NREL is a national laboratory of the U.S. Department of Energy, Office of Energy 

Efficiency & Renewable Energy, operated by the Alliance for Sustainable Energy, LLC.

Contract No. DE-AC36-08GO28308

Wind Power Plant Short Circuit 

Current Contribution for 

Different Fault and Wind Turbine 

Topologies 

Preprint 

V. Gevorgian and E. Muljadi

National Renewable Energy Laboratory

To be presented at The 9th Annual International Workshop on 

Large-Scale Integration of Wind Power into Power Systems as well 

as on Transmission Networks for Offshore Wind Power Plants, 

Québec, Canada

October 18-19, 2010

Conference Paper

NREL/CP-5500-49113

October 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 

various fault conditions such as single, two, and three-phase 

faults in different network locations. This task can be 

challenging to protection engineers due to the topology 

differences between different types of wind turbine generators 

(WTGs) and conventional generating units. This paper 

presents simulation results for SC current contribution for 

WTGs obtained through transient simulation. The obtained 

waveforms are analyzed to explain the behavior, such as peak 

values and rate of decay, of the WTG.

The effect of turbine and substation transformer winding and 

grounding configuration on positive, negative, and zerosequence current and voltage magnitudes is demonstrated. 

The behavior of fault currents is illustrated by the output of 

simulations in positive, negative and zero sequence 

components.

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

based on the type of the installed WTGs. The SC current will 

be determined by the generator’s physical characteristics and 

system transformers configurations. For some wind turbine 

types, the SC current will also depend on power converter’s 

control algorithms, which are usually considered proprietary 

information by the wind turbine manufacturers.

Index Terms—Wind Power Plant, Short Circuit Current, 

Voltage Fault. 

I. NOMENCLATURE

WPP – wind power plant

WTG – wind turbine generator

SC – short circuit

SCC – short circuit current

II. INTRODUCTION

Recently, 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. 

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

connected to the grid. In high penetration scenarios, the 

WPP’s 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.

A. Operation of Wind Turbine Generator 

The generator at each turbine should be protected 

individually and independently because of the WPP 

diversity. In practice, this is an advantage of a WPP 

compared to a conventional power plant. During a 

disturbance, the electrical characteristic at each terminal of 

the turbine is different from the other WTGs, and only the 

most affected WTGs 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 [3]. 

This is partially because WPPs are required to have zero 

voltage ride-through capability. Thus, the loss of generation 

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

At the turbine level, the WTG generates at low voltage 

levels (480 V-690 V). Type 1 and Type 2 WTG are

typically compensated by switched capacitor banks to 

generate at a unity power factor. Type 3 and Type 4 

generators are operated to generate a constant voltage at a 

designated bus, or they may be operated at a 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.

B. Wind Power Plant Equivalent

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. They are 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 a single equivalent turbine representation 

or as a multiple turbine representation [4],[5]. 

C. Organization of the Paper

The organization of this paper is as follows: in section 

III, the SCC characteristics of different WTG types will be 

summarized and discussed. In section IV, the aggregated 

SCC contribution of a WPP and the impact of the wind 

plant configuration will be presented. Finally, in section V, 

the conclusion will summarize the paper findings. 

III. OVERVIEW OF SHORT CIRCUIT CURRENT FAULT 

CURRENT FOR DIFFERENT WIND TURBINE TOPOLOGIES 

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). 

Vahan Gevorgian, Member, IEEE Eduard Muljadi, Fellow, IEEE

Wind Power Plant Short-Circuit Current 

Contribution for Different Fault and Wind Turbine 

Topologies
2

A. Three-Phase Symmetrical Fault on R-L Circuits 

SC faults can occur in various locations of the power 

system in a number of different ways including line-toground and line-to-line faults. For simplicity purposes, we’ll 

consider a symmetrical three-phase fault since it is the easiest 

to analyze. A simple equivalent diagram of a power system 

under such fault conditions is shown in Fig. 1. 

Fig. 1: Equivalent diagram of symmetrical fault

The fault in Fig. 1 is represented by a shorting switch. 

Immediately after the fault, the SCC contribution from the 

generator can be found using the following equation.

ug = L

di

dt + iR (1)

Where ug is the instantaneous voltage on the generator 

terminals, and R and L are line resistance and inductance. 

