university of craiova doctoral school of electrical …

UNIVERSITY OF CRAIOVA

DOCTORAL SCHOOL OF ELECTRICAL AND ENERGETICS ENGINEERING ELECTRICAL ENGINEERING

CONTRIBUTION ON THE STUDY OF SYNCHRONOUS GENERATORS USED IN

ELECTRIC TRACTION

ABSTRACT

Scientific Coordinator: Prof. PHD. Eng. Alexandru BITOLEANU

PHD STUDENT:

Eng. Ion PETROPOL-ŞERB

CRAIOVA 2020

Contributions on the study of synchronous generators used in electric traction

CONTENTS

INTRODUCTION 3

1. CRITICAL STUDY ON EVOLUTION OF DIESEL ELECTRIC TRACTION SYSTEMS WITH SYNCHRONOUS GENERATOR

6

2. CURRENT STAGE OF USING THE SYNCHRONOUS GENERATOR IN ELECTRIC TRACTION

7

3. FUNDAMENTAL ASPECTS OF THE TRACTION SYNCHRONOUS GENERATOR

8

4. COMPUTER AIDED DESIGN OF THE SYNCHRONOUS GENERATORS USED IN ELECTRIC TRACTION

9

5. ANALYSIS OF THE SYNCHRONOUS MACHINE BY USING THE FINITE ELEMENT METHOD

11

6. NUMERICAL METHODS USED IN SYNCHRONOUS MACHINE ANALYSIS

13

7. TEST BENCH TO STUDY SOME OPERATIONAL ASPECTS OF THE TRANSMISION “DIESEL ENGINE – SYNCHRONOUS GENERATOR”, SPECIFICS TO ELECTIC TRACTION

18

CONCLUSIONS 23

REFERENCES 26


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INTRODUCTION

I.1. Context and problematic of the research

I.1.1. International context of the research; I.1.2. National context of the research;

I.1.3. Research issues.

The European Transport Vision Europe 2050 [66], [145] defines them as the ‘Mobility as a service’ skeleton for passengers and ‘Delivery as a service’ for goods. Among the tools necessary to achieve the objectives of this vision are education and lifelong learning, standardization, research and innovation, management development, quality and operational capacity [66]. From the point of view of education and lifelong learning in the field of railway in Vision 2050, objectives have been identified [66] according to which, the research aims to approach the study of the synchronous traction generator from the perspective of elaborating materials for educational and training activities in the railway field.

In this context, in accord with the European vision regarding railway area, the objectives of human resource policy of CFR SA Company, aims ‚attracting, selecting, training and motivating staff’ [157].

Starting from the analysis of the national context in close connection with the international one, the research issue is defined as “Study of the synchronous traction generator in order to increase the quality of education in the railway field in order to technically harmonize electric diesel locomotives to ensure interoperability’.

Research objectives will be: 1. Identification and analysis of the directions of evolution / development of electric diesel transmission with synchronous generators. 2. Analysis and synthesis of theoretical methods for the study of synchronous traction generators. 3. Proposing a solution for the computer aided design of synchronous traction generators. 4. Application of the Finite Element Method in the study of synchronous traction generators. 5. Application of numerical methods for the analysis of synchronous traction generators. 6. Proposing an experimental stand for the study of some fundamental aspects of the diesel engine transmission - synchronous generator, specific to electric traction.

I.2. Thesis structure

In order to achieve its objectives, the research is structured in seven chapters, annexes and a chapter of conclusions.


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The introductory chapter aims to define the research issue and to justify the topicality of the topic in the context of national and international strategies for the development of the railway transport system. Using the method of critical analysis, the chapter provides a presentation of the concerns and evolutions of railway traction systems. The purpose of the chapter is to highlight global issues regarding electric diesel traction with synchronous generators. The research results will be the starting point in addressing the peculiarities of the operation of synchronous traction generators in accordance with current development needs..

Chapter 7, Test bench to study some operational aspects of the transmission 'diesel engine - synchronous generator', has as general objective the conception and design of certain experimental platforms and related work procedures, necessary for experimental simulation of specific aspects of electric rail traction with diesel engine and synchronous generator. The aim of the experiment is to create, at a laboratory scale, a correspondence for certain conditions, similar to those encountered in the operation of a railway electric diesel transmission, and to analyze the behavior of the synchronous generator with apparent poles in this energy chain. Three tests benches were proposed, realized and used to acquire the quantities necessary for the processing and tracing of the operating characteristics of the synchronous generator, to obtain specific traction characteristics, to study the behavior of the synchronous generator to the sudden variation of the load, to analysis of waveforms of currents and voltages in the proposed situations, as well as for their harmonic analysis. Features were plotted using processing in LabView and Matlab..

