Journal of Environmental Protection, 2009, 1, 59-67
Published Online November 2009 (http://www.SciRP.org/journal/jep/).
1
Impact of Reactive Power in Power Evacuation
from Wind Turbines
Asish RANJAN1, S. Prabhakar KARTHIKEYAN1, Ankur AHUJA1,
K. PALANISAMY1, I. Jacob RAGLEND2, D. P. KOTHARI3
1School of Electrical Sciences, Vellore In stitute of Technology, Vellore, India-632014; 2Christian College of Engineering and Tech-
nology, Ottanchatiram, Dindugal District. India-632014; 3Vellore Institute of Technology University, Vellore, India-632014.
Abstract
Application of Distributed Generation (DG) to supply the demands of a diverse customer base plays a vital
role in the renewable energy environment. Various DG technologies are being integrated into power systems
to provide alternatives to energy sources and to improve reliability of the system. Power Evacuation from
these remotely located DG’s remains a major concern for the power utilities these days. The main cause of
concern regarding evacuation is consumption of reactive power for excitation by Induction Generators (IG)
used in wind power production which affects the power system in variety of ways. This paper deals with the
issues related to reactive power consumption by Induction generators during power evacuation. Induction
generator based wind turbine model using MATLAB/SIMULINK is simulated and its impact on the grid is
observed. The simulated results are analyzed and validated with the real time results for the system consid-
ered. A wind farm is also modeled and simulations are carried out to study the various impacts it has on the
grid & nearby wind turbines during Islanding and system event especially on 3-Phase to ground fault.
Keywords: Distributed Generation (DG), Grid, Wind Turbines, Induction Generator, Islanding, Power
Evacuation, Point of Common Connection 3 Phase to Ground Fault
1. Introduction
Wind is one of the most important resources found in
nature’s bounty totally free of cost and without any
hazardous effects. Perhaps that is why, in this hour of
energy crisis,the entire human race has diverted its
attention to wind energy as a suitable alternative to the
conventional sources of energy we have been using for
more than a century.
Having an insight into the statistics concerning
installed wind power capacity,we see that the total
capacity as of today is 93,849MW (2008). India
stands fourth in wind power commissioning with an
installed capacity of 7844.5MW (2008). But
Germany with a capacity of 22,247MW (2008) shows
that the distance to be covered is still huge. Of
course, it instills a hope that the future will be bright
with no reliance on conventional sources of energy
and wind energy forming a large chunk of the
installed capacity.
There are two types of utility-scale wind turbines,
fixed-and variable-speed. Fixed-speed wind turbines
operate at a near constant rotor speed at all times and
are directly connected to the power grid [1]. Fixed
speed wind turbine which is used here for analysis
operates within a very small range (around 5% of the
nominal value) and in general they use a fixed shunt
capacitor to provide reactive power compensation
[2].
1.1. Islanding
A phenomenon which generally occurs in a network with
Wind Generation in which a portion of the distribution
network becomes Electrically Isolated from utility grid
due to transmission system events & after disconnection,
wind generator maintains supp ly to local loads. Islanding
can be categorized as Intentional Island and Unintentional
Island. Islanding is a condition in which local Distribution
Generation systems continue to supply stable real power
and reactive power to the local loads at a sustained voltage

60 R. ASISH ET AL.
and frequency while the main Energy system is de-ener-
gized. An islanding condition creates a safety hazard and
may cause damage to power generation and power supply
facilities as a result of unsynchronized re-closure [3]. In
general, after loss of the main source, the DG has to take
charge of the remaining network and the connected loads;
therefore, the loading condition of the DG is suddenly
changed after islanding. Since the distribution networks
generally include single-phase loads, it will be highly pos-
sible that the islanding changes the load balance of DG [4].
1.2. Intentional Island
Planned islanding is often called Intentional Islanding.
This condition arises when a portion of the network is
separated from the rest of the network for the sake of
system reliability & maintaining the safety of the network .