Solving equation (1) for current 

i = Vg

Z sin �ωt + α − atan �

X

R��

− e− R

L t �

Vg

Z sin �α − atan �

X

R

��� (2)

Where Vg is peak generator voltage, Z = √R2 + X2 - line 

impedance, and α is the voltage phase. The solution (2) 

has two components; the first component is stationary and 

varies sinusoidally with time. It represents the steady SCC. 

The second component decays exponentially with a time 

constant equal to R

L . It represents the DC component of the 

current. The steady state simmetrical fault current Isc from 

the generator can be calulcated from the first component 

of equation (2).

Isc = Vg/√2

√R2 + X2 (3)

Obviously, the steady state fault current depends on 

impedance of the line. The closer the fault occurrence 

location to generator terminals, the larger the SCC 

contributed to the fault. The peak magnitude of the 

transient component in equation (2) depends on line 

impedance as well, but it also depends on impedance angle 

φ = atan �

X

R

� at the point of the fault. The DC term does 

not exist if = φ , and will have its maximum initial value 

of Vg

Z where α − φ = ± π

2 . So, depending on the time when 

the fault occurs and the circuit characteristics, the transient 

current waveform will be different. This means that in 

three-phase systems the phase transient currents will have 

different peaks due to a 1200 shift in voltages. 

In large power systems with many generators and 

transmission lines, the actual fault current at any location 

in the grid will be the sum of collective contributions from 

all generators, making the above described analysis 

extremely complicated. So, some sort of simplification is 

needed for the fault current calculation in such a case. 

B. Short Circuit Current from a Type 1 WTG 

The first generation of utility-sized WTGs were a fixed 

speed turbine with a squirrel-cage induction generator 

(SCIG) and is called a Type I generator in wind-related 

applications. The SCIG 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 

percent). 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 

simplified single-phase equivalent circuit of a squirrel-cage 

induction machine is shown in Fig. 2 [6].

Fig. 2: Equivalent circuit of a Type 1 generator

The circuit in Fig. 2 is referred to the stator where RS

and Rr are stator and rotor resistances, LSσ and Lrσ are 

stator and rotor leakage inductances, Lm is magnetizing 

reactance, and S is rotor slip. The example single-line 

connection diagram of a Type I generator is shown in Fig. 

3. In the case of voltage fault, the inertia of the wind rotor 

drives the generator after the voltage drops at the generator 

terminals. The rotor flux may not change instantaneously 

right after the voltage drop due to fault. Therefore, voltage 

is produced at the generator terminals causing fault current 

flow into the fault until the rotor flux decays to zero. This 

process takes a few electrical cycles. The fault current 

produced by an induction generator must be considered 

when selecting the rating for circuit breakers and fuses. The 

fault current is limited by generator impedance (and can be 

calculated from parameters in Fig. 2) and impedance of the 

system from the SC to the generator terminals. 

Fig. 3: Type 1 WTG

The initial value of fault current fed in by the induction 

generator is close to the locked rotor inrush current. 

Assuming a three-phase symmetrical fault, an analytical 

solution can be found to estimate the current contribution 

of the generator. According to [7], the SCC of an induction 

generator can be calculated as
3

i(t) = √2VS

XS

′ [e

− t

TS

′

sin(α) − (1 − σ)e

− t

Tr

′ sin(ωt + α)] (4)

Where δ is the voltage phase angle for a given phase, σ

is the leackage fator, XS

′ = ωLS′ is stator transient 

reactance, and TS

′ and Tr

′ are stator and rotor time constants 

for damping of the DC component in stator and rotor 

windings. The transient stator and rotor inductances LS

′ and 

LS

′ can be determined as

LS

′ = LSσ + LrσLm

Lrσ+Lm

; Lr

′ = Lrσ + LSσLm

LSσ+Lm

(5)

TS

′ = LS

′

RS

; Tr

′ = Lr

′

Rr

(6)

σ = 1 − Lm

2

LSLr

 (7)

LS = LSσ + Lm ; Lr = Lrσ + Lm (8)

The current calculated from equation (4) is shown in 

Fig. 4 using parameters for a typical 2-MW induction 

generator when α = 300 + π/2 and pre fault voltage

VS = 0.7 pu. As can be seen from Fig. 4, the current 

reaches the maximum value at t = T/2 (first half a 

period). Therefore, it may be a good approximation to 

calculate the maximum (peak) current by substituting 

t = T/2 into (4). The resulting equation for peak current 

will be 

imax = √2VS

XS

′ [e

− T

2TS

′

+ (1 − σ)e

− T

2Tr

′

] (9) 

It was demonstrated experimentally in [8] that equation 

(9) gives satisfactory accuracy for peak current 

assessment. The resulting current is shown in Fig. 4.

