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Contract No. DE-AC36-08GO28308

Impact of Increasing Distributed 

Wind Power and Wind Turbine 

Siting on Rural Distribution 

Feeder Voltage Profiles

Preprint

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

National Renewable Energy Laboratory

To be presented at the International Workshop on Large-Scale 

Integration of Wind Power into Power Systems as Well as on 

Transmission Networks for Offshore Wind Power Plants 

London, England

October 22 – 24, 2013

Conference Paper

NREL/CP-5D00-60310

September 2013
NOTICE

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Impact of Increasing Distributed Wind Power and 

Wind Turbine Siting on Rural Distribution Feeder 

Voltage Profiles

Alicia Allen, Yingchen Zhang, Bri-Mathias Hodge

National Renewable Energy Laboratory

Golden, CO

Abstract—Many favorable wind energy resources in North 

America are located in remote locations without direct access to 

the transmission grid. Building transmission lines to connect 

remotely-located wind power plants to large load centers has 

become a barrier to increasing wind power penetration in 

North America. By connecting utility-sized megawatt-scale 

wind turbines to the distribution system, wind power supplied 

to consumers could be increased greatly. However, the impact 

of including megawatt-scale wind turbines on distribution 

feeders needs to be studied. The work presented here examined

the impact that siting and power output of megawatt-scale wind 

turbines have on distribution feeder voltage. Many possible 

siting locations and wind power output levels for wind turbines 

connected to the distribution system were studied. This is the 

start of work to present a general guide to megawatt-scale wind 

turbine impact on the distribution feeder and finding the 

amount of wind power that can be added without adversely 

impacting the distribution feeder operation, reliability, and 

power quality. Preliminary results indicate that inclusion of 

wind turbines near heavily-loaded feeders at farther distances 

from a substation increases per-unit bus voltages and could 

cause overvoltage conditions.

Keywords-distributed generation; distributed wind; impact 

studies

I. INTRODUCTION

The need for transmission lines to connect remote wind 

power plants to major load centers is a barrier to increasing 

the wind power penetration level in North American 

interconnections. By adding utility-sized megawatt-scale 

wind turbines to existing distribution networks, the amount 

of wind power supplied to consumers can be increased 

without the associated political difficulties and additional 

cost of building transmission lines. The focus of this work is 

to assess the limitations on the amount of wind power that 

can be added to the distribution system without adversely 

impacting distribution system operations. Results are 

presented on one specific power quality issue: the impact of 

megawatt-scale wind turbines on distribution feeder bus 

voltages as a function of wind power production and of the 

electrical distance of wind turbine sites from a distribution 

substation. 

Megawatt-scale wind turbines connected to the 

distribution circuit are generally located away from heavilypopulated areas, therefore the impact megawatt-scale wind 

turbines will have on rural distribution feeders in particular 

was studied. Characteristics of rural distribution feeders 

differ from more-heavily-populated and -loaded urban and 

suburban areas. Rural distribution feeders tend to be radial, 

have longer feeder lengths, and are relatively lightly loaded. 

Also, rural feeders have a higher ratio of the number of 

overhead lines compared to underground distribution cables. 

Detailed models of rural distribution feeders are available 

from GridLab-D in SynerGEE format [1]. In the future, these 

models will be used to study the effects of wind power on the 

rural distribution circuit. The work presented here used a 

distribution circuit made available by the Electric Power 

Research Institute in OpenDSS script. The distribution 

circuit modeled in OpenDSS is radial and contains mostly 

residential load. A simple wind turbine model with power 

factor controls was used. This model is similar to the 

standard Western Electricity Coordinating Council Type 3 

doubly-fed induction generator and Type 4 full-converter 

wind turbine models, both of which were used in the study

because Type 3 and Type 4 wind turbines have the ability to 

maintain the desired power factor at the wind turbine 

terminals. The Institute of Electrical and Electronics 

Engineers Standard 1547 specifications and requirements for 

interconnection of distributed generation were applied [2]. 

Similar impact studies and distribution analyses have been 

performed but instead studied the impact of rooftop 

photovoltaic on feeder voltage profiles [3-5]. However,

distributed wind differs from rooftop photovoltaic in terms of 

scale and distribution of the resource. Traditionally, the 

power available from a distribution-connected wind plant is 

fed in at one bus in the distribution circuit, as opposed to the 

many locations of distributed solar power. Wind and solar 

resource variability and uncertainty are also significantly 

different. The lack of solar generation at night is the most 

basic example of the many differences.

