coordination of overcurrent relays protection systems for wind power plants

Coordination of Overcurrent Relays Protection Systems for Wind Power Plants

Nima Rezaei 1, 2, *; Mohammad Lutfi Othman 1, 2; Noor Izzri Abdul Wahab 1, 2; Hashim Hizam 1, 2 1 Department of Electrical & Electronic Engineering, Universiti Putra Malaysia, 43400 Serdang, Selangor, Malaysia

2 Centre for Advanced Power and Energy Research (CAPER), Universiti Putra Malaysia, 43400 Serdang, Selangor, Malaysia *Corresponding Author: Nima Rezaei, Email: [email protected]

Abstract-Wind farms are one of the most indispensable types of sustainable energies which are progressively engaged in smart grids with tenacity of electrical power generation predominantly as a distribution generation system. Thus, rigorous protection of wind power plants is an immensely momentous aspect in electrical power protection engineering which must be contemplated thoroughly during designing the wind plants to afford a proper protection for power components in case of fault occurrence. The most commodious and common protection apparatus are overcurrent relays which are responsible for protecting power systems from impending faults. In order to employ a prosperous and proper protection for wind power plants, these relays must be set precisely and well coordinated with each other to clear the faults at the system in the shortest possible time. This paper indicates how the coordination of overcurrent relays can be effectively attained for wind power plants in order to protect the power constituents during fault incidence. Through this research Matlab/Simulink as a powerful simulation software have been applied to model a wind farm and achieve precise setting for coordination of overcurrent relays.

Keywords-Overcurrent Relay, Coordination of Overcurrent Relay, Wind Power Plant, Power System Protection

I. INTRODUCTION The ever increasingly air pollution rate and the

limitation of fossil fuel sources have led to comprehensive implementation of renewable energies specifically wind energy. Wind power plants have been vastly employed as the means of power generation in smart grids as a distribution generation (DG) system [1]. Undoubtedly, wind power has come to be mainstay of the energy systems in several countries and is regarded as a reliable and financially reasonable source of electricity. The contribution of wind energy to power generation has reached a considerable share even on the worldwide level. Among many countries that are investing hugely on wind power generation, the top 10 leading nations in total power generation capacity are: China, USA, Germany, Spain, India, United Kingdom, Italy, France, Canada and Portugal [2].

Progressively amplification of grids by wind farms have led to emergence of some significant electrical issues including security, protection, stability, reliability and power quality. Among these issues, protection aspect plays an enormous role which needs a serious attention by researchers. Although protection of wind farms is a crucial issue that needs a huge attention, wind power plants still

implement simple protection schemes which leads to different levels of damages to power components in the plant. Moreover, most of the researches conducted regarding wind farm protection has been abundantly restricted to literatures and methodologies [3 - 5]. Some researchers have been studied the effect of fault on wind plants specially the generators and have investigated the effectiveness of crowbars in protecting the wind turbine generators [6]. However an overall protection scheme has yet to come to solve the protection crisis in wind plants.

One of the most important studies of power quality and power system protection in wind plants is providing adequate and continual power to the loads, therefore in order to ensure having perpetual power from wind farms, wind plants must feed grids continually. One way of meeting this phenomena is applying a proper protection in the system that in case of fault, only the section of faulty feeder is disconnected from the system and the rest of healthy parts are kept connected to the system. By using overcurrent relays (OCRs) as a protection system and applying an accurate coordination in wind plants, not only in case of fault, the power components are protected from damages from excessive currents but also continual power flow is fed to the grid and superb power quality is provided by wind power plants.

This paper demonstrates how OCRs have been successfully used and properly coordinated in a wind power plant. The software which has been used is Matlab/Simulink which is known as one of the best simulation software for electrical engineers and researchers. All of the OCRs have been modelled and designed and the accurate settings have been selected to protect the wind plant.

Section 2 of this paper, discusses about OCRs, their function, how they are set and coordinated to provide proper protection. Moreover IEC standards for setting the OCRs have also been represented. In section 3, the wind plant model studied in this paper has been illustrated and load flow during normal operation and during fault occurrence have been simulated as well. Section 4 has been dedicated to OCRs settings for the wind plant based on the results obtained in section 3. Beside that OCRs have been tested in order to assure their credibility and validity of relays function. At the end, Conclusion has been brought to summarize all of the materials discussed in the paper. 978-1-4799-7297-5/14/$31.00 2014 IEEE2014 IEEE International Conference Power & Energy (PECON)394

II. OVERCURRENT RELAY OCRs have the same basic I/O signal op

types of relays. In these relays, if the incohigher than the preset current value, the relan output signal to the circuit breaker (CBthe circuit in order to protect the power cothe result of current excess. There are threOCRs used in power systems, which are: relay, definite time relay and inverse time common type is inverse time relay whichcurve characteristic. This curve defines the relay which functions in a faster time increases. These types of relays are usuallan instantaneous unit which causes the rinstantaneously when the current reachemagnitude thus eliminating the damagecomponents.