Fig. 4: Short circuit current from a Type I WTG

C. Short Circuit Current from Type 2 WTG 

The variable slip generator is essentially a wound-rotor 

induction generator with a variable resistor connected in 

series to the rotor winding (Type 2 generator). This external 

resistor is controlled by a high-frequency switch. Below rated 

power, the resistor control is inactive, so the system operates 

as a conventional induction generator. Above rated power, 

the resistor control allows the slip to vary, so variable speed 

operation is possible for a speed range of about 10% [9]. If 

the blade pitch angle is kept constant at zero degrees, the 

rotor speed, and thus the slip, will vary with 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 blade pitch angle is 

controlled to keep the rotor speeds within a small deviation 

from the rated slip, the losses in rotor resistance can be 

minimized. An equivalent electrical diagram of a variable 

slip induction generator is shown in Fig. 5, with a variable 

external resistor Rext. 

Fig. 5: Equivalent circuit for a Type 2 generator

Fig. 6: Connection diagram for a Type 2 WTG

The connection diagram example for this type of 

generator is shown in Fig. 6. In case of three-phase 

symmetrical fault, the same equations as for a Type I 

generator are applied. The only difference will be for rotor 

time constant Tr

′ that needs to account for additional 

external resistance Rext . The modified rotor time constant 

can be calculated as 

Tr.ext

′ = Lr

′

Rr+Rext

 (10) 

Where Rext is the value of external resistance that 

happens to be in the circuit at the time of a fault. The effect 

of such additional resistance on SCC is shown in Fig. 7 for 

the case where Rext = Rr = 0.005pu. So, adding the 

external resistors doubles the overall rotor resistance. The 

modified equation for maximum current can then be written 

as [7]

imax = √2VS

�XS

′2+Rext

2

[e

− ∆T

TS

′

+ (1 − σ)e

− ∆T

Tr.ext

′ ] (11)

Fig. 7: Effect of external resistance for a Type 2 WTG

Where ∆T is the time after a fault when current reaches 

its first peak. In this case, this additional resistance 

decreases the overall AC component in current, but does 

not much affect the first peak value of the current since the 

increase in resistance is relatively small. The same 

conclusion can be made by analyzing equations (4) and 
4

(9), where the additional external resistance has an effect 

on a second term that represents the AC component of the 

current.

D. Short Circuit Current from a Type 3 WTG

A Type 3 WTG is implemented by a doubly fed 

induction generator (DGIF). It is a variable speed WTG 

where the rotor speed is allowed to vary within a slip 

range of ±0.3. Thus, the power converter can be sized to 

about 30% of rated power. The equivalent electrical 

diagram of a DFIG generator is shown in Fig. 8. It is 

similar to one for a regular induction generator except for 

additional rotor voltage Vr, representing voltage produced 

by a power converter. The typical connection diagram for 

a DFIG (Type 3) WTG is shown in Fig. 9. A crowbar 

system is usually used for protecting the power electronics

converter from overvoltage and thermal breakdown during 

SC faults. Additional dynamic braking on the dc bus is 

also used to limit the dc bus voltage.

Fig. 8: Equivalent diagram of a DFIG

Fig. 9: Connection diagram for a Type 3 WTG

During faults, the rotor windings are essentially short 

circuited by an equivalent crowbar resistance RCB. 