Utility personnel monitor the islanded system continu-
ously & it poses no problem for the utility.
During the occurrence of a system outage, when sev-
eral groups of generators can go out of-step with each
other, it may be desirable to have selected islands where
there is a minimal mismatch between load and generation.
Switching operations carried out to split the system into
such self-sufficient regions is called intentional islanding.
1.3. Unintentional Island
Sudden and unpredicted islanding is termed as uninten-
tional islanding which mainly results due to th e failure of
anti-islanding techniques resulting in electrical isolation
of an energized portion [5]. The energized portion will
continue to su pply power to the loads present in the island
affecting the safety concerns for the utility personnel.
A section of the grid having balanced load and gen-
eration may become isolated from the rest of the grid
by a sudden opening of a switch or a circuit breaker
that causes the disconnection of the feeder from the
grid. A common form of disconnection would typically
arise from a momentary ground fault on the feeder,
which is detected by the feeder ground relay and results
in tripping of the feeder circuit breaker. Such an event
is described in Figure 1. The single line to ground fault
shown in the Figure1 is assumed to be transient in na-
ture [6]. This fault could cause operation of utility
breaker shown as a disconnection point suggested by
the given Figure 1.
However, the transient fault may be undetectable by
the DG and cause to exist after opening of the utility
breaker. In this scenario, an unintentional island is
formed after opening of the utility breaker. After dis-
connection from the grid, this island may be initially
deficient in active and reactive power. The deficiency
of active power is balanced by the release of kinetic
energy from the rotating machinery connected to the
system, and hence reduction in system frequency [6].
The deficiency of reactive power is mainly balanced
by the export of reactive power from the embedded
synchronous generator .An islanding event, such as
described in this section, can be conveniently illus-
trated by a frequency and voltage versus time graph of
Figure 2.
1.4. Implications of Inadvertent Islanding
Inadvertent islanding presents a number of safety, com-
mercial, power quality, and system integrity p roblems [7].
In summary, the major issues are:
1) Line worker safety can be threatened by DG sources
feeding a system after primary sources have been
opened and tagged out.
2) Public safety can be compromised as the utility does
not have the capab ility of de-energizing downed lines.
3) The voltage and frequency provided to other customers
connected to the island are out of the utility’s control, yet
the utility remains responsible to those customers.
4) Protection systems on the island are likely to be unco-
ordinated , du e to the dr astic ch ang e in short circuit cu r-
rent availability.
5) The islanded system may be inadequately grounded by
the DG interconnection.
Figure 1. Ground fault disconnection.

R. ASISH ET AL. 61
Figure 2. Voltage and frequency response
6) Utility breakers or circuit reclosers are likely to re-
connect the island to the greater utility system when
out of phase.
2. System Configuration
The parameters used for the simulation of the above model
of an Induction Generator based wind turbine are as follows:
2.1. Induction Generator
A 3-phase squirrel cage induction generator with a nomi-
nal power of 843KVA, 690V (φ-φ), 50 HZ is used for the
above system wi t h the parameters shown in Table 1.
2.2. Three Phase Transformer
A Yg/ ∆ (D1) configuration of three phase (2-winding)
transformer is used with a nominal power of 1MVA with
following primary/Secondary Windings given in Table 2.
Parameters used for the simulation of three phase PI sec-
tion Line was given in Table 3.
Table 1. Induction generator parame ter s
Parameter Unit
Stator Resistance R1 0.0045 Ω
Stator Leakage Reactance X1 0.0513 Ω
Magnetizing Reactance Xh 2.2633 Ω
Rotor Reactance(referred to Stator) X’2 0.066 Ω
Rotor Resistance( referred to Stator) R’2 0.004 Ω
Magnetizing Resistance Rfe 83.3 Ω
2.3. Grid
A three-phase source with internal R-L impedance is
used to implement a grid which is connected to the wind
Generator through a T-Line & Transformer. The three
phase Short-circuit Level at base voltage of 33KV is
25MVA with X/R ratio of 10.