The experimental chapter has a strong inter- and trans-disciplinary character (electric machienes, diesel- electric traction, mathematical and numerical calculation, data acquisition). The experiments took place in the Laboratory of Electric Machines of the Technical University "Gheorge Asachi" in Iasi. The chapter is, for the most part, original. The design of the stands, of the working procedures, of the analysis programs of the data obtained by experiment (programs elaborated in LabView for tracing the different characteristics, the representation of the harmonic spectra in Excel) belong entirely to the author, being elements of originality..

The paper ends with a chapter of conclusions, annexes and an extensive bibliography with 165 bibliographic references (books, articles, standards, web bibliography), among which, 25 belong to the author.


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* **

At the end of my doctoral internship, I feel fully satisfied with the experience of completed studies. Therefore, I consider it an opportune moment to sincerely thank all those who offered me high quality scientific guidance.

To Mr. Prof. PHD. Eng. Alexandru Bitoleanu, with gratitude, I would like to thank him sincerely for the generosity and patience with which he guided me in the entire research activity. By sharing the rich activity and scientific experience, Mr. Professor supported and helped me to complete the thesis, identifying each time, with great precision, the blockages and proposing clear and safe directions for overcoming them. Mr. Professor, I send you a respectful THANK YOU.

I would like to thank the members of the steering committee: Mrs. Prof. PHD. Eng. Mihaela Popescu, Mr. Prof. PHD. Eng. Mircea Dobriceanu and Mr. Lect. PHD. Eng. Mihăiţă Lincă, for the scientific advice, extremely valuable and opportune, given throughout the elaboration of the thesis.

Throughout the research period I was honored to collaborate and share professional and scientific experience with Mr. Prof. PHD. Eng. Aurel Câmpeanu. In performing experimental determinations in the Laboratory of Electrical Machines at the Faculty of Electrical Engineering and Applied Informatics of Iaşi, I benefited from the support and advice of Mr. Prof. PHD. Eng. Lorin Cantemir, Mr. Prof. PHD. Eng. Alexandru Simion and Mr. Assoc. Prof. PHD. Eng. Adrian Munteanu, to which I sincerely thank.


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CHAPTER 1

CRITICAL STUDY ON EVOLUTION OF DIESEL ELECTRIC TRACTION SYSTEMS WITH SYNCHRONOUS GENERATOR

In the context of national and international strategies for the development of the railway transport system, the chapter aims to make a presentation of the concerns and evolutions of the railway traction systems addressing topics such as:

1.1. Analysis of the evolution of electric diesel railway traction: 1.1.1. Electric diesel traction: compact and reliable; 1.1.2. Electric diesel traction: increasing the speed, 1.1.3. Electric diesel traction - priority direction in environmental protection;

1.2. Generalities regarding the study of thermoelectric transmission; 1.3. Study of thermoelectric transmission in diesel locomotives: 1.3.1. The use of

synchronous generator in electric traction; 1.3.2. Study of the diesel engine group - synchronous generator;

1.4. Analysis of the evolution of electric diesel traction systems with synchronous generators.

Using critical study as a means of analyzing the added value of a new configuration to a particular system, the research answers the following problems: ‚1. What are the peculiarities of thermoelectric transmission? 2. How are they influenced by electrical transmission? Why was it necessary to replace the DC generator? What are the effects of using a synchronous generator electric transmission? ' The final goal of the study is to highlight the current directions for the analysis of the synchronous traction generator, viewed in permanent interaction with the other elements of the system.

A first objective of the chapter is to analyze and highlight the efficiency of the traction system by optimizing and harmonizing the components. The secondary objective of the chapter research is to structure and prioritize the information so as to propose and develop future modern educational materials, necessary for the training and continuing education of the personnel involved in the study, design, manufacture and maintenance of railway systems.

The results of the chapter research underline, by way of example, the fact that the transition to the use of the synchronous traction generator was imposed by the optimization requirements of the electric diesel transmission; that the technological premises of the solutions were favored by the development of related fields such as: electric machines and drives, power electronics, computer science, materials science, etc., and the analysis of the literature confirms that the study algorithm used for diesel engine - synchronous generator is similar to the one used for the study of the diesel engine - direct current generator assembly.