According to [7], the transient time constant for a DFIG 

generator will be 

Tr.CB

′ = Lr

′

Rr+RCB

 (12) 

And, the maximum SCC of a DFIG will be

imax = √2VS

�XS

′2+RCB2

[e

− ∆T

TS

′

+ (1 − σ)e

− ∆T

Tr.CB

′

] 

(13)

If RCB ≫ Rr, then Tr.CB

′ is small and the time of the first 

peak ∆T → 0. In such a case, [7] proposes a simplified 

equation for DFIG maximum SCC

imax ≈ 1.8VS

�XS

′2+RCB2

(14)

Calculated SCCs for a DFIG for two different crowbar 

resistance values are shown in Fig. 10. In this case RCB2 >

RCB1 ≫ Rr. The red plot represents zero crowbar resistance 

when Rr = 0.005pu. The blue and green plots represent 

cases when RCB = 0.05pu and RCB = 0.1pu respectively. 

As can be seen in Fig. 10, larger crowbar resistance will 

lead to a lower peak current and smaller AC component.

The maximum value of crowbar resistance RCB.max can be 

found from equation (14) if maximum allowable rotor 

voltage is specified. 

Fig. 10: Effect of crowbar on max DFIG current

E. Short Circuit Currents from a Type 4 WTG 

An example of a Type 4 direct drive WTG with 

permanent magnet synchronous generator (PMSG) 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. 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.

The SCC 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 output current is controlled to stay 

within the current limit (e.g., 1.1 p.u.). 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 aerodynamic input 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 
5

bus voltage. 

Fig. 11: PMSG direct drive WTG diagram

F. Short Circuit Current from WTG with Synchronous 

Generator Directly Connected to Grid 

The latest advances in hydro-dynamic torque converter 

technology allowed development of variable-speed wind 

turbines with synchronous generators (SG) directly 

connected to grid. The torque converter allows decoupling 

of the variable speed mechanical output of a turbine 

gearbox from the generator shaft. As a result, the 

synchronous generator rotates at constant speed, so no 

power electronics converter is needed. The SC analysis for 

such WTGs then becomes an SC analysis of a regular 

synchronous generator that has been studied extensively in 

the literature. A simplified equivalent electrical diagram of 

a synchronous generator is shown in Fig. 12, where Laσ is 

the armature leakage reactance, Laris the armature reaction,

and Ef is the generator EMF at no load. A more detailed 

diagram for a two-axis representation is available from 

multiple sources and is not considered in this report. A 

configuration diagram example of a WTG with a directly 

connected SG is shown in Fig. 13.

Fig. 12: Equivalent diagram of a SG

Fig. 13: WTG with a directly connected SG.

In the case of a three-phase symmetric short-circuit, the 

analytical solution for current contribution of the 

synchronous generator according to [10] can be written as

i(t) = VS � 1

Xd

+ � 1

Xd

′ − 1

Xd

� e

− t

Td

′

+ � 1

Xd

′′ − 1

Xd

′� e

− t

Td

′′� cos(ωt −

α) − VS

2 �� 1

Xd

′′ + 1

Xq

′′� cos (α) + � 1

Xd

′′ − 1

Xq

′′� cos (ωt − α)� e

− t

Ta (15)

Where Xd, Xd

′ , Xd′′ is the d-axis synchronous, transient,

and sub-transient reactance; Xq

′′ is the q-axis sub-transient 

reactance; Td

′

, Td

′′ are the transient and sub-transient time 

constants; Ta is the armature time constant; α is the angle 

between phase A, and d-axis at the beginning of the SC. 

The current in equation (15) has both AC and DC 

components. The maximum current will vary depending on 

phase angle α as shown in Fig. 14 for a typical megawatt 

size SG. Although machine reactances are not true 

constants and depend on saturation of the magnetic circuit, 

their values are usually within certain predictable limits. 

Fig. 14: SG short circuit current for two different angles 

G. Standard Practices for Short Circuit Level 

Calculation

A procedure for fault current calculation based on an 

equivalent voltage source at the fault point is used in the 

IEC 60909 standards [11]. The Thevenin theorem is 

applied to the unloaded networks with a corrected source 

voltage. The voltage correction factor for voltages is used 

to account for the variations of the actual voltage from 

nominal value. In the case of a symmetrical fault, the IEC 

60909 method suggests calculating initial symmetrical 

SCC as

Ik

′′ = cVn

√3 Zk

 (17)

Where c is a voltage scaling factor, Vn is the nominal lineto-line voltage at the point of fault, and Zk is the Thevenin 

impedance of the grid. The standard suggests using values 

c=1.05 for MV/HV networks and c=1.10 for LV networks. 

