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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
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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
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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
20
40
60
80
100
120
Time (S)
Curr
ent (A
)
0 10 20 30 400
100
200
300
400
500
Time (S)
Curre
nt (A
)
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 5. Load Flow through C
Fig 6. Load Flow through C
Fig 7. Load Flow thro
50 60
50 60
0 10 200
50
100
150
200
T
Curre
nt (A
)
0 10 200
50
100
150
200
T
Curre
nt (A
)
0 10 200
50
100
150
200
250
300
350
T
Curre
nt (A
)
CB7 during Normal Operation
CB2 during Normal Operation
CB1 during Normal Operation
ough CB8 during Fault
30 40 50 60Time (S)
30 40 50 60Time (S)
30 40 50 60Time (S)
2014 IEEE International Conference Power & Energy
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Fig 8. Load Flow through CB7 during Fault
Fig 9. Load Flow through CB2 during Fault
Fig 10. Load Flow through CB1 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
0 10 20 30 40 50 600
500
1000
1500
Time (S)
Curre
nt (A
)
0 10 20 30 40 50 600
500
1000
1500
2000
Time (S)
Curre
nt (A
)
0 10 20 30 40 50 600
500
1000
1500
2000
Time (S)
Curre
nt (A
)
29 30 31 32 33 34 35 36-1
-0.5
0
0.5
1
1.5
2
Time (S)
Curre
nt (A
) Tripping at 30.1141
2014 IEEE International Conference Power & Energy
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Fig 12. Relay7 Tripping during Fault
Fig 13. Relay2 Tripping during Fault
Fig 14. Relay1 Tripping during Fault
Fig 15. Operation of Relay 7, 2 and 1 in Case Relay 8
malfunctions
Fig 16. CB8 Operation during Fault
Fig 17. CB7 Operation during Fault
Fig 18. CB2 Operation during Fault
Fig 19. CB1 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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29 30 31 32 33 34 35 36-1
-0.5
0
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