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CHAPTER 2

CURRENT STAGE OF USING THE SYNCHRONOUS GENERATOR IN ELECTRIC TRACTION

Through an extensive analysis and bibliographic synthesis on: 2.1. Requirements imposed on the synchronous traction generator in the current

context; 2.2. Current solutions for using the synchronous traction generator; 2.3. Customization of the excitation system of the synchronous traction generator.

Case Study The aim is to highlight the way in which the design, construction and operation of

traction generators are influenced by the balance of economic, technical and quality requirements. The chapter applies the method of functional analysis (fig. 2.1) to justify certain technical solutions for modernizing or designing new electric traction systems with synchronous generators.

Fig. 2.1. State diagram of the thermoelectric transmission with diesel engine

Evolution of the excitation systems of synchronous generators and customized by concrete solutions in a case study are presented analytically. The chapter ends with a set of conclusions:

A. For diesel engines used in rail traction: - it is necessary to correlate the design conditions with the operating conditions;


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- the conditions imposed on the diesel engine used on locomotives with electric transmission with synchronous generator are the same as those imposed on the transmission with direct current generator; - the diesel engine operates in a speed range between a maximum value and a minimum value; - the speeds corresponding to the partial power regimes are established so that the engine operates on an economic characteristic.

B. For the synchronous generator used in railway traction: - the synchronous generator used in railway traction must operate on an external characteristic corresponding to the operation of the heat engine at constant power (both nominal and partial); - the load current of the synchronous generator must change according to the need of the traction motors, fact for which the presence of some regulation devices is required; - the external characteristic of the synchronous generator used in the railway traction can be established for several speeds; - the excitation current of the synchronous generator varies accordingly to ensure the operation at constant power.

CHAPTER 3

FUNDAMENTAL ASPECTS OF THE TRACTION SYNCHRONOUS GENERATOR

Going through an extensive bibliographic analysis on topics such as: 3.1. Constructive and functional aspects of synchronous traction generators; 3.2. General operating equations of synchronous generator with apparent poles:

3.2.1. Equations of salient synchronous generator in the phase space; 3.2.2. Equations of salient synchronous generator expressed with vectors; 3.2.3. Equations of the salient synchronous generator in the theory of the two axes; 3.2.4. Equations of the synchronous generator in relative units;

3.3. Operating characteristics of the synchronous traction generator: 3.3.1. The idle characteristic of the synchronous traction generator; 3.3.2.

Operating load characteristic of the synchronous traction generator; 3.3.3. External characteristics of the synchronous traction generator; 3.3.4. Adjustment characteristic of the synchronous traction generator; The chapter aims to make a theoretical synthesis on the constructive and functional features of the synchronous traction generator.

In order to achieve this objective, the following specific objectives were met: - establishing the constructive particularities of the synchronous traction generators; - establishing the working hypotheses and operating equations of synchronous

generators with apparent poles in different analysis systems;


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- establishing and interpreting the operating characteristics of salient synchronous generators.

- the final goal of the research is to obtain the theoretical background necessary for the modeling and designing the synchronous generator used in electrical traction.

An important conclusion of the chapter research is that the knowledge of the operating characteristics, customized for the synchronous traction generator, allows the further development of tools to simulate the operation of the diesel engine synchronous traction generator assembly.

CHAPTER 4

COMPUTER AIDED DESIGN OF THE SYNCHRONOUS GENERATORS USED IN ELECTRIC TRACTION

Researching topics such as: - 4.1. Problematic of computer aided design of synchronous generators used in

diesel electric traction: 4.1.1. Formulation the theme; 4.1.2. Formulation the numerical problem;

- 4.2. Electromagnetic calculation of the synchronous traction generator: 4.2.1. Calculation of main dimensions; 4.2.2. Stator winding and slots; 4.2.3. Rotor sizing; 4.2.4. Inductor winding parameters; 4.2.5. Magnetic characteristics and excitation ampere turned at rated load; 4.2.6. Calculation of excitation winding; 4.2.7. Rotor winding parameters in steady state; 4.2.8. Parameters and time constants of the transient regime; 4.2.9. Time constants of the transient regime; 4.2.10. Short-circuit currents;

the chapter proposes and realizes an computer aided design algorithm dedicated to the synchronous generator used in electric diesel traction. With the help of this algorithm the electromagnetic calculation of the generator will be performed, the main dimensions will be established based on the data established by the theme, the recommended electromagnetic demands and the parameters and technical characteristics obtained from the adopted geometry will be calculated.

