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Electric Power Consulting Pty Ltd 1 University of Wollongong Country Energy Predicting the Voltage Sag Performance of Electricity Distribution Networks by Dr Robert Barr, Electric Power Consulting Pty Ltd Prof. Vic Gosbell, University of Wollongong Mr Chris Halliday, Country Energy

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Electric Power Consulting Pty Ltd

1

University of WollongongCountry Energy

Predicting the Voltage Sag Performanceof Electricity Distribution Networks

by

Dr Robert Barr, Electric Power Consulting Pty Ltd

Prof. Vic Gosbell, University of Wollongong

Mr Chris Halliday, Country Energy

Electric Power Consulting Pty Ltd

2

University of WollongongCountry Energy

Figure 1 - Typical Rectangular Voltage Sag

-1.2-1

-0.8-0.6-0.4-0.2

00.20.40.60.8

11.2

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

Time seconds

PU S

uppl

y V

olta

ge .

Sag duration 0.3 seconds

Sag voltage 0.3 PU

Electric Power Consulting Pty Ltd

3

University of WollongongCountry Energy

Voltage Sag Patterns - Multiple Sites - Typical Data - Log Time Scale

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0.01 0.1 1 10Time seconds

PU

Sag

Vol

tage

SMPS

Protection Curve

ITIC Curve

Typical Sag Data

log scale

Electric Power Consulting Pty Ltd

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University of WollongongCountry Energy

Voltage Sag Patterns - Multiple Sites - Typical Data Linear Time Scale

0

0.1

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0.5

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0.8

0.9

1

0 0.2 0.4 0.6 0.8 1 1.2 1.4Time seconds

PU S

ag V

olta

ge

SMPS

Protection Curve

ITIC Curve

Typical Sag Data

Electric Power Consulting Pty Ltd

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University of WollongongCountry Energy

Typical Distribution Network

66kV

11kV

66kV

230/400V

“A”

Range of possible

11kV faultlocations

High Speed Translay Protection (~0.1secs)

High Speed Bus Zone Protection (~0.1secs)

High Speed Differential Protection (~0.1secs)

“B”“C”“D”

“E”“F”

Low Speed Over Current/Earth FaultFeeder Protection - must grade above distribution Tx fuse protection. (~0.3 to 1.0sec)

Customer see sag voltage from faults on feeders“A” ,”B” and “C” feeders plus upstream faults

O/C E/F protection at “E” &”F” must grade above “A”, “B”, “C” &”D”

Electric Power Consulting Pty Ltd

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University of WollongongCountry Energy

Standard Inverse Protection Voltage Sag Model

11kV busbar

“A”

NetworkSourceImpedance(Zsrc Per Unit)

“B”“C”“D”“Standard Inverse”overcurrent protection relay

Customers see a sag voltage from the short circuit fault on feeder “A”

Variable fault impedancegoverned by fault location

variable fault location

)1...(seconds1 - )I/I

0.140.02uppick

timeoperating O/C(

= τ

...(3)seconds1 - up)I/Ipick

0.14 (Tsag)Duration Sag

...(2)volts. (Vsag) SagVoltage

0.02

src

(=

−=τ

ZIVsrc

Source Voltage Vs

I

Notes> X/R ratio constant throughout 11kV feeder> Network at zero load before voltage sag generating fault.> Circuit breaker opening time is 0.1 seconds.> Overcurrent protection relay has a Standard Inverse characteristic.

Electric Power Consulting Pty Ltd

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University of WollongongCountry Energy

Fault Model Single Radial 11kV Line

230/400V

11kV faultlocations

11kV busbar

“A”“B”“C”“D”

