Estimation of Fault Resistance from Fault Recording Dataapic/uploads/Forum/P2014_6.pdf · Bulk...

Estimation of Fault Resistance from Fault Recording Data

Daniel Wong & Michael Tong 2014-November-5

Agenda

• Project Background & Introduction

• Fault Resistance & Effect

• Estimation Algorithm

• Estimation Results

• Conclusion

Project Background

• Canada’s only fully independent transmission company

• Own and operate more than half of Alberta’s Transmission Grid

• Serve 85% of Alberta population

• Interconnections to BC, Saskatchewan and Montana (US)

• 12,000 km transmission lines 69kV to 500kV

• 300 substations

• More than 20,000 protection relays

• Own and operate a telecommunication (in-house) system

About AltaLink

Project Background

• Impedance Protection - one of the widely used line protections

• Impedance relay responds to Voltage and Current

• Line impedance contains reactance and resistance

• Ground fault impedance contains line impedance and ground fault resistance

• For correct relay operation, relay setting needs to coverage ground fault resistance

• The question is “how much resistance to cover”

Line Protection Coverage

Project Background

• AltaLink in-house guideline (up to December 2004)

• For transmission lines, impedance protection were applied most of the time

• For zone 1 impedance setting, it needs to cover 5 Ohms

• Based on actual operating experience, line protection performance was good

• No problem was identified with the 5 Ohms coverage

AltaLink relay setting guidelines (Pre December 2004)

Project Background

AESO Protection Standard

Alberta Interconnected Electric System Protection Standards: • Effective: December 1, 2004

• Valid for 5 years

• Expired: December 1, 2009

• Document Size: 65 pages

Project Background

AESO Protection Standard

Section 3.6 on Fault Types

Protection applied to the Alberta Interconnected Electric System must be capable of detecting:

• Single line to ground fault with 20 Ohms (tower footing plus arc) impedance

• Phase to phase to ground fault with 20 Ohms (tower footing plus arc) impedance

Project Background

ISO (AESO) Rules

ISO Rules – Section 502.3 Interconnected Electric System Protection Requirements:

• Draft rules posted on 2012 August 15 for consultation

• Final rules posted on 2012 December 31

• Effective: 2012 December 31

• Expiry: No date declared yet

• Document size: 12 pages

Project Background

ISO (AESO) Rules - Section 502.3 Interconnected Electric System Protection Requirements

Ground Fault Resistance Coverage:

• Single line-to-ground fault with impedance up to 5 Ohms

• Phase-to-phase-to-ground fault with impedance up to 5 Ohms

Project Background

• Based on protection guidelines, standards and rules, requirements on ground fault resistance coverage changes from 5 to 20 and back to 5 Ohms again

• No improvement or deterioration in protection performance was observed with these changes

• No study has been carried out to determine the magnitude of ground fault resistance in the AltaLink system

• In mid 2012, a study project was initiated with University of Alberta

Project Introduction

• Alberta Power Industry Consortium (APIC) Project – (Report No. 2013A-1) Develop an algorithm to estimate the fault resistances from fault

data recorded and verify the algorithm through simulation and experimental studies

Apply the algorithm to a large number of fault cases with COMTRADE fault files in single phase to ground faults on 2-terminal lines

Identify the typical value of the ground fault resistance in AltaLink system in order to assess the Protection Setting Guidelines

• Department of E&C Engineering, University of Alberta

• P&C Engineering and System Operations, AltaLink

Single Phase to Ground Fault:

• Electric arc: Traditionally considered as a resistance Dependent on the arc current/length Value is variable during the fault

• Tower grounding: Mainly resistive Not dependent on the fault current Value is stable during the fault

• Objects in the fault path: Usually considered mainly resistive Might be zero or very high Value is unpredictable