The peak SCC is then calculated as

IP = k√2Ik

′′ (18)

Where the factor k is given as a function of R/X and can be 

calculated as

k = 1.02 + 0.98e−3

R

X (19)

The factor k takes into account the transient component 

of SCC and allows estimating the highest possible 

instantaneous value of the SCC. The equation (19) is valid 

for a case of a single-fed far-from-generator fault. The 

standard proposes different equations for k factor 

calculations for different types of circuits. The IEC method 

for SCC calculations is applied to both 50-Hz and 60-Hz 

systems. 

H. Asymmetrical Faults

Balanced three-phase faults can be analyzed using an 

equivalent single-phase electrical circuit similar to the one 

shown in Fig. 1. For example, a comparison for SCC from a 

Type I wind turbine is calculated using Equation 4 and a 

three-phase PSCAD model is shown in Fig. 15. For a 

symmetrical fault, Equation 4 gives good approximation for 

peak current and decay time. 
6

Fig. 15: Comparison of SCC for Type 1 WTG

Single or two-phase faults can be analyzed using 

symmetrical components to reduce the complexity of the 

calculations. The symmetrical components method splits 

the unbalanced three-phase system into three balanced 

components: positive, negative, and zero sequence. The 

symmetrical components method and its applications to 

power system fault analysis have been described in detail in 

the technical literature. It is important to note that this 

method is based on steady-state analysis and does not 

consider transient effects in power systems. In a case with 

power systems with high wind penetrations, such approach 

may be used with Type I wind turbines. It may become 

inaccurate for Type II, III, and IV wind turbines since it 

does not account for damping and transient effects in such 

non-linear elements of wind turbines as slip control systems 

or power converters. 

Based on the above consideration, it was decided to 

conduct detailed time domain modeling of various types of 

wind farms operating with a power system under different 

fault conditions. Such time domain transient analysis allows 

capturing peak values of fault currents and accompanied 

voltage surges at different locations throughout the 

network. Results from such a simulation will be more 

realistic than results obtained from steady-state circuit 

analysis. The programming environment used for power 

system time-domain simulation is PSCAD (also known as 

PSCAD/EMTDC), developed by the Manitoba HVDC 

research Centre. PSCAD has been adopted worldwide by 

utilities, manufacturers, and research institutions, so it 

became an industry standard for electromagnetic transient 

simulations in power systems. 

IV. MODELING RESULTS

A. Power System Model

The power system model used for wind farm SC

behavior simulation was adopted from a modeling guide 

developed by the Western Electricity Coordinating 

Council (WECC) Wind Generator Modeling and 

Validation Work Group (WGMG) [12]. The WGMG 

recommends the use of a single-machine equivalent 

representation of multiple wind turbines operating in a 

single wind farm. Based on industry experience, this 

representation is also considered adequate for positivesequence transient stability simulations. The WECC single 

machine equivalent power flow representation is shown in 

Fig. 16. The interconnection transmission lines, 

transformers, and reactive power compensation are present 

in this representation. 

Fig. 16: A single-machine equivalent power flow 

representation

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. Power factor correction capacitors are 

necessary for Type 1 and Type 2 WTGs. And in some 

cases (e.g., weak grid condition or variation of the power 

factor or voltage control at the POI), it may be necessary 

to install additional plant-level reactive compensation 

implemented by a Static VAR Compensator (SVC), 

STATCOM (Static Compensation), Mechanically 

Switched Capacitor (MSC), or a combination of them. 

Under normal conditions, the Type 3 and Type 4 WTGs 

have the capability to vary the reactive and real power 

instantaneously and independently. Plant-level reactive 

compensation may be omitted for these WTG types.

B. Transformer Configuration within a WPP

The WPP will have two different types of transformer. 

