into electrical energy to eliminate the controller for the turbine. Controller on turbine side is avoided to make the system simple and cost effective. Thus, whenever the consumer load is reduced, the surplus generated energy from induction generator must be dumped somewhere else so as to maintain constant voltage and frequency in the system. These drawbacks can be overcome by using an electronic load controller and VAR compensator. Already, many different types of electronic load controller exist for the stand-alone system. When several induction generators involve in a micro grid system, reactive power compensation required by these generator become more significant and fixed capacitor compensation technique may not be effective. Synchronous condenser, Static Var Compensator (SVC) or Static Synchronous Compensator (STATCOM) may be used in this situation.

Consumer load is fluctuating and varies continuously. This type of load can be named as uncontrolled load. Whenever induction generators have surplus electrical energy it must be dumped somewhere else to maintain the input essentially constant. This can be achieved by using load controller, which diverts the surplus energy to dump load placed parallel to uncontrolled load. Objective: The objective for this work is to model, design and simulate a load controller and Var compensator. Matlab/Simulink will be used for the modeling and simulation of the system. Funding: I have started my PhD work in August 2003 and am scheduled to be finish by the end of 2006. Quota Program funds my PhD work. My supervisor and co-supervisor are Prof. Arne T. Holen and Dr. Kjetil Uhlen respectively. Personal Background: I did my masters degree from BITS Pilani, India. After that I started working in Kathmandu University, Nepal in Electrical and Electronics Engineering Department.

Fig.1 Micro Hydel units for stand alone system [1]

References: [1] Murthy, S.S.; Jose, R.; Singh, B.,“ Experience in the development of microhydel grid independent power generation scheme using induction generators for Indian conditions” TENCON '98. 1998 IEEE Region 10 International Conference on Global Connectivity in Energy, Computer, Communication and Control, Volume: 2, 17-19 Dec.1998 Pages: 461 - 465 vol.2 [2] John, E.M., “ Reactive compensation tutorial”, Power Engineering Society Winter Meeting, 2002. IEEE, Volume: 1, 27-31Jan. 2002 Pages: 515 - 519 vol.1

Power Electronics in Distributed Generation of Electrical Energy

Pål Andreassen January 2004

I. INITIATION I graduated from NTNU, Department of Electrical

Power Engineering in March 1999. Since then I have been working in the company SmartMotor. The main part of my work consisted of designing, implementing and testing inverters for motor control. I started my Ph.D. studies in August 2003. These studies are due to be finished in 2006.

The Ph.D. work is part of the project Technologies

for Reliable Distributed Generation of Electrical power from Renewable Energy Sources. The project is funded by the Research Council of Norway and Power-One.

Professor Tore M. Undeland is my supervisor. II. INTRODUCTION

The use of small to medium sized distributed power

sources can complement the centralized structure of power generation. The prospect of local generation of reliable power near customers and generating power from renewable energy sources is the motivation for the work on distributed power supply systems.

One important part of the distributed power supply

system is the power electronic converters/inverters that will be needed to complement and stabilize the existing power system. With the use of power electronic converters the output can be controlled to match local demand. The requirements to the P.E. converters in order to deliver electrical energy at a reasonable price is that they must be flexible, reliable, and both cost and energy efficient.

In my Ph.D. alternative inverter topologies,

semiconductor devices and digital control strategies will be studied in order to optimize the power supply system with regard to size, cost, reliability and energy efficiency. Methods to reduce EMI noise is also a subject of interest and is of importance if EMI sensitive systems are to be located in the surroundings of the power supply. When AC power is supplied also

requirements to THD on the output must be met. With a large amount of digital load such as PCs the control dynamics of the inverter must be fast in order deliver sufficient power quality.

Fig. 1. Distributed power system

III. STATUS OF WORK I started my studies August 2003. Previous semester

I have followed compulsory studies. The subjects in my compulsory studies are to be; “Digital Signal Processing”, “Magnetic Construction”, “Digital Signal Processing in Power Electronic Systems” and “Power Semiconductor Devices and Snubber Circuits”. I have also started my literature search on the subjects of importance for my Ph.D.

During this semester I will be working on a paper

for the NORPIE conference in June 2004. The subject this paper will be on alternative power semiconductor devices in resonant switching circuits. Different power transistor technologies such as MOSFETs, PT IGBTs and the new ultra thin wafer NPT IGBTs are compared with regard to their suitability in Zero Voltage Switching circuits.

A digitally controlled Quasi Square Wave buck

converter is designed and used as test circuit for this purpose. This test circuit is specifically chosen because this topology can be extended to a three phase Resonant Pole Inverter, a subject of interest in my Ph.D.

Fig. 2. ZVS Quasi Square Wave Buck Converter

IV. PRIMARY GOALS The primary goals of my Ph.D. is to develop a

competitive alternative to standard front end converters and UPS inverters of today that are using hard switched converters and standard filters. The focus will be on dimensioning and size of output filters, energy efficiency and requirements to heat sink, reliability and reducing stress on the main power transistors, and measures reducing EMI noise. Also focus will be put on

the dynamics of an alternative digital control of the inverter.

V. REFERENCES

[1] R.Francis, M. Soldamo “A New SMPS Non Punch Thru IGBT replaces MOSFET in SMPS High Frequency Application”, International Rectifier, APEC 03

[2] G.Hua, F.C.Lee, “Soft-Switching Techniques in PWM

converters”, Industrial Electronics, Control and Instrumentation, Proceedings of the IECON ’93, p.637-643

[3] D. Maksimovic, “Design of the zero-voltage-switching

quasi-square-wave resonant switch”, PESC ’93, p.323-329 [4] D. Maksimovic, S. Cuk, “Constant-frequency control of

Quasi-Resonant Converters”, IEEE Transactions on Power Electronics, Volume: 6, Issue:1, Jan. 1991, p.141-150

[5] N. Mohan, T.M. Undeland, W.Robbins, ”Power

Electronics Converters Applications and Design”, 2nd Edition, John Wiley Sons, 1995

[6] R.W. Erickson , “Fundamentals of Power Electronics” , 5 th

Printing, Kluwer Academic Publishers, 1999

Introduction Best utilization of existing resources is important in most areas. Even more so if the resource is limited as the case is for hydropower. Unfortunately one single criterion for measuring the optimality of the hydropower usage is difficult to formulate and use in practical models. The Norwegian power system based so far on 100 % on renewable energy from hydropower, and with a positive export balance. The expected future growth of the consumption together with reluctance to usage the remaining hydropower resources shifts the balance. Today the Norwegian power system has no export in normal inflow years, and without the reduction in consumption seen in 2002-2003 the energy deficit in the 2003 would have been hard to neglect. If the reduction in consumption growth can be maintained and utilization of the existing renewable resources including hydropower resources can be increased Norway may be able to depend 100 % on renewable energy sources also in the years to come. The criterion for the thesis is to contribute to an efficient usage of the hydropower system in compliance with other natural energy resources in Norway. This is an enormous task and the work has to be limited to some part of this big picture. Narrowing the theme to production planning is a step in the right direction but still this is a broad topic. It might be necessary to concentrate on some part of production planning process, but this is still to be seen. Criteria for optimal use The socio-economic criteria for utilization of hydropower seems like usable criteria except from the latest development where costs for ”soft” values are included in this type of criteria. Soft

values could for instance be connected to ecological or recreational values. The salmon population i the river should be maintained, the riverbed should not be dried out in the tourist season just to mention a few of many possible criteria. The socio-economic criterion is not unambiguous. As an example one can imagine the following statement:

Optimal utilization of hydropower = maximum energy output.

This means that power plants should run at best efficiency at highest possible head. This is not practically because the generation must balance the demand of electric power, and the end-use customers cannot be dictated to use energy at specific times. But at the same time if the generation varies with the energy demand alone it might prove disadvantageous for the fish in the river along with other environmental effects. There are different ”optimal” criteria and they might be conflicting. Another example is economic growth (low energy prices) contra implementation of CO2 quotas [2]. Techniques Various techniques have been developed over the years for modeling the Norwegian power system. Every period: starting with electric islands, the joint venture of the Scandinavian power utilities to the disaggregation and introduction of the power market from 1991 and on has called for new development and techniques. The boundary conditions for a power utility have changed from local supply obligation to market operation without special obligations. Typically the process of production scheduling for power utilities consists of long-term and short-

Optimal utilization of the hydropower system

by Michael Martin Belsnes

term problems. The main difference is that one typically uses stochastic aggregated models for long-term decisions [1], [4] and detailed deterministic models [5],[8], for short-term decisions. The deregulation has increased the focus on short-term models as the tool to ensure the realization of the revenues in the power market for the power companies. In hydropower dominated systems stochastic programming as SDP and SDDP [6] has been used to deal with future uncertainty with regard to energy. In a thermal system as Denmark the system is designed for enough capacity and uncertainty is not precipitation but availability of the units in the peak load periods. The same can be seen regarding short-term models where one focus on water balance (typically LP) in hydropower systems and on unit constraints (typically DP) in the thermal system. The borders between these techniques seem to become more and more overlapping. In addition new techniques are implemented and adapted to new problem groups. There is hence room for revision of the techniques used by utilities and official bodies in order to find the mixed that gives the best solution to the overall problem. Parallel new problems arises that need to be handled. This could be: closer connection through cables to Europe, wind power integration and distributed generation, transmission constraints as suggested in [3] and [7] Status A plan for the research education has been established. The more specific lines of the research in the project and how it will contribute to an efficient use of the hydropower systems will be addressed in the spring 2004. References: [1] Haugstad A. Mo B. and Belsnes M., ”Evaluating

Hydro Expansion or Refurbishment in a Deregulated Electricity Market”, Hydropower 1997.

[2] Michael M. Belsnes, Arne Haugstad, Birger Mo and Peter Markussen ”Quota Modeling in Hydrothermal Systems” PowerTech, June 2003.

[3] Warland, G. and Belsnes, M., “A Model for Planning Of Distributed Generation in the Local Transmission System”, AUPEC 2001

[4] A. Gjelsvik, M. M. Belsnes and A. Haugstad, “An algorithm for stochastic medium-term hydrothermal scheduling under spot price uncertainty”, Proceedings 13th Power Systems Computation Conference, Trondheim, Norway, June 28-July 2nd, 1999, pp. 1079- Bellman, R. 1957. Dynamic programming. Princeton, New Jersey: Princeton University Press.

[5] Belsnes, M. M., Røynstrand, J., Fosso, B. O. & Huse, E. S. 2001. Planlegging i serievassdrag med hensyn til start/stopp problematikk. Technical Report A5355, SINTEF Energy Research, Trondheim, Norway.

[6] M. V. F. Pereira, “Optimal stochastic operations scheduling of large hydroelectric systems”, Electrical Power & Energy Systems, vol 11, no. 3, pp. 161-169, July 1989.

[7] Michael M. Belsnes, Olav Bjarte Fosso, Geir Warland. ”Combining production and transmission system using relaxed constraints.” PSCC, June 2002.

[8] M. M. Belsnes, O. B. Fosso, J. Røynstrand, T. Gjengedal, E. Valhovd. ”Unit Commitment in Hydro Operation Scheduling” Hydropower 2001

I. BIOGRAPHIES

Michael Martin Belsnes was born in Denmark, on August 28, 1967. He received his MSc from DTU in 1995, and has been employed at SINTEF Energy Research since then. He has worked with models for hydropower scheduling, integration of distributed energy, mainly wind power, and lately models for the CO2 quota challenge.

High frequency modelling of Power Transformers- Condition monitoring and fault detection

Eilert Bjerkan

Introduction

Power transformers are usually designed to with-stand shortcircuit forces. Ageing or erroneous de-signs may lead to mechanical deformations inside the windings when exposed to such forces. The de-formations don’t necessarily degrade the opera-tional characteristics of the transformer, but the insulation level and the short circuit withstandlev-el may be degraded severly.

Detailed modelling of transformer windings has been a fundamental problem for almost a century [1]. A lot of effort has been put into identifying correct models for different phenomenas.

This project has mainly been focusing on high fre-quency modelling using FEM-calculations, com-pared to some analytical models. High frequency transformer models have a wida area of appliance:

• Determining impulse-overvoltages in wind-ings, during both design-stage and when coor-dinating isolation-levels. The same parameter is often checked during factory acceptance tests.

• Understanding measurements and propagation of signals in windings due to partial discharges (locating partial discharges).

• Determining resonances in power networks and transformers (related to the first point).

• Understanding frequency response measure-ments (FRA) when applied in diagnosis and condition assessment.

Models developed in this project has principally been aiming at analyzing FRA as a diagnostic method.

Project Objectives

The main objectives in this work is to analyze the sensitivity of the methods related to FRA on power transformers through modelling and real scale ex-periments. Different instrumentation is also tested to find the best solution for applying the method industrially.

Modelling

Several methods have been proposed during the years. The most difficult parameters have been the modelling of frequency-dependent properties of the inductances and losses. Fergestad and Henrik-sen [2] made an extensive contribution regarding inductance calculations. And in the last years sev-eral improvements, both analytically [3] and FEM-based[4] have made the accuracy of the models better by replacing and correcting earlier assump-tions regarding both losses and inductances.

The method applied in this project uses a software called SUMER[5]. This software is FEM-based and it is capable of modelling frequency dependent inductances and losses. It applies the theory of complex permeability to keep mesh-size at a rea-sonable level. Figure 1 shows the dielectric part of the model.

Figure 1: Dielectric model of testobject

The winding is usually divided into lumped ele-ments. An accurate calculation needs about 200 to 400 elements [6]. Depending on the required pre-

cision, a lump element can represent one to twenty turns. A typical model[6] has about 10 terminals, 30 tappings and 300 internal winding nodes.

Frequency Response Analysis (FRA)

FRA is, during the last decade, introduced as an ad-ditional diagnosis tool for power transformers. The frequency response is measured and compared with a reference-measurement from the factory, with measurements from identical transformers, a computerized model of the transformer or else an interphase comparison is used (not possible if del-ta/z-winding is present and cannot be opened).

The reason for applying such measurements is to get an early warning of damages because of faults.

Another major objective in this project is to identi-fy the characteristics of the most common faults in the frequency response measurements through modelling (applying faults to the model). The sen-sitivy of FRA will be analysed by applying meas-urements on a full scale transformer and comparing these with models of the same trans-former.

The main testobject in this project, is a 20MVA transformer manufactured in 1965. This was scrapped due to upgrading of the voltage-level. The iron core is removed due to practical prob-lems. The measurements are conducted by using single windings within an earthed arrangement to simplify comparisons between measurements and model. The tank has appeared to be a bit difficult to model because the boundary conditions change with frequency.