Inverse time OCRs based on their securrent and time can have several charactereliant on the application. These OCRs typIEC standard are depicted in Table 1. Below

Table 1. Different Characteristic of OCRs Based o

Type of OCR OpeNormally Inverse T

Very Inverse TExtremely Inverse TLong Time Inverse T

In power systems, all of these OCRs mcoordinated with each other in order to prelements from the currents. To do so, the OCRs, which are the Plug Setting Multipthe Time Setting Multiplier (TSM), must PSM is varied in the range of 50% to 200%25% [7]. This setting is only used for inverwhich detect phase to phase fault. For the rphase to ground fault, the PSM is quitevaried in in the range of 10% to 40% in stethe range of 20% to 80% in steps of 20%should be taken into consideration is thatSetting (PS) the relay has, the higher curequires to trip. TSM ranges from 0 to 1 However, sometimes it varies in stepsmaximum TSM is 1 and the minimum is 0coordinate OCRs with each other, there isbetween a primary relay and a backup relathis is called the Coordination Time Intertime interval is in the range of 0.3 and conventional relays, while for numerical r0.2 seconds, which means they operate fasconventional relays [8]. So in order to co

peration as other oming current is lay will send out B) to disconnect omponents from ee main types of

definite current relay. The most

h has an inverse operation of the as the current

ly included with relay to operate es a high limit e to the power

ensitivity to the eristics which is

pes, according to w. on IEC Standards

eration time.TSM

II.

.TSM II TSM II TSM II

must be properly rotect the power vital settings of

plier (PSM) and be set suitably.

% and in steps of rse current relays relays that detect e different. It is eps of 10%, or in

%. The point that t the more Plug urrent the relay in steps of 0.1.

s of 0.05. The 0.05. In order to s a time interval ay operation and rval (CTI). This 0.5 seconds for

relays it is set at ster compared to oordinate relays

with each other, the relay optaken into consideration. Aftrelays are designated, then tbe properly undertaken.

Coordination of OCRs barelay to the fault location, primary relay, must first trip does not trip or malfunctionsprimary relay, which is calleThis coordination is extremeorder to decrease the expandequality compromise. The cdepicted in Fig 1. In thisprotection must trip to tmalfunction, OCR2 as backuif OCR2 does not operate, protection must trip and disco

Fig 1.The Concept o

III. SIMULATION RESULTS FOWIND

Matlab/Simulink as a powto model the wind plant, relcoordinate them well with power plant has been modellthe load flow, OCRs usindesigned, set and coordinated

The wind power plant mof 3 wind turbines that eacpower. Their voltage and frerespectively. Transformers turbine has voltage ratio oconfiguration where the staTransformer corresponding toof 25KV/110KV and delta stearthed. The transmission linThe wind power plant modelfigure, since the protection apaper, the breakers have benamed by CB1, CB2 CB8to each breakers, are highlighR1, R2 R8.

peration time and CTI must be ter the characteristics of these the coordination of OCRs can

asically means that the closest which is referred to as the

the CB, and in case the relay s, the other relay closest to the ed the backup relay, must trip. ely crucial and is conducted in ed power loss and avert power coordination phenomenon is s figure, OCR1 as primary the fault. In case of any up protection should trip. Also OCR3 as the second backup

onnect the feeder.

of OCRs Coordination

OR OCRS COORDINATION IN A PLANT werful software has been used ays, set the relay settings and each other. A typical wind

led in this paper and based on ng IEC standard has been

d.

modelled in this paper, consists ch of them produce 2.5 MW equency are 575V and 60 Hz corresponding to each wind

of 575V/25KV in star delta ar side is earthed. The last o the grid has the voltage ratio tar configuration where star is nes have 20 Km length each. l is illustrated in Fig 2. In this area is the main scope of this en highlighted as Red colour 8 and the corresponding relays hted as green colour shown by

2014 IEEE International Conference Power & Energy (PECON)395

In wind power plants, since the windstable and is fluctuating all the time, theregenerated by the wind turbines is also varythe wind velocity. The minimum adequatewind turbines to produce electricity is 5mmaximum wind speed that wind turbines25mps. If the wind velocity exceeds that vadamage the wind turbine generators and sfire in case of long duration of high wind spprotect the wind turbines from high winpaper, a protective block is located to trip tas soon as the wind speed exceeds 25. Wipaper is selected to be varying in range of wind plant currents characteristics at eachin Fig 3 to 6 at normal operation.

