Conference Paper

NREL/CP-550-47193

March 2010

Short Circuit Current 

Contribution for Different Wind 

Turbine Generator Types

Preprint

E. Muljadi and V. Gevorgian

National Renewable Energy Laboratory

N. Samaan

Pacific Northwest National Laboratory

J. Li

EnerNex Corporation

S. Pasupulati

Oak Creek Energy Systems Inc.

To be presented at the IEEE Power and Energy Society 

2010 General Meeting

Minneapolis, Minnesota

July 25–29, 2010
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1 

Abstract— An important aspect of wind power plant (WPP) 

impact studies is to evaluate the short circuit (SC) current contribution of the plant into the transmission network under different 

fault conditions. This task can be challenging to protection engineers due to the topology differences between different types of 

wind turbine generators (WTGs) and the conventional generating 

units. 

This paper presents simulation results for SC current contribution for different types of WTGs obtained through transient 

analysis using generic WTG models. The obtained waveforms are 

analyzed to explain the behavior, such as peak values and rate of 

decay, of the WTG. The effect of fault types and location, and 

the effect of the control algorithms of power converters on SC 

current contribution are also investigated. 

We show that the response of the WPP to faults will vary based 

on the type of the installed WTGs. While in Type 1 and Type 2 

WTGs, SC current will be determined by the physical characteristics of the induction generator, the contribution of Type 3 and 

Type 4 WTG will be mostly characterized by the power converter’s control algorithms, which are usually considered proprietary information by the wind turbine manufacturers.

 

Index Terms — Fault contribution, induction generator, protection, short circuit, wind power plant, wind turbine. 

I. INTRODUCTION

ECENTLY, the energy and environmental crises have 

become one of the biggest issues around the world. In 

response to energy needs and environmental concerns, renewable technologies are considered the future energy technologies of choice [1], [2]. Renewable energy is harvested from 

nature, and it is clean and free. However, it is widely accepted 

that renewable energy is not the panacea that comes without 

challenges. With the federal government’s aggressive goal of 

achieving 20% wind energy penetration by 2030, it is necessary to understand the challenges that must be overcome when 

using renewable energy. 

One aspect of planning a wind power plant is the calculation of short circuit (SC) current contribution from a wind 

power plant (WPP). With the different types of wind turbine

 This work was supported financially by the Department of Energy and the 

California Energy Commission. 

Eduard Muljadi and Vahan Gevorgian are with the National Renewable 

Energy Laboratory, Golden, CO 80401 USA (e-mail: 

eduard.muljadi@nrel.gov, vahan.gevorgian@nrel.gov).

Nader Samaan is with the Pacific Northwest National Laboratory, Richland, WA 99352 USA (e-mail: nader.samaan@pnl.gov).

Jun Li is with EnerNex Corporation, Knoxville, TN 37932 USA (e-mail: 

jun@enernex.com).

Subbaiah Pasupulati is with Oak Creek Energy Systems Inc, Mojave, CA 

93501 USA (e-mail: subbaiah@oakcreekenergy.com).

generators (WTGs) available from different turbine manufacturers, the task of computing SC current is no longer a simple 

task as in calculating SC current for a synchronous generator 

in a conventional power plant [3], [4]. In a synchronous generator, the magnetizing flux is controlled by the field current 

exciting the field winding, thus, the electromagnetic force

(EMF) driving the fault currents is available during the fault. 

In contrast, in an induction generator the magnetizing flux is 

depleted during the fault and the fault currents are not sustainable for a long duration.

In the years to come, there will be more and more WPPs

connected to the grid. With the goal of 20% wind penetration 

by 2030, the WPPs operation should be very well planned. 

The power system switchgear and power system protection for 

WPPs should be carefully designed to be compatible with the 

operation of conventional synchronous generators connected to 

the same grid. This paper attempts to illustrate the behavior of 

SC current contributions for different types of WTGs. 

The organization of this paper is as follows: In section II, 

the SC characteristics of different WTGs types will be presented. In section III, the aggregated SC current contribution 

of a WPP will be presented. In section IV, the conclusion will 

summarize the paper. 