Figure 2: FRA-results: Buckled winding

Figure 2 shows a model comparison of FRA-re-sults with and without buckling. In this case the buckling is applied as a forced mode buckling.

Status of work

The first 2 years where mainly spent on attending mandatory coarses, and studying the literature published within the field of high frequency mod-elling and FRA. Getting familiar with FRA-meas-urements on different transformers has also been an element in the preliminary part of this project.

In 2003, 5 months were spent at EdF’s R&D-dept. in Paris, using their FEM-based software (SUM-ER) dedicated for transformer modelling.

Experiments are started regarding axial displace-ment, radial is planned this year. The rest of 2004 will mainly be spent writing the thesis. The project is planned to finish at the end of this year.

Initial sensitivity guidelines are developed for axi-al displacement and radial deformations (buck-ling).

Advisors

The supervisor for my work is Assosiate Professor Dr.Ing. Hans Kristian Høidalen.

References[1] Abetti, P.A., "Bibliography on the surge performance of transformers and rotating machines", AIEE Trans., vol.77, pt.III Dec. 1958, 1958, pp.1150-68. First suppl., AIEE Trans., vol.81, pt. III, Aug. 1962, pp. 213-219. Second. Suppl., IEEE Trans., vol. PAS-83, Aug. 1964, pp.855-58.[2] Fergestad, P.I., Henriksen, T., "Inductances for the calcu-lation of transient oscillations in transformer windings", IEEE Trans., 1974, PAS-93, (3), pp. 510-517[3] Wilcox, D.J, Hurley, W.G, Conion, M., "Calculation of self and mutual impedances between sections of transformer windings", IEE proc. Vol.136, Pt.C, No.5, september 1989[4] Moreau, O., Popiel, L., Pages, J.L., "Proximity Losses Computation with a 2D Complex Permeability Modelling", IEEE Trans. on Mag., Vol. 34, No.5, September 1998, pp. 3616-3619[5] O. Moreau, Y. Guillot, "SUMER: a Software for Over-voltage Surges Computation inside Transformers ", Int. Conf. On El. Machines. 1998, pp.965-970[6] Glaninger; P., Willy, B., "Calculation and visualisation of surge voltages in transformer windings", Int.conf.on power transformers, may 2001

Maria CatrinuJanuary 2004

Complex local energy systems involve multipleenergy carriers and different conversion and sto-rage technologies. The planning of these systemsmust deal with a wide range of options and con-flicting objectives. It is also subject to a largedegree of uncertainty due, for example, to demandgrowth for different types of energy, price (orprice elasticity) for different energy carriers, beha-viour of different players in the energy or financialmarkets, cost and availability of fuels and techno-logies, economic growth, environmental regula-tion, inflation and interest rates and publicopinion. A robust modelling approach should ena-ble decision makers to analyse comprehensivescenarios of local energy systems with respect toenvironmental impacts and consequences of diffe-rent regulatory regimes.

Generally, the planning problem for a complexenergy system can be formulated as following:decide the best operation plan and the new invest-ments (in different conversion technologies, trans-port networks, etc.) in order to meet the futuredemands for energy, at minimum possible costwhile taking into consideration all types of techni-cal and resources constraints, the environmentaland social requirements and an uncertain planningenvironment.

This complex system involves several energyresources (hydro, oil, gas, coal, uranium, sun, bio-mass, wind, wave, etc.) and energy carriers (elec-tricity, gas, hydrogen, oil, etc.) together withdifferent conversion, storage and transport techno-logies. Moreover some of the resources (hydro,wind, wave) must be converted to other forms ofenergy while others can be also energy carriers

(gas, coal, biomass) and consequently a key ele-ment in the planning must be where in the systemthe necessary conversions should take place.

This representation is only an example of a speci-fic problem and the ’construction’ of it can be rela-tively difficult and most of the time highlydependent on the perspectives of the decision-makers involved in the process. These can be thelocal administrators, utility companies, industrialcustomers and even residential users or associa-tions of residential users. For each of them it isvery probable that the system will look different,at least from the point of view of the selection ofcriteria of analysis and uncertainty characterisa-tion. When modelling a planning problem from amulticriteria perspective, it is very important tounderstand that the choice of these criteria shouldbe totally left to the decision-maker. Thus, theanalyst should create a comprehensive model toinclude relevant criteria for many decision situa-tions. The whole source of uncertainty of the plan-ning problem comes from the necessity toestablish the system limits, and in doing this, thedecision maker must be aware about a series offeedback loops that connect together the marketsfor different technologies, useful energy demands,

developments of energy technologies and not atleast, the environment. However, a robust model-ling approach of the whole system must be a relia-ble tool that can be applied by any decision makerin most of the decision situations.

The doctoral study will be closely connected tothe SINTEF project “Analysis of Energy Trans-port Systems with Multiple Energy Carriers”which aims to develop a robust and flexible met-hodology for optimization of distributed energysystems. This methodology must be able to handlemultiple energy carriers in a geographically distri-buted network with energy transmission, conver-sion and storage technologies.Moreover, the resultwill be a planning tool that will allow differenttypes of decision-makers, with different intereststo use it in an equally efficient manner. At themoment only a cost optimisation is implemented,but future developments of the linear model willallow addition of multiple criteria and uncertain-ties. The optimisation process will be interactive

(see also the fig.) and, depending on the size of theproblem, will probably necessitate the presence ofan analyst to supervise it.

First the decision-maker will 'build' his ownsystem model by selecting, from an availablelibrary, the components of the energy system thathe wants to analyse. Then he will have to specifywhich types of uncertain situations to include intothe analysis, from several available types providedby the planning tool. The optimisation model willneed also as input, the specification of a decisionparadigm that will capture the attitude of the deci-sion-maker towards risk. This decision paradigmcan be related to expected value, regret, etc. Thenext step is selection of criteria. Depending on thenumber of it and on the size of the problem, the

intervention of an analyst might be needed toassist the decision process. Within an interactivedialog the analyst will capture the preferences ofthe decision-maker regarding different criteria.

The project will contribute to an improvedquantification and survey of economic, environ-mental and technical consequences of operation ofenergy systems with new types of energy resour-ces.

I started this PhD program at the end ofFebruary 2002. Until now I complete all coursescompulsory for this PhD program, and I did mostof the literature review necessary to my study.The basic issues were related with the premisesand expectations of introducing multicriteria anduncertainty analysis into a robust and reliabledecision process. Further research will focus ondefining and modelling a coherent family of crite-ria, relevant uncertainty situations and investiga-ting possible ways to include these into a planningtool.

This project is funded by The Norwegian Rese-arch Council and it is due to be finished at the endof January 2006.My supervisors are: Professor Arne T. Holen,from the Electrical Power Engineering Depart-ment-NTNU, and Research Scientist Bjørn H.Bakken, from SINTEF Energy Research.

I graduated in 1999 ‘Politehnica’ University ofBucharest -Power Engineering Department. In July 2000 I obtained a MSc diploma in EnergySystems Management, in the same university.After that I was training and working for one and ahalf years for the Romanian National Authorityfor Electricity and Heat (ANRE), Department forElectricity Tariffs.

Integration of Large Scale Wind Power By Giuseppe Di Marzio

January 2004

Personal background

I graduated from the Politecnico di Torino (Italy), Department of Industrial Electrical Engineering in July 2002 with a MSc thesis in Power Distribution in Large Buildings. In January 2003, I started a trainee program of six months on hydropower stations (building and maintenance) at ENEL POWER S.P.A. (before the unbundling the former Italian National Utility). Initiation and funding

This doctoral study has started in August 2003 and is scheduled to be finished in 2007. The program is funded by SEFAS. My supervisors are: Prof. Olav Fosso at NTNU Senior Research Scientist Kjetil Uhlen at SEFAS Introduction

The European system is facing new challenges resulting from the unbundling of the electric power sector, as a consequence of the implementation of the internal market of electricity, and from the large integration of dispersed generation with a large contribution of intermittent energy sources namely wind power. It is therefore of utmost importance to identify the main operating problems and tools that can be used to help system operation under this new paradigm. The main advantages of conventional thermal, nuclear and hydro power generation are the price of the generated electricity and the controllability and flexibility of their output. On the other hand, the main advantages of renewable power generation are the usage of an infinitely available primary energy source (such as sunlight, wind or biomass) and the less severe environmental consequences. Worldwide, many governments tend to value the advantages of renewable power generation more than those of conventional

power generation. Hence, they support the expansion of the renewable energy generation capacity in various ways, which basically aim at reducing both disadvantages of most technologies for renewable energy generation: cost and lack of controllability.

Fig.1 Installed wind power capacity in the US, Europe and the world (sources :European Wind Energy Association, Wind Power Monthly). As can be seen from the depicted figure, the installed wind power capacity shows an approximately exponential growth: during the last five years, annual growth has been higher than 30%. The reason that wind power is the renewable energy source that seems to benefit most from stimulation regimes is that the cost of wind power is relatively low when compared to other renewable energy sources [1]. The growing utilization of such a not controllable energy sources, especially in remote locations, can contribute to make the transmission system unstable until, in certain critical situations, the collapse of it. New protection systems and managing strategies have to be adopted in order to prevent such a catastrophic events. Project objective

The doctoral study will be closely connected to the SINTEF project “Increased utilization of the Nordic power transmission systems”, in cooperation with Statnett and other Nordic system operators. It is aimed at developing of

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concepts, methods and competences for the management of power systems, and exploiting of the capacity of the transmission system in the best way possible. The project consists of three main activities:

• Flexible transfer limits

• Models and simulation tools for TSOs

• System-oriented control and monitoring

So far I have been reading technical papers, articles and relevant literature concerning the topics I have mentioned above, furthermore I have taken one course in linear programming and one in power system relaying in Chalmers ( Sweden). Further work

The main focus of my study will mainly deal with: The addressing of problems encountered in

planning and operation of wind farms with favorable wind conditions, but long distance to load centers and relatively weak transmission systems. The development of IEC 61400-21 [2]

concepts for providing the basis of a detailed assessment of the impact of the wind turbines on voltage quality. This should enable secure and acceptable operations of large wind farms in areas close to the thermal capacity and stability limits of the power system, and open for an increased utilization of wind energy in weak grids.

References

[1] Johannes Gerlof Slootweg (2003) Technische Universiteit Delft, Modeling and Impact on Power System Dynamics, PHD thesis pp 3-5.

[2] IEC 61400-21 (2001) Measurements and assessment of power quality characteristic of grid connected wind turbines.

2

End-user flexibility by efficient use of ICT

Torgeir Ericson Introduction During the last ten years we have seen an increase in the consumption of energy and effect in Norway. At the same time there has been a decrease in investments in power production. As an example, there was an average growth in installed capacity (measured in MW) on 4,1 percent each year from 1970 to 1985. During the 1990’s this percent dropped to 0,1 each year. The power that is available during winter peak loads in the Norwegian power system is around 24 000 MW [1]. 5. February 2001 we used ca 23000 MWh/h. Because of the tighter effect situation in Norway there are a need to decrease the use of effect during peak- load hours. Two-way-communication project The project “End-user flexibility by efficient use of ICT” (Information and Communication Technology) started in 2001, with SEfAS, EBL-kompetanse, NVE and other players in the energy field as participants. The objective of the project is to increase the end-user flexibility in periods with scarcity of electrical energy and power. Two network operators will install technology for two-way communication to 10.000 end-users (mostly household customers). With this technology the operator can control loads and read the meter automatically on an hourly basis. The electricity consumers can choose a time variable network tariff and/or a spot price based power tariff that will give the customer an incentive to reduce load during high priced hours. The test period started November 2003 and will finish April 2004. There will be given questionnaires to a part of the end-users in the project. This will give information of the dwelling and the people living there.

My project As a participant in the project described above I will have energy consumption data and information on household characteristics, together with weather related measurements. This information gives a panel data set that will be used in a statistical analysis. I will try to reveal whether the electricity consumers respond to the price signals or not. The possibilities the household has for responsiveness depend on their usual electricity consumption pattern, and how easy this pattern can be changed. Three main causes of variations in electricity usage by a single household can be distinguished [3]: 1) Those resulting from the life-style of the family, such as hours at home and at work or school for the different family members. 2) Reactions to changes in the environment, either social or physical, such as levels of temperature or humidity. 3) The above two sets of causes will interact with the basic characteristics of the household, such as number of members of the family and their age distribution, the type, age and size of the house or apartment and the contents of the appliance stock utilized. Because households differ in many ways they will probably not react on the prices to the same extent. For instance, for households who use moderate amounts of electricity for general uses other than heating, and with electricity as the only heating source, the opportunities for load shifting may be severely limited. With the data set it might be possible to distinguish responsive customers from non-responsive, and investigate if there are any common factors that characterize the subgroups. If the results shows that some of the electricity consumers do respond, another important question will be whether they select the off-peak periods instead of peak periods to use some of the energy (substitution response), or whether they

simply conserve, and use less during the peak periods without taking it back during the off-peak period (conservation response). If the consumers mostly choose the former reaction pattern, time varying electricity pricing will primarily have an impact on the effect situation. If the latter dominates this pricing scheme will also have an energy saving effect. Status I started in January 2002, and my work is scheduled to be finished December 2004. This year I will work on the data gathered in the test project. Initiating and funding This study is initiated by EBL-Kompetanse. It is a part of the project End-user flexibility by efficient use of ICT, which will be running from 2001 to 2004. My PhD is funded partly by the Nordic Energy Research, and partly by The Research Council of Norway. My supervisor is Professor II Per Finden. Personal background I graduated from NTNU, Dept. of Mechanical Engineering in 1999. Until November 2001 I worked for Rembra AS as an environmental and energy consultant. References [1] TR A5668 ”Prissignaler og sluttbruker-fleksibilitet i knapphetssituasjoner”, A. Hunnes, O. S. Grande, August 2002 [2] Granger, C.W.J., R. E, R. Ramanathan and A. Andersen. 1979. Residential load curves and time-of-day pricing : An econometric analysis. Journal of Econometrics. 9, Issues 1:13-32 [3] http://www.energy.sintef.no/prosjekt/ Forbrukerflex/no_index.asp

Figure: Two-way communication system. [3]

System solutions for electrical installations in buildings

by Oddbjørn Hansen

2004-01-28

Introduction

This project was initiated by an NTNF-programmecalled New Technology for electrical installations.I started my Dr. ing. study in September 1992 andthe defence is set to March 2004.

The NTNF-programme financed the first part(1992-93) of the scholarship and the departmentfinanced the years 1994-95. My present employer,Sør-Trøndelag University College, has made itpossible to conclude my work by granting leaveof absence the autumn of 2002.

