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Contract No. DE-AC36-08GO28308

Impact of DistributionConnected Large-Scale Wind 

Turbines on Transmission 

System Stability during Large 

Disturbances

Preprint 

Y. Zhang, A. Allen, and B.-M. Hodge

National Renewable Energy Laboratory

To be presented at the IEEE Power and Energy Society 

General Meeting

National Harbor, Maryland

July 27–31, 2014

Conference Paper

NREL/CP-5D00-60910

February 2014
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1 

Abstract—Many favorable wind resources are located in rural 

areas that do not have direct access to the high-voltage 

transmission systems. Therefore, it is practical and cost-effective 

to seek the installation of utility-scale, megawatt-level wind 

turbine generators on distribution feeders. Common study for 

interconnection of distributed generation typically focuses on 

stability impacts within the distribution feeder itself, such as the 

impact on feeder voltages. Efforts to investigate the impact of 

transmission events on distributed wind generation, as well as the 

impact of distributed wind generation at high penetration level on 

transmission stability, are much needed. 

This study models a power system with both the bulk 

transmission grid as well as distribution feeders. Megawatt-level 

wind turbine generators are connected to distribution feeders. 

Transmission disturbances are simulated to analyze their impacts 

on distributed wind generators. This study also investigates the 

reaction from all the distributed generation to a single 

transmission disturbance when the wind penetration is high, 

which could have a great impact on system stability. 

Index Terms—distributed generation, wind turbine generator, 

wind energy 

I. INTRODUCTION

IND power installations are growing rapidly worldwide, 

with total global installed capacity exceeding 318 GW 

at the end of 2013 [1]. In the United States alone, there are 

now more than 60 GW of installed capacity as of the third 

quarter of 2013 [2]. However, the vast majority of these U.S. 

installations are in large wind power plants that required 

building additional transmission lines to reach the best 

resources. These required transmission build-outs come with 

additional costs and are often delayed because of political 

difficulties in the siting process. Installing megawatt-scale 

wind turbines on existing distribution networks can help 

increase the amount of energy supplied by wind without the 

associated transmission build-outs. 

 

This work was supported by the U.S. Department of Energy under 

Contract No. DE-AC36-08-GO28308 with the National Renewable Energy 

Laboratory.

Y. Zhang, A. Allen, and B-M. Hodge are with are with National 

Renewable Energy Laboratory, Golden, CO 80401 USA.

Installing such large wind turbines on distribution feeders 

require interconnection studies to ensure that power quality 

and reliability are not impacted. There have been quite a few 

investigations on distributed-generation’s impact on 

distribution feeder power quality [3-4]. In previous work, the 

authors also examined the impact of distributed wind power on 

feeder bus voltages as a function of wind power production 

and the electrical distance of wind turbine sites from 

distribution substations [5]. This work focuses on the dynamic 

impacts of distributed wind power at the transmission level. 

This is particularly relevant to bulk power system operators 

who are interested in the impact of IEEE 1547 standards [6] at 

higher penetrations of distributed renewable energy. These 

standards specify the actions distributed generators should take 

to protect themselves through disconnections in response to 

abnormal frequency and voltage conditions. However, with 

large amounts of distributed generation, the simultaneous 

disconnection of these generators during a contingency event 

could exacerbate voltage or frequency issues. The impact of 

distributed generation at high penetrations of renewable energy 

cannot be neglected, thus the transmission grid may need 

support from the distributed resources to maintain stability 

after certain disturbances. Distribution-connected generators 

are increasing world-wide. There is quite a bit of interest in 

looking into the impact from a legislative point of view [7]. 

There has been some study on the economic and commercial 

impacts of interconnecting distributed generation on a 

transmission system [8]. Probabilistic methods have been 

applied to determine the security impact from distributed 

generation on distribution and transmission systems [9] [10]. 

Transmission planning considering distributed generation was 

also studied [11]. This study will take a fresh look at the 

interactions between the distributed generation and 

transmission system in terms of stability impacts. 

Section II describes the components of the test system 

model. The investigation of a transmission fault’s impact on 

distributed wind is made in Section III. The analysis on a 

transmission disturbance with high wind penetration is made in 

Section IV. Conclusions are drawn in Section V.