Fault Resistance

http://www.google.ca/url?sa=i&rct=j&q=&esrc=s&source=images&cd=&cad=rja&uact=8&docid=aidFQYf155tOCM&tbnid=zLELnWZdEHmwCM:&ved=0CAUQjRw&url=http://www.ejrc.com.au/links.html&ei=6HDyU9vSFcmHogSJj4HwCw&bvm=bv.73231344,d.cGU&psig=AFQjCNEOO6Cx_pvsYQnKpCHiTmv2WFOEkw&ust=1408483858358441

ZL1

Rf

X

R

Z (apparent impedance)

Fault Resistance Effect

Homogeneous System

ZL1 ZL1

Overreach Underreach

X X

R R

Z(apparent impedance)

Z(apparent impedance)

Fault Resistance Effect

Non-Homogeneous System

Estimation Algorithm

• Two stages:

Stage 1: Fault location estimation

Stage 2: Fault resistance estimation

Relay Relay

SV

SI

LmZ 1 Lm Z

FR

RI

RV

F

Z1S mZ1L (1-m)Z1L Z1R



S S S-End R-End

V1S V1R

3RF

I1S

I2S

I0S

I1R

I2R

I0R

-

V2F

+

IF


Stage 1 – Fault Location Estimation

Two-Ended Negative-Sequence Impedance Method

• Negate the effect of pre-fault load and fault resistance, zero-sequence mutual impedance.

• No source are involved, calculation is based on Magnitude. Data alignment is not required.


I2S I2R

-

V2F

+

2 2 2 2F S S LV I Z mZ 2 2 2 21F R R LV I Z m Z


Stage 2 – Fault Resistance Estimation

Relay Relay

SV

SI

LmZ 1 Lm Z

FR

RI

RV

F

1 0 3AS L AS r F FV Z I k Im RI


For an A-G fault, Voltage and current at end S:

Estimation Results

• 54 fault cases in AltaLink 240KV and 138KV transmission system. 92% of the faults on the studied lines have a fault resistance of less than 5Ω

• Average/Median value of the fault resistance in 240KV system < Average/Median value of the fault resistance in 138KV system

Estimation Results (All Fault Cases) M

ay-0

7Ju

l-0

9Ju

l-0

9Se

p-0

9M

ar-1

0A

pr-

10

May

-10

Jun

-10

Au

g-1

0A

ug-

10

Jan

-11

Ap

r-1

1M

ay-1

1M

ay-1

1M

ay-1

1Ju

l-1

1Ju

l-1

1Ju

l-1

1A

ug-

11

Au

g-1

1A

ug-

11

Sep

-11

Sep

-11

Ap

r-1

2A

pr-

12

Sep

-12

May

-13

0

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

240KV Line Fault Resistance Level (All Fault Cases)

Estimated Value (Ω) Median Value ( 0.76)

Average Value (1.31)

Feb

-08

Mar

-08

Jul-

08

Au

g-0

8M

ar-0

9Se

p-0

9Ju

l-1

0Se

p-1

0Fe

b-1

1A

pr-

11

May

-11

May

-11

May

-11

Jul-

11

Jul-

11

Ap

r-1

2M

ay-1

2A

ug-

12

Au

g-1

2A

ug-

12

Au

g-1

2O

ct-1

2N

ov-

12

Feb

-13

Mar

-13

Jun

-13

Au

g-1

3

0

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18


Estimated Value (Ω) Median Value (2.33)


Estimation Results (Excluding Outlier) M

ay-0

7Ju

l-0

9Se

p-0

9M

ar-1

0A

pr-

10

May

-10

Jun

-10

Au

g-1

0A

ug-

10

Jan

-11

Ap

r-1

1M

ay-1

1M

ay-1

1M

ay-1

1Ju

l-1

1Ju

l-1

1Ju

l-1

1A

ug-

11

Au

g-1

1A

ug-

11

Sep

-11

Sep

-11

Ap

r-1

2A

pr-

12

Sep

-12

May

-13

0

1

2

3

4

5

6

7

8

240KV Line Fault Resistance Level (Excluding Outlier)