Needs analysis

In order to perform a good planning of electrotech-nical installations in buildings, one has to find theneeds of the users. In my dissertation I’m lookingat this issue on a fundamental level. I start with thepsychological and practical needs of the users andthe activity. This needs analysis leads to a func-tional description for rooms, areas and the build-ing as a whole. Table 1 shows a needs analysiscarried out for an office. This is just an example,other functions could also be taken into consider-ation especially if a higher grade of user interven-tion is wanted.

With such tables for all room categories in abuilding, or part of a building, one can choosestrategies and structures for the electrotechnicalsystems. It is of special interest to coordinate allthe systems. Installation bus technology should beconsidered to do that.

Installation bus systems

European Installation Bus (EIB) and LonWorksare used more and more in commercial buildings.

Ring

Mesh

Figure 1: Alternative structures

Both systems can perform a variety of functionslike light and heat control, fire and burglary alarmand power and energy control.

The costs of the electrotechnical installationscan be reduced when choosing to use a bus sys-tem. This is not only true for the investments, butalso for operating costs. Another important advan-tage is when a rebuilding is needed. If the systemis planned carefully, a rebuilding will only involvea reprogramming of the system without having toreplace much of the installation.

The power system structure is almost fully dis-connected from the functions when choosing a bussystem. I have taken advantage of this by suggest-ing alternative structures for the power system asshown in the next section.

Level Needs Person Activity Building, etc.

1 Safety and Orientation and General lighting

security needs attention

Emergency functions

Warning of danger Fire alarm

Protection against Burglary alarm Burglary alarm

damage Fire alarm

2 Functional needs Communication Telephone

Intercom

Computer network

Activity Working light PC

3 Environmental Climate Heating

needs Ventilation

Light control

Heat control

Transport

Table 1: Needs analysis for an office

Power system structures

The need for flexible power supply call for newstrategies and structures. Radial structures are al-most exclusively chosen today. Figure 1 shows twoalternative structures I have considered in my dis-sertation.

I have calculated load and short circuit currentsfor these alternative structures to find advantagesand disadvantages. One advantage with ring andmesh are lower voltage drops even when usingsmaller sized cables than for the corresponding ra-dial solution. The cable sizing does not need to bethe same throughout the whole ring or mesh. Thecables can be sized due to the actual load current ineach branch. This will reduce cable costs, but canbe difficult to implement with today’s protectiondevices.

Smart protection system

Ring and mesh structures will demand special pro-tection strategies. If it is a goal is to maintainpower supply to most of the installation during afault, one have to install a lot of protection devices.It can be done with todays protection devices asshown in [1], but it could be solved more elegantlywith a smart protection system.

I suggest a system which measures the currents

either in each branch or for each load. These valuesare sent to a central unit which processes the dataand checks for overload situations. If an overloadis detected or predicted, the system can disconnectloads by priority or refuse an enquiry from a loadwhich wants to connect. The protection system canbe a part of a general installation bus system or beseparate.

This system can be used in any power systemstructure, not only for ring and mesh. The systemcan also include power and energy control whichmakes it possible to reduce the energy bill. An-other advantage is that the cable sizes can be keptsmall if the loads must ask for permission. The ca-ble utilisation can be much higher compared withtraditional installations.

References

[1] Frode Larsen. Discrimination by use of nonradial distribution systems in buildings. Mas-ter’s thesis, The Norwegian University of Sci-ence and Technology, Department of Electri-cal Power Engineering, December 1997.

Overhead power lines, as any slender structure, issusceptible to vibrations when exposed to wind. Itis usual to classify the vibrations according to howthey are generated. Galloping is a low-frequencyvibration that can develop if the conductor has orgets (because of icing on the conductor) an aero-dynamically unstable shape. Aeolian vibrationsare caused by vortex shedding from the conductorgiving a oscillating lifting force on conductor.Sub-span oscillations develops when one conduc-tor is laying in the vortex wake of an upstreamconductor.

Galloping can cause conductors to clash into eachother or, in extreme conditions, to fall down if themechanical strength of the line or suspensions areexceeded. Aeolian vibrations and sub-span oscil-lations can shorten the life of the power line if thevibrations causes fatigue, or breaking of indivi-dual strands.

It is common to use vibration dampers on powerlines to reduce the level of vibrations. A numberof designs for dampers have been used, but todaythe most common damper is the stockbridge-dam-per were damping is a achieved by friction bet-ween strands in the messenger wire between thetwo masses.

Fig 1, Example of stockbridge damper

The the need for dampers are usually determinedby calculating the frequency and magnitude of

possible vibrations in a worst case scenario, usingan energy balance between wind energy feed intothe conductor and energy dissipated in internal(self-damping) and external damping.

The background for my project is a combinationof two things: the need to measures vibrations onlong fjord crossings with end-span damping, andthe development of new measurement technolo-gies based on optical fibres.

Fjord crossings (in Norway and elsewhere) tend tobe very long, up to 5000 meters, and with the rightwind conditions vibrations of the conductors canbe severe. Damping is then required, and this isfitted as end-span damping close to the suspensionpoints. It is easy to verify that the vibrations closeto the suspension points are small enough to notcause damage. It is however not that easy saysomething about the vibrations at mid span, bet-ween the dampers at each end. There have beensome observations that clearly proves that thevibrations in the mid span can be large, even if thevibrations at the ends are small. There is thereforea need to be able to measure vibrations in midspan.

New developments in the field of fiber optics havegiven a possible solution to this problem. Byexposing a doped optical fiber to ultraviolet lightis it possible to create areas in the fiber where theindex of refraction is different from unexposedareas. With this method is it possible to make gra-tings, named Bragg gratings, in the fiber thatworks as filters to laser light, in the sense thatsome wavelengths are reflected, while otherwavelengths are transmitted. The wavelengthsthat are reflected are determined by the gratingspacing, and this spacing changes with the strainin the fiber. This effect is it possible to use as astrain gauge to measure strain, by finding the

Mechanical and thermal monitoring of overhead power lines using fibre optical sensors.

Svein Magne Hellesø

wavelength for maximum reflection from theBragg grating.

Fig 2, Bragg grating

The aim of my work is to develop a system thatcan measure vibrations in the mid-span of a longfjord crossing using the strain-sensitive Bragg-grating. To do this is there necessary to establish arelation between the amplitude of the vibration ofthe conductor and the resulting strain in the indivi-dual strands of the conductor. For a solid conduc-tor will this be a fairly trivial relation, if oneassumes sinusoidal movement, with a relation bet-ween the curvature of the conductor and the resul-ting strain on the surface of the conductor. For amulti-strand, multi-layer conductor used in over-head lines, this relation becomes much more com-plex, due to the fact that the strands and the layerscan slide in relation to each other. A relation bet-ween amplitude of vibration and strain will nowalso require knowledge of how the sliding willinfluence the strain in the strands.

A part of my work will consist of developing afinite element model of a conductor, and use thismodel to find the strain in the strands of a conduc-tor when it moves and sliding occurs. I will alsomeasure the same strains on an experimentalindoor line to verify the model. Some of the workwill also involve field testing of the method on afull scale fjord crossing in Norway.

A full scale installation of a measurement systemon a span with a length of 3 km across the Glom-fjord, operating at 420 kV, was put into operationin the autumn of 2002, and was operating as plan-ned during the winter 2002/2003. This span has ahistory of vibration damage, and the current vibra-tion monitoring is done for verification of exten-ded damping installed.

Fig 3, Overview of the Glomfjord span

One reason for this span being particularly sensi-tive to vibrations is due to the high tension of theline, operating at almost 50% of the breakingstrength of the line. Increased tension reduces theself-damping of the line, increasing the need forexternal damping to control vibrations. An analy-sis of measured vibration amplitudes for variousline types at different tensions indicates that theundamped vibration amplitude for this spanshould be about 70% of the line diameter. Thisvibration level will result in rapid accumulation offatigue damage and reduced operational life forthe span.

Analysis of the measurements revealed that thevibrations on the span fell into two distinct frequ-ency ranges. There was vibrations with frequen-cies in the ranges 22-27 Hz and the range 3-5 Hz.The estimated amplitudes of the vibrations in thetwo frequency ranges were around 0.2 mm for therange 22-27 Hz, and around 2 mm for the range 3-5 Hz. Compared with the line diameter of 57 mm,this is well below the expected amplitudes for anundamped span, indicating that the span is welldamped. However the presence of vibrations indistinct bands also indicates that the damping ofthe span is not equally efficient at all frequencies.

My work will take place from january 2001 tojanuary 2005, and is financed partly by NorgesForskningsråd (75%) and Institutt for Elkrafttek-nikk at NTNU (25%).

Bragg grating

Reflected Transmitted lightlight

Incominglight

Bragg wavelength

Optical fiber

Control and monitoring for distributed power supply

by Erik Hoff

Initiation I received my M.Sc. in Electrical Engineering from the Norwegian Institute of Technology (NTNU) in 2002. Then I worked as an assembly programmer at SensoNor ASA in Horten. I started my PhD in 2003, and will finish in 2007. My work is a part of the project Technologies for Reliable Distributed Generation of Electrical power from Renewable Energy Sources. It is founded by the Norwegian Research Council as a KMB project (Competence project with user cooperation). Power-One is the industrial partner. Professor Lars E. Norum is my supervisor. Introduction Distributed power supply consists of many small power sources, producing electric power near the consumer. It is advantageous because it enables energy sources such as solar cells, wind power and cogeneration. In addition, it may increase the reliability if suitable control is implemented. Main scope Describing and building reliable AC grid interface, is the main objective. The system will consist of several typical DC sources such as solar, wind and cogeneration. They will share a small energy storage, giving a limited UPS (Uninterruptible Power Supply) functionality. The interface to the AC grid will consist of several 3-phase inverters in parallel. The system is shown in figure 1.

Figure 1: System block diagram, for a local distributed power supply. Thick arrows indicate power flow, while thin arrows show information flow. Communication for monitoring A good solution will need communication at two levels (figure 1):

1. Internally within the local system. 2. Communication from a geographically

located cluster of units, and up to a central monitoring master.

Communication internally The local communication has high reliability requirements. Timing will also be important for phase locking, etc. Therefore a time triggered communication protocol will probably be best. Communication for central monitoring A central monitoring master will only deal with asynchronous communication. This means that there are no timing restrictions. Dynamics will be slow. The flexibility on the other hand, is important.

Capacitor

Battery

Sun

Wind

:

Renewable energy sources

=/~

=/~

:

3-phase inverters DC

Energy storage

AC grid

Consumers

1. Local control and monitoring

2. Central control and monitoring

One master should be able to handle thousands of units, without problems. Status I am now working on 3-phase converter control for paralleling, control of solar cells, and literature search on communication protocols. Future work My plan is to do the following:

- Simulate and implement three 3-phase paralleled inverters, feeding a diode rectifier load.

- Specify the communication between the different converters, and finding suitable standards.

Electric pipe heating – secular effects

Martin Høyer-Hansen January 2004

Initiation I graduated from the Department of Physics at NTNU June 2003, where I studied low-field behaviour of a high temperature superconductor in my Diploma Thesis. In December 2003 I started working on my PhD degree on electric heating of subsea flowlines. The PhD project is financed by NTNU, and is scheduled to be finished fall 2007. My supervisor is Prof. Arne Nysveen. Background The temperature of the oil in the underground reservoirs is typically about 90 °C. This wellstream contains several liquid substances that freeze when the temperature drops. This is a problem when the pipes are cooled in seawater, particularly during a shutdown of oil production, which causes the flow in the line to be impeded or even blocked due to the formation of hydrates or wax plugs. To solve this problem chemical treatments are mainly used. However, this method has considerable operational costs and presents a risk to the environment should a leakage occur.

As an alternative to chemical treatment, electric heating has been suggested. Three methods may be used: i) electric heating cables, ii) electromagnetic induction heating, or iii) direct electric heating of the pipeline. The first alternative is found to be rather inefficient, and the second very expensive. In the last alternative, the consequences of direct electric heating of the pipeline needs further research, and are what I will study during my PhD. The project The direct heating system is based on the fact that an electric current in a metal conductor generates heat due to ohmic loss. The power supply is then connected directly to the electrically insulated steel pipe. See Figure 1. The system is electrically connected to surrounding seawater through several sacrificial anodes at both ends where the power cables are connected. This is for security reasons and to

Figure 1: Model of the directly heated pipe “earthed” with sacrificial anodes.

prevent corrosion of the pipeline. The galvanic contact with seawater leads to inefficiency due to currents travelling in seawater rather than the pipe. See Figure 2. In an ideal case the sacrificial anodes are needless, as perfectly insulated pipes prevent

corrosion. In real life, however, defects may occur and result in uncontrolled stray currents if sacrificial anodes are not used. The main goal of my PhD is to study the current and potential distribution near the ends of the pipeline. Furthermore, I will investigate the influence on the corrosion protection system.

Figure 2: Schematic presentation of distribution of electric currents in the direct heating system.

Cost efficient restoration- information and methods by Børre Johansen

Januar 2004.

Introduction I graduated from the Department of Electrical Power Engineering at NTNU in June 2002. At May 2003 I joined the Power System group at NTNU, and I was formally employed as a PhD. candidate in October 2003. I planned to finish my PhD. work within the year of 2006. My main supervisor is Adjunct Associate Professor Eivind Solvang, NTNU. Supplemented by Research Scientist Bjørn Inge Langdal, SINTEF Energy Research. Initiation and founding My PhD. work is founded by SINTEF Energy Research through the eBee project. eBee – electricity Business enters eBusiness. eBee is a strategic institute program at SINTEF Energy Research, and it is founded 100 % by The Research Council of Norway. eBee project The main idea within the eBee project is to make SINTEF Energy Research, with its cooperating partners, capable to be an innovative centre for R&D- activities related to exploitation of eBusiness technologies within the Electricity Industry [1]. The term eBusiness is defined as: A way of improving exchange of information, knowledge, service and goods through the use of network supported technology, including real-time exchange [1]. With a pre- study performed in 2001 and some further discussion a set of research topic was defined [1]. Objectives for the PhD. work With the project history stated above and with consideration of my background I established my research area as the cross-over between three areas, se figure 1.