The design of the synchronous traction generator not only involves a large volume of information, but also takes into account a wide variety of calculation methods. The study method will be based on the algorithm of the analytical design methodology, and the implementation of the algorithms will be done in various programming environments, aiming, for the generality, that these subroutines are compatible with several software such as MathCAD, MATLAB, Excel etc..

The method of partial magnetic characteristics will be used to determine the excitation ampere turned at rated load. With the help of Matlab a subroutine is made for plotting the magnetic characteristics of the designed synchronous generator (figure 4.1). For an easy user dialogue with the computer, a graphical interface representation


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of the phased diagram of the designed synchronous generator with apparent poles was created, using the Matlab programming environment and the GUIDE graphics representation package.

a b

Fig. 4.5. Magnetic characteristics of the synchronous traction generator: a. Variant q = 4; b) variant q = 7/2.

For the two calculation variants the results of using the interface are presented in figure 4.2.

With the help of the Matlab software package, the phase diagram and the partial magnetic characteristics are represented in the same system of axes (for example, figure 4.3 for q = 7/2).

a b

Fig. 4.2. Graphical interface for defining the parameters of the synchronous generator: a. Variant q = 4; b) variant q = 7/2.


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Fig. 4.3. Determination of the excitation solemnity at rated load for the synchronous generator with

apparent poles (variant q = 7/2)

CHAPTER 5

ANALYSIS OF THE SYNCHRONOUS MACHINE BY USING THE FINITE ELEMENT METHOD

Proposing research topics such as: 5.1. Using the Finite Element Method to solve partial differential equations

(PDEs); 5.2. Using the Finite Element Method in magnetic field modeling; 5.3. 2D modeling of the magnetic field in MATLAB: 5.3.1. Introduction on

PDEtoolbox Matlab; 5.3.2. Use of PDEtoolGUI in magnetostatics; 5.4. Case study,

The chapter performs the numerical modeling of the stationary magnetic field of the synchronous generator with apparent poles. For the analysis of the magnetic field, the principles of the Finite Element Method were applied. The numerical modeling tool used was the Magnetostatics application from PDEtoolbox which belongs to the Matlab software package. The main goal of the research is to obtain the 2D geometry of a synchronous generator with apparent poles and to visualize the magnetic field produced by the conduction currents that pass through the windings of the machine.

The results of the simulations allow the following observations: a. On magnetic field lines

If the representation of the magnetic field lines is desired, these are considered to be the lines along which the magnetic flux flows. Therefore, in viewing the solution of


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the proposed problem, the field lines are contours of the magnetic potential vector A (figure 5.1) and it is easily observed that the distribution of field lines in the variable air gap of the synchronous generator with apparent poles is different: under the polar shoe, the field lines are approximated by linear segments, perpendicular to the reinforcements, parallel to each other; and at the end of the polar shoe, they deform, becoming arcs.

Fig. 5.1. Representation of magnetic field lines

b. On magnetic induction In figure 5.1 it is observed that the field lines are closed curves, tangent to the

magnetic induction vector B at each point in space (figure 5.2) and have a density proportional to the size of B in the considered point. In those places where the field lines are close, the induction of the magnetic field has high values. It is observed that the field lines are denser near the conductors traversed by conduction currents and rarer at a great distance from them.

Fig. 5.2 Representation of the magnetic induction vector, B


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c. On the intensity of the magnetic field The intensity of the magnetic field is obtained in figure 5.3..

Fig. 5.3 Representation of the magnetic field intensity vector, H

It is observed that: the magnetic field intensity vectors tangent to the field lines; under the polar shoe, in the area of constant air gap, the intensity of the magnetic field is uniform and constant, having a value; towards the ends of the polar shoe, with the increase of the air gap, the value of the intensity of the magnetic field decreases, and the linear shape of the field line becomes a circular arc.

CHAPTER 6

NUMERICAL METHODS USED IN SYNCHRONOUS MACHINE ANALYSIS

The chapter aims to develop numerical calculation models in MATLAB to help and validate the general assisted design algorithm developed in MathCAD, dedicated to the synchronous generator used in electric diesel traction.