Source Voltage Vs

Observation point

Electric Power Consulting Pty Ltd

8

University of WollongongCountry Energy

LV Phase to Neutral Voltages

Electric Power Consulting Pty Ltd

9

University of WollongongCountry Energy

Voltage Sag ModelLV Phase to Neutral

0

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0 0.5 1 1.5Time Seconds

Sag

Volta

ge P

U

Va Vb & Vc - MV 3Ph fault

ITIC Curve

Protection Curve

© Electric Power Consulting Pty Ltd June 2005

7km line - 0.1km steps

Electric Power Consulting Pty Ltd

10

University of WollongongCountry Energy

Voltage Sag ModelLV Phase to Neutral

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0 0.5 1 1.5Time Seconds

Sag

Volta

ge P

U

Van LV - MV Ph toPh fault

Vbn LV - MV Ph toPh fault

Vcn LV - MV Ph toPh fault

Va Vb & Vc - MV 3Ph fault

ITIC Curve

Protection Curve

© Electric Power Consulting Pty Ltd June 2005

7km line - 0.1km steps

Electric Power Consulting Pty Ltd

11

University of WollongongCountry Energy

Voltage Sag ModelLV Phase to Neutral

0

0.1

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1

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0 0.5 1 1.5Time Seconds

Sag

Volta

ge P

U

Van LV - MV Ph toPh fault

Vbn LV - MV Ph toPh fault

Vcn LV - MV Ph toPh fault

Van LV - MV Ph toE fault

Vbn LV - MV Ph toE fault

Vcn LV - Ph to Efault

Va Vb & Vc - MV 3Ph fault

ITIC Curve

Protection Curve

© Electric Power Consulting Pty Ltd June 2005

7km line - 0.1km steps

Electric Power Consulting Pty Ltd

12

University of WollongongCountry Energy

LV Phase to Phase Voltages

Electric Power Consulting Pty Ltd

13

University of WollongongCountry Energy

Voltage Sag ModelLV Phase to Phase

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1

0 0.5 1 1.5Time Seconds

Sag

Volta

ge P

U

Vab Vbc & Vca -MV 3 Ph fault

ITIC Curve

Protection Curve

© Electric Power Consulting Pty Ltd June 2005

7km line - 0.1km steps

Electric Power Consulting Pty Ltd

14

University of WollongongCountry Energy

Voltage Sag ModelLV Phase to Phase

0

0.1

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0 0.5 1 1.5Time Seconds

Sag

Volta

ge P

U

Vab LV - MV Ph toPh fault

Vbc LV - MV Ph toPh fault

Vca LV - MV Ph toPh fault

Vab Vbc & Vca -MV 3 Ph fault

ITIC Curve

Protection Curve

© Electric Power Consulting Pty Ltd June 2005

7km line - 0.1km steps

Electric Power Consulting Pty Ltd

15

University of WollongongCountry Energy

Voltage Sag ModelLV Phase to Phase

0

0.1

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0.9

1

1.1

0 0.5 1 1.5Time Seconds

Sag

Volta

ge P

U

Vab LV - MV Ph toPh fault

Vbc LV - MV Ph toPh fault

Vca LV - MV Ph toPh fault

Vab LV - MV Ph toE fault

Vbc LV - MV Ph toE fault

Vca LV - Ph to Efault

Vab Vbc & Vca -MV 3 Ph fault

ITIC Curve

Protection Curve

© Electric Power Consulting Pty Ltd June 2005

7km line - 0.1km steps

Electric Power Consulting Pty Ltd

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University of WollongongCountry Energy

Comparison of Phase to Neutral & Phase to Phase LV Connections

Electric Power Consulting Pty Ltd

17

University of WollongongCountry Energy

Voltage Sag Model - Comparison of 11kV Ph to Ph Faults

0

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0 0.5 1 1.5Time Seconds

Sag

Volta

ge P

U

Van LV - MV Ph toPh fault

Vbn LV - MV Ph toPh fault

Vcn LV - MV Ph toPh fault

ITIC Curve

Protection Curve

Vab LV - MV Ph toPh fault

Vbc LV - MV Ph toPh fault

Vca LV - MV Ph toPh fault

© Electric Power Consulting Pty Ltd June 2005

7km line - 0.1km steps

Electric Power Consulting Pty Ltd

18

University of WollongongCountry Energy

Voltage Sag Model - Comparison of 11kV Ph to E Faults

0

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0 0.5 1 1.5Time Seconds

Sag

Volta

ge P

U

Van LV - MV Ph toE fault

Vbn LV - MV Ph toE fault

Vcn LV - Ph to Efault

ITIC Curve

Protection Curve

Vab LV - MV Ph toE fault

Vbc LV - MV Ph toE fault

Vca LV - Ph to Efault

© Electric Power Consulting Pty Ltd June 2005

7km line - 0.1km steps

Electric Power Consulting Pty Ltd

19

University of WollongongCountry Energy

Zone Substation – 4 11kV Feeders

Electric Power Consulting Pty Ltd

20

University of WollongongCountry Energy

11kV Network Exposure ~ k L2

1 3 6 8 101 4 10 18 28

L

Cumulative 11kV Network Exposure (km)