II. EXPLANATION OF THE NATURE OF THE SHORT CIRCUIT 

CURRENT OF DIFFERENT WIND TURBINE GENERATORS 

In the early development of wind energy, the applications 

were mostly non-grid applications (water pumping, battery 

charging, etc.). Eventually, application of wind turbine generators included grid-connected wind turbines, where the owner 

of wind turbine sells electricity to consumers via a power system grid. A utility sized wind turbine is larger than non-grid 

wind turbine applications. In the early days, the turbines were

sized from 10 kW – 100 kW. Nowadays, wind turbines are 

sized above 1000 kW (1 MW). 

A. Type 1 - Squirrel Cage Induction Generator

The first generation of utility sized wind turbine generator is 

a fixed speed turbine with a squirrel-cage induction generator 

(SCIG). The induction generator generates electricity when it 

is driven above synchronous speed. The difference between 

the synchronous speed and the operating speed of the induction generator is measured by its slip (in per unit or in percents). A negative slip indicates that the wind turbine operates 

in generating mode. Normal operating slips for an induction 

generator are between 0% and -1%.

The induction generator torque increases (almost) linearly 

with the speed. A typical real power versus slip characteristics 

Eduard Muljadi, Senior Member, IEEE, Nader Samaan, Member, IEEE, Vahan Gevorgian, Member, IEEE, 

Jun Li, Member, IEEE, Subbaiah Pasupulati, Member, IEEE

Short Circuit Current Contribution for 

Different Wind Turbine Generator 

R
2 

profile is shown in Fig. 1, where the WTG reaches its rated 

(ωrated) output at 105% synchronous speed (ωs

The connection diagram of a Type 1 WTG connected to the 

grid via a pad-mounted transformer equipped with switched 

capacitor banks to compensate the induction generator at unity 

power factor is shown in 

) or slip= - 

0.005 p.u. or -0.5%. The real power output varies in similar 

fashion within the narrow rated slip range. By its nature, an 

induction generator consumes reactive power both in the motoring and generating regions. The reactive power increases 

significantly as the output power increases.

Fig. 2. 

Fig. 1. The relation between real power and slip of a Type 1 WTG. 

 

Fig. 2. Type 1 wind turbine generator connected to the grid.

The waveforms of SC currents of Type 1 WTGs for different fault types are shown in Fig. 3—the generator is shorted at 

its terminals. Notice that Type 1 WTGs are able to contribute 

significant fault current. Depending on the time of the SC, the 

contribution during the initial cycle of the fault (asymmetrical 

current) can be as high as six times the rated current or more. 

As the fault persists, the contribution decreases in magnitude.

More simulation results and analysis for a Type 1 WTG are 

given in [5]. 

 

Fig. 3. SC currents of Type 1 WTGs for different fault types. 

B. Type 2 – Wound-Rotor Induction Generator with Variable 

External Rotor Resistance 

Another type of utility size WTG is the variable-slip wind 

turbine with a wound-rotor induction generator (WRIG). The 

three-phase rotor winding is connected to a power electronic 

component and three-phase external resistance. The external 

rotor-resistance controller (ERRC) is a very fast controller that 

allows the effective rotor resistance to vary, thus the torque 

speed characteristic of the WRIG can be shaped accordingly. 

The connection of a Type 2 WTG is illustrated in Fig. 4. 

Fig. 4. A Type 2 wind turbine generator connected to the grid.

The equivalent circuit of a Type 2 WTG is shown in Fig. 5. 

The power speed characteristic can be seen in Fig. 6. 

0 0.005 0.01 0.015 0.02 0.025 0

1

2

3

Type 1 WTG

Power versus |Slip|

|Slip| in p.u.

Power WTG (p.u.)

0

5.0

1.0

-1.0

-5.0

0 0.4 0.8 1.2 1.6 1.8

 Time (seconds)

ia

ib

ic

5.0

1.0

-1.0

-5.0

5.0

1.0

-1.0

-5.0

Short Circuit

Generator

Slip power

as heat loss

PF control capacitors

ac

to

dc

Wind power plant feeders

Induction 

Generator

Wind power plant feeders

PF control capacitors

Rated 

power 

Rated slip

3LG fault

Single line to ground fault
3 

jXlr

\ Rs jXls

jX\

m

Is

Vs

S

Rr

\

S

Rex

\

I

\

m

Fig. 5. An equivalent circuit for a Type 2 WTG. 