The target is to develop graphical interfaces that use different numerical calculation subroutines such as: interpolations, phasing diagrams, representation of synchronous generator operating modes (example: short circuit mode). The results of the chapter research are:

6.1. Development of graphical interfaces for the study of the synchronous traction generator: 6.1.1. Graphical interface for the representation of the phase diagram of the synchronous traction generator (figure 6.1)


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a. b.

Fig. 6.1. a. Dialog interface, b. Phase diagram of G.S.T projected in variant q = 7/2

6.1.2. Graphical interface for choosing the form factor of t.e.m. kB and the ideal polar step coverage factor α i for the calculation of the synchronous traction generator (figure 6.2)

a b

Fig. 6.2. Example of using the designed interface: obtaining the family of curves (δ / τ = 0.01): by pressing the F1 key: a. Choosing the point of interest; b. Reading the point in the command window


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6.2. Estimation by numerical calculation of the operation of the synchronous traction generator: 6.2.1. Geometric location of the current of the synchronous traction generator (figure 6.3)

Fig. 6.3. The geometric locus of the current of the synchronous generator with apparent poles

6.2.2.Torque of synchronous machine with apparent poles at ctU ee ='

Fig. 6.4. Torque of synchronous machine with apparent poles at ctU ee =' .


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6.2.3. Numerical estimation of synchronous generator behavior at sudden symmetric short circuit. The purpose of the numerical application developed is to obtain the representation of the variation in time of the short-circuit current of phase A of the stator for the synchronous generator, calculated in chapter 4. Representations will be made for different frequencies and different β.

Case I: f1=110Hz; UeE=1.09 u.r; β=0.

a.

b. c. Fig. 6.5. Short-circuit currents for phase A


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By analyzing the simulations (table 6.1) qualitative and quantitative assessments can be made on the way in which the components of the phase current vary depending on the connection time β, the frequency and the excitation voltage (UeE).

Table 6.1. Parameters of shortcircuit regime

Parametrul Caz

f1 [Hz]

β Imaxsc [u.r.]

Iminsc [u.r.]

Ip [u.r.]

Ia0 [u.r.]

Ip0 [u.r.]

C [u.r.]

tsc [s]

UeE=1.09 u.r Cazul I 110 π/2 5.6 1.8 1.2 3.18x10-

16 8.08x10-

17 2.37x10-

16 0.072

Cazul II 110 π/4 9 1.8 1.2 3.67 0.93 2.74 0.104 Cazul III 110 0 10 1.8 1.2 5.19 1.32 3.87 0.12

Cazul IV 60 π/2 4.2 1.5 1.2 3.18x10-

16 8.08x10-

17 2.37x10-

16 0.065

Cazul V 60 π/4 7.2 1.5 1.2 3.67 0.93 2.74 0.12

Cazul VI 60 0 8.1 1.5 1.2 5.19 1.32 3.87 0.18 UeE=1.89 u.r

Cazul VII 110 π/2 9.8 2.5 2.2 5.53x10-

16 1.4 x10-

16 4.12

x10-16 0.082

Cazul VIII 110 π/4 15 2.5 2.2 6.3 1.62 4.76 0.12 Cazul IX 110 0 17.5 2.5 2.2 9.03 2.29 6.74 0.13

Cazul X 60 π/2 7.5 2.5 2.2 5.53x10-

16 1.4 x10-

16 4.12

x10-16 0.08

Cazul XI 60 π/4 12.5 2.5 2.2 6.3 1.62 4.76 0.125 Cazul XII 60 0 14.5 2.5 2.2 9.03 2.29 6.74 0.13

It is observed that, by connecting to 20 πβ ≠ , there is a large increase of the

short-circuit currents (Imaxsc) that cross the winding, being all the more disadvantageous as the value approaches zero. Their knowledge is particularly important for the choice of the actuating current of the rectifier protections and for the analysis of the electrodynamics stability of the circuit components and of the switching elements. For example, the graph obtained may show the value of the maximum current supported by an arm of diodes.