The first one is the substation transformer. The substation 

transformer interfaces between the WPP and utility. It steps 

up the voltage of the collector system (e.g., 34.5 kV) to a 

transmission level voltage (e.g., 230 kV). The size of the 

substation transformer is the same size as the wind plant 

output in MVA. However, it is common to use several 

transformers (for redundancy, reliability, and economic 

consideration). Many WPPs use a three winding 

transformer as the substation transformer Yg /Δ/Yg. Note 

that the subscript g is used to indicate solid ground 

connection at the star point of the transformer. The second 

one is the pad-mounted transformer. It is installed at each 

turbine to step up the voltage from generation voltage (e.g., 

690 V) to the medium voltage used in the collector system 

(e.g., 34.5 kV). In many wind plants, the Yg/Δ connection is 

used for the pad-mounted transformer. With this 

connection, the zero sequence contribution from the power 

plant is blocked. Only positive and negative sequence 

components can flow to the fault along the transmission 

line. As shown in Fig. 16, a WPP can be represented by the 

wind turbine, the pad-mounted transformer, the collector 

system, the substation transformer, and the interconnecting 

transmission line [13] [14] . 

Most WPPs consist of uniform turbines from a single 

turbine manufacturer. Thus, a single turbine representation 

should be sufficient to represent the WPP. In some cases, a 

WPP may need to be represented by multiple turbines to 
7

capture the unique characteristics of the turbine generators 

within the WPP. 

The SC behavior of a WPP is affected by the type of 

generator, type of faults, configuration of the transformer, 

and other components such as reactive power compensation 

and cable capacitance. Other factors that may impact the SC 

behavior include unbalanced impedance within the WPP, 

unbalanced switching (stuck breaker), non-linear behavior 

of the transformer magnetic saturation, harmonics within 

the plant, and many other factors. 

Fig. 17: SCC for a single line-to-ground in a Type 1 

WPP

The symmetrical component is often used in calculating 

the unbalanced condition in a power system network. In a 

normal balanced condition, only the positive sequence 

component of voltage and current are found within the 

network. In an unbalanced condition, the negative and the 

zero sequence components of voltage and current can be 

found in the power system network. Using the symmetrical 

component, we can perform fault analysis and predict the 

SCCs and the bus voltages from a steady-state power 

system network. However, the steady state calculation 

considers only the fundamental component of voltage and 

current. Thus, the DC offset, the non-fundamental 

component occurring during the transient, are not 

accessible. 

The simulation performed in this paper uses a three-phase 

network [13][14]. The WPP is subject to different SC 

conditions at the transmission lines. The power system 

configuration within the WPP will have an impact on 

operation. Depending on the system configuration, the 

simulation will capture the positive, negative, and zero 

sequence components during transients, as well as the DC

and non-fundamental components of voltage and current.

As an illustration, a different transformer configuration 

and grounding will be studied in this section to illustrate the 

path of ground current. As an example, Fig. 17a shows SCC 

for a wind plant with a Type 1 turbine. The substation 

transformer is connected as Y-Δ (230 kV-Yg / 34.5 kV-Δ). 

The pad-mounted transformer is connected as Y-Y (34.5 

kV-Yg / 0.690 kV-Yg). A single-line–to-ground-fault occurs 

at the high side of the substation transformer. The line 

currents and the sequence currents are shown at the 

transmission line (i.e., the contribution from the wind plant 

only) and at the turbine side. As might be expected from the 

transformer configuration (YgΔ), there is no zero sequence 

current contribution from the WTG side. 

In Fig. 17b, the substation transformer is reconfigured to 

Y-Y (230 kV Y-grounded / 34.5 kV Y-grounded). Shown 

in Fig. 18 is the simplified equivalent circuit of the power 

system derived from Fig. 16 to illustrate the SC paths. The 

positive, negative, and zero sequence diagrams are 

connected in series for a single-line-to-ground-fault. The 

switch indicates the difference between YgYg versus Yg∆

configurations at the substation transformer. 

Figure 18: The equivalent circuit for a single line-toground fault

The collector system and the transmission line are 

actually represented by the pi circuit to represent the 

inductance and capacitance of the lines. It is not shown in 

Fig. 18 to simplify the drawing. Note that the flow of 

sequence currents (positive, negative, and zero sequence) 

are affected by two sources (i.e., the network bus and the 

wind turbine equivalent within the wind plant).