In my PhD. work I will focus on Outage Management, i.e. how to have an optimal handling (minimum cost) when an extensive breakdown occurs in a medium voltage net. To evaluate and suggest solution for handling this kind of breakdown it is necessary to look at the organization (i.e. workflow) and the use of ICT system (i.e. DMS, SCADA relay etc.), together with a systematic approach dealing with the reliability of the net and the frequency of large scale restoration. Thereby this cross-over focus. Background In Norway electricity utilities has been constantly under pressure for changing towards more efficient performance since the deregulation in 1991. In parallel there has been a tremendous development in the capability and functionality for ICT system. Deregulation is also occurring in other countries, and the effect of it is the basis for many research projects. Regarding ICT system, there are several research papers that points at the needs for- and suggested different- ICT strategies [2], [3]. A paper [4] points on have to chose and implement an ICT system that will increase the overall efficiency. Despite all this research effort, it seems like there is a lack of overall thinking about how to adapt an ICT system within a deregulated

Outage Management

Organization

theory

The use, procurement and

requirement of ICT

Figure 1. Illustration of research area.

electricity industry. It is my opinion that this absence is making the electricity utilities more inefficient, particularly when there is a need for efficiency, during an extensive breakdown. PhD. work progress The autumn of 2003 I attended an optimizing course. The winter of 2004 I will have two PhD courses, Reliability, and Power Control. The winter of 2005 I will take my last PhD course, ICT and Organization development. The main goal of my work is to increase the efficiency, and thereby have an optimal handling. To do this I will approach the problem from three different sides. First of all I will have a closer look upon the “state of art” regarding ICT systems that support the handling of a breakdown, to clear out ICT systems limits and possibilities. This work will be done in close connection with the eBee- project and is expected to be done within June 2004. Second, I will approach the workflow within the organization. This includes the establishment of a model and the use for simulate workflow during a breakdown. For this work I will consider different models, and a possible model can be PETRI NET. At the moment I haven’t decided yet what model to use. See figure 2 for an example of this type of model.

Figure 2. An example of a workflow net system [5].

Results from the simulation are going to be used together with the “best” suitable ICT system found from the “state of art” study. By seeing this two together I hopefully will be able to say something about how an ideal restoration should be. To prove my theory I will establish some cases for testing my findings. This I hope to do together a few electricity companies and one or two producers of ICT system. It is my intention to have results clear for publishing and writing at the end of 2005. References [1] SINTEF Energy Research 2001, Project plan, eBee – electricity enters eBusiness. Implementation of eBusiness Technologies brings Changes into the Electricity Industry. [2] Cheong, K.H, 1999, “A framework towards effective IT strategy for modern electric utilities”, CIRED, Nice, paper 6.1. [3] Cegrell T., Ekstedt M., Forsgren P. 2002. “Management of Enterprise Information System for Power System Control and Operation”, Power System Management and Control, 17 – 19 April 2002 Conference Publication No. 488. [4] Bargigia A., Fioriti G., Veglio G., Zaffanella A., 2003. “Power Quality. A New Method to Achieve System Improvement”, CIRED Barcalona 12 – 15 May 2003. [5] Reijers Hajo A. 2003. “Design and Control of Workflow Processes, page 46”. Lecture notes in computer science. Springer-Verlag Berlin Heidberg 2003.

One of the most difficult challenges in the field ofwind energy and other renewable energy sourcesis the fluctuating power output. Regulation of con-ventional power plants is absolutely essential tobalance the loads. For that reason several sourceshave claimed that the installed wind power shouldnot exceed 20% of the total installed capacity inan electricity network. In addition locations withhigh wind potential are often found in rural areaswith weak distribution lines. Development ofwind power plants in such areas could requireextensive grid expansions, which results in lowutilization of the grid capacity due to the lowcapacity factor of wind power plants. Grid expan-sions may also lead to unwanted interference withthe local environment.

By using a locally sited energy storage for powersmoothing conventional generators could berelieved from some of their power smoothingfunctions. As a result, this would increase thepotential wind power penetration in electricitynetworks. In rural areas with weak grid connec-tion, a properly dimensioned energy storage couldalso be an alternative to grid expansions. Themanagement of daily and weekly wind variationsrequires both high energy capacity and powercapacity of the storage devices, especially forwind power plants consisting of generators in theMW range. Technologies like conventional batter-ies, flywheels and superconductive magneticenergy storage have the disadvantage that theenergy capacity is related to the power capacity.Moreover, the usage of pumped hydro and com-pressed air storage is limited to certain sites. Onthe contrary, fuel cell systems with hydrogen stor-age are modular devices with separated power andenergy capacity, and are promising alternatives forlarge-scale energy storage. Hydrogen-oxygen sys-

tems are the most commonly known, but there arealso other favourable hydrogen-based systemssuch as hydrogen-bromide and hydrogen-chlorideregenerative fuel cells which use one and the sameelectrochemical cell for charging and discharging.A different regenerative fuel cell technologyknown as Regenesys, which is commerciallyavailable today, is based on a polysulphide/bro-mide redox-couple.

Using hydrogen as a storage medium for intermit-tent energy sources is a very interesting alternativein the long run, especially because of the possibil-ities of using hydrogen as a fuel in the transportsector. The hydrogen storage system can in thiscase simultaneously be used for power smoothingand provide clean fuel for vehicles. In order tooptimize the usage of the hydrogen storage sys-tem, it is necessary to develop a control strategythat takes into account

- the stochastic properties of the energy resource

- electricity price variations

- the value of providing firm power to the grid

- the demand for hydrogen fuel.

Figure 1 shows a wind power plant with hydrogenstorage system. A schematic illustration of anelectrolyser and a fuel cell Polymer ExchangeMembrane (PEM) technology is given in figure 2.

Magnus Korpås27.01.2004

In june 2001, I participated at the IASTED Power& Energy Systems Conference, Rhodes, Greecewith the paper “Hydrogen Energy Storage forGrid-connected Wind Power Plants”. In thispaper, local hydrogen energy storage is proposedas an alternative to grid reinforcements in ruralareas with high wind power potential and weakdistribution lines. Present and future productioncost estimates of electricity are calculated for dif-ferent wind-storage systems assuming optimaloperation in a competitive power market. It isshown that hydrogen energy storage couldbecome an economically feasible alternative togrid expansions if cost and performance goals ofhydrogen technology are obtained. The controlla-ble power from the wind-storage system must thenbe valued 2-3 times higher than fluctuating powerin the market.

In june 2002, I presented the paper “Operation andSizing of Energy Storage for Wind Power Plantsin a Market System” at the Power Systems Com-putation Conference in Seville, Spain. A dynamicprogramming algorithm is employed to determinethe optimal energy exchange with the market for aspecified scheduling period, taking in accounttransmission constraints. During operation, theenergy storage is used to smooth variations inwind power production in order to follow thescheduling plan. The method is suitable for anytype of energy storage and is also useful for otherintermittent energy resources than wind. An appli-cation of the method to a case study is also pre-sented, where the impact of energy storage sizingand wind forecasting accuracy on system opera-tion and economics are emphasized. The paperhas later been published in the International Jour-nal of Electrical Power & Energy Systems.

In 2003, I presented the paper “Optimal OperationStrategy of Hydrogen Storage for Energy Sourceswith Stochastic Input” at the IEEE Power TechConference in Bologna 2003. In this work, theoperation strategy described in the previos paperhas been improved by including a strategy for on-line optimization of the storage operation. Ademand for hydrogen is included in the model,which for instance could be a filling station forfuel cell vehicles.

This doctoral study started in November 1999 andis scheduled to be finished early in 2004. The pro-gramme is funded by Statkraft and the NorwegianResearch Council and my supervisor is prof. ArneT. Holen. Since knowledge of electrochemicalenergy technology is required, a co-operation withthe Department of Materials Technology andElectrochemistry is established. My own back-ground is from Department of Physics at NTNU,and I graduated in December 1998.

~- -

~

Electrolyser

Hydrogentank

Fuel cell

AC 22 kV

AC 66 kV

AC 22 kV

Localloads

H2 O2

e-

H+

H2O

Fuel cell

H2+½O2→H2O+power

H2

e-

O2H+

H2O

H2

Electrolyser

power+H2O→H2+½O2

Risk Management in Electricity Markets

by Tarjei Kristiansen January 2004

Personal background I graduated from the University of Oslo, Department of Physics in July 1995, with an MSc in theoretical nuclear physics. Afterward, I served my compulsory military service at the Norwegian Defence Research Establishment (FFI) as a research assistant. I worked with programming and system development of computer code used in the monitoring of radioactive contamination by the Norwegian Defence. I also worked for six months as a researcher with theoretical models for contamination of radioactivity. I have one year’s experience as a high school science teacher. In January 1999, I began work toward a doctoral degree at NTNU. My research is risk management in electricity markets, emphasising how risks associated with transmission congestion can be hedged. I plan to finish my dissertation in 2004. Initiation and funding This work is financed by The Research Council of Norway and is a part of the Strategic Institute Program (SIP). My supervisors are Professor Ivar Wangensteen at the Department of Electrical Power Engineering and senior researcher Birger Mo at Sintef Energy Research. Study and objectives My study first focused on hydropower scheduling and risk management. In 2000 I switched to the field of risk management associated with transmission congestion. The subject interests me because such risks can be managed by transmission congestion contracts (TCCs) [1].

The payoff from the contract is given in the following formula: TCC = (λj -λi) Pij ≤ ≥ 0 (1) where λj is the spot price of location j, λi is the spot price of location i and Pij is the directed quantity specified in the TCC for the path from i to j. When there is congestion, the prices at the locations will differ and a player injecting power at location i and withdrawing at location j, will receive a positive payoff equal to the fee paid for congestion. In this way it hedges against the congestion fee. In the context of the Nordic market, the situation is illustrated in Figure 1. If there is congestion in the Nordic power system the Area Prices will differ from the System Price, with prices lower in the surplus area and higher in the deficit area. To hedge the Area/System Price differential the player can buy a Contract for Difference, with payoff equal to the price differential. In 2002/2003 I received an appointment as a Doctoral Fellow at the JFK School of Government at Harvard University under Professor William Hogan, a leading expert on electricity economics and the architect of TCCs. My research is now concentrated on the following topics: • congestion risks and financial products

for hedging against these in the Nordic area and the USA

• evaluation of transmission rights and techniques for risk management.

I have written a paper describing how the Nordic contracts for hedging transmission congestion were priced at Nord Pool. Currently I am researching and writing several papers.

Results I have completed my coursework in energy economics, operations research and power systems reliability, and been a research assistant in the courses, Energy Planning and Power Markets, at NTNU. I have also taken courses in economics and finance. The academic year 2003-04 I am attending the Power Market Analyst study at the Norwegian School of Economics and Business Administration. During the academic year 2001-02 I worked for Norsk Hydro ASA as a generation planner in its Department of Electricity Portfolio Management and Trading. This gave me a better understanding of how the power market works, and I implemented a model for integrated risk management there. To date I have presented ten papers at international conferences. Two papers have been accepted for publication in the journals “Modelling, Identification and Control” and “Energy Policy.” I have also refereed a paper for a journal.

References [1] W. W. Hogan, “Contract Networks for Electric Power Transmission,” Journal of Regulatory Economics, 4:211-242, 1992.

Demand

Supply Area Price Sweden

Demand

Supply

Area Price Norway

Demand

Supply System Price

• Transmission constraints between Sweden and Norway • Assume electricity flow from Sweden to Norway

Area Price Norway > System Price > Area Price Sweden

Figure 1. Transmission congestion in the Nordic region.

Design and Construction of Large Electric Permanent Magnet Machines

by Øystein Krøvel

Initiation and funding

The project was initiated by professor Robert Nilssen and is funded by strategic funds from NTNU. This project has been incorporated in the project Energy Efficient All Electric Ship (EE-AES) as one of NTNU’s contributions. At the moment 7 PhD and 5 scientific employees (professors and associate professors) are participating in the EE-AES project.

I graduated from the Department of Electrical Power Engineering June 2002 and started as a scientific assistant in august the same year. I started my PhD in October 2002 and the plan is to finish within October 2006.

Prof. Robert Nilssen and prof. Arne Nysveen are my supervisors.

Introduction As the quality has increased and the price decreased on permanent magnets (PM) the interest for PM-machines has grown.There are mainly three types of PM-machines. Radial flux machines (RFPM) has usually a rotor with PM and a stator similar to induction machines. This type has a higher power density than induction machines and competes with them in aeas where especially speed control is necessary. Since the RFPM machines have large similarities with classic AC-machines it is relative cheap to change the production lines and the computational tools for the manufacturer. This gives an advantage compared to the other types of PM-machines.

In Axial flux machines (AFPM) the flux goes longitudinal to the shaft. These types of machines have a higher power density than RFPM. Mechanically AFPM are somewhat more complex than RFPM. Basically the AFPM consists of a stator disk and a rotor disk with air between. Usually there are two or more

air gaps. This means that the disk in the middle only is supported in the inner or the outer diameter. This puts limits to the mechanical construction and great care has to be taken concerning forces and vibration, especially with large machines.

Figure 1 A simple cross-section of a AFPM

machine The third type of PM-machine is the

transversal flux machine (TFPM). It has a rather complex design but the best power density. Due to the complexity the price is rather high and only in applications where size, volume and weight is more important than price, will the TFPM machine be the best choice.

Objectives

The first objective in my PhD-study will be to make a thorough summary of the state of the art of large PM-machines. A study of the

universities in the Nordic countries has been conducted.

Since this project is a part of the EE-AES, much time will be used on ship propulsion. This is an area where direct driven PM machines have a good possibility to compete with traditional induction and synchronous machines and gears. With the possibility for high number of poles and still with a reasonable diameter PM-machines can replace existing electrical motors. The PM technology also makes it possible to integrate the electrical machine and the propeller in new ways. The Department of Electrical Power Engineering, NORPROPELLER AS and SMARTMOTOR AS has developed an integrated PM-machine for an azimuth thruster. The machine is placed around the propeller blades which gives a better hydrodynamic construction.

Figur 2 Integrated PM machine in azimuth

thrusters. Usually PM-machines require an inverter to

feed it with the correct frequency and voltage. But there are proposed a solution with an electric propulsion system without the converter to drive the motor. In principle a large combustion engine with a relative high nominal speed will drive a generator with a low number of poles. This generator can be a PM-machine or a machine with field windings. The generator will be connected directly to a PM-motor with a high number of poles which in turn drives the propeller. This means that the speed of the propeller is controlled directly by the speed of the combustion engine.

PM-machines for other applications as well as ship propulsion will also be focused on. At NTNU research on wind energy is strongly prioritised. And PM-machines are ideal for large direct driven wind generators. Wind generators have a much lower speed, and therefore also more poles, than PM-machines for ship propulsion, but many of the challenges will be similar.

My contribution to these different projects will be the machine design. My research will not necessarily be focused on building the machine, but more focused on details around windings, field distribution, harmonics etc. The goal is to find methods which can improve the electric machines.