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CHAPTER 7

TEST BENCH TO STUDY SOME OPERATIONAL ASPECTS OF THE TRANSMISION “DIESEL ENGINE – SYNCHRONOUS GENERATOR”,

SPECIFICS TO ELECTIC TRACTION

The main objective of the chapter is to design an experimental platform and the working procedures necessary for the simulation by experiment of some aspects specific to the railway electric traction with diesel engine and synchronous generator. The purpose of the experiment is to create, on a laboratory scale, a similarity, for certain conditions, similar to those encountered in the operation of a railway electric diesel transmission, and to analyze the behavior of the synchronous generator with apparent poles in this energy chain. The approach of experimental research has two stages: establishing work tasks and designing and applying work procedures. Three experimental stands and related work procedures were proposed and completed. These were used to acquire the sizes needed to process and trace the operating characteristics of the synchronous generator. These results were used in the data processing phase to draw specific traction characteristics, to study the behavior of the synchronous generator to the sudden variation of the load, to analyze the waveforms of currents and voltages in the proposed situations, as well as for a model of the analysis of the deforming regime. Features were plotted using processing in LabView and Matlab. The experimental chapter has a strong inter- and trans-disciplinary character (electric machines, diesel-electric traction, mathematical and numerical calculation, data acquisition). The experiments took place in the Laboratory of Electric Machines of the Technical University "Gheorge Asachi" from Iasi.

The design of the experimental situations was based on an extensive research on both the choice and establishment of work tasks and the design and application of work procedures following the following topics of interest:

7.1. The research approach 7.2. Test Bench for the study of the operation of the synchronous generator - rectifier

group - inductive / resistive load 7.2.1. Design and application of the working procedure; 7.2.2 Method for determining the control characteristic of the synchronous traction generator under constant power operation; 7.2.3. Method for determining the external traction characteristic of the synchronous generator with apparent poles; 7.2.4. Data processing for analysis of synchronous generator behavior at sudden load variation; 7.2.5 Harmonic analysis of the waveforms of the voltages and currents of the studied synchronous generator.


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7.3. Test Bench for the study of the operation of the synchronous generator - inverter - asynchronous motor assembly: 7.3.1. Design and application of the working procedure

7.4. Test Bench for the study of the operation of the synchronous generator assembly - asynchronous motor.

For example, for the topic “Test Bench for the study of the operation of the synchronous generator - rectifier - inductive / resistive load” design, the working procedure was designed and applied, analyzing the results..

Design and application of the working procedure A. The purpose of the experiment - is to propose a practical training situation,

designed to study the behavior of the synchronous generator - rectifier assembly, in working conditions specific to electric railway diesel traction.

MO. The main objective is to study the behavior of the synchronous generator when the shaft torque is given by an electric machine that operates on constant power steps, with constant speed, and the load (inductive / resistive type) is supplied by means of a rectifier.

The specific objectives are: OS1. Plot the characteristics specific to the different modes of operating for the

synchronous generator (no load operation curve, internal, control, external, short circuit curves).

OS2. Plot specific traction characteristics OS3. Quantitative and qualitative assessment of waveforms for synchronous

generator currents and voltages, both at the significant variation of the load and during the experimental situations created.

OS4. Develop harmonic analysis of the waveforms of the voltages and currents of the studied synchronous generator.

Starting from the conclusion of the theoretical analysis that it is required that the power required by the generator be as constant as possible, regardless of the torque or speed required, the characteristic )I(fU gg = must have a hyperbolic variation (figure7.1). This variation is considered satisfactory when the deviations from the constant power level of the diesel engine do not exceed 3% over the entire range of variation of the locomotive speed.

In the operation of the synchronous traction generator, on the external characteristic (fig. 7.1) three zones are distinguished, corresponding to the segments AB, BC, CD:

The segment AB represents the upper limit of the synchronous generator voltage. In this area the power required by the locomotive decreases, the voltage is maximal, the currents are low and the speed of the locomotive is maximum.


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In the BC area the operation is done on a characteristic close to a hyperbola, so at constant power, which ensures the most economical regime of the diesel engine.

The CD segment corresponds to the current limitation of the synchronous generator. In this area, the voltage drops suddenly, but the high value currents required for starting are approximately constant

ctI g ≈ .

Fig.7.1. Ideal external feature of three-phase synchronous traction generator [108]

In order to meet these considerations, the experiment aims to approximate the nominal characteristic of the synchronous traction generator as follows:

The segment AB can be obtained by raising the adjustment characteristic of the synchronous generator ctU)I(I geg = .

The BC segment is given by the own external characteristic of the synchronous generator, ctI)I(U egg = .