Fig. 6. The relation between real power and slip of a Type 2 WTG. 

A Type 2 WTG is controlled in a similar way as the Type 1 

WTG. In the low to medium wind speeds, the pitch angle is set 

to the optimum value (e.g., 0 deg) and the ERRC is controlled 

to keep the external resistance to be minimum (e.g., 0 ohm). 

Thus, in this wind speed range, the operation of a Type 2 WTG

is the same as for a Type1 WTG. When the output power of 

the wind turbine reaches its rated value (at rated slip), the fast 

EERC is adjusted to keep the output power constant. If the 

pitch angle of the blades is kept constant at zero degree, the 

rotor speed and thus, the slip will vary with the wind speed. 

However, operation at higher slips generates a lot of loss because of the rotor resistance, thus, the heat loss can be excessive. On the other hand, if the pitch angle of the blades is controlled to keep the rotor speeds within a small deviation from 

the rated slip, the losses in the rotor resistance can be minimized. As shown in Fig. 6, the path OA is operated at optimum pitch angle (0o

From the equivalent circuit shown in Fig. 5, we can derive 

the following equation to freeze the equivalent circuit as the 

slip varies. 

), and the path AB is operated with an 

adjustable external rotor resistance to keep the rated power 

constant, while the pitch angle is controlled to minimize the 

slip and it attempts to operate the turbine as close to point A as 

possible.

Rr’/Srated = (Rr’ + Rex’)/Slip (1)

Rex’ = Slip Rr’/Srated – Rr’ (2)

Rex’ = Rr’ (Slip/Srated – 1) (3) 

The rotor resistance can be controlled as shown in Fig. 7. 

Fig. 7. The variation of R\

ex to maintain the output power constant at Prated

from slip = Srated to slip = 1.1 Srated . 

Normal operating slip for an induction generator is between 

0% and -1%; however, in a Type 2 wind turbine, the slip is 

allowed to vary within -10% slip although the pitch angle is 

controlled to minimize the operating slip (to be as close to 

rated slip, thus minimizing the heat loss in the rotor resistance). 

The SC contribution of a Type 2 is similar to a Type 1. 

When the external rotor resistance is shorted, (i.e., operation 

below rated slip), the SC current is similar to the squirrel-cage 

induction generator. Operation in higher slip than the rated 

slip requires that the external rotor resistance is adjusted higher 

than zero. Operating at higher rotor resistance produces a 

lower SC current than the SC current of a squirrel-cage induction generator (Type 1 WTG). The SC current for three different sizes of total rotor resistance values is shown in Fig. 8. In 

this case, the total resistance is scaled as the multiples of the 

original rotor resistance. The highest rotor resistance generates the lowest SC current and the highest damping coefficient. The blue line is the predicted SC current for zero external rotor resistance. The peak value of the SC current is computed using the (4) given in [6]. 

Isc_peak = Vph_peak/(Xls + Xlr’//Xm’) (4)

Where the symbol // indicates the parallel reactance of Xlr’ and 

Xm’. Note that the computed value (blue-line) predicts only 

the peak value of the sinusoidal (non-dc) component of the 

waveforms; the dc offset of the fault current depends on the 

current flow at the beginning of the fault. 

Fig. 8. SC current (3LG) of a Type 2 WTG for different values of rotor resistance. 

Plot

Time (sec)

4.9 4.94 4.98 5.02 5.06 5.1

-350

0

350

700

1050

1400

1750

Srated 1.1Srated Slip

R\

ex

0.1R\

r 

Rr

’

2 Rr

’

4 Rr

’

Rr

’

2 Rr

’

4 Rr

’

O

A B
4 

C. Type 3 – Doubly Fed Induction Generator

A Type 3 WTG is implemented by a doubly fed induction 

generator (DFIG) as shown in Fig. 9 –it is a variable speed 

WTG. The rotor speed is allowed to vary between 0.3 slip to -

0.3 slip, thus, the power converter can be sized to about 30% 

of rated power (partial rating). The wind turbine is operated at 

optimum Cp below rated wind speed, and it is operated at Prated

above rated wind speeds. Thus, maximum energy yield is accomplished for low to medium wind speeds. Above rated 

wind speeds, the aerodynamic power is controlled by pitch to 

limit rotor speed and to minimize mechanical loads.