2.4. Load
A 3-Phase resistive load of 675KW is used which is con-
nected at the terminals of wind turb ine. Simple wind farm
based on fixed speed wind turbines is connected to a grid
through a T-Line at Point of Common Connection (PCC)
Table 2. WG Transformer parameters
Parameters Primary Winding Secondary Winding
Voltage (φ-φ) rms(KV)33 0.690
Resistance(R) pu 0.0125 0.039
Inductance(L) p u 0.0125 0.039
Table 3 Parameters for PI section Transmission line
Parameters Positive Sequence Zero Sequence
Resistance(Ω/Km) 0.1153 0.413
Inductance(mH/Km) 1.05 3.32
Capacitance(μF/Km) 11.33 5.01
Figure 3. System configuration in SIM ULINK.
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62 R. ASISH ET AL.
The second module of the paper deals with the Imple-
mentation of a Wind Farm & its Impact on Grid during
Islanding which can be categorized as:
1) Wind Farm Configuration in SIMULINK.
2) Impact on Grid during Disconnection of a Wind
Generator.
2.5. Wind Farm Configuration
A Wind Farm with three Identical Wind Turbines con-
nected together to form a Wind farm of capacity
2.25MW is shown in the Figure 5.
In implementing a wind farm connected to a grid
through a PCC needs a separate step-up Transformer at
the PCC which is finally connected to the grid via Pi
section T-Line. The difference between a single wind
Turbine connected to a grid & a wind farm connected
to grid can be seen by an additional Transformer’s &
Individual short transmission lines connecting each
Generator to PCC with their parameters mentioned
below.
2.6. Transformer
With nominal power 10MVA a 33/66KV transformer
2.7 T-Line
with same parameters specified before.
Short transmission lines connecting Individual Wind
generators are of length 1 Km each with same parameters
specified before.
The Islanding of a Wind turbine model is shown in
Figure 6 using SIMULINK. The Impact of Disconnec-
tion of one of WG from the rest of the network is im-
plemented here by Inserting a 3-phase breaker in series
with the same WG & PCC in which switching of all the
three phases from closed to open condition takes place
after 1.5 Sec of operation of WG.
The parameters for the Breaker are Transition Time:
1.5 Sec, Breaker Resistance: 0.001 Ω, Snubber Resis-
tance: 0.000001 Ω, Snubber Capacitance: ∞.
Figure 7 is implemented in SIMULINK to Simulate
Unintentional Islanding Condition.
2.7. Induction Generator
A 3-phase squirrel cage induction generator with a
nominal power of 1.66MVA, 575V (φ-φ), 60 HZ is
used for the above system with the parameters shown in
Table 4.
Q
P
Tx Line
T
r
GRID
LOAD
PCC
Figure 4. Outline of grid connected wind farm.
Figure 5. Wind farm connected to grid using SIMULINK.

R. ASISH ET AL. 63
Figure 6. Islanding of a Simulated Wind turbine model.
Figure 7. Netw ork layout used for Simulation [8].
Table 4. Parameters for Induction Gener ator [8].
Parameter Unit
Stator Resistance R1 0.004843 pu
Stator Leakage inductance L1 0.1248 pu
Magnetizing Inductance Lm 6.7 pu
Rotor inductance ref to Stator L’2 0.1791 pu
Rotor Resistance ref to Stator R’2 0.004347 pu
Table 5. Three Phase Transformer parameters [8].
3-Phase 4MVA transformer
(Yg/Yn) 47MVA grid side trans- former Yg/∆(D1)
Parameters Primary
Winding Secondary Winding Primary Winding Secondary Winding
Voltage (φ-φ)
rms(KV) 33 0.575 132 33
Resistance(R) pu 0.025/30 0.025/30 0.08/30 0.08/30
Inductance(L) pu 0.025 0.025 0.08 0.08
A grounding Tr ansformer is used to create a ground ing
point at the secondary side (∆) of grid 47MVA trans-
former with Xo=4.7 Ω [8].
