1431928792session ii ct & vt

7/26/2019 1431928792session II Ct & Vt

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CT & VT PARAMETERS

ByVivek Pushpakar

Dy MANAGER(EMD)

NTPC BARH

7/26/2019 1431928792session II Ct & Vt


BASICS OF ONE ANDHALF

CIRCUIT BREAKERSCHEME

7/26/2019 1431928792session II Ct & Vt


ONE & HALF BREAKER DESCRIPTIONBUS-1

BUS-2

BUS-1 BUS-2

1. IN THIS TWO BUSES ARE PRIOVIDED.

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BUS-2

BUS-1 BUS-2

2. THESE TWO BUSES ARE INTER-CONNECTED BY THREE CIRCUIT BREAKERS.

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BUS-2

BUS-1 BUS-2

1-52 CB

2-52 CB

3-52 CB

1-52 CB

2-52 CB

3-52 CB

3. THEY ARE DESIGNATED AS 1-52 CB, 2-52 CB, 3-52 CB.

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BUS-2

BUS-1 BUS-2

1-52 CB

2-52 CB

3-52 CB

1-52 CB

2-52 CB

3-52 CB

LINE-1

LINE-2

LINE-1 LINE-2

4. LINE - 1 IS CONNECTED IN BETWEEN 1-52 CB & 2-52 CB.

5. LINE - 2 IS CONNECTED IN BETWEEN 3-52 CB & 2-52 CB.

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BUS-2

BUS-1 BUS-2

1-52 CB

2-52 CB

3-52 CB

1-52 CB

2-52 CB

3-52 CB

LINE-1

LINE-2

LINE-1 LINE-2

6. LINE-1 HAVING TWO FEEDING PATHS i.e

A. VIA BUS-1 & 1-52 CB

B. VIA BUS-2, 3-52 CB & 2-52 CB

7. LINE-2 HAVING TWO FEEDING PATHS i.eA. VIA BUS-2 & 3-52 CB

B. VIA BUS-1, 1-52 CB & 2-52 CB

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BUS-2

BUS-1 BUS-2

1-52 CB

2-52 CB

3-52 CB

1-52 CB

2-52 CB

3-52 CB

LINE-1

LINE-2

LINE-1 LINE-2

8. FOR INTURUPTING LINE-1 THE 1-52CB AND 2-52CB IS TO BE TRIPPED.

9. FOR INTURUPTING LINE-2 THE 3-52CB AND 2-52CB IS TO BE TRIPPED.

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BUS-2

BUS-1 BUS-2

1-52 CB

2-52 CB

3-52 CB

1-52 CB

2-52 CB

3-52 CB

LINE-1

LINE-2

LINE-1 LINE-2

10. FOR ANY PROBLEM IN LINE-1 OR LINE-2 ALONG WITH MAIN BREAKER

THE MIDDLE BREAKER OR SAY TIE BREAKER (2-52 CB) MUST TRIP.

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BUS-2

BUS-1 BUS-2

1-52 CB

2-52 CB

3-52 CB

1-52 CB

2-52 CB

3-52 CB

LINE-1

LINE-2

LINE-1 LINE-2

13. SO THESE TWO FEEDERS CONTROLLED BY THREE CIRCUIT BREAKERS

IT IS CALLED ONE & HALF BREAKER SYSTEM.

11. NORMALLY IN ALL TYPES OF BUSBAR CONFIGUARATIONS ONE BREAKER

IS SUFFICIENT FOR ONE FEEDER.12. HERE TWO FEEDERS ARE CONTROLED BY THREE BREAKERS.

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BUS-2

BUS-1 BUS-2

1-52 CB

2-52 CB

3-52 CB

1-52 CB

2-52 CB

3-52 CB

LINE-1

LINE-2

LINE-1 LINE-2

14. THE BAY BETWEEN BUS-1 & LINE-1 IS CALLED MAIN BAY FOR FEEDER-1.

M A I N B A Y ( 1 S T B

A Y ) F O

R F E E D E R - 1


A Y ) F O R F E E D E R - 1

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BUS-2

BUS-1 BUS-2

1-52 CB

2-52 CB

3-52 CB

1-52 CB

2-52 CB

3-52 CB

LINE-1

LINE-2

LINE-1 LINE-2


A Y ) F O

R F E E D E R - 1



15. THE BAY BETWEEN LINE-1 & LINE-2 IS CALLED TIE BAY FOR FEEDER-1 & 2.

T I E B A Y ( 2 N D

B A Y ) F O R F E E D E R - 1 & 2

TIE BAY (2 ND BAY ) FOR FEEDER-1 & 2.