Fig. 9. A Type 3 WTG connected to the grid.

With the use of power converter, the real and reactive power can be controlled independently and instantaneously within 

design limits. Generally, the real power control capability is 

used to maximize Cp below rated speed and to limit output 

power above rated wind speeds. The reactive control capability is used to control the reactive power, or power factor, or 

voltage. 

The use of the power converter allows the rotor speed to rotate at a different speed with respect to the synchronous speed, 

thus the rotor speed is not synchronized to the air-gap flux. 

With this capability, the generator is capable of not participating in power system oscillation that may result in the post transient condition. Flexible grid integration, good power quality, 

and voltage ride through can be realized in this type of WTG. 

An example of typical SC current of Type 3 WTG for different fault types is given in Fig. 10. The SC current contribution for three-phase fault is shown to have the shortest decay 

time with the peak current around 3 per unit. The line-to-lineto-ground (LLG) gives about the same peak as the three-phase 

faults, but the decay time is longer. The single line-to-ground 

fault produces the lowest peak current− about 2 per unit − and 

it also decays longer than the three-phase fault. From Fig. 10, 

it is shown that the remaining normal voltage connected to the 

terminal of the generator contributing to keeping the air gap 

flux relatively high enough, although unbalanced, to keep the 

SC current feeds the fault in an extended time, while in a 

three-phase fault case, the voltage collapse depleted the air gap 

flux and the SC current decreased to zero in a short time.

 

Fig. 10. SC current of a Type 3 WTG for different fault types.

D. Type 4− Full-Converter Wind Turbine Generator

A Type 4 WTG is the fourth generation of WTGs, and its 

depiction is shown in Fig. 11. This is a variable-speed wind 

turbine generator implemented with full power conversion. 

Recent advances and lower cost of power electronics make it 

feasible to build variable-speed wind turbines with power converters with the same rating as the turbines.

Fig. 11. A Type 4 wind turbine connected to the grid.

The control algorithm is similar to a Type 3 WTG. The 

wind turbine is operated at optimum Cp below rated wind 

speed, and it is operated at Prated above rated wind speeds. 

Thus, maximum energy yield is accomplished for low to medium wind speeds. Above rated wind speeds, the aerodynamic 

Line-line to ground fault

Single-line to ground fault

Generator

Full power converter

ac

to

dc

dc

to

ac

Wind power plant feeders

generator

Partial power converter

Wind power plant feeders

ac

to

dc

dc

to

ac

3LG fault
5 

power is controlled by pitch to limit rotor speed and to minimize mechanical loads.

With the use of a power converter, the real and reactive 

power can be controlled independently and instantaneously 

within design limits. Generally, the real power control capability is used to maximize Cp below rated speed and set the 

output power at Prated

The full power conversion allows separation between the 

WTG and the grid, thus, the mechanical dynamic can be buffered from entering the grid and the transient dynamic on the 

grid can be buffered from entering the wind turbine dynamic. 

Thus, while the grid is at 60 Hz, the stator winding of the generator may operate at variable frequencies. The temporary 

imbalance between aerodynamic power and generated power 

during a transient is handled by the pitch control, dynamic 

brake, and power converter control.

above rated wind speeds. The reactive 

control capability is used to control the reactive power, or 

power factor, or voltage.

Like a Type 3 WTG, a Type 4 WTG has flexible grid integration, good power quality, and, voltage ride-through can be 

easily realized in this type of wind turbine. Figure 11 shows 

the relationship between the reactive power and the real power. 

Note that the current limit of the power converter needs to be 

respected due to the use of power electronics switches (i.e., 

IGBTs) shown as dash-dot lines in Fig. 12. 