2.8. Grid
A three-phase ideal voltage source along with a 3-phase
mutual inductance block is used a grid with a capacity of
2500MVA&Xo/X1=3 [8].
3. Case Studies and Results
3.1. Normal Condition without any C ompe nsat ion
For a Wind Farm of 2.25 MW under normal working
condition, following results were obtained.
The waveform of P & Q at the Wind Generator termi-
nals is shown in Figure 9. The waveform of P & Q at the
Grid terminals are shown in Figure 10.The waveform of
V, I, P & Q at the load terminals are shown in Figure
11.The loading conditions without any reactive power
compensation are Load= (750+360j)*3, C1=C2=C3=0.
It is found that the requirement of reactive power by
Induction generators witho ut compensation is fulfilled by
the grid which results in large deviation from the standard
oltage values. v
Grid supply
point and sub-
station
132 kV
/
2500 MVA
12345
132
/
33 kV
L1L2 L3 L4 L5
678
3×33 kV/575V
WTIG-3 WTIG-2 WTIG-1
250
kVAR
1.5 MW3 MW4.5 MW
500
kVAR 1000
kVAR
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64 R. ASISH ET AL.
Figure 8. Simulated Model for Unw a nte d Islanding.
3.2. Islanding Condition
Following results were obtained under Islanding condi-
tion. The waveform of P & Q at the Wind Generator ter-
minals are shown in Figure 12. The Frequency Response
at the Wind Generator Terminal is shown in Figure 13.
The waveform of V, I, P & Q at the Grid terminal are
shown in Figure 14. The waveform of V, I, P & Q at the
Load terminal are shown in Figure 15.
3.3. Unintentional Islanding Condition
Following results were obtained under Unintentional
Islanding condition where Islanding can be detected by
conventional method.
For PG=1.5MW , QG=-750 KVAR, PL=1.2 MW, QL=20
KVAR, QC=250KVAR.
The waveform of V, I, P & Q at islanded Wind Gen-
erator terminals are shown in Figure 16.
Table No. 6 shows the simulated results of the Voltage
at Generator Terminal for the clearing time. And Table 7
shows the IEEE Standards for Interconnection system
response to abnormal voltages.
From the waveform as df/dt=1.19 HZ/Sec, ∆f =2.38HZ,
f’ = f-∆f = 57.62Hz.
It is found that Islanding can be detected by the Con-
ventional methods based on local parameters. Thereafter
Islanding can be prevented in accordance with IEEE
1547 standards.
Table 8 shows the IEEE Standards for Interconnection
system response to ab normal frequencies.
The Impact of 3-phase to ground fault is analyzed by
considering the Wind Farm Capacity of 2.25MW and
4.5MW.
Table 6. Voltages at WG terminal (PL=1.2MW).
4 SEC 6 SEC
0.961 pu 0.46 pu
Table 7. IEEE 1547 standard (for voltage).
Voltage Range (% of Base Voltage) Clearing Time
50≤V≤88 2 Sec
Table 8. IEEE 1547 standard (for frequency).
WG size Frequency range Clearing Time
＞30KW ＜(59.8-57) Adjustable 0.16s to 0.3s

R. ASISH ET AL. 65
Figure 9. P & Q waveform at WG terminals.
Figure 10. P & Q waveform at Grid terminals.
Figure 11. V, I, P & Q waveform at Load End.
Figure 12. P & Q waveform at WG terminal during disconnection of one WG.
Figure 13. Frequency Response at WG Terminal.
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66 R. ASISH ET AL.
Figure 14. V, I, P & Q waveform at Grid End.
Figure 15. V, I, P & Q waveform at Load terminal.
Figure 16. V, I, P, Q waveform at islanded WG End (PL=1.2 MW).