II. TEST SYSTEM MODEL

The purpose of this study is to investigate the stability issue 

on both transmission and distribution systems when megawattscale wind turbine generators (WTGs) are installed on 

Impact of Distribution-Connected Large-Scale 

Wind Turbines on Transmission System 

Stability during Large Disturbances

Yingchen Zhang, Member, IEEE, Alicia Allen, Member, IEEE, and Bri-Mathias Hodge, Member, 

IEEE

W

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2 

distribution feeders. Thus, a transmission system with a 

distribution feeder connection needs to be modeled in a 

dynamic simulation environment. For this purpose, the 23-bus, 

6-generator test system provided by the Power System 

Simulator for Engineering (PSS/E) tool [12] is utilized. The 

system diagram is shown in Fig. 1. This test system mainly 

consists of 230-kV and 500-kV lines. 

This system has a total load of 3,200 MW. Since the system 

has such few buses, the loading and generation levels are

apparently an aggregation compared with a real-world system 

(e.g., the Western Interconnection of North America has 

approximately a 100-GW load and 20,000 buses [13]). If 

several megawatt-scale WTGs were connected to some 

distribution feeders embedded in such a system, their impact 

on the entire grid would be essentially negligible. Therefore, 

the test system needs to be modified to a smaller scale to make 

the small amount of distributed wind generation become 

visible. The total load and generation in the modified system 

are displayed in Table 1. Part of the reactive load is served by 

shunt capacitors installed in the system.

Fig. 1. PSS/E 23-bus transmission system

TABLE 1. FACT SHEET FOR THE MODIFIED 23-BUS SYSTEM

Total Load

(MW)

Total Load

(MVar)

Total Gen

(MW)

Total Gen

(MVar)

320 195 325.8 96.4 

The most ideal locations to install WTGs are usually rural 

feeders, which typically have radial configurations [5]. The 5-

bus distribution feeder shown in Fig. 2 was selected from the 

IEEE 16-bus distribution test system [14] to be applied to this 

study. The original 16-bus system contains three separate 

radial feeders connected at the same substation. For this study, 

only Feeder 1 in the 16-bus system was used. The branches 

and load parameters of this distribution feeder are given in 

Table 2. This entire distribution feeder consists of three-phase 

balanced lines and loads at 12.65 kV, because utility-scale 

WTGs are most certainly connected at three-phase buses. 

1 4 6 7

5

Transmission

Fig. 2. Distribution feeder from IEEE 16-bus distribution system

TABLE 2. FACT SHEET FOR THE DISTRIBUTION FEEDER

Section

Section 

Resistance 

(p.u.)

Section 

Reactance

(p.u.)

End Bus 

Load

(MW)

End Bus 

Load 

(MVar)

1-4 0.075 0.1 2 1.6

4-5 0.08 0.11 4.6 1.5

4-6 0.09 0.18 1.5 0.4

6-7 0.04 0.04 1.5 0.5

The WTG models used are the Western Electricity 

Coordinating Council standard models [15] [16] for Type 4 

turbines. Type 4 generators are full-power-converter 

generators that have power electronic controls that allow for 

power factor and voltage control at the terminals. This model 

was chosen because most new megawatt-scale wind turbines 

installed in the United States are either Type 3 (doubly-fed 

asynchronous) or Type 4 generators. Type 1 and Type 2 

generators, known as fixed-speed and variable-slip WTGs, are 

much less common at this scale and do not have the ability to 

provide decoupled real and reactive power control. The chosen

models, Type 3 and Type 4, represent the dynamic response of 

the WTG to various voltage and frequency issues experienced 

during disturbance, including the ability to control the 

magnitude and angle of current injection. The WTGs in this 

study are rated at 3.6 MW because typically the Type 4 WTGs 

are rated from 1.5 to 3.6 MW, therefore we want to push the 

distribution generation capacity to higher end. The WTG uses 

power factor controls to maintain unity power factor output so 

that the analysis will isolate the pure impact from the WTG 

power output from a mixed control scenarios. 

III. TRANSMISSION DISTURBANCE IMPACTS ON 

DISTRIBUTED WIND

Although we are ultimately interested in seeing what 

impact utility-scale wind turbines installed on the distribution 

system will have on the transmission system, it is important to 

first consider the impact of the WTGs on local distribution 

system. In this section, we examine the impact of transmission 

contingencies on the WTGs installed at the distribution level. 

For this, we simulated the 23-bus system shown in Fig. 3 in the 

PSS/E environment, modified with a distributed feeder 

connected at the bus marked by the blue circle. 