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BUS-2

BUS-1 BUS-2

1-52 CB

2-52 CB

3-52 CB

1-52 CB

2-52 CB

3-52 CB

LINE-1

LINE-2

LINE-1 LINE-2


A Y ) F O

R F E E D E R - 1



T I E B A Y ( 2 N D

B A Y ) F O R F E E D E R - 1 & 2


M A

I N B A Y ( 3 R D

B A Y ) F O R F E E D E R - 2

16. THE BAY BETWEEN BUS-2 & LINE-2 IS CALLED MAIN BAY FOR FEEDER-2.

M A I N B A Y ( 3 R D B A Y ) F O R F E E D E R - 2

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BUS-2

BUS-1 BUS-2

1-52 CB

2-52 CB

3-52 CB

1-52 CB

2-52 CB

3-52 CB

LINE-1

LINE-2

LINE-1 LINE-2


A Y ) F O

R F E E D E R - 1



T I E B A Y ( 2 N D

B A Y ) F O R F E E D E

R - 1 & 2


M A

I N B A Y ( 3 R D



17. IN THIS SYSTEM FULL DIA MEANS 2 FEEDERS CONTROLLED BY 3 CBs.18. HALF DIA MEANS 1 FEEDER CONTROLLED BY 2 CBs.

(Nothing but Double CB System)

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BUS-2

BUS-1 BUS-2

1-52 CB

2-52 CB

3-52 CB

1-52 CB

2-52 CB

3-52 CB

LINE-1

LINE-2

LINE-1 LINE-2


A Y ) F O

R F E E D E R - 1



T I E B A Y ( 2 N D

B A Y ) F O R F E E D E

R - 1 & 2


M A

I N B A Y ( 3 R D



GOPALA KRISHNA PALEPU

ADE/MRT/ T&C/400KV SS/

O/O CE/400KV / L&SS/ VS

APTRANSCO, HYDERABAD

[email protected]

Mobile: 9440336984

SUBSTATION DESIGN/LAYOUT

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SUBSTATION DESIGN/LAYOUT(I-CONFIGUARATION)

FEEDER2 FEEDER4 FEEDER6 FEEDER8 FEEDER10 FEEDER12


BUS-2

BUS-1

B A Y 1

B A Y 2

B A Y 3

B A Y 4

B A Y 5

B A Y 6

B A Y 7

B A Y 8

B A Y 9

B A Y 1 0

B A Y 1 1

B A Y 1 2

B A Y 1 3

B A Y 1 4

B A Y 1 5

B A Y 1 6

B A Y 1 7

B A Y 1 8

DIA1 DIA2 DIA3 DIA4 DIA5 DIA6


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SUBSTATION DESIGN/LAYOUT(D-CONFIGUARATION)

BUS-2

BUS-1



B A Y 1

BAY2

B A Y 3

B

A Y 4

BAY5

B A Y 6

B A Y 7

BAY8

B A Y 9

B A Y 1 0

BAY11

B A Y 1 2

B A Y 1 3

BAY14

B A Y 1 5

B A Y 1 6

BAY17

B

A Y 1 8

DIA1

DIA2

DIA3

DIA4

DIA5

DIA6


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SUBSTATION DESIGN/LAYOUT(DOUBLE BUS & DOUBLE BREAKER SYSTEM)