Fig. 12. Commanded reactive power versus real power for different control 

objectives. 

An example of a typical SC current for a Type 4 WTG is 

given in Fig. 13. The SC current contribution for a three-phase 

fault is limited to its rated current or a little above its rated 

current. It is common to design a power converter for a Type 

4 wind turbine with an overload capability of 10% above rated. 

Note that in any fault condition, the generator stays connected 

to the power converter and is isolated from the faulted lines on 

the grid. Thus, although there is a fault on the grid, the generator operates in normal mode. However, keep in mind that with 

a fault on the grid, the output power delivered to the grid is 

less than rated power. Although the currents can be made to 

balance, due to reduced voltage and/or unbalanced voltage, 

only a reduced output power can be delivered. Therefore, the 

wind turbine must be controlled to reduce the output accordingly (pitch control and converter control). Any difference in 

the power converter (i.e., between output power to the grid and 

input power from the generator) will rise or drop the DC bus 

voltage. This control algorithm has been used in the industry 

and it is well understood. Note that in the power converter, the 

output current to the grid can be balanced and symmetrical

regardless of the type of fault.

Fig. 13. SC currents of a Type 4 WTG for different fault types.

III. AGGREGATED SHORT CIRCUIT CONTRIBUTION OF WIND 

POWER PLANT

In section II, the SC currents are based on the SC at the 

terminals of the generator. This calculation is valuable especially for power system planners or wind turbine manufacturers to design system protection of the turbines under SC conditions. 

In this section, the WPP scenario is considered. A WPP

consists of many (hundreds) of wind turbines. Currently, 

available WTG sizes are between 1 MW and 5 MW. The 

prime mover of the wind turbine generator is wind, and it is 

free, natural, and pollution-free. The controllability of the 

wind power plant is typically curtailment (spilling the wind). 

Q

Constant voltage V*

Constant PF*

P

Constant Q*

Current Limit of 

the power converter

3LG fault

Line-line to ground fault

Single-line to ground fault 
6 

A WPP depends on the wind variability, and dispatch capability is based on wind forecasting, and it is influenced more by 

nature (wind) than human factors, with the goal set on maximizing energy production (i.e., unscheduled operation). The 

WPP is located in a high-wind resource region, and it may be 

far from the load center. As described in section II, there are 

four different types of generators commonly used (fixed speed, 

variable slip, variable speed, and full converter). For Type 3 

and Type 4, the wind turbine is variable speed with a fluxoriented controller (FOC) via a power converter. The rotor 

does not have to rotate synchronously with the rotating flux as 

in a synchronous generator. Thus, mechanical oscillation of 

the rotor does not have to be translated into electrical oscillation and vice versa. 

A. Conventional power plant versus wind power plant

A conventional power plant consists of a single or several 

large (e.g., 100 MW) generators. The prime mover of the generator can be steam, gas, or a combustion engine. The generator is controllable and it is adjustable up to a maximum limit 

and down to minimum limit. The power output is dispatched 

according to the load forecast, influenced by human operation 

based on optimum operation (i.e., scheduled operation). It is 

usually located relatively close to the load center. The generator used is a synchronous generator. The rotational speed is 

fixed speed – no slip; and the flux is controlled via exciter 

winding. The magnetic flux and the rotor rotate synchronously. 

Because of a WPP covers a very large area, there are power 

output diversities found in a WPP. Each turbine in a power 

plant will be located at different electrical distances from the 

substation (diversity in line impedance). Each turbine may be 

driven by different instantaneous wind speeds. Thus, the operating condition of each turbine may be different from each 

other. 

B. SCt current at the turbine level

The generator at each turbine should be protected individually and independently because of the diversity of the wind 

power plant. In practice, this is an advantage of a wind power 

plant compared to a conventional wind power plant. During a 

disturbance, the electrical characteristic at each terminal of the 

turbine is different from the other, and only the most affected 

turbines will be disconnected from the grid. For general faults 

(distance faults at the transmission), only 5%-15% of the turbines are disconnected from the grid [7]. Thus, the loss of 

generation is not as severe as in a power plant with large generators.