Status

Most of the compulsory courses have been completed and I have finished my obligatory time as scientific assistant. A litterateur study has been started. I also take part in the design of a new wind energy laboratory at the department with a direct driven PM-generator. In which field I will specialize is yet to decide, but the results from the literature study and other current projects will give important pointers.

References [1] Rosu, M. Large output-power, low-speed permanent magnet

synchronous motor designs for ship propulsion drive. Licentiate Thesis, Helsinki University of Technology, Laboratory of Electromechanics, Report 64, Espoo 2001, 77 p. ISBN 951-22-5430-1, ISSN 1456-6001.

[2] Hystad, J. Transverse Flux Generators in Direct-driven Wind Energy Converters, Dr thesis, NTNU Trondheim, Faculty of Electrical Engineering and Telecommunication, Department of Electrical Power Engineering, 2000. ISBN82-7984-116-4, ISSN 0809-103X

[3] Grauers, A., Design of Direct-Driven Permanent Magnet Generator for Wind Turbines, Dr. thesis, 1996, ISBN 91-7197-373-7.

[4] Lampola,P. Directly Driven, Low-Speed Permanent-Magnet Generators for Wind Power Applications. Acta Polytechnica Scandinavica, Electrical Engineering Series No 101, Finnish Academies of Technology, Espoo 2000. 62 p + 84 appendices

[5] Ådnanes, A. K. High efficiency, high performance permanent magnet synchronous motor drives. Dr. thesis, The University of Trondheim, Department of Electrical Engineering and Computer Science, Division of Electrical Power Engineering. sept 1991.

[6] Løvli, E. ”Bygging av PM-motor for bruk i truster for fremdrift av skip” Diploma Thesis, 2002, Department of Electrical Power Engineering, NTNU, Trondheim, Norway

[7] Nilssen, R., Skaar, S.E., Lode, J., ”Integrert propell og motor for elektrisk fremdrift av skip” Prosjektrapport, 2000, Department of Electrical Power Engineering, NTNU, Trondheim, Norway

Multilevel Power Electronic Converters for High Power Drives Richard Lund

30.01.04

Initiation I graduated from the Dept. of Elec. Power Engineering, NTNU in March 1999, I attended the Electric Energy Conversion Group as a research assistant in April 1999, and started on my Ph.D. degree in January 2000. My Ph.D. project was initiated by my advisor Prof. Roy Nilsen, and is financed by the Dept. of Elec. Power Eng., NTNU. The plan is to finish my work during the spring 2004.

Introduction Multilevel Power Electronic Converters (MLPCs) have become attractive the resent years in high voltage and high power applications such as adjustable speed drives and electric utility applications. The development of MLPCs began in the early eighties when Nabae et al. [1] presented a neutral-point clamped (NPC) PWM Inverter in 1980. Since then, a variety of topologies have been presented.

The general structure of the MLI is to synthesise a sinusoidal voltage out of several levels of volt-ages. The MLI can therefore be described as a voltage synthesiser.

For a three phase Voltage Source Inverter (VSI), often named 2-level inverter, the maximum voltage level output is determined by the voltage blocking capability of each device. By using a multilevel structure, the stress on each device can be reduced proportional to the number of levels, and the inverter can handle higher voltages. This means that an expensive and bulky step up transformer can be avoided in the application. Another advantage of a multilevel output waveform is that several voltage levels leads to a better and more sinusoidal voltage waveform,

thus a lower Total Harmonic Distortion (THD) is obtained. With several levels in the output waveform the switching dv/dt stresses are reduced, and hence the lifetime of motor and cables are increased.

The different MLPC topologies can be divided into the following categories: a) Diode Clamped Converters (Figure 1) b) Flying Capacitor Converters c) Series Connected Single Phase H-Bridge

Converters d) Configurations with Multiple Three-Phase

Converters

Figure 1: One phase leg of a generalized Diode Clamped Converter.

Topology c) in Figure 1 needs separate isolated dc supplies for each DC-bus, thus a complicated transformer/rectifier system is needed. The Diode Clamped Inverter can be supplied through a single dc-source, which is favourable in most applications. The problem of this topology is the balancing of the capacitors in the dc-link. By using advanced Space Vector PWM (SVPWM),

these voltages can be controlled as Figure 2 shows for a 3-level prototype.

Figure 2: Control of DC-bus voltages by SVPWM.

Two different MLPC prototype converters have been built. One 3-level 50kW converter, and one 5-level 5kW converter. Figure 3 shows an example of the output voltages.

Figure 3: 3-level (left) and 5-level (right) converter output waveforms.

In the extrapolation of converters to higher power level, the fundamental question of increasing the converter current rating (devices in parallel) or the converter voltage rating (devices in series) always has to be answered. The conduction losses in converters always favour the increased voltage model. All these factors contribute to the necessity for multilevel converter topologies. Analytical expressions for both the conduction and switching losses for Diode Clamped Converters are developed. In Figure 4, results from a analytical calculation are shown for a drive application at 1 MW at full speed, 2500 V DC-bus, 1 KHz switching freq., constant load torque and IGBTs from EUPEC. The results show that for this application, the total losses are

reduced by more than 50 % using a multilevel topology [3].

Figure 4: Normalized total losses for 1 MW drive.

Status of work Analytical expressions for switching- and conduction losses for MLPCs are developed. Harmonic analysis of the output waveforms has also been done. Laboratory prototypes have been built and control strategies implemented.

Primary Goals The main goals for my work are to analyse the different topologies presented in the literature and optimise the most interesting topologies with respect to losses and harmonics. Another topic is the dc-bus balancing problems in Diode Clamped Multilevel topologies. The theory is supported by converter prototypes in the lab.

References

[1] A.Nabae, I.Takahashi, H.Akagi: "A Neutral-point Clamped PWM Inverter", IEEE-IAS’80 Conference Proceedings pp. 761-766, 1980.

[2] B.K.Bose (editor): "Power Electronics and Variable Frequency Drives, Technology and Applications", IEEE Press 1996.

[3] R.Lund et.al: "Analytical Power Loss Expressions for Diode Clamped Converters", EPE PEMC 2002.

Multi-criteria Decision Methods for Planning and Operation of Energy Distribution Systems

by Espen Løken, January 04

Introduction The Department of Electrical Power Engineering at NTNU started in 2003 a research project in co-operation with Sintef Energy Research. Other partners are The Department of Energy and Process Engineering at NTNU (EPT) and Institute of Energy Technology (IFE). The project is called SEDS – Sustainable Energy Distribution Systems. The payers of the project are The Research Council of Norway, and the Statkraft Group (including BKK and TEV), Statoil, Lyse Energi and Viken Nett. The two main tasks of the SEDS-project are to:

• “Develop methods and models that allow several energy sources and carriers to be opti-mally integrated with the existing electric power system”

• “Develop a scientific knowledge base built on a consistent framework of terminology and concepts for mixed energy systems, in the field of planning methods and models.”

In this context a mixed energy distribution system is “a local (regional/local) energy system with different energy carriers (electricity, district heating, natural gas, hydrogen) and a mix of distributed energy sources and end-uses.” Notice that a distribution system in this context also includes some parts of the converting of energy (“energy production”). A mixed energy distri-bution system is illustrated in Figure 1.

Figure 1: A mixed energy distribution system

There will be 3 PhD-students in the project that work with different aspects of the planning methods. The PhD-studies will concentrate on the first main task in the project: the developing of methods and models. My project has the preliminary title “Multi-criteria decision methods for planning and operation of energy distribution systems”. Except for my work, there will be one student (Linda Pedersen in EPT) that works with load and customer modeling of combined end-use, and one student (will join in 2004) that will work with either quality and reliability of supply or environmental aspects and consequences. I will work closely together with the two other students. My doctoral project started August 2003 and will finish in the winter/spring 2007. The Problem Statement What is the problem? The problem is that methods which are used for planning and operation of energy systems today are not good enough for modern, integrated energy systems with multiple energy carriers and sources. There is a need for more sophisticated methods that can take into consideration many criterias and objectives simultaneously. Why is this important? Norway’s energy system (apart from the trans-portation sector) has traditionally been based almost exclusively on hydroelectric power. Cur-rently there is a trend towards a more complex and flexible energy industry. More and more energy sources and energy carriers are in use, often in the same area. Examples on energy carriers are electricity, district heating, natural gas and hydrogen. This development is in accordance to national goals regarding development of supplemental energy supply to the hydroelectric system.

Because of this development, it is absolutely necessary with more knowledge and research on complex and integrated energy systems. The con-ventional method in energy planning until now is minimization of the cost, provided that all neces-sary requirements are satisfied. These require-ments may be environmental, technical etc. This classical optimization will give a solution, but not necessarily the best solution. Multiple criteria decision making in stead of classical cost opti-mization gives the decision maker a much better view of the alternatives, and it will be easier to make “The Right Decision”. Therefore it is necessary to find methods that will give good recommendations to the decision makers in regard of their objectives. What have others done? There has been done pretty much work in the area of multi-criteria decision making in miscel-laneous areas. Many methods are developed, also for specialized fields of energy technologies and planning aspects. Examples on this are methods and computer programs used for planning when electricity is the only energy carrier. Some of these programs are developed at Sintef Energy Research. The problem with these methods is that they do not come together to make a framework that meets the needs of planning future complex, inte-grated energy systems. Nevertheless; these meth-ods will be an important basis for the project work.

What must be done? The task is to find and establish methods that are suitable for multi-criteria decision making for planning and operation of energy distribution systems. The study will focus on integration of technical, economical and environmental aspects related to planning and operation of mixed energy distribution systems. Important areas in the work are:

• Testing, evaluation and adaptation of available methods and models

• Conflicting objectives and criteria • Uncertainties and risks • Identification and quantification of

parameters • Model development • Case studies

It is important that the methodology can cope with risk attitude such that it is able to handle uncertainties in the planning process. The study will provide methods that give much responsibility to the decision maker, which will have to specify priorities and weights for the different criterions. Figure 2 shows one possible solution on how the planning process can be built up.

Figure 2: “Behavior” information model for the methodology

V(P

)-I,

F(P

)

0 50 100 150 200 250-10000

-8000

-6000

-4000

-2000

0

2000

4000

6000

Forward Price, P

F(P)

V(P)-I

Hybrid Electrical Insulation Systems

Frank Mauseth January 2004

Introduction Gas insulated high voltage systems today applies mainly atmospheric air, pressurized sulphur hexafluoride (SF6) or various mixtures as dielectric medium. Open air installations are widely used due to the high reliability and low cost. Breakdown due to temporary over-voltages are not necessarily destructive to the equipment as the insulation restores when the over-voltage disappears. Since air has, compared to other insulation mediums, a moderate withstand voltage, installations tend to become physically large. Several techniques can be applied to increase the impulse withstand voltage. Increasing pressure results in an increased impulse withstand voltage proportionally to the pressure rise (Paschens law). The installation needs to be installed in pressurized vessels, increasing the costs and risks for personnel and equipment in case of a failure. The use of SF6, a strongly electronegative gas, improves the impulse withstand voltage considerable compared to air. At moderate pressures, the withstand voltage might be 5-10 times that of atmospheric air. However, SF6 has one severe drawback; it contributes to the greenhouse effect and is therefore included in the Kyoto Protocol as one of the gases whose emissions should be limited. Objectives Studies performed on field geometries [1-3] shows that the withstand voltage can be increased considerably if one or both of the electrodes are covered with a layer of solid insulation. The main theme of this work is to study hybrid insulation systems in inhomogeneous field geometries in addition to the influence of the material properties of the solid insulation (e.g. permittivity and conductivity). Other subjects to be studied are the influence of the voltage shape on the withstand voltage, discharges and space charge distribution.

Parallel to the practical experiments, modelling of the insulation system are made. The modelling is based on experimental results and might be divided in two parts; analytical and numerical. The analytical part is concentrated around the withstand voltage, breakdown criteria and the space and surface charge distribution. The numerical part is concentrated around breakdown criteria, charge distribution and material modelling Hybrid insulation The breakdown voltage of an air gap between two electrodes can be improved considerably if one or both of the electrodes are covered with a thick (some millimetres) dielectric coating. If free charges are available in the gap or in the air volume surrounding the structure, charges accumulates on the dielectric surfaces due to electrostatic attraction. This accumulation process continues as long as there is a driving field, i.e., as long as |Eg| > 0. The electric field in the hybrid insulation system can be calculated as the vector sum of the applied field and the charge induced field:

total capacitive charge inducedE = E + Eur ur ur

(1)

Figure 1 – Fundamental idea of hybrid insulation. The anode is covered with a layer of silicone rubber

Ed

Eg

3 mm

16 mm

The charge formation on the insulation surface builds up an electric field that reduces the field Eg in the air gap and increases the field Ed in the solid insulation. The net result is an overall increased insulation performance. This technique may be used in design and construction of compact high voltage equipment in the future. However, the physics of the phenomena is not yet fully understood. Figure 3 – Partial discharges under a positive lightning impulse. The streamers bridge the air gap but does not cause breakdown of the insulation system. Progression I started my PhD studies in August 2003, and have finished all except one of the compulsory courses. The first months of the PhD study have been used for literature studies of hybrid insulation and breakdown criteria.

An experimental set-up has been built (see fig. 2). The first experiments are completed and some results will be presented in a paper submitted to ICSD2004. Initiation and funding This PhD project started in August 2003 and is scheduled to be finished during the fall 2006. The work is funded by ABB and the Norwegian Research Council. Supervisor is prof. Arne Nysveen and co-supervisor is prof. Erling Ildstad. My background is from High Voltage Technology and Management, Delft University of Technology, where I graduated in September 2001. References [1] Jörgen H. M. Blennow, “Active High Voltage Insulation”, PhD thesis 2000 [2] Mats Sjöberg, “Charge Accumulation in Hybrid High Voltage Insulation”, PhD thesis 2003 [3] L. Ming, U. Fromm, M. Leijon, D. Windmar, L.Walfridsson, A. Vlastos, M. Darvenzia and J. Kucera, “Insulation Performance of Covered Rod/Plane Air-gap under Lightning Impulse Voltage”, ISH1997, Montreal, Canada.

Figure 2 – Experimental set-up. For the current measurement, the current is directly coupled to the oscilloscope via a coaxial cable (50Ω) terminated with an internal 50Ω resistance. In case of breakdown of the insulation system, protection is added both at the start of the coaxial cable and at the input of the oscilloscope. Camera and oscilloscope is connected to a pc for recording.

R

Voltage divider

Rf

Rt

Rf

Rr

Marx impulse generator (1.2MV)

Cs Udc Osc.