Figure 17. Waveform of V, I, P, Q at Grid terminal during 3 phase fault at t= 1 sec.
Figure 18. Waveform of P, Q at Grid terminals du ring 3 phas e fault at t=1sec (Wind Farm Capacity= 4.5MW, Grid =25MVA).

R. ASISH ET AL. 67
Figure 19. Waveform of P, Q at Grid terminals during 3 ph as e fault at t=1sec (Wind Farm Capacity=4.5MW, Grid=50MVA).
3.4. Wind Farm Capacity of 2.25MW The oscillation in frequency is not acceptable where
deviation is more than 5 Hz. Maximum oscillation is
observed when the wind farm capacity is observed when
the wind farm capacity is 4.5 MW.
In Figure 17, response of 3 phase fault at grid terminals is
shown when the capacity of wind farm is 2.25 MW &
that of Grid is 25MVA. The fault is initiated at t= 1sec &
gets self cleared at t=1.1sec.
5. References
3.5. Wind Farm Capacity of 4.5MW
[1] S. Santoso, H. T. Le, “Fundamental time-domain wind
turbine models for wind power studies,” Renewable En-
ergy 32, pp. 2436-2452, 2007.
When the capacity of the grid is doubled to 50 MVA,
following res ponse is obtained at grid term inal s.
4. Conclusions [2] K. C. Divya and P. S. N. Rao, “Models for wind turbine
generating systems and their application in load flow
studies,” Electric Power Systems Research 76, pp. 844-856,
2006.
This paper demonstrates the impact of islanding during-
power evacuation from wind turbin es. It is found that the
problems associated with power evacuation from wind
farms entirely depends on the network topology. A
Smaller generating system (i.e. for 2.25MW) can sustain
and function stably with a grid capacity of 25MVA. To
keep the system in stable, the grid capacity has to be in-
creased doubly (i.e. 50 MVA). It is found that Index
based methods for anti-islanding doesn’t ensure preven-
tion from islanding as Index threshold could change due
to change in system load, generation and configuration.
The Voltage based Anti-Islanding technique fails to de-
tect Islanding if the transfer of reactive power from grid
to wind farm is kept minimum. The Islanding of single
wind turbine has very little impact on nearby wind tur-
bines and grid if it is detected in the given time.
[3] C. Diduch, J. Yin, and L. C. Chang, “Recent developments
in islanding detection for distributed power generation,”
Large Engineering Systems Conference, pp. 124-128, 20 04.
[4] S. I. Jang and K. H. Kim, “An islanding detection method
for distributed generations using voltage unbalance and to-
tal harmonic distortion of current,” IEEE transactions on
power delivery, Vol. 19, No. 2, April 2004.
[5] IEEE Standard 15477M, “Standard for interconnecting
distributed resources with electric power systems”, June
2003.
[6] N. Farhan, A. Rajesh, and V Y. Mohammad, “Uninten-
tional islanding and comparison of prevention tech-
niques,” Proceedings of 37th Annual North American
Conference, pp. 90-96, 2005.
The impact of three phase fault power evacuation from
wind turbines is found that the problems associated with
power evacuation from wind farms entirely depends on
the network topology.
[7] R. A. Walling and N. W. Miller “Distributed generation
islanding-implications on power system dynamic per-
formance,” Proceedings of the IEEE/PES, Summer Power
Meeting, Chicago, July 2002.
When the capacity of the Wind farm is doubled,
system events results in unstable operation of the network.
Instability can be seen from the changed operation condition
after the fault is cleared at 100ms. The impact is minimised
by increasing the capacity of the grid to 50 MVA.
[8] S. Panda and N. P. Padhy, “Investigating the impact of
wind speed on active and reactive power penetration to
the distribution network,” International Journal of Electri-
cal Systems Science and Engineering, Vol. 1, No. 1, ISSN
1307-8917, 2008.