In order to set the relays and coordinatethe exact value of current and short circuitthrough each CB should be derived. FigDepicts the characteristic of current in AmCB before, during and after fault. In thistotal simulation time is 60s. A three phasimposed to each breaker at time 30 lasting f

Fig 3. Load Flow through CB8 during Norma

0 10 20 30 400

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0 10 20 30 400

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Fig 2. Simulink Model for Wind Power Plant

d is not always efore the current ying according to e wind speed for mps however the s can tolerate is alue, then it will

sometimes cause peed. In order to

nd speed in this the wind turbine ind speed in this 5 to 25mps. The

h CB is depicted

e them properly, t current flowing g 7. to Fig 10.

mper unit at each s simulation, the e fault has been for 5s.

al Operation

Fig 4. Load Flow through C



Fig 7. Load Flow thro

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CB7 during Normal Operation



ough CB8 during Fault

30 40 50 60Time (S)

30 40 50 60Time (S)

30 40 50 60Time (S)


Fig 8. Load Flow through CB7 during Fault



As it can be seen from the simulation, at time 30, when a three phase fault is imposed to the system, current is increased abundantly and voltage dips drastically which can damage the power systems and compromise the power quality. Therefore a proper protection must be employed to prevent this catastrophe. In this paper OCRs as the best protection relay in wind power plants have been implemented and the results in the next section have affirmed its prosperity, effectiveness and accuracy.

IV. RESULTS AND DISCUSSION After getting the required data for setting the relays,

including exact value of load current and short circuit current at each CB, OCRs can then be modelled, set and coordinated. In order to get the best results with purpose of relays coordination, the exact value of short circuit current located near each CB should be extracted and based on the maximum load current, relays can be set.

The results below demonstrates that relays have been successfully set and are well coordinated with each other. CTI has been opted as to be 0.3s and normal inverse relay has been chosen in this simulation. Fig 11. To Fig 14. Illustrates the relays behaviour at each fault occurred from time 30 to 35. In these figures, 1 means the relay is in normal condition and has not tripped, and 0 means the relay has tripped due to the fault current. Fig 16. To Fig 19. Depicts the CBs operation corresponding the each relays.

As an example, when there is fault near CB8, relay 8 must detect the fault and send the proper tripping signal to the CB8 to disconnect the system until the fault is cleared. As it is clear in the pictures, relay8 trips at time 30.1141 and the CB8 has disconnected the feeder exactly at 30.1141 which shows the relay and CB are working well.

The other scenario that must be taken into consideration is that in case relay 8 has not tripped and malfunctioned, the closest relay to relay 8 which is relay7 must trip after a specific delay time which is known as CTI. In Fig 15. This phenomena is shown. Since the CTI is set to be as 0.3s, then as it is expected, relay7 must trip and command the CB7 to disconnect the feeder at time 30.5055. This concept is repeated for the rest of the relays as well.

This procedures have been tested for all of the faults at each CB and the results of relay settings, have been compiled in Table 2. In this table all of the current measurements are in Amper unit. Ipickup and Ipickup relay refers to the minimum magnitude of current that the relay trips before and after the Current Transformer (CT) respectively. The fourth column represents the CT ratio at each relay. PS, PSM and TSM corresponds to the relay settings that describes how each relay has been set and behaves in case of fault. The last column illustrates T that is the amount of delay time that the relay trips. One thing that should be taken into consideration is that since all of the 3 wind turbine feeders have the same current characteristics, therefore relay settings for relays1, 3 and 5 are the same. Also the relay setting for relays2, 4 and 6 are the same as each other too.

Through the simulation results it is resulted that relays have been set accurately and are well coordinated with each other in order to protect the wind power plant. All of the relays settings have been conducted using IEC standards and according to section 2 of this paper regarding OCRs settings, all of the TSM has been set by standardization of 0.05 which means the value of each TSM has been rounded to higher value with value of 0.05. Thus OCRs can be considered as one of the best and most successful technique of protection for wind farms.

Table 2. OCRs Settings for the Wind Power Plant

Relay Ipickup Ipickup relay CT PS PSM TSM TR1 75 3.75 100:5 75% 45.27 0.65 1.1484R2 75 3.75 100:5 75% 13.51 0.30 0.8055R3 75 3.75 100:5 75% 45.27 0.65 1.1484R4 75 3.75 100:5 75% 13.51 0.30 0.8055R5 75 3.75 100:5 75% 45.27 0.65 1.1484R6 75 3.75 100:5 75% 13.51 0.30 0.8055R7 187.5 6.25 150:5 125% 3.91 0.1 0.5055R8 37.5 3.75 50:5 75% 19.59 0.05 0.1141

Fig 11. Relay8 Tripping during Fault

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Fig 15. Operation of Relay 7, 2 and 1 in Case Relay 8 malfunctions

Fig 16. CB8 Operation during Fault




V. CONCLUSION In this paper, a comprehensive protection for wind

power plants has been successfully implemented by using OCRs. Three phase fault has been imposed at each CB and the settings for each relay has been conducted. Moreover all of the relays have been modelled based on IEC standards in order to provide proper protection for the system, prevent the damage from fault current to the power components, provide perpetual power to the grid and contribute to superb power quality. The results have shown that OCRs can be successfully employed for wind power plants and has proved to be effective, accurate, and be considered as the best method for protection.

Acknowledgement

The authors wish to thank the Universiti Putra Malaysia for the research grant Geran Putra IPB, project no. GPIPB/2013/9412101 and vote no. 9412101 that funds this work.

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coordination of overcurrent relays protection systems for wind power plants

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