Camera Cf

prot

ectio

n

Current measurement

PC R1=10kΩ

R2=5Ω

Utilization of Power Electronics in Wind Farms Bjarne Idsøe Næss

30/01-04

Introduction In the past decade wind turbines has infiltrate the power grid and this trend seems to continue in the future. When develop the power grid using wind turbines instead of conventional power plants the performance of wind turbines has to be investigated and taken in consideration. Specifications must be required for the wind plants to maintain the reliability of the power grid. Disconnection of wind plants can occur under grids fault such as temporary short circuits or temporary voltage drops. Because of protecting the power electronics or prevent voltage instability wind turbines may be disconnected under such faults. If the penetrating of wind power plants is large, the conventional power plants may not manage to replace this production. Then to prevent the grid to collapse the wind turbines should withstand such transient failures.

Generating System Used in Wind Turbines

GearBox

Induction Generator

Power Grid

Fig 1. Squirrel Cage induction Generator.

The most common wind turbine generator is the squirrel cage induction machine , illustrated in Fig 1. This is a low cost and robust machine and it requires little maintains. The main drawbacks are:

- The required demand of reactive power that vary with the slip. It is well known that large introduction of induction machines is risky due to voltage stability.

- The machine has a stiff coupling between the grid frequency and speed. Then the wind gust will stress the mechanical equipments, in particular the gear.

- The system efficiency is lower than a variable speed turbine because the optimal turbine speed is a function of the wind speed.

GearBox

Induction Generator

Power Grid

Converter

Control

Doubly Fed Induction Generator

QS,RefPS,Ref Vdc,Ref

Fig 2. Doubly Fed Induction Machine.

The doubly fed induction machine , illustrated in Fig 2, is also a serial produced generator for wind turbines. This is a wound inductions machine with a converter connected to the rotor windings and a converter connected to the grid. These converters fed the slip power back into the grid when the generator operates in sub synchronous speed and fed slip power into the machine when it is operating over the synchronous speed. This allows the speed to vary between ±30percent. Thus the wind gusts which stress the mechanical equipments can be damped by vary the generator speed. The main drawbacks are:

- Extra cost due to the converters (must be rated 30percent of the generator).

- Extra maintains due to slip rings. - The turbine had to be disconn ected when

fault currents occur - Extra losses due to the converter

Synchronous Generator

Converter

Power Grid

Fig 3. Direct Driven Generator

For large wind turbines a low speed synchronous generator and full rated converters connecting the wind turbine to the power grid is often used. A schematic illustration is shown in Fig 3. In this topology the gearbox is taken away and the converters gives the opportunity to control the system with very few restrains compared to a doubly fed induction machine. The main drawbacks are:

- Extra cost due to the full rated converters - Generator costs (new technology) - Sensitivity of the power electronics to over

currents - Extra losses due to the converter

A large amount of investigation on generator topologies for wind turbines are carried out world over. The manufactures tests and make use of several different topologies. There are many circumstances which can influence on the choice of generator topology. To mention some of them:

- With an advanced pitch control the control requiring to the generator topology could be less. Then a cheaper generator topology could be preferred.

- The robustness and the utility of the gearbox. If the gearbox tolerates large torque pulsations the control requirements of the generator topology could be less. If the speed ratio of the gearbox can be controlled there is no need to control the generator speed.

- If there is a large amount of wind power in the grid the failure requirements must be taken in consideration . This means that the wind power plants had to withstand transient failures in the main power grid. A transient failure in the main grid will lead to a voltage drop at the connections to the power plants. Thus the generator technology should be robust to voltage drops and overcurrents due to this.

- If the wind power plant supplies local loads, disturbances such as flicker and harmonics should be as low as possible. If using a converter in the topology this should have a high switching frequency and the control system should annul the 3-p effect caused by the wind shadow of the tower. The generator should also be able to supply short circuit currents to trigger local protection schemes. In particular if the wind power plant is connected to a weak power grid where this could be a problem.

Progression The main task for the project is to investig ate the advantages and problems power electronics gives both to each wind turbine and to the whole wind plant system. To carry out the investigation laboratory setups and simulation s in Matlab and PSCAD/EMTDC will be used as the most important tools.

Founding The project is part of NFR KMB "Development of Norwegian wind power technology" (2001-2005) where John Olav G. Tande is the project manager and it is financed by NFR, Statkraft, Umoe Ryving and Norsk Hydro. My advisor is professor Tore M. Undeland and I have benefits in cooperating with other PhD students and fifth year students at the department. The PhD study was started January 2003 and will be finished within spring 2006.

Guiding of lightFibre optics has for several years become a moreand more common system for decorative andother kinds of interior illumination. Solid coreplastic cables made from transparent dielectricsare now available for diameters up to 12-15 mm.These optical guides will typically conduct lightfrom a 50-100 W high intensity discharge lamp(HID) to a light emitting point 5-15 m from thesource. Meanwhile a substantial limitation forsuch systems is the relatively low capacity of lighttransmittance. For more basic illumination of non-residential buildings, light guide systems based onsome type of hollow pipes have to be used.

Specular metallic light guides are based on specu-lar reflections inside metallic pipes of dimensionstypical 150-300 mm. A typical light source canher be a 400 W metal halide discharge lamp colli-mated by a parabolic or elliptic reflector.

The fundamental parameter for a light guide sys-tem is the transmittance of the system, the systemattenuation. For a hollow system the attenuation isdetermined by the reflective properties of theinner surface of the guide, and the collimation ofthe light rays when passing through the inputaperture of the pipe. A simple illustration of atwo-dimensional metallic light guide is shown inthe figure 1:

Figure 1 Meridional ray propagating through a hollow specular light guide

For a meridional ray the attenuation through aguide of length k and diameter b can be expressedby the approximation

(1)

where r is the specular reflectance of the tubesinner surface.

It can be shown that if the input aperture of aguide is illuminated by a uniform and circular-symmetric radiation, an approximation for thetotal attenuation can be expressed by [Loewen-stein 1969]:

(2)

A rough calculation for a light pipe of aspect ratio

, max imum inc iden t ang l e

and specular reflectance

gives a total attenuation, or transmit-tance, of . That says 98% of the inputlight energy is absorbed during the reflectionsthrough the guide for this system, which of courseis unacceptable. If the reflection for the surface ofthe guide is increased to , the total atten-uation for the pipe is substantially increased to

, which in many cases can be reasona-ble. A specular reflectance of 0.99 can hardly beachieved for metallic surfaces to a reasonablecost, so therefore other materials with otherreflective properties have been developed.

The two main materials for highly reflective hol-low light guides are based on reflection in trans-parent dielectrics. The micro-prismatic filmutilize total internal reflection (TIR) in micro-prisms, while the multilayer polymer mirror filmachieve very high reflectance by repeated Fresnelreflections. For both materials the reflectance areclose to 1 under controlled conditions.

θ

k

bΦi

r

Φo

θi θr

AmΦoΦi------- r

kb--- θtan⋅

≅=

At r0.85 k

b--- θmax⋅ ⋅

≅

kb--- 100=

θmax 0.44rad 25o( )=

r 0.90=At 0.02=

r 0.99=

At 0.69=

Hollow light guides for general illumination of office buildings

Knut Opdal11. February 2004

The micro-prismatic film from the 3M company,is based on TIR in longitudinal right-angle micro-prisms in parallel to the axis of the tube. A sheetof such a film is sketched in figure 2.

Figure 2 Structure of micro-prismatic film

The film is smooth at the incident inner side of theguide, and with longitudinal microprisms at theother. It can be shown from Snell’s law that alight-ray with incident angle θ < θmax willundergo TIR, which is in theory a reflection with-out any absorption of energy [Whitehead 1982].Such a film is therefore very convenient as reflec-tive material in hollow light guide systems.

Research projectsThe thesis is dealing with the use of highly reflec-tive hollow light guide systems for basic illumina-tion of office buildings. Three projects have beenaccomplished till now. The first introductorymeasurements were done as a student’s diplomaproject during autumn 1998. We here comparedthe attenuation of full-scale models of metallicand micro-prismatic tubes. The results from thisproject are to be found in [Mork 1998].

The next project were done during a visit to theUniversity of British Columbia (UBC) in Vancou-ver in 2000. Here a scale-model of offices with alight-pipe system with so-called dynamic extrac-tors were built and evaluated. The results fromthis measurements are in [Opdal 2000].

A third project is treating what we have men-tioned as intelligent light guides. Two student-projects, one at UBC and the other at NTNU, in2001 are analysing how to control dynamicextractors by the use of installation buses for auto-matic building control. This results can be foundin [Cheng 2001] and [Jucknischke 2001].

The dissertation will be finished during theautumn this year. The main part of the work isnow to write the thesis. In addition there areplaned to do some photometry for a full-scalemodel of a dynamic extractor, and also probablysome computer simulations of so-called laser cutpanel (LCP) solutions for branching- and corner-devices for complete light guide systems. AMonte-Carlo ray-tracing program named ASAP isacquired and tested for this purpose.

ReferencesLoewenstein 1969

Ernest V. Loewenstein and David C. NewellRay Traces through Hollow Metal Light-Pipe ElementsJournal of the optical society of America, 59 (4), 1969, pp 407-414

Whitehead 1982-2L. A. WhiteheadSimplified ray tracing in cylindrical systemsApplied Optics, 21(19), October 1982, pp 3536-3538

Mork 1998Arvid MorkBruk av hule lysledere i bygningerDiplom, Institutt for elkraftteknikk, NTNU, Desember 1998, 60 p

Opdal 2000Knut OpdalDynamic extractors and intelligent light guides in light guide systems based on micro prismatic filmReport from a project at SSP Lab, UBC, October 2000, 18 p

Cheng 2001Ju-Chieh (Kevin) Cheng and Dr. KotlickiIntelligent prismatic light guideDepartment of Physics and Astronomy, UBC, April 2001, 22p

Jucknischke 2001Daniel JucknischkeControl of a dynamic extractor in hollow light guides by use of LonworksProject Work, NTNU, November 2001, 90 p

γγγ

θθθ

IntroductionExternal electric fields have been applied extensi-vely to break water in oil emulsions. Historically,the electric treatment has been established sincethe beginning of the 20th century. The electro-static treaters use the electric field to enhance coa-lescence of water droplets in crude oil and thenreduce the settling time. Although the exact wayin which this occurs is not yet clearly understood.Water-in-oil type emulsions are readily formed inthe production of crude oil. This is causing pro-blems at different stages of the production.Corrosion of pipes, pumps and other processingequipment and the complications due to increasedemulsion viscosity are consequences of presenceof water. There are number of commercial reasons forremoving the emulsified water from the crude oil.The cost of transporting water in pipeline or tan-ker and the extra processing equipment requiredto produce quality crude oil add to the productioncost. The slow rate at which liquids may be naturallyseparated in many water-in-oil type dispersionshas important commercial consequences.Currently there are several available methodssuch as chemical demulsification, gravity or cen-trifugal settling, filtration, heat treatment mem-brane separation and electrostatic demulsification.Each of these methods has its own advantages anddisadvantages. The conventional electroseparators are huge, aslarge residence time are required for the electro-coalescense regions and settling zones to separatethe enlarged water droplet from the crude oil.however this could cause complications for off-shore as platforms structures usually has limitedspace. Optimisation of the coalescense processwould be able to reduce the residence time of thedroplets in a given physical system, and therebyincreasing the volumetric throughput and enab-ling the utilisation of more compact and conse-cuently cheaper units.

ObjectivesThe main aim of this work is to study and charc-terize the forces on the droplets in an emulsionstressed wtih an electric field.

Forces on a droplet in an electric fieldTo describe the electric forces on a droplet it ishelpfull to compare the responses of charged andof neutral matter in both uniform and nonuni-formfields. In a uniform field (fig 1a) a chargedroplet is pulled along the field lines towards theelectrode carrying the charge of the opposite tothat on a droplet. There will act a coulomb forceon the object written as:

In the same field a neutral droplet will be polari-zed. There will be induced a negative charge onthe side nearer the positive electrode and positive

charge on the side nearer the negative electrode,as shown in fig 1a. Since the field is equal on bothside of the matter in an uniform field, there willnot be any net translation force on it. The matter

Principle of electrocoalescence in crude oil

Atle Pedersen

(-)(+)

(+)(-)

---------------

+++++++++++++++

(a) (b)

eq. 1FE qE=

Fig.1 Different respons on neutral matter in uni-form and nonuniform field

will not move to any of the electrodes. In fig. 1b a nonuniform field is applied, there is adifferent behaviour of the charged and unchargedobjects. The charged behaves much as before,being pulled along the field line. It is still attrac-ted toward the electrode with opposite polarity.The neutral matter will in this case get an transla-tion force on it. Since the matter is neutral the twocharges due to polarisation will be equal. But thefield operating on the two sides on the matter isunequal. This gives a net force towards the regionof stronger field. Under the assumption that theneutral matter can be considered as a dipole theforce can be written as below.

Fig 1b also show that the force on the neutral mat-ter is in the same direction no matter which elec-trode is charged positive and which is negative.Therefore will the object in an AC field move inone direction towards the region of stronger field

Drag forces. When a droplet is moving in a fluid a drag forcewill act on the droplet. This is a sum of the fricti-on drag and the pressure drag. In a stagnant fluidthe force can be quantified by the drag coefficientthrough the equation

where ρc is the density of the continuous phase,CD is the drag coefficient, A is the representativearea of the droplet and v is the velocity of the dro-plet.

Forces in an emulsionAn aqueous droplet will distort the field due to thedifference of the permittivity of the water and theoil. This will result in a nonuniform field aroundthe droplets. In principle the forces between twodroplets will be as described above. But in anemulsion there is mutual polarisation of the dro-plets by any neighbouring droplets. Therefore willthe assumption of regarding the droplets as dipolenot be applicable. To allow for mutual polarisati-on the forces must be simulated numerically. Thiscan be done with Finite element method (FEM)or boundary element method (BEM).

Experimental method. The velocity of the drops is measured with a highspeed video camera with a microscope lens. Theoptical bench used in the measurements is shownin figure 2. From eq 3 the drag forces can be esti-mated and the electric forces can be derived fromnewtons 2. law. The forces measured with the camera will be com-pared with the forces simulated numerically.

Further workFurther experiments will be designed in order tomeasured the forces between the droplets in anemulsion. Numerically, Boundary ElementMethod, simulations will be performed on compa-rable distributions of droplets to investigate theforces between droplets in an emulsion

AdvisorsProf Erling Ildstad is the main advisor in thiswork. Prof Arne Nysveen is co-advisor.