The CD segment is experimentally equated by an internal characteristic of the synchronous generator, ctI)I(U geg = .

In order to fulfill the proposed objectives, the components of the Wuekro type teaching stand, belonging to the “Electric Machines” laboratory of the Faculty of Electrical, Energy and Applied Informatics of the “Gh. Asachi Technical University” from Iaşi, were used. The stand provides various DC and AC electric machines that can be coupled to the same shaft as a DC machine, which can operate in torque, current or speed control from an external central unit.

After a study of the technical characteristics of the component electrical machines (Annex E1), the following were chosen for the realization of the experimental stand:

the direct current machine controlled, because it can operate in torque, current or speed control and can be used for the physical modeling of the diesel engine;

synchronous machine with salient poles because it can be used to physically model the synchronous traction generator.


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the rectifier through which the synchronous generator will discharge on an inductive / resistive type load.

the data acquisition and processing system, which includes the transducer blocks for capturing the measured parameters, the DAQCARD 6024E acquisition board placed in a computer and the data processing environment with which the operating characteristics are plotted.

Fig.7.2. Assembly diagram of the experimental stand for the study of the operation of the synchronous

generator - rectifier group - inductive / resistive load Through this case study, a numerical method was proposed and developed,

elaborated in LabView, based on the transposition of the graphic and analytical method for determining the excitation currents necessary to trace the control characteristic at constant power.

We started from the family of external characteristics obtained for various excitation and constant speed currents plotted in the same axis with the constant power characteristic. The characteristic resulted is shown in figure 7.3.

Fig. 7.3. Family of external features at Ie = (0.2; 0.3;0.4;0.5;0.6)=ct, n=1500 rot/min and constant power

characteristic, P= 600W


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In order to obtain the final traction diagram, we processed the data files in LabView so that only the data of interest for each of these regimes are represented in the U (I) axis system (figure 7.4).

Fig. 7.4. Traction characteristic of the synchronous generator: I-operation with constant voltage

(adjustment characteristic, - blue), II- operation on external characteristic (red), III- operation at constant load current (black).

It is also proposed to carry out a qualitative and quantitative analysis of the quantities of interest for the deforming regime introduced by the rectifier in the concrete case of the idling regime and for the operation in charge of the synchronous generator considered.

Results: Case I: It is proposed the analysis of the deforming regime at no load operation of

the synchronous generator used in the experiment, for the case n = 1500 rot / min, Iex = 0.6 A. The visualization of the waveforms for voltages is given in figure 7.5.

Fig. 7.5. Waveforms of line, phase and rectified voltages when the synchronous generator is no load


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a. b.

Fig. 7.6. a. Phase voltage harmonic spectrum; b. Share of Uf harmonics (OY - logarithmic scale).

Conclusions

A. On the proposed experimental situations The proposed experimental stand, in the three conceptual variants, covers quite

well a wide range of situations encountered in the operation of the synchronous generator used in traction.

Analysis of the operation of the diesel engine - synchronous generator assembly is performed based on the operating characteristics of the synchronous generator, respectively of the diesel engine

B. On the behavior of the synchronous traction generator When operating the synchronous generator on the rectifier or inverter, it is

observed that we have a strongly deforming regime, which implies its consideration in the design stage of the generator, in order to sizing it appropriately.

When supplying the asynchronous motor directly from the synchronous generator, it was found that when increasing the load of the asynchronous motor, the adjustment of the generator requires specific regulators.

Traction load dictates the current value at the traction motor and automatically at the synchronous generator terminals.

For a constant power imposed on the generator, as the current increases, IGS, generator voltage, UGS, decreases.

When an operating load occurs, the generator current increases, causing the excitation system to increase the generator flow.


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The main contributions of the author are summarized below. With over 28 years of experience in the field of locomotive repairs, the author aimed

to capture and highlight, clearly, the need to form the systemic, inter- and trans-disciplinary thinking of the personnel who carry out, or are going to carries out activity in the vast area of railway traction: practice or research.