Feb

-08

Mar

-08

Jul-

08

Au

g-0

8M

ar-0

9Se

p-0

9Ju

l-1

0Se

p-1

0Fe

b-1

1A

pr-

11

May

-11

May

-11

May

-11

Jul-

11

Jul-

11

Ap

r-1

2M

ay-1

2A

ug-

12

Au

g-1

2A

ug-

12

Au

g-1

2O

ct-1

2N

ov-

12

Feb

-13

Jun

-13

Au

g-1

3

0

1

2

3

4

5

6

7

8

138KV Line Fault Resistance Level (Excluding Outlier)



Estimation Results (Pie Chart)

> 5 Ohm 8%

2 ~ 5 Ohm 24%

< 2 Ohm 68%

Fault Resistance Level (All Fault Cases)

> 5 Ohm 4%

2 ~ 5 Ohm 25%

< 2 Ohm 71%

Fault Resistance Level (Excluding Outliers)

Estimation Results (Ω vs. Cause) u

nkn

ow

nTr

acto

rU

nkn

ow

nu

nkn

ow

nlig

htn

ing

Co

nta

min

atio

nB

ird

Nes

tB

ird

Nes

tB

ird

Nes

tU

nkn

ow

nU

nkn

ow

nU

nkn

ow

nu

nkn

ow

nU

nkn

ow

nLi

ghtn

ing

Un

kno

wn

un

kno

wn

Un

kno

wn

Un

kno

wn

Un

kno

wn

Un

kno

wn

Ligh

tnin

gU

nkn

ow

nC

VT

failu

reLi

ghtn

ing

Un

kno

wn

Co

nd

uct

or

0

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18




Cro

ss-a

rmC

ross

-arm

Ligh

tnin

gC

on

tam

inat

ion

Co

nd

uct

or

Ligh

tnin

gC

on

du

cto

rC

on

tam

inat

ion

Gra

vel T

ruck

Ligh

tnin

gU

nkn

ow

nU

nkn

ow

nLi

ghtn

ing

Du

mp

Tru

ckC

ross

-arm

We

ath

er

un

kno

wn

Ligh

tnin

gC

on

tam

inat

ion

un

kno

wn

un

kno

wn

un

kno

wn

Icin

gu

nkn

ow

nU

nkn

ow

nU

nkn

ow

nSh

ield

Wir

e

0

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18




Existing Protection Setting Guidelines for Line Protection …….. Impedance Zone 1: Generally zone 1 is the zone set to underreach the end of the protected line. Zone 1 reach shall be set to 85% of the actual impedance of the protected line with no intentional tripping delay. Mutual coupling with parallel lines causes overreaching for some faults; the zone 1 reach may be reduced to no less than 60% of the line impedance to allow the two opposite zone 1 reaches to overlap with 15% margin, provided a ground fault with 5 ohms resistance still produces high-speed operation. ……..

Protection Setting Guidelines

Section 502.3 Interconnected Electric System Protection Requirements …….. Bulk Transmission Line Ground Fault Resistance Coverage 15 If a bulk transmission line experiences a fault of the following type, then each of the two (2) protection systems for the bulk transmission line must initiate isolation of the fault: (a) single line-to-ground, with a minimum impedance of five (5) ohms; or (b) phase-to-phase-to-ground with a minimum impedance of five (5) ohms.. ……..

ISO Rules – Part 500 Facilities

Conclusion (Project Specifics)

• An off-line method is proposed for estimating the fault resistance in single phase-to-ground faults. The method eliminates the need to synchronize the fault data.

• The developed program makes it possible to estimate the fault resistances in a large number of fault cases, and to obtain a statistical picture of typical fault resistance values.

• More than 50 fault events are studied and the estimation result aligns with AltaLink Protection Setting Practice.

Conclusion (Application Specific)

• With the outliers excluded, 96% of the recorded ground fault resistances were less than 5 Ohms

• The “5 Ohms” requirement for ground fault resistance coverage, as stated in the ISO (AESO) Rules 502.3 is appropriate

• AltaLink provides “5 Ohms” ground fault resistance coverage in full compliance with Rules 502.3

Questions

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