When connecting the feeder at the marked location, the load 

at the transmission bus was reduced to keep the total load at 

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3 

this bus unchanged—i.e., the new load equals the old load 

minus the total load of the distribution feeder. As a result, the 

existing generation—real power, in particular—in the test 

system was reduced roughly equal to the WTG output. 

To simulate a transmission disturbance that has immediate 

effect on the distribution feeder, a fault at an adjacent bus (as 

marked by the red arrow in Fig. 3), was applied at 5 seconds. 

The fault cleared at 5.18 seconds, which might be too long in 

reality, but would be explicit for demonstration purposes. 

Fault location

Distribution Feeder

Fig. 3. Locations of the distribution feeder as well as the fault

The main goal of this practice is to determine whether the 

impact from a transmission contingency will be the same when 

a WTG is connected at different locations on the distribution 

feeder. First, Fig. 4 illustrates the voltages at all distribution 

buses when the transmission contingency occurred. The Y-axis 

in Fig. 4 (and in Fig. 5 and Fig. 6) is the percentage of voltage 

at the current time step to the initial voltage, which is kept 

close to 1per unit. In this case, a WTG was connected at Bus 

7. It is obvious that the voltage at Bus 7 changed the most 

during the event, and, according to the IEEE standard 1547, 

the distributed generation at this bus should be disconnected 

after 0.16 second. 

From [3], we know that when a WTG is at different buses, 

the feeder voltage profile will be different. In the previous 

simulation, the WTG happened to be installed at the bus with 

the most voltage change during the event. But what if a WTG

is connected at another bus? Fig. 5 demonstrates the voltage at 

Bus 7 when a WTG was connected at different buses. The 

voltage at Bus 7 changed the most when the WTG was 

connected at the same bus. It changed the least when the WTG 

was connected at the substation. But what happens when a 

WTG is actually connected at Bus 1? Will the voltage change 

at Bus 1 be big enough to trip the generator? Fig. 6 

demonstrates voltages at different buses when the WTG was 

connected at the same bus. When the WTG was connected at 

Bus 4, Bus 5, and Bus 6, the maximum changes were well 

below the tripping threshold (50%) as defined in the IEEE 

standard 1547. However, only the voltage at Bus 7 exceeded

the threshold long enough (0.16 second) to trigger generation 

trip action. 

WTGs installed at different locations will be impacted

differently by transmission disturbances. In this simulation, the 

worst case was when a WTG was installed at Bus 7. 

4.8 5 5.2 5.4 5.6 5.8 0.4

0.5

0.6

0.7

0.8

0.9

1

1.1

Time (s)

% of Voltage

Bus 1

Bus 4

Bus 5

Bus 6

Bus 7

Fig. 4. Voltages at different buses when a WTG was connected at Bus 7

4.8 5 5.2 5.4 5.6 5.8 0.4

0.5

0.6

0.7

0.8

0.9

1

1.1

Time (s)

% of Voltage

Bus 1

Bus 4

Bus 5

Bus 6

Bus 7

Fig. 5. Voltages at Bus 7 when a WTG was connected at different buses

4.8 5 5.2 5.4 5.6 5.8 0.4

0.5

0.6

0.7

0.8

0.9

1

1.1

Time (s)

% of Voltage

Bus 1

Bus 4

Bus 5

Bus 6

Bus 7

Fig. 6. Voltages at buses when a WTG was connected at the very same bus

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4 

IV. TRANSMISSION IMPACT FROM DISTRIBUTED 

WIND

Having shown the local distribution system impacts 

associated with distributed utility-scale WTGs during a 

contingency event, we next examine how these changes will 

propagate back up in the bulk power system. Obviously, at 

very small distributed wind power penetrations the impact on 

the transmission system will be negligible. For this reason, we 

produced a scenario in which approximately 8% of the power 

is supplied by distributed WTGs and examined how various 

voltage and frequency issues experienced at the WTG can 

impact the transmission system depending on the WTG 

response.

The same feeder that was modeled in Section III was 

duplicated and connected to all the load buses in the 23-bus 

system, as shown by the blue circles in Fig. 7. Each feeder had 

a 3.6-MW WTG, so the total wind generation in this scenario 

was 25.2 MW. Each WTG was connected at Bus 7 of each 

feeder, so that when a transmission contingency occurred, they 

were most likely to be affected. 