Section II provides a description of the distribution feeder 

and the megawatt-scale wind turbine model. Section III

describes the analysis applied to the feeder model. Results 
2

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from the analysis are presented in Section IV, and the

findings summarized and future areas for research identified

are presented in Section V.

II. DISTRIBUTION CIRCUIT AND WIND TURBINE 

GENERATOR MODELS

Descriptions of the distribution circuit and wind turbine 

generator (WTG) models used in this work are provided in 

this section. Although the results shown are specific to this 

particular distribution feeder, the methodology developed and 

the issues examined are of interest for other distribution 

feeder models in which megawatt-scale wind turbines could 

potentially be connected.

A. Distribution Circuit Model

The distribution circuit model used in the study was made 

available by the Electric Power Research Institute in 

OpenDSS script [6]. This circuit was selected as an example 

of how to analyze some of the impacts megawatt-scale wind 

turbines have on the distribution system. The analysis

methods developed are broadly applicable to other circuits,

which is the intended focus of future work. The distribution 

circuit used in this paper has a rated system voltage of 12.47 

kV, which is connected through a 16.3-MVA rated service 

transformer. The location of the substation in the distribution 

circuit is indicated in Fig. 1. The locations of switched 

capacitor banks with capacitor controls to determine when to 

switch capacitor banks on or off are indicated in Fig. 1. 

Three-phase and single- or two-phase lines in the circuit are 

also labeled in Fig. 1. 

This radial distribution circuit serves mostly residential 

load. The load locations and relative sizes are shown in Fig. 2. 

The radius of each circle representing a single-phase load is 

proportional to the power of the load. All loads are singlephase loads; the phase of each load is labeled in the figure. 

The total three-phase load for the circuit is 7.01 MW.

B. WTG Model

Four typical WTG model types are used for power flow 

representations of wind power plants, as described in [7]. The 

Western Electricity Coordinating Council standard Type 1 

and Type 2 models, also known as fixed-speed and variableslip WTGs, respectively, represent WTGs with capacitor bank 

controls to supply reactive power to the WTG. Western 

Electricity Coordinating Council standard Type 3 and Type 4

WTGs, also known as doubly-fed asynchronous and fullpower-converter generators, respectively, have power 

electronic controls that allow for power factor control or 

voltage control at the terminals. In this paper, a combined 

Type 3/Type 4 WTG model was used because most 

megawatt-scale modern WTGs are either Type 3 or Type 4. 

For the research presented here, the active power factor 

controls for the generator models representing the Type 

3/Type 4 WTGs were set so that the power factor at the WTG 

terminals was held at unity (pf = 1.0). The ranges of the 

power output of the WTG models are described in Section III

and Section IV.

Figure 1. Distribution circuit model.

Figure 2. Distribution circuit single-phase loads.

Substation

3-ph Line 1- or 2-ph Line Capacitors

A phase B phase C phase
3

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III. METHODOLOGY

In most of the previous literature on megawatt-scale 

distributed-connected wind turbines, the site of the WTG was 

known and the impacts on the distribution system indices 

were studied to determine if the location, power output, and 

connections were acceptable [8] [9] [10]. In this work, 

however, to establish general guidelines for integrating 

megawatt-scale turbines in distribution circuits, all possible 

WTG locations, with varying levels of installed wind power 

capacity, were examined to determine the maximum 

acceptable wind power for the system without a significant 

decrease in power quality

A. Software

The analysis was performed in the MATLAB and 

OpenDSS programs. As mentioned in Section II, the 

distribution circuit model was provided in OpenDSS. 

MATLAB is used to drive OpenDSS through the COM 

interface, which allows for easy parameter changes in the 

circuit between runs, and advanced analysis of simulation 

results. Results were taken from steady-state solutions.

B. Analysis

For the research presented in this paper, the changes in 

bus voltages were examined for the steady-state analysis. 

First, bus voltage baselines were established in the 

distribution feeder model by running a simulation without any 

WTGs connected. The simulation was conducted and the perunit voltages at each bus were recorded as baseline voltages.

Next, the change in bus voltages when a WTG was 

interconnected at each possible location was examined. 