Digitalt Camera Long Distance Microscope Test Cell

Background Light

Test object

Laptop

Electrodes

Translation stages

Strobe Light

Figure 2. Optical bench be used for investigation of droplets and emulsions

eq. 2FE µ∇E=

eq. 3FD12---ρcCDAv2

=

Optimial Design of Permanent Magnet Generators for Distributed Power Generation

Stev E. SkaarJanuary 2004

Initiation and fundingI graduated from NTNU, Department of ElectricalPower Engineering in December 2000. Aftergraduation I have been working as a scientificresearch assistant with the Energy ConversionGroup at the same department. I started my stud-ies towards a Ph. D. in September 2002. The the-sis is planned to be finnished during the fall 2005.

The Ph. D. work is a part of the project Technolo-gies for Reliable Distributed Generation of Elec-trical Power from Renewable Energy Sources,funded by the Research Council of Norway andwith Power-One as industrial partner.

Professor Robert Nilssen is my supervisor.

Main objectivesThe main goal for the project is to develop energyefficient components and enviromental friendlysolutions that enables different distributed renew-able energy sources to work as stand alone electri-cal power supplies or to be optimally integratedwithin the future electric power infrastructure.Having a transfere of this knowledge to industryor eventually establish new industry and toimprove scientific knowledge and develope a sci-entific competent staff in the field of renewableenergy systems.

BackgroundElectric power systems include power generation,distribution and control, and consumption of elec-tric power. The electric utility industry has histori-cally utilised a centralised, hierarchical structurewhere electricity is generated in large powerplants and then distributed through an extensivetransmission and distribution network to thepoints of demand.

The Energy Conversion Group at Department ofPower Engineering at NTNU also has a definedRenewable Sources of Energy strategy. To devel-ope cost-optimal power electronics and electricalmachines which enable best utilization of theenergy sources with respect to energy-efficiencyand environmental issues.

GoalThe goal for my thesis is to develope a computertool for calculation and optimization of a perma-nent magnetized (PM) generator/starting motor tobe integrated in several types of distributed powersystems using reciprocating engines. With use ofcompact winding, integration of permanent mag-nets and using the generator as a starting motorwith minimum energy consumption. Optimizationwill focus on minimal material cost and maximumefficency, combined with a focus on the cost of thepower electronic converter and control of the gen-erator.

Genetic Algorithms used in optimizationSince Holland developed the first genetic algo-rithm (GA) in 1975 [1], GA’s have been adaptedto many problems in various areas of science andengineering. A study of the work done in the fieldof electical machine optimization has revealed awide use of binary encoding of the GA’s. At thesame time books covering the theory of GA inoptimization give a warning in using this encodingmethod for these problems and instead use a real-number encoding to cope with the problem ofHamming cliff. The Hamming cliff is the phenom-ena accouring when, e.g the pair 0111111111 and1000000000 belong to neighboring points in thephenotype space but have a maximum Hammingdistance in the genotype space. To cross this Ham-ming cliff all bits have to be changed simultane-ously. The probability of this to accour withcrossover and mutation can be very small and a

premature convergence of the optimization couldbe the result [2].

In my work I will focus on real-number encodingon permanent magnet machines when using GAoptimization. From a study of previous work donein the field I feel confident that this will lead togood results for the optimization part of my work

Use of Field Analyse computer softwareUsing GA for optimzation require a good mathe-matical description of the problem optimized. Tomake sure that quantities like magnetic field in thecalculation is as correct as possible there has beendone a research on different softwares solvingmagnetic field problems. In my work there will bea main focus on axial magnetized PM machines.Getting a correct 2D model for this problems aredifficult because of the field orientation. To get thebest model as possible the use of 3D field calcula-tion software has been started. At this stage I’monly in the evoluation phase of different soft-wares. From this work there are many softwaresolutions available, but it seems like they all gottheir advantage and disadvantage. The resultsfrom field calculation is planned to be used as val-idation of paramters used in optimization and cal-culation of PM machines.

Future workMathematical description and genetic optimiza-tion of the PM machines is planned to be realisedin a Matlab environment. Structure of this Matlabbased program, or toolbox, is going to be devel-oped. In this development a graphical user inter-face (GUI) is going do be made. This will,hopefully, make the program userfriendly andeasy to use. The structur of the program wouldalso be made with aim on futher development, sothat additional features can be implemented easilyat a later stage.

References[1] J. Holland, Adaption in natural and artificialsystems, MIT Press, 1975[2] M. Gen, R. Cheng, Genetic Algorithms &Engineering Optimization, Wiley, 2000, pp. 3-14

InitiationI graduated from Department of Power Engineer-ing at NTNU December 1999. In January 2000 Istarted as a scientific assistant and continued on aPhD from September 2000. The project wasscheduled finished in December 2003 but I will beapproximately 1 year delayed. The project is initi-ated by my advisor Prof. Roy Nilsen and isfounded by NFR and ABB Corporate Research.

BackgroundABB in Norway has world responsibility withinABB of offshore and subsea installations. Theelectric power in these installations is increasing.Use of controllable switches as high voltageIGBT’s can open up for more competitive andcompact components and systems. ABB want tobuild up competence about these new high voltageIGBT's design, control and practical use. It is nowavailable samples of power electronic componentsfor 4.5 to 6 kV. It is important to study how thesecomponents can be controlled and how new topol-ogies can be used to reduce the losses in thesecomponents.

The projectThe primary goal in my PhD study is to develop atopology and the power electronic components tomake a high power, high voltage electronic dc-dcconverter with galvanic separation. It means useof high voltage IGBT and high frequency trans-formers in the MW area.

I am going to study, analyse and develop topolo-gies for the power circuit for the converter. I willalso study and test new high voltage IGBTswitches and design of high frequency transform-ers.

A prototype of the converter will finally be madeand tested. The results from the measurement will

be compared to the theoretical analysis. Cost andpower factor is important criteria's that must bemaintained in the design.

Some parts of the work will be published in inter-national conferences and in scientific magazines.The goal is to publish at least two articles.

StatusI have chosen to use a Dual Active Bridge topol-ogy as the figure below shows.

Figure 1: DAB converter

This topology gives galvanic separation betweeninput and output. It is also possible to run the con-verter as a resonant converter. This can reduce thestress on the switches and give lower losses in theconverter.

Modern IGBT switches has a blocking voltage upto 6kV. The input voltage on the converter is in therange of 30kV. This implies serial connection ofIGBT’s to be able to block the voltage.

Power supply to the gate driver for these serialconnected IGBT’s are difficult. The supply volt-

Transformatorn:1

D1A+T1A+ D1B+T1B+

D1A-T1A- D1B-T1B-

D2A+T2A+ D2B+T2B+

D2A-T2A- D2B-T2B-

L

IL

A

B

C

D

High power high voltage electronic dc-dc converter

Gjermund Tomta30.01.2004

age of a gate driver is in the order of 15 - 30Vdc.Some of the IGBT switches may be at a potentiallevel 20 to 30kV. This level is also jumping. To liftthis voltage from ground level up to a potentiallevel of 30kV require bulky transformers althoughthe power transfer may be small.

To solve this problem I have made a self suppliedgate driver. It extracts the energy from the turn offsnubber over the switch and converts it to a properDC voltage for the gate driver. Figure 2 belowshow one of the series connected IGBT’s and itsgate drive and power supply.

Figure 2: Self supplied gate driver

This power supply is tested and functions well.The power supply is independent of the number ofswitches series connected. Figure 3 below showsthe scheme of the power circuit.

Figure 3: Circuit scheme of power supply

This solution does not avoid galvanic separationfor the gate driver power supply completely, butthe transformer is reduced to the same voltage asthe switch is rated for. A regenerative solution ofthe power supply is also made but not tested yet.This passes the surplus energy of the from the turnoff snubber back to the dc-grid.

Further workThe remaining work is to make build the trans-former between the two bridges in the Dual ActiveBridge.

The control system of the Dual Active Bridgetopology must be designed.

References

[1] K. Vangen, T. Melaa, S. Bergsmark R. Nilsen,“Efficient high-frequency soft-switched powerconverter with signal processor control”INTELEC’91

[2] P. R. Palmer, A. N. Githiari “The series con-nection of IGBT’s with active voltage sharing”IEEE Transactions on power electronics vol.12no.4 july 1997

[3] R. Roesner, J. Holtz, R. Kennel “Self poweringdriver circuit for series connected power semicon-ductors” EPE 2001

CS

Dsw

TswB2

DS

Gatedrive

Powersupply

switching signalby fibre optic

+

-

+-

R0 1.2k

Rc 7.5

VoltageregulatorVout=15V

Cs 0.1u

D0

Rg 100k

Zg=10V

Rs 10k

Lc 1.5m

Cc 470u Zc=22VDs

Dsw

Tcharge

Tsw

Dc

C

E

+

-

Vout=15v

+

M:\e-post\Attach\infoartikkel.fm

IntroductionThis dr.ing study is a part of the project“Polymerisolasjon for neste generasjon HVDCkabel.” The initiation is made by Nexans NorwayAS which is also responsible for the financestogether with Norsk Forskningsråd and Statnett.My work started in August 2001 and is due to befinished in 2005.Superviser will be Erling Ildstad and RolfHegerberg.

BackgroundDuring the last 50 years HVDC distribution hasbecome more common, especially use of subseacables. For long distance bulk distribution HVDCis often the only available technology. Since the1950’s the insulation of the cables has been massimpregnated paper, which has shown good quali-ties with few problems. Still investigations havebeen done on another type of insulation, polymermaterials. These are already widely used in ACcables, but with HVDC electric charge builds upin the insulation and may cause breakdown of thecable. Also, the conductivity of this insulation arestrongly dependent of temperature and field gradi-ent.

A and B are material constants and these varywidely for different materials as well as with theadditives added. When the properties of the poly-mer insulations are investigated properly the resultwill be cables with a technical, economical andenvironmental advantage to the mass cable.Projects in the close future may be the connectionfrom an oil-platform in the North Sea to the distri-bution system on the mainland.

WorkThis work will be conserned with the conductivityin Crosslinked polyethylene (PEX.) Investigationswith constant field and varying temperature orvice verca will be accomplished

The measurements will be done with PEX insula-tion material. Rogowski shaped objects are made,and electrodes of aluminium is used for currentmearsurements while semiconductors are used forthe space charge measurements.

The conductivity of a object is measured by a cur-rent measurement. It is often assumed that thefield through an object is uniform given by E=U/d. This will not be the case with a polymer as thefield is given from the space charge in the object,and the space charge is influenced by the tempera-ture and the amount of time the object has beenstressed. To investigate this, space charge measur-ments are done using the pulsed elctro-acousticmethode (PEA.) The objects are charged by avoltage and a temperature gradient, and this givesa variation of the field through the object. Thebuild up of space charge in a 1 mm object during24 hours is shown in figure 1.Comparing these measurements with the conduc-tivity measurement should give an understandingof how temperature and field influence the con-ductivity of the HVDC insulation.

σ A ϕkT------

B E( )sinh( )1 E

--------------------------------exp=

Polymer insulation of HVDC cable (preliminary title)

written by Sidsel Trætteberg

1.5x101

1.0

0.5

0.0

-0.5

-1.0

nC/m

m3

2.01.51.00.50.0

mm

12/12/02 10:42

Fig.1 Build up of space charge during 24 hours.The red curve is taken at t=0.

A long-term system dynamic analysis of the Nordic power marketThis work has developed a long-term system dy-namic model of the Nordic power electricity mar-ket. It represents an alternative to the existingquasi-dynamic, partial equilibrium models EMPS(Samkjøringsmodellen, SINTEF) and Nordmod-T(Statistics Norway) while being a based on dise-quilibrium, continuous nonlinear differentialequations using the theory of system dynamics.The importance of understanding the dynamic as-pects of power systems have been fully recognisedat the component and system level in electrical en-gineering. Modifying a power system without pri-or testing and careful dynamic analysis would beunthinkable. The same can, unfortunately, not besaid about the design of electricity markets andeconomic systems. An electricity market is inher-ently dynamic. With Kraftsim, it is now possibleto analyse the dynamics of electricity markets andtest system responses of various electricity marketand energy/environmental regulations. These ca-pabilities are now especially important, as the roleof authorities have shifted from direct planning tomarket design. Botterud et al. (2000-02) launched

the first version of this model, with Vogstad et al.(2001-03) taking the development further. Figure1 shows the main feedback relationships that areimportant for the long-term development of theNordic power market, where 7 different genera-tion technologies are present: Hydro, wind, bio,nuclear, coal and finally natural gas with and with-out CO2 capture . In the next sections, we willpresent two interesting applications and results.

The final resolution to the Norwegian marginal CO2-controversyA remarkable debate has dominated the Norwe-gian energy policy discourse over the last decade:The question whether new gas power will increaseor reduce CO2-emissions in the Nordic electricitymarket. Despite many efforts, energy researchershave failed in convincingly resolving this contro-versy. Figure 2 shows the system response of in-

troducing 3200 MW of gas power into the Nordicmarket in 2005. In the short run, some coal poweris substituted (middle graph) this substitution ef-fect is modest as baseload coal is cheap. In thelong run - future investments in renewables arealso substituted (upper graph). The net effect isthat gas power increase total CO2-emission in thelong run (lower graph). For more detailed explana-tions, see Vogstad et al. (2002) and homepage.The difference in results from those of previoussimulation studies is that the long-term effect oninvestment decisions are taken into account. Sim-ulation studies with EMPS and Nordmod-T werere-run for comparison of results.

Figure 1 Main feedback loops of the electricity supply sidein Kraftsim

Price of electricity

Capacity factor

operational costs

Electricitygeneration

Capacity

Expected profitabilityof new capacity

Investment &operational costs

Technologicalprogress

Resourceavailability

+

-

-

+

+

-

-

+

B1 - Unitcommitment

B2 - Capacityacquisition

R1 - Learningcurve

B3 - Resourcedepletion

-

+

-

+

B4- erosion ofCF

Demand

Fractional growthrate

Price elasticity ofdemand

-+

-

+

B0 - Demandbalance

+

Figure 2 Simulation results. Thin lines show reference runscenario: The Nordic power system with 100 NOK/MWhsubsidies for renewables, no CO2 taxes. Bold lines showwhat happens when 3200 MW of gas power is introduced in2005. (see presentations at homepage for larger graphs)

Installed Capacity

01/01/2000 01/01/2010 01/01/2020 01/01/20300

10,000

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30,000

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Capacity Gas

*Capacity Bio

Capacity Bio

*Capacity hp

Capacity hp

*Capacity NuP

Capacity NuP

*Capacity co

Capacity co

*Capacity WP

Capacity WP

Capacity Gas Peak Load

Non-commercial use only!