Fig. 7. 8% of wind penetration at distribution level

Section III concentrated on studying the bus voltage change 

under disturbances. However, voltage change is a localized 

problem when propagated from distributed generation to the 

transmission system; distributed generation at other locations 

will not have a great impact on the event. The aggregated 

effect from all the distributed wind will be of concern with 

regard to the system frequency. The current IEEE standard 

1547 has rather big security margins in terms of underfrequency tripping; however, if a big event happens, such as 

the N-2 generation tripping as described in Fig. 7, the system 

frequency may fall below 59.8 and remain below for a certain 

period of time. Fig. 8 illustrates the frequency at all the 

distribution feeder connection points when the large generation 

tripping event happened. All distributed wind stayed online 

during the event. 

If the distributed wind follows the standard and trips offline 

when the system frequency reaches 59.8 and stays there for 

more than 0.16 second, the endangered system is further 

pushed down, as displayed in Fig. 9. This could lead to underfrequency load-shedding thresholds and trigger a series of 

severe events. It is worth noting that in this system the 

electromechanical wave propagated fairly fast and thus the 

time delay between each bus was small. Thus the WTGs 

roughly tripped simultaneously. Compare the frequency trace 

in Fig. 9 with in Fig. 8, the portion above 59.8 Hz are 

identical. Below 59.8 Hz, the frequency slope in Fig. 9 is much 

steeper than in Fig. 8, plus the lowest frequency is much 

smaller in Fig. 9 than in Fig. 8.

0 10 20 30 40 50 60 59.65

59.7

59.75

59.8

59.85

59.9

59.95

60

60.05

Time (s)

Freq (Hz)

Fig. 8. System frequency response when distributed WTGs rode through a 

contingency

0 10 20 30 40 50 60 59.65

59.7

59.75

59.8

59.85

59.9

59.95

60

60.05

Time (s)

Freq (Hz)

Fig. 9. System frequency response when distributed WTGs tripped offline 

during a contingency

In such a small system dropping two major generation units 

can cause the system to be non-recoverable. Fig. 8 shows that 

when the event happens, there is not enough frequency 

response to bring the system frequency close to the pre-fault 

conditions. Operating under frequency could lead to 

synchronous machines unstable and eventually causing system 

cascading failure. However in reality, a large interconnected 

system will have sufficient frequency response from inertias, 

primary and secondary frequency reserves to bring the system 

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5 

frequency back to nominal after severe N-1 or N-2 

contingencies. 

Fig. 10 shows a real-time frequency event occurs in Western 

Interconnection. The data is collected by a real-time 

measurement device in NREL campus at a distribution circuit. 

During the event, the system frequency dropped down as low 

as 59.7Hz but then stabilized approximately to 59.8Hz due to 

the reaction from inertias and primary frequency response. It 

fully recovered to 60Hz after roughly 20minute due to the 

response from secondary and tertiary reserves. So we can 

conclude that the problems discovered in Fig. 9 will be 

definitely possible given certain system conditions.

Fig. 10. Example of Real Grid Frequency Response After a disturbance

In a case like this, if the penetration of distributed 

generations in the system is high, and they starting to response 

to frequency as specified in IEEE standard 1547, the event will 

definitely be exacerbated. 

V. CONCLUSION AND FUTURE WORK

In this work, we examined the dynamic impacts of 

distributed utility-scale wind power during contingency events 

on both the distribution system and the transmission system. A 

transmission disturbance can propagate into distribution 

feeders and cause distributed, megawatt-level WTGs to trip 

offline. The interconnection location within the feeder matters 

because it decides the severity of the impact from the 

transmission disturbance. When the distributed wind reaches

higher penetration levels, the aggregate effect of their response

to a transmission contingency can lead to more severe system 

conditions.

This work will be the first step to investigate the high 

penetration of distribution-connected wind power’s impact on 

both distribution and transmission stability. Future work 

includes determining the impact of the distributed generation 

providing low voltage and frequency ride through, and how 

this will impact transmission system. It also includes studying 

the combined distributed generation with controllers such as 

capacitors and batteries to support transmission system should 

disturbance occurs. Furthermore, the potential islanding issue 

with high penetration of distributed wind will be examined.

VI. ACKNOWLEDGMENT

The authors gratefully acknowledge Mr. Dave Bertagnolli, 

Mr. Jonathan Black, and Mr. William Henson from ISO New 

England for their involvement in the technical discussions for 

this project. The authors are greatly appreciative of the data 

provided by Dr. Vahan Gevorgian from NREL to illustrate the 

real system event shown in Fig. 10. 