Therefore, in the first part of the thesis, the author proposes models of thinking and analysis of the specialized literature with the clearly defined purpose of identifying exactly the context of a practical application and the current level of technical and applied research in the field. The personal touch of the models of thinking of the approached technical problem (the synchronous traction generator) was found in the application and development of some:

critical analyzes regarding the evolution of the product: the approach of the railway transport from the point of view of the transport market; the response of specialized companies to market challenges, direct current excitation systems; alternating current excitation systems; static excitation systems.

comparative analyzes on product and technology: comparative analysis of the electric transmission „c.c.-c.c.” - „c.a.-c.c.”; electrical transmission limits c.a. - c.c./Technical solutions; comparative analysis of d.c. generator replacement solutions with synchronous generator; analysis of the advantages and disadvantages of the options for choosing the configuration solutions of the designed model (example: criteria for choosing the number of stator notches);

functional product analyzes: State diagram of electric diesel transmission; Design features of the synchronous traction generator.

The structuring of the theoretical analysis tools (fundamental elements of electric machines, the analysis of the Finite Element Method), as well as the learning to use numerical calculation tools such as MathCAD, Matlab, LabView, allowed the author to identify the issues of the context 'Operation of synchronous generator for traction' and propos original numerical solutions for solving one of them:

Computer aided design of the synchronous traction generator using numerical calculation in MathCAD: development the calculus algorithms and implement it in the programming language (examples: 'DMC - Determination of calculation sizes';' DPM - Main dimensions of the machine ';' CLI: Calculation of the width of the air gap ', etc.);

Representation of the magnetic field induced by the current passing through the windings of a synchronous machine with salient poles using the Finite Element Method and the PdeGUI Matllab graphical interface.

Creating and using graphical interfaces in Matlab to support and complete the developments of the numerical design algorithm. The graphical interfaces were created for: defining the parameters of the synchronous generator to be designed, tracing the magnetic characteristics of empty and partial operation in


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relative units for the synchronous generator to be designed; construction of the phasor diagram in u.r. of the generator to be designed, determination of the excitation solemnity at nominal load for the synchronous generator with apparent poles (variants q = 4, q = 7/2); Graphical interface for choosing the form factor of t.e.m. kB and the ideal polar step coverage factor αi for the calculation of the synchronous traction generator.

Creating programs in Matlab for the analysis of the operation of the designed synchronous traction generator: representation in Matlab of the variation of some parameters of the designed synchronous generator (torque, active power, current); numerical estimation in Matlab of the behavior of the synchronous generator at the sudden symmetrical short circuit.

Design and practical implementation of experimental tests bench. Design of LabView diagrams for the analysis of data obtained through data

acquisitions of quantities of interest. LabView diagrams were made for tracing the different operating characteristics, the families of operating characteristics. A numerical method was developed and applied in LabView for determining the control characteristic of the synchronous traction generator under constant power operation, as well as a method for determining the external traction characteristic of the synchronous generator with apparent poles.

Analysis and interpretation of the results of the harmonic analysis of waveforms for currents and voltages.

The research was the occasion of a unique experience, which allowed the author to collaborate and share professional and scientific experience with outstanding/brilliant personalities of the moment, such as: Mr. Prof. PHD. Eng. Al. Bitoleanu, Mr. Prof. PHD. Eng. A. Câmpeanu, Mr. Prof. PHD. Eng. L. Cantemir, Mr. Prof. PHD. Eng. Al. Simion, Mr. Assoc. Prof. PHD. Eng. A. Munteanu and more.


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https://www.researchgate.net/profile/Mihaela_Popescu/publication/228643424_Harmonic_current_reduction_in_railway_systems/links/54aa40570cf256bf8bb96678.pdf

https://www.researchgate.net/profile/Mihaela_Popescu/publication/228643424_Harmonic_current_reduction_in_railway_systems/links/54aa40570cf256bf8bb96678.pdf


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[110] Popescu,M., Bitoleanu,A., Suru,C.V., Dobriceanu,M., DC-Traction Substation with Improved Power Quality and Regeneration Capability, Annals of the University of Craiova, Electrical Engineering series, No. 41, 2017; ISSN 1842-4805, http://elth.ucv.ro/fisiere/anale/wp-content/uploads/2018/01/DC-Traction-Substation-with-Improved-Power-Quality-and-Regeneration-Capability.pdf [111] Popescu,M., Bitoleanu,A., Dobriceanu,M.,, Teodorescu,F.A., On the AC-connecting of a system for active filtering and regeneration in active DC-traction substations, 2018 International Conference on Applied and Theoretical Electricity

https://ieeexplore.ieee.org/abstract/document/8551439/

https://ieeexplore.ieee.org/abstract/document/8551439/

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