Possible WTG locations were all buses connected to threephase lines and locations that had an electrical distance of at 

least 0.1 km from the substation. Two aspects of the change in 

bus voltage were examined when a WTG was connected at 

each of the possible locations. The first was the change in 

voltage at each bus, and the second was the sum of changes in 

bus voltages as a reflection of feeder-wide voltage change.

The WTG locations that caused the maximum amount of 

change and the minimum amount of change were identified 

and are discussed in Section IV. For these cases, the capacitor 

bank controls were turned off to determine how sudden 

changes in WTG power output may affect the system bus 

voltages before the capacitor banks have time to react. 

For the work presented here, only single WTG locations 

were studied, rather than having multiple WTGs located 

throughout the distribution circuit. Multiple, simultaneouslyconnected WTGs and the impact they have on the distribution 

feeder will be considered in future work. The WTG model 

was rated at 1.5 MW and included multiples of 1.5 MW

depending on the case studied. 

IV. ANALYSIS RESULTS

The first step was to find all possible buses within the 

distribution feeder that fulfilled the requirements for WTG 

placement previously mentioned. At this time, only the 

electrical characteristics of the distribution circuit were taken 

into account. Future work will consider the geographical 

location of the distribution feeder and detailed wind resource 

information when the data is available. To illustrate the 

impact different WTG bus locations have on bus voltages, the 

voltages at the buses indicated in Fig. 3 were examined. Phase 

A of the monitored bus voltages for all possible WTG bus 

locations is shown in Fig. 4. In Fig. 4, the x-axis is the WTG 

bus location represented as the distance along the feeder from 

the substation (in kilometers). The solid line in each plot 

represents the per-unit baseline voltage at the monitored bus 

before a WTG was added to the circuit. 

Fig. 3. Location of monitored buses to study the impact that 

the distance of a WTG from the substation has on bus 

voltages.

From the results shown in Fig. 4, we concluded that the 

change in voltage is not solely a function of the distance

between the WTG bus and the substation. For WTG 

distances greater than 1 km, the per-unit bus voltages at Bus 

63662, Bus 28247, and Bus 39575 began to diverge. Similar 

results were seen for Phase B and Phase C. Further analysis 

indicated that other factors may influence changes in feederwide bus voltage.

The next step in the analysis was to find the WTG 

locations that caused the most change in bus voltages. The 

heat map in Fig. 7 shows the change in feeder-wide bus 

voltages caused by the placement of WTGs at different 

buses. The buses in darker green represent WTG locations 

that caused the most change in bus voltages across the entire 

feeder. The buses in a lighter shade of yellow represent WTG 

locations that caused the least change in voltage across the 

entire feeder. 

The WTG bus locations that experienced the most change 

(red) and the least change (green) in feeder-wide bus voltages 

are identified in Fig. 8. These buses were used in the 

following analysis. All buses in green were located near the 

substation, as was expected. The red buses were located 

 63662

 28247

 39575

 56766

Substation

3-ph Line 1- or 2-ph Line Monitored Buses
4

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farther from the substation. However, there were buses along 

the right branch of the feeder, located farther from the 

substation, that did not cause as much change to the bus 

voltages. Therefore, we concluded that distances of WTGs 

alone do not impact feeder-wide bus voltages. The total load 

for each of the braches was different—the load along the 

leftmost branch was higher than that along the rightmost 

branch (in which WTGs caused more change in bus voltages). 

Therefore, we concluded that the loading of the feeder where 

the WTG is located and the distance from the substation 

influences the change in voltages.

To illustrate the larger percentage change in feeder-wide 

bus voltages experienced by the buses identified in red, a 

WTG was placed at Bus 28288 and the change in voltage was 

calculated at each bus, as shown in Fig. 7. The WTG bus in 

blue is indicated in Fig. 7. The wind power output for the case 

presented here was 1,500 kW. The maximum change in 

voltage was 1.7%. Fig. 8 is a heat map of the change in 

voltage for a WTG located at Bus 74439 (shown in blue). 

This bus was along the rightmost branch, where the total load 

was less than the WTG branch location shown Fig. 7. The 

wind power output was also 1,500 kW for this case. Even 

though the WTG is located farther from the substation, the 

change in bus voltage was not as high as compared to the 

previous case. For this case, the maximum percent change in 

bus voltage was 1.1%. 

Figure 4. Phase A bus voltages at monitored buses without 

wind power and with wind power and WTG location as a 

function of distance (*).