The modeling results for a Type 1 wind power plant are 

consolidated in Fig. 19 and Fig. 20. These figures show 

peak transient and sequence component values for current I3

(as shown in Fig. 16) for different sub-station and padmounted transformer configurations after a single line-toground fault (phase A is faulted). As can be seen in Fig. 19, 

the highest transient current in phase A corresponds to the 

case when the substation transformer is configured as Y-Y

(230 kV Y-grounded / 34.5 kV Y-grounded) and the padmounted transformer is configured as Y-Δ (34.5 kV-Yg / 

0.690 kV- Δ). Both negative I3- and zero I30 sequence 

components are also highest in this case (Fig. 20). The zero 
8

sequence components are completely eliminated when the 

substation transformer’s 34.5-kV winding is configured as 

Δ or ungrounded Y. However, the positive and negative 

sequence current contribution always exists for all 

configurations, as seen in Fig. 20. 

Fig. 19: Peak transient currents for different transformer

configurations

Fig. 20: Peak sequence currents for different transformer 

configurations.

V. CONCLUSIONS AND FUTURE PLANS

This paper describes a simple approach to compute and 

understand the behavior of the SCC for different types of 

WTGs. Five different types of WTGs were investigated.

The method describes and approximates the peak and the 

settling time of the SCCs. From the comparisons made 

between the detailed high level model and the simple SC

representation, the simple method can predict and 

approximate the SCCs with good accuracy.

Another part of the paper describes the short circuit 

behavior of Type 1 wind plant for different transformer 

configurations. The effect of the transformer configuration 

impedes or passes the zero sequence current from the wind 

plant, while the positive and negative sequence portions are 

not impeded.

Future plans include conducting similar type of SCC 

modeling for other types of WPP. 

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] 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.

[4] 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

[5] 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.

[6] Kundur, P. (1994). Power system stability and control. McGraw-Hill, 

New York, ISBN 0-07-035958-X

[7] J. Morren, S. Haan. Short-circuit current of wind turbines with doubly 

fed induction generator. IEEE Transactions on Energy Conversion, 

Vol. 11, No.1, March 2007

[8] Sulawa, Zabara, et al. Short circuit current of induction generators. 

IEEE ISCAS 2007 proceedings.

[9] O. Anaya-Lara, N. Jenkins, et al. Wind energy generation: modeling 

and control. Wiley. ISBN 9780470714331

[10] Ivanov-Smolensky. Electrical Machines. Text book for universities. 

Moscow. Energy, 1980

[11] International Electrotechnical Commission. Short-circuit currents in 

three-phase AC systems. IEC TR 60909-1, 2002

[12] WECC Modeling and Validation Work Group, “WECC Wind 

POWER Plant Power Flow Modeling Guide” May 2008.

[13] Muljadi E.; Gevorgian, V.; Samaan, N.; Li, J; Pasupulati, S. (2010). 

Sort circuit current contribution for different wind turbine generator 

types., presented at the IEEE-PES Conf., Minneapolis, MN, 2010

[14] Muljadi, E.; Samaan, N.; Gevorgian, V.; Pasupulati, S., Different 

factors affecting short circuit behavior of a wind power plant, 

Presented at IEEE-IAS Conf., Houston, TX, 2010 

VI. BIOGRAPHIES

Vahan Gevorgian (M’97) 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 wind turbine based power systems. He is 

a member of IEC61400-21 wind turbine power quality standard 

development group.

Eduard Muljadi (M’82-SM’94-F’10) 

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 9 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 

Fellow of the IEEE. He is involved in the activities of the IEEE Industry 

Application Society (IAS), Power Electronics Society, and Power and 

Energy 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.

The Alliance for Sustainable Energy, LLC (Alliance), is the manager 

and operator of the National Renewable Energy Laboratory (NREL). 

Employees of the Alliance, under Contract No. DE-AC36-08GO28308 

with the U.S. Dept. of Energy, have authored this work. The United 

States Government retains and the publisher, by accepting the article for 

publication, acknowledges that the United States Government retains a 

non-exclusive, paid-up, irrevocable, worldwide license to publish or 

reproduce the published form of this work, or allow others to do so, for 

United States Government purposes.
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This paper presents simulation results for SC current contribution for different types of WTGs obtained through 

transient and steady-state computer simulation software.

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Wind power plant; short circuit current; voltage fault.

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