At the turbine level, the wind turbine generator generates a 

low voltage (480V-690V). For the type 1 and type 2 generators, it is compensated by switched bank capacitors to generate 

at a unity power factor. For the type 3 and type 4 generators, it 

is operated to generate a constant voltage at a designated bus, 

or it may be operated at constant power factor or constant reactive power. The generator is connected to a pad-mounted 

transformer to step up the voltage to 34.5 kV.

C. Short circuit current at the collector system 

The collector system consists of miles of line feeders connecting the high side of the pad-mounted transformer to the 

substation. Usually, the wind turbines are divided into groups 

of turbines connected in a daisy chain fashion using underground cables. It is then connected to the substation by either 

underground cables or overhead lines at 34.5 kV. Since it is 

not practical to model hundreds of turbines in a power flow 

calculation or in a dynamic simulation, it is common to find 

the equivalent of the turbines as either single equivalent turbine representation or multiple turbine representation [8],[9]. 

 

Fig. 14. A typical single-line diagram of WPP. 

D. SC current at the point of interconnection (POI)

The POI is the node where the utility meets the wind power 

plant. At this node, meters are installed to monitor the WPP 

operation (under normal or disturbance conditions, for technical reasons, or for a revenue calculation). This node is usually 

the high side of the substation transformer, where the voltage 

is stepped up from 34.5 kV to higher voltages (230 kV or 500

kV). 

A typical single turbine representation of a WPP is shown 

in Fig. 13 as given in [10]. By considering a single turbine 

representation, all the WTGs in the WPP are assumed to be 

operating at the same operating condition, thus, a study of the 

worst case scenario is obtained. 

The traces of stator currents, voltages at different nodes, 

output power and generator speed for a three-phase fault at 

Node 2 (i.e., high side of the substation transformer) are shown 

in Fig. 15. 

Note that the fault current contribution is smaller than the 

case with the fault at the terminal of the generator discussed in 

Section II. This is a result of sufficient impedances between 

the generator terminals and the fault (i.e., the impedances of 

the pad mounted transformer, the collector systems, the substation transformer). The terminal voltage of the generator is non 

zero because there is sufficient voltage drop due to the fault 

current through the line and the impedance between the fault, 

the generator terminals, the capacitor compensation at the turbine, and the line capacitance within the collector systems. 

The output power of the generator decays very rapidly as both 

the fault currents and the voltage at the terminals die out 

quickly as the fault progresses.
7 

Fig. 15. Traces of currents, voltages, power, and rotor speeds for a Type 2 

WTG under three-phase fault at the high side of substation transformer. 

The traces for a two-phase to ground fault and a single line 

to ground fault for a Type 2 WTG is shown in Fig. 16. For 

both cases, the faults occur at bus 2 (high side of substation 

transformer). Note that the remaining phases (non-fault phases) contribute to the sustenance of the stator voltage and it 

helps to sustain the fault current longer than the case for a 

three-phase fault.

Similar plots can be derived for Type 1, Type 3, and Type 4 

WTGs. 

For a Type 4 WTG, the fault current into the POI will be 

symmetrical because the power converter has the capability to 

control the current directly. A current-regulated PWM is 

commonly used to control the output of the power converter. 

Thus, although the voltages on the grid may be an unbalance 

voltage due to the faults, the line current waveforms can be 

made balanced output by the power converter control.

Fig. 16. Generator fault currents and terminal voltages for a fault at bus 2 

(high side of substation transformer) for two different faults

 a) Line-line to ground b) Single line to ground 

IV. CONCLUSIONS

In this paper, the SC current contributions of different wind 

turbine generator for faults at the terminal of the generator are 

explored. For the Types 1, 2, and 3, as expected, the largest 

SC current is for the three-phase fault. The duration of the 

fault is the shortest because the air gap flux collapses without 

the support of sufficient line voltages. Although this type of 

fault is the least likely to occur, however, planners use this 

fault to calculate the circuit breakers duty and other switch 

gear devices. The single line to ground is the most likely to 

occur in the power grid. The terminal voltage and currents are 

sustained longer because the line voltages, except from one 

phase, are able to sustain air gap flux. Although the SC current contribution from this type of fault is the lowest among 

the three different faults considered, planners should use this 

type of fault to determine the minimum fault current setting for 

protection. 