Electric Power Consulting Pty Ltd

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University of WollongongCountry Energy

Key 11kV Feeder Parameters

28181041Cumulative km 11kV Line Exposure

36%29%21%11%4%% 11kV Line exposure

10 km8 km6 km3 km1 kmkm 11kV Line Exposure

4 – 5km

3 – 4km

2 – 3km

1 - 2 km

0 – 1 km

L - km Distance Range from Zone Substation

Electric Power Consulting Pty Ltd

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University of WollongongCountry Energy

Model Parameters

years of history to model2

faults per year80

faults/100km/year8

RMS Average feeder length10

11kV feeders10

km of 11kV1000

Electric Power Consulting Pty Ltd

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University of WollongongCountry Energy

Model Parameters

11kV Ph to E Faults C16%

11kV Ph to E Faults B16%

11kV Ph to E Faults A16%

11kV Ph to Ph Faults C - A14%

11kV Ph to Ph Faults B - C14%

11kV Ph to Ph Faults A - B14%

11kV 3 phase Faults13%

Total 100%

Electric Power Consulting Pty Ltd

24

University of WollongongCountry Energy

Probabilistic Voltage Sag ModelLV Phase to Neutral

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Sag

Volta

ge P

U

V LV - MV Ph A toPh B faultV LV - MV Ph B toPh C faultV LV - MV Ph C toPh A faultV LV - MV Ph A toE faultV LV - MV Ph B toE faultV LV - Ph C to EfaultV LV - MV 3 Ph fault

ITIC Curve

Protection Curve

© Electric Power Consulting Pty Ltd June 2005

Electric Power Consulting Pty Ltd

25

University of WollongongCountry Energy

Probabilistic Voltage Sag ModelLV Phase to Phase

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1

0 0.5 1 1.5

Time Seconds

Sag

Volta

ge P

U

Vab LV - MV Ph toPh faultVbc LV - MV Ph toPh faultVca LV - MV Ph toPh faultVab LV - MV Ph toE faultVbc LV - MV Ph toE faultVca LV - Ph to EfaultVab Vbc & Vca -MV 3 Ph faultITIC Curve

Protection Curve

Electric Power Consulting Pty Ltd

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University of WollongongCountry Energy

Applications for Industrial Customers

• In general – use 400V Phase to Phase connections for control equipment

• Choose common phasing for control equipment –e.g. 400V Red to Blue phases across the entire plant

• Assess the benefits of using 3 phase 400V supplies for low power control equipment

• Understand the likely frequency and severity of voltage sags

Electric Power Consulting Pty Ltd

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University of WollongongCountry Energy

Applications for Distributors• Understand and quantify the benefits of

minimising Network Exposure• Understand the benefits of star point

resistor/inductor earthing• Understand the critical role of Protection Settings

and Protection Arrangements on voltage sag performance

• Inform customers of “expected” voltage sag performance levels at various parts of the network

Electric Power Consulting Pty Ltd

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University of WollongongCountry Energy

Applications for NewStandards

• Forcast expected sag activity for specific sites without long duration surveys

• Allows generation of standardised voltage sag environments for equipment immunity

• Develop immunity guidelines as alternative to generic CBEMA curve

Electric Power Consulting Pty Ltd

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University of WollongongCountry Energy

ConclusionsThe Voltage Sag Model• Gives distributors a tool to predict the comparative

voltage sag performance at key parts of the network

• Helps explain plant & network options available to improve voltage sag performance for customers

• Has an application in defining a standardised voltage sag environment for use in assessing the immunity of electrical equipment

Electric Power Consulting Pty Ltd

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University of WollongongCountry Energy

Questions?Voltage Sag ModelLV Phase to Neutral

0

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1.1

0 0.5 1 1.5Time Seconds

Sag

Volta

ge P

U

Van LV - MV Ph toPh fault

Vbn LV - MV Ph toPh fault

Vcn LV - MV Ph toPh fault

Van LV - MV Ph toE fault

Vbn LV - MV Ph toE fault

Vcn LV - Ph to Efault

Va Vb & Vc - MV 3Ph fault

ITIC Curve

Protection Curve

© Electric Power Consulting Pty Ltd June 2005

7km line - 0.1km steps