Figure 5. WTG locations and the resulting change in feederwide bus voltages.

Figure 6. Phase B per-unit voltage change (red) maximum

and (green) mininum for 1,500-kW WTG power output.

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 1

1.01

1.02

1.03

1.04

Bus 63662 A Phase

Voltage (pu)

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 1

1.01

1.02

1.03

1.04

Bus 28247 A Phase

Voltage (pu)

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 1

1.01

1.02

1.03

1.04

Bus 39575 Phase A

Voltage (pu)

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 1

1.01

1.02

1.03

1.04

Bus 56766 Phase A

Wind Turbine Distance from Substation (km)

Voltage (pu)

More

Change

Less

Change

Substation

WTG Location Max Change WTG Location Min Change
5

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Figure 7. Maximum change in per-unit bus voltage seen at

WTG location for Phase B with WTG power output of 1,500 

kW at Bus 28288.

Figure 8. Increased distance of a WTG from the substation 

on a different branch experienced less per-unit bus voltage 

change for Phase B with WTG power output of 1,500 kW at 

Bus 74439.

To illustrate how placing the WTG near the substation 

has minimal impact on bus voltages, a case in which the 

WTG was placed at one of the buses indicated in green in

Fig. 6 was simulated. The heat map with the WTG located at 

Bus 63657 (indicated in blue) indicating the change in perunit voltage at each bus is shown in Fig. 9. The maximum 

percent change in bus voltage was 0.3% when the WTG was 

located near the substation. Fig. 7, Fig. 8, and Fig. 9 show 

results only for Phase B. Similar results were seen for Phase 

A and Phase C.

Figure 9. The WTG located near the substations experienced

minimum change in per-unit bus voltages for Phase B with 

WTG power output of 1,500 kW at Bus 63657.

Next, the change in bus voltages when the WTG power 

output was changed to 15,000 kW was simulated. As 

expected, larger changes in the per-unit bus voltages were 

seen when the WTG power output was increased to 15,000 

kW. The heat maps for the change in per-unit bus voltages 

are shown for Bus 28288 and Bus 63657 in Fig. 10 and Fig.

11, respectively. The scale of the color map increased in 

these figures with respect to the previous figures, and the 

maximum change in voltage was 5.9% for the case in Fig. 10

and 0.9% for the case in Fig. 11. In both cases when the 

WTG power output was 15,000 kW, some buses began to 

experience a negative change in bus voltage. For these high 

wind power output cases, it was important to check for 

undervoltage conditions at these buses. 

The work presented shows the percentage change in bus 

voltage to provide general guidelines and indicate that it is 

possible that including a WTG to a distribution system can 

cause overvoltage and sometimes undervoltage conditions. 

The overvoltage conditions depend on the distance of the 

WTG from the substation and the load along the feeder 

 Substation

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

2

WTG Location

 Substation

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

2

WTG Location

 Substation

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

2

WTG Location
6

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where the WTG is placed. Increasing the wind power output 

also increases the change in bus voltages. 

Figure 10. The per-unit bus voltage seen at the WTG location 

for Phase B with WTG power output of 15,000 kW at Bus 

28288 saw an increase in change in voltage compared to Fig. 4.

Figure 11. The WTG located near the substation experienced

minimum change in per-unit bus voltages for Phase B with 

WTG power output of 15,000 kW at Bus 63657.

V. CONCLUSION

The impact megawatt-scale wind turbines have on 

distribution feeder bus voltages was studied. WTGs with 

power factor control were used in the study. The distance of 

the WTG from the substation influenced the amount of 

change in feeder-wide bus voltages as well as the amount of 

load on the feeder to which the WTG is connected. The 

percent change in bus voltages was used to represent general 

results. Large changes in bus voltages could result in 

overvoltage and, in the case of high wind power output,

undervoltage conditions for specific feeders. Future work will 

apply the methodology used here to other distribution circuits,

including actual distribution models provided by utilities. The

coordination of wind turbines and voltage control devices will 

also be studied. A variety of scenarios for different voltage 

control devices (switched capacitor banks, load tap changers,

and voltage regulators) and different load and wind power 

profiles will be studied. 

ACKNOWLEDGMENT

This research was supported by the U.S. Department of 

Energy under Contract No. DE-AC36-08-GO28308 with the 

National Renewable Energy Laboratory.

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