Type 1 and Type 2 WTGs have very similar behavior. The 

fact that external rotor resistance is used in a Type 2 WTG, the 

fault contribution for Type 2 WTG may be lower from a Type 

1 WTG because the impact of additional rotor resistance reduces the fault current. 

For a Type 3 WTG, although there is a power converter at 

the rotor side, the controllability of this power converter is 

significantly compromised during a fault event, especially 

when the fault occurs in the vicinity of the generator (i.e., generator terminals). For a far-away fault in the transmission 

vgen 

igen

vgen 

igen

a) Line - line -

a) Line - line -

b) Single line to 

b) Single line to 

vgen 

vSub

iSub

pgen 

speedgen

igen
8 

line, the remaining terminal voltage may be sufficient to allow 

an active control of fault current by the power converter, however, for a near fault event, the crow-bar switch is used to control the DC bus (via dumping resistor), thus avoiding the DC 

bus voltage from an over voltage condition. With a SC rotor 

winding, the maximum current condition can be as high as 

squirrel-cage induction generator (i.e., Type 1 wind turbine).

For a Type 4 wind turbine, the generator and the grid is separated by a power converter. The power converter is limited 

by its current carrying capability of the power semiconductor 

used. Thus, the SC current contribution from a Type 4 wind 

turbine is limited to 110% of rated current (assuming temporary overload current is designed to be 110% rated).

V. ACKNOWLEDGMENT

 The authors wish to thank Dr. Surya Santoso and Mohit 

Singh of the University of Texas, Austin, for the development 

of PSCAD models for Type 1 and Type 2 wind turbines used 

in this paper. 

VI. REFERENCES

[1] U.S. Department of Energy – Energy Efficiency and Renewable Energy, 

“20% Wind Energy by 2030 – Increasing Wind Energy’s Contribution to 

U.S. Electricity Supply,” May, 2008. 

[2] J. Charles Smith, Michael R. Milligan, Edgar A. DeMeo and Brian Parsons, "Utility wind Integration and operating impact state of the art," 

IEEE Trans. Power Systems, vol. 22, pp. 900-908, Aug. 2007.

[3] Short-circuit currents in three-phase a.c. systems–Part 0: Calculation of 

currents, IEC Standard 60909-0, July 2001.

[4] IEEE Application Guide for AC High-Voltage Circuit Breakers Rated on 

a Symmetrical Current Basis, IEEE Standard C37.10-2000, Sept. 2000.

[5] Nader Samaan, Robert Zavadil, J. Charles Smith and Jose Conto, “Modeling of Wind Power Plants for Short Circuit Analysis in the Transmission Network,” in Proc. of IEEE/PES Transmission and Distribution 

Conference, Chicago, USA, April 2008.

[6] H. Wayne Beaty, “Handbook of Electric Power Calculations,” McGraw 

Hill, Third Edition, 2001. 

[7] E. Muljadi, Z. Mills, A. Ellis, R. Foster, ” Fault Analysis at a Wind Power Plant for a One Year of Observation”, presented at the IEEE Power 

Engineering Society, General Meeting, Pittsburgh, PA, July 20-24, 2008.

[8] E. Muljadi, S. Pasupulati, A. Ellis, D. Kosterev, “Method of Equivalencing for a Large Wind Power Plant with Multiple Turbine Representation”, presented at the IEEE Power Engineering Society, General Meeting, Pittsburgh, PA, July 20-24, 2008

[9] E. Muljadi, C. P. Butterfield, A. Ellis, J. Mechenbier, J. Hochheimer, R. 

Young, N. Miller, R. Delmerico, R. Zavadil, and J. C. Smith, “Equivalencing the collector system of a large wind power plant,” in Proc. 2006 

IEEE Power Engineering Society General Meeting.

[10] “WECC Wind Power Plant Power Flow Modeling Guide" prepared by 

WECC Wind Generator Modeling Group, May 2008. 