VII. REFERENCES

[1] Global Wind Energy Council, “Global wind statistics 2013,” Brussels, 

Belgium, May 2014. 

[2] U.S. Energy Information Administration, “Electric Power Monthly,” 

Washington, D.C., 2013.

[3] K. P. Schneider, Y. Chen, D. P. Chassin, R. G. Pratt, D. W. Engel, and 

S. Thompson, Modern grid initiative: Distribution taxonomy final 

report: Pacific Northwest National Laboratory, 2008.

[4] W. U. Consulting, "Distributed Wind Generation Study for Northeast 

Colorado," 2005.

[5] A. Allen, Y. Zhang, and B.-M. Hodge, “Impact of increasing distributed 

wind power and wind turbine siting on rural distribution feeder voltage 

profiles,” in Int. Workshop on Large-Scale Integration of Wind Power 

into Power Systems as Well as on Transmission Networks for Offshore 

Wind Power Plants, London, UK, 2013.

[6] IEEE 1547 Standard for Interconnecting Distributed Resources

with Electric Power Systems

[7] A. Moreno-Munoz, J. De La Rosa, M. Lopez, A. Gil De Castro, “Grid 

interconnection of distributed generation: The Spanish normative”, in 

Int. Conf. on Clean Electrical Power, Capri, Italy, 2009.

[8] L. Dale, “Distributed generation and transmission”, in IEEE PES Winter 

Meeting, New York, USA, 2002.

[9] R. Allan, P. Djapic, G. Strbac “Assessing the Contribution of 

Distributed Generation to System Security”, in Int. Conf. on 

Probablistic Methods Applied to Power Systems, Stockholm, Sweden, 

2006. 

[10] D. Newman, B. Carreras, M. Kirchner, I. Dobson, “The Impact of 

Distributed Generation on Power Transmission Grid Dynamics”, In the 

44th Hawaii International Conf. on System Sciences, Kauai, USA, 2011.

[11] J. Zhao, J. Foster, Z. Dong, K. Wong, “Flexible Transmission Network 

Planning Considering Distributed Generation Impacts”, in IEEE Trans. 

Power Sys., vol. 26, no. 3, pp. 1,434-1,443, Aug. 2011. 

[12] PSS/E operation manual, Siemens PTI, 2005.

[13] TSS base cases, www.wecc.biz

[14] S. Civanlar, J. Grainger, H. Yin, and S. Lee, “Distribution feeder 

reconfiguration for loss reduction,” in IEEE Trans. Power Del., vol. 3, 

no. 3, pp. 1,217–1,223, July 1988. 

[15] E. Muljadi and A. Ellis, “Final project report: WECC wind generator 

development,” Prepared by National Renewable Energy Laboratory, 

University of California–California Institute for Energy and 

Environment, March 2010. 

[16] W. W. G. M. Group, "WECC Wind Power Plant Power Flow Modeling 

Guide," Western Electricity Coordinating Council 2008.

VIII. BIOGRAPHIES

Yingchen (YC) Zhang received his B.S. from Tianjin University, Tianjin, 

China, in 2003, and his Ph.D. degree from Virginia Polytechnic Institute and 

State University, Blacksburg, in 2010. He is currently with the National 

Renewable Energy Laboratory. His research interests include power system 

stability with large-scale integration of renewable energies, power system 

wide-area monitoring, and PMU applications for renewable integrations. Dr. 

Zhang previously worked for the California Independent System Operator 

developing and implementing steady-state and dynamic analysis tools to 

improve power system situational awareness. 

Alicia J. Allen received the B.S., M.S. and Ph.D. degrees from The 

Department of Electrical and Computer Engineering at The University of 

Texas at Austin. She is currently at the National Renewable Energy 

Laboratory, Golden, CO, USA. Her research interests include distributed wind 

and solar, distribution system modeling, power quality, system protection and 

synchronized phasor measurements.

Bri-Mathias Hodge is a senior engineer in the Transmission and Grid 

Integration group at NREL. He has experience in dealing with a number of 

different grid integration issues, including: wind and solar power forecasting, 

distributed wind power, power systems modeling, and the impacts of electric 

vehicles. He has a Ph.D. from Purdue University.

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