Generation

01/01/2000 01/01/2010 01/01/2020 01/01/20300

50

100

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200TWh/yr

*avg Generation Gas

avg Generation Gas

*avg Generation Bio

avg Generation Bio

*avg generation hp

avg generation hp

*avg Generation wp

avg Generation wp

*avg generation co

avg generation co

*avg Generation GasC

avg Generation GasC

N i l l !

CO2 emissions

01/01/2000 01/01/2010 01/01/2020 01/01/20300

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*Avg CO2 emission co

Avg CO2 emission co

*Avg CO2 emission gas

Avg CO2 emission gas

*Avg CO2 emission pl

Avg CO2 emission pl

*Total CO2 emissions

Total CO2 emissions

*Avg CO2 emission GasC

Avg CO2 emission GasC

Non commercial use only!

A system dynamics analysis of the Nordic power market:The transition from fossil fuelled to renewable electricity supply within a deregulated electricity market

Klaus-Ole Vogstad, MSc. Mech.engineering, NTNUklausv@stud.ntnu.no http://www.stud.ntnu.no/~klausv mob: +47 928 510 67

Designing electricity markets: The case of Tradable green certificatesTradable green certificates (TGCs) has been pro-posed as a market-oriented subsidy for renewablesin EU, and already implemented in a few coun-tries. Norway is now considering joining Swedenin their TGC system. However, the price forma-tion raises some concerns, due to the strong yearlyfluctuation of renewables. Numerous studies usingstandard economic theory and partial equilibriummodels have already been conducted on TGCs.While these studies provide useful insights of thepotential benefits of introducing the TGC market,they implicitly assume perfect market conditions.Consequently, the equilibrium approach does notsuggests which type of market design is best suitedto ensure a stable, well-working market. Vogstad

et al.(2003) presents an analysis of the TGC mar-ket design implemented in Sweden. Using the sys-tem dynamics approach in combination withexperimental economics, we were able to analysethe performance of various market designs experi-mentally from our network experimental simula-tion game involving interactive players. The studyreveals serious weaknesses in the current design,and suggest improvements that overcome theweaknesses. This study was awarded Dana Mead-ows students prize at the International System Dy-namics conference in New York, 2003.

Utilising the complementary characteristics of hydro and wind in hydro schedulingA simplified EOPS (Vansimtap) model based onthe water value method using stochastic dynamicprogramming was designed in order to study thehow the complementary characteristics of windand hydro can be utilised in hydro scheduling. TheSDP formulation contains price and reservoir asstate variables and wind and hydro as stochasticvariables. A price model utilise scenarios from the

EMPS model. Fig 4 shows typical results of themodel implemented in Matlab. As a by-product,the simplified EMPS model can be used in educa-tion and in research for studies on hydro schedul-ing problems combined with the experimentaleconomics and system dynamic modelling con-cept. Collaboration with the SINTEF-project

“New renewable energy production in Norway”took place 1999-2000, reported in four conferencepublications and a final SINTEF report (Vogstad,2001) The work was financed by The ResearchCouncil of Norway (NFR), under the “EFFEKT”programme. The PhD work started in Sept. 98’,extended through an 8-month Marie Curie Fellow-ship stay this year at CML Leiden, Netherlands.Thesis will be completed within 1st of April 04’.

Selected publications (available at homepage)Vogstad K, MM Belsnes, JOG Tande, KS Hornnes, G Warland(2001): Integrasjon av vindkraft i det norske kraftsystemet. SintefTR A5447 EBL-K 32-2001_Vogstad K (2000a) Utilising the complementary characteristicsof wind power and hydropower through coordinated hydro produc-tion scheduling using the EMPS model. Proceedings, Nordic WindPower Conference, March 2000, Trondheim, Norway. _Vogstad K, Holttinen H, Botterud A, JOG Tande (2000b): Systembenefits of coordinating wind power and hydro power in a deregu-lated market. Published in proceedings "Wind power for the 21stCentury" 23-25. Sept 2000, in Kassel, Germany_Tande JOG, K Vogstad (1999): Operational implications of windpower in a hydro based power system. Proceedings European WindEnergy Conference, 1.-5.3.1999, Nice, France_Holttinen H, K Vogstad, A Botterud, R Hirvonen, (2001): EffectsOf Large Scale Wind Production On The Nordic Electricity Market.Ewec‘2001, Copenhagen, Denmark, 2-6 July, 2001._Botterud A, M Korpås, K Vogstad (2000): En langsiktig systemdy-namisk kraftmarkedsmodell. Proceedings, NEF technical meeting.pp157-165, Trondheim, Norway._Botterud A, M Korpås, K Vogstad, I Wangensteen (2002): A Dy-namic Simulation model for Long-term Analysis of the Power Mar-ket. Paper accepted for the Power Systems ComputationConference, 25th -28th June 2002, Sevilla, Spain. _Vogstad K, A Botterud, KM Maribu, S Grenaa (2002): The transi-tion from a fossil fuelled towards a renewable power supply in a de-regulated electricity market. Proceedings, 20th System DynamicsSociety International Conference 28th -1st August, 2002, Palermo,Italy._Vogstad K, I Slungård, O Wolfgang (2003): Tradable green cer-tificates: The dynamics of coupled electricity markets. Proceedings,21st System Dynamics Society International Conference, Jul 20-25,2003, New York. USA.

Figure 3 Stray Spetalen-wannabes trading TGC certificatesin the experimental laboratory: Models are convertedinto interatcive simulations in a computer network.

Figure 4 Water values from SDP computation and the corresponding reservoir level curves used for hydro scheduling.

1 2 3 4 5 6 7 8 9 10 11 120

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Sensorless control of Permanent Magnet Synchronous Machines

Sigurd Øvrebø

Initiation The work is supported by the Norwegian University of Science and Technology. Industrial partner for the project is Smart Motor. The study was started in January 2000, and the thesis is due by February 2004. Introduction The development of electric machine drives must meet new challenges as the cost of electronic equipment rapidly decreases. Electric machines are becoming a part of most people’s lives as their arena continues to expand through household equipment, office equipment and even in new car designs. The enormous expansion of the application arena for electric machines gives new criteria for integration and reliability of the drive systems. High performance drives have earlier been dependent on sensors for flux and position measurement. The reliability of these systems depends on cabling, connectors and the sensors located at the motor location. Great advantages can be obtained if flux and position estimates can be obtained without the sensors located at the motor. During the last decade a lot of research has been done to make a high performance drive system without a position sensor. Most of the research use saliency’s in the electric machines as the input to the position estimators. This saliency’s can be apparent in the machines for different reasons. With interior permanent magnet the magnetic properties in the rotor are inherently different in the d-q axis. This is due to the different magnetic permeability of iron and magnet.

Machines with surface mounted magnets have no saliency if there is no saturation in the machine. When the permanent magnets are introduced in the machine there will be some parts of the stator that goes into saturation. This results in a position dependent variation in the machine inductance. Several different methods are used to extract the variations in the current resulting from the position dependent inductance. Common for all methods is that one needs to use an additional signal to get the position information from the measured currents. Different machines have different behavior of the position dependent inductance. The inductance in the machine is frequency and load dependent. To precisely describe the saliency position one has to understand totally the electromagnetic behavior of the machine. Also one has to describe the different test signal flux pats in the machine. Two different methods are tested on booth surface mounted and buried magnet machines. The first method [1] is developed in University of Wisconsin, Madison, USA. This method use a balanced three phase high frequency test signal (pulsating signal also tested).

Current

Regulator

PWM - Voltage

Source Inverter

( PWM-VSI)

AC Machinewith Saliency

HPF

+

–

++

θr, ωr

scV

sfI

sfV

sVαβ

sIαβ

s_ cIαβ

Figure 1 Balanced three phase voltage superimposed

The high frequency component of the current is filtered out and fed trough an observer.

Kp

Ki1s +

+

sin(2θ –ωct)^cos(2θ –ωct)

+

–

Heterodyning Process

ε

Controller

^

s_ cIα

s_ cIβ

θ

ω

1s

1J

dKJ

+

+1s

emT Physical Model

LPF

Figure 2 Position observer The second method was developed by M. Shrodl at “Technischen Universitat”, Wien. This technique use the same physical phenomena as the first method but the test signal is different. The derivation of the position estimate is also different. Shrodl use the step response in the current to estimate the inductance. Three voltage vector directions are used to describe the position dependent part of the inductance. By summing the three derivatives from the currents in a space phasor manner the result is a space phasor describing the double rotor position. Figure 3 show the phasor relationships.

d

q

u2β

uβ

u

sdid βτ

e2k2µ

−

e0kµ

γ

stator s,A(U ) Figure 3 Phasor diagram

Primary Goals Develop a high performance drive system for PMSM. Compare different excitation methods and their electromagnetic response in the machines. Status of Work The PhD work is in the final stage. The methods are implemented and tested on a IPMSM. Saliency models and frequency dependency in the saliency is described. The axial flux prototype from Smart Motor is redesigned for sensorless control. A new prototype is under construction where saliency is introduced in the stator leakage flux path. Advisors My advisor is Prof. Roy Nilsen. References [1] P.L.Jansen, R.D.Lorenz: “Transducerless position andvelocity estimation in induction and salient AC machines ” IEEE Transactions on industry applications Mar/Apr 1995, pp2 40-247 [2] M. Shrødl: “Sensorless control of A.C machines” PhD. Thesis, Wien 1992

Dr. ingeniørs from Department of Electrical Power Engineering from 1990:

Year Name Title

2003

Botterud, Audun Long Term Planning in Restructured Power System: Dynamic Modelling of Investments in New Power Genera-tion under Uncertainty

Ettestøl, Ingunn Analysis and modelling of the dynamics of aggregate energy demand

2002

Kolstad, Helge Control of an Adjustable Speed Hydro Utilizing Field Pro-grammable Devices

Norheim, Ian Suggested Methods for Preventing Core Saturation Insta-bility in HVDC Transmission Systems

Warland, Leif A Voltage Instability Predictor using Local Area Measure-ments. VIP++

Ruppert, Christopher Thermal Fatigue in Stationary Aluminium Contacts

2001

Larsen, Tellef Juell Daily Scheduling of Thermal Power Production in a Dereg-ulated Electricity Market

Kleveland, Frode Optimum Utilization of Power Semiconductors in High-power High-frequency Resonant Converters for Induction Heating

Myhre, Jørgen Chr. Electrical Power Supply to Offshore Oil Installations by High Voltage Direct Current Transmission

Oldervoll, Frøydis Electrical and thermal ageing of extruded low density poly-ethylene insulation under HVDC conditions

2000

Doorman, Gerard Peaking capacity in Restructured Power Systems

Hystad, Jan Transverse Flux Generators in Direct-driven Wind Energy converters

Pleym, Anngjerd EMC in Railway Systems. Coupling from Catenary System to Nearby Buried Metallic Structures.

1999

Gjerde, Oddbjørn Systemanalyser av skipselektriske anlegg

Evenset, Gunnar Cavitation as a Precursor to Breakdown of Mass-Impreg-nated HVDC Cables

Hvidsten, Sverre Nonlinear Dielectric Response of Water Treed XLPE Cable Insulation

Pálsson, Magni Tor Coberter control design for Battery Energy Storage systems applied in autonomous wind/diesel systems

Warland, Geir Flexible transfer limits in an open power market.Congestion versus risk of interruption.

1998 Hans Kristian Høi-dalen

Lightning-induced overvoltages in low-voltage systems.

Selvik, Eirik Information models as basis for computer-aided tools.

Huse, Einar Ståle Power generation schedulingA free market based procedure with reserve constraints included.

1997 Bjørn Harald Bakken Technical and economic aspects of operation of thermal and hydro power systems.

Ole-Morten Midtgård Construction and assessment of hierarchal edge elements for three-dimensjonal computations of eddy currents.

Qing Yu Investigation of dynamic control of a unified power flow control-ler by using vector control strategy.

1996 Gerd Hovin Kjølle Power supply interruption costs: Models and methods incorpo-rating time dependent patterns.

Tom Fagernes Nestli Modelling and Identification of Induction Machines

Bjørn Sanden XLPE cable insulation subjected to HVDC stress.Space charge, conduction and breakdown strenth

Gisle Johannes Tor-vetjønn

Switchmode PowersuppliesOptimum topologies and magnetic components

1995 Lars Arne Aga A Laboratory Platform for Theoretical and Experimental Research on Rotor Flux Oriented Control of Motor Drives.

Knut Styve Hornnes A Model for Coordinated Utilization of Production and Trans-mission Facilities in a Power System Dominated by Hydropower

Rolf Ove Råd Converter Fed Sub Sea Motor Drives

1994 Snorre Frydenlund A study of voltage stresses in ARC furnace transformers due to switching operations

Anne Cathrine Gjærde Multifactor Ageing of Epoxy - The Combined Effect of Temper-ature and Partial Discharge

Arne Nysveen A Hybrid Fe-Be Method for Time Domain Analysis of Magnetic Fields Involving Moving Geometry

Feng Xu Power System Security Assessment. Identification of Critical Contingencies and Outage Distance by a Zone Filter

Year Name Title

1993 Bjørn Alfred Gus-tavsen

A study of overvoltages in high voltage cables with emphasis on sheath overvoltages.

Svein Thore Hagen AC breakdown strength of xlpe cable insulation

Olve Mo Time Domain Simulation and Modelling ofPower Electronics Circuit.Development of a Simulation Tool

Terje Rønningen Internal faults in oil-filled distribution transformers.Fault mechanisms and choice of protection.

Gorm Sande Computation of Induced Currents inTthree Dmensions

1992 Per Hveem Computer Aided Learning, Simulations, and Electrical Motor Drives.

Ståle Johansen Energy resource planning a conceptual study of a multiobjective problem.

Astrid Petterteig Development and Control of a Resonant DC-link Converter for Multiple Motor Drives

Bendik Storesund Resonant overvoltage transients in power systems

1991 Jonny Nersveen Kvalitetskriterier og helhetlig planlegging av innendørs belysn-ingsanlegg.

Torbjørn Strømsvik Kraftelektronikk som kilde til forstyrrelser i fordelingsnettet.

Alf Kåre Ådnanes High Efficiency, High Performance Permanent Magnet Synchro-nous Motor Drives

1990 Eilif Hugo Hansen Bruk av kunstig lys og lysmanipulering for styrt produksjon av laksefisk.

Guijun Yao Modelling, Dynamic Analysis and Digital Control of PWM Power Converters

Year Name Title