VII. BIOGRAPHIES

Eduard Muljadi (M’92-SM’94) received his Ph. D. (in Electrical Engineering) from the University of Wisconsin, Madison. From 1988 to 1992, he 

taught at California State University, Fresno, CA. In June 1992, he joined the 

National Renewable Energy Laboratory in Golden, Colorado. His current 

research interests are in the fields of electric machines, power electronics, and 

power systems in general with emphasis on renewable energy applications. 

He is member of Eta Kappa Nu, Sigma Xi and a Senior Member of IEEE. He 

is involved in the activities of the IEEE Industry Application Society (IAS), 

Power Electronics Society, and Power Engineering Society (PES). He is currently a member of Industrial Drives Committee, Electric Machines Committee, and Industrial Power Converter Committee of the IAS, and a member of 

Working Group on Renewable Technologies and Dynamic Performance Wind 

Generation Task Force of the PES. He holds two patents in power conversion 

for renewable energy. 

Nader Samaan (S’00, M’04) received his Ph.D. degree in electrical engineering from Texas A&M University, USA in 2004. He is currently a senior 

power systems engineer at PNNL, Richland, WA, USA. Prior to that, he was a 

power systems engineer at EnerNex Corp. for four years. He was a visiting 

assistant professor at the department of electrical and computer engineering, 

Kansas State University during the academic year 2004-05. 

His research interests include wind integration studies, power system reliability, harmonics and transient analysis for wind power plants, wind turbine 

dynamics molding, distributed generation, artificial intelligence and intelligent 

optimization techniques application to power systems. 

Dr. Samaan is a registered professional engineer in the state of Ohio, a 

member of the IEEE Power Engineering Society and a member of CIGRE. 

Vahan Gevorgian (S’01- M’05- SM’08) graduated from the Yerevan Polytechnic Institute (Armenia) in 1986. During his studies he concentrated on 

electrical machines. His thesis research dealt with doubly-fed induction generators for stand-alone power

Systems. He obtained his Ph.D. degree in Electrical Engineering Dept. from 

the State Engineering University of Armenia in 1993. His dissertation was 

devoted to a modeling of electrical transients in large wind turbine generators.

Dr. Gevorgian is currently working at the National Wind Technology

Center (NWTC) of National Renewable Energy Laboratory (NREL) in Golden, Colorado, USA, as a research engineer. His current interests include 

modeling and testing of various applications of small wind turbine based power systems.

Jun Li (S'01, M'05) is working at EnerNex Corp. as a power systems engineer, currently conducting simulation and analytical studies of power systems, such as wind generator dynamic modeling, load flow analysis, stability, 

and short circuit analysis. He has developed wind turbine models using several 

power system simulation packages such as PSLF and PSCAD. He has a B. 

Eng. and M. Eng. in Electric Power from Xi'an Jiaotong University, Xi'an, 

China, and a Ph.D. in Electrical Engineering from Texas A&M University, 

College Station, TX. He had worked for four years in Shaanxi Electric Power 

Research Institute, Xi'an, China as a Power Systems Engineer.

Subbaiah Pasupulati (M’05) graduated from University of Texas, Arlington with an M.S. in Electrical Engineering in 2003. From 2003 to 2005, he 

was with Energy Unlimited Inc., a Wind Power Plant in Palm Spring, California where he was responsible to oversee the operations of the plant. He joined 

Oak Creek Energy System Inc. (OCES) in 2006. He is currently the Power 

System Engineer at OCES, he involved in design and development of 2.5 GW 

plus wind power plants in the Tehachapi area. He participated in California 

Southern Regional Transmission Plan 2006 conducted by California Independent System Operator which came up with Tehachapi's Renewable Transmission Plan. He is a member of the IEEE. He is an active member of WECC's 

Technical Studies Subcommittee & Wind Generator Modeling Group. 
F1147-E(10/2008)

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Short Circuit Current Contribution for Different Wind Turbine 

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This paper presents simulation results for short-circuit current contribution for different types of WTGs obtained 

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Fault contribution; grid integration; induction generator; protection; short circuit; wind power plant; wind turbine

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