FEEDER1

B A Y 1

B A Y 2

B

A Y 3

B

A Y 4

FEEDER2

FEEDER3

B A Y 5

B A Y 6

B

A Y 7

B

A Y 8

FEEDER4

FEEDER1

BUS-2

BUS-1

B A Y 1

B A Y 2

BUS-2

BUS-1

FEEDER2

B A Y 3

B A Y 4

FEEDER3

B A Y 5

B A Y 6

B A Y 7

B A Y 8

FEEDER4

FOR ECONOMICAL& RELIABULITY PURPOSE THIS SYSTEM ADOPTED IN 800KV SYSTEM

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MESH / RINGLAYOUT

FEEDER 1 FEEDER 2

FEEDER 3

FEEDER 4FEEDER 5FEEDER 6

FEEDER 7

FEEDER 8

1-52 CB 2-52 CB

3-52 CB

4-52 CB

5-52 CB6-52 CB

8-52 CB

7-52 CB


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SUBSTATION DESIGN/LAYOUT(DOUBLE MAIN BUS & TRANSFER BUS SYSTEM)

FEEDER1

BUS-2

BUS-1

FOR ECONOMICAL& RELIABULITY PURPOSE THIS SYSTEM ADOPTED IN 400 & 220 KV SYSTEM

FEEDER2

T R A N S F E R B U S

C O U P L E R

T/F-1 T/F-2

B U S C

O U P L E R

TRANSFER BUS

FEEDER3 FEEDER4

BAY1 BAY2

BAY3 BAY4 BAY5

BAY6 BAY7 BAY8


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SUBSTATION DESIGN/LAYOUT(DOUBLE MAIN BUS & CB BYPASS ISO SYSTEM)

FEEDER1

BUS-2

BUS-1

FOR ECONOMICAL& RELIABULITY PURPOSE THIS SYSTEM ADOPTED IN 220KV SYSTEM

T/F-1

B U S C O U P L E R

FEEDER2

T/F-2

FEEDER3 FEEDER4

BAY1 BAY2

BAY3

BAY4

BAY5

BAY6 BAY7

WHEN ANY CB PROBLEM OR FORPREVENTIVE MAINTANENCE THEN ALL

OTHER FEEDERS SHIFTED TO ANOTHER

BUS OF FAULTED CB BUS AND CLOSE

THE BYPASS ISOLATOR, THEN

PROTECTION IS SHIFTED TO BUS

COUPLER AND OPEN THE FAULTY CB.


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SUBSTATION DESIGN/LAYOUT(SINGLE BUS & TRANSFER BUS SYSTEM)

FEEDER1

BUS-1

TRANSFER BUS

FOR ECONOMICAL& RELIABULITY PURPOSE THIS SYSTEM ADOPTED IN 220 & 132 KV SYSTEM

FEEDER2

T R A

N S F E R B U S C O U P L E R

T/F-1 T/F-2

FEEDER3 FEEDER4

BAY1 BAY2 BAY3 BAY4 BAY5 BAY6 BAY7

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CT METHODSIN

ONE AND HALFCIRCUIT BREAKER

SCHEME

DIFFERENT CT METHODS OF ONE & HALF BREAKER SYSTEM

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DIFFERENT CT METHODS OF ONE & HALF BREAKER SYSTEM

3 CT METHOD

4 CT METHOD

6 CT METHOD

6 CT METHOD

LINE

LINE

LINE

LINE

CB CB CB

CB CB CB

CB CB CB

CB CB CB

AT/F

AT/F

AT/F

AT/F

5 CT METHODLINE

CB CB CB

AT/F

6 CT METHOD

LINECB CB CB

AT/F

ONE & HALF BREAKER SYSTEM

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LINE 1

1-89

1-89A

1-52CB

3-89

3-89A

3-52CB

2-52CB2-89A 2-89B

1-89L 3-89T

BUS-1 BUS-2

T/F-1

1-CT 3

P1

P2

3-CT

P1

3P2

2-CT

P1 3

P2 3

(3CT METHOD)


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LINE 1

1-89

1-89A

1-52CB

3-89

3-89A

3-52CB

2-52CB

2-89A 2-89B

1-89L 3-89T

BUS-1 BUS-2

T/F-1

1-CT 3

P1

P2

3-CT

P1

3P2

2-ACT

3

P1P2

2-BCT

3

P1 P2

(4CT METHOD)


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LINE 1

1-89A

1-52CB

1-CT

3-89

3-89A

3-52CB

3-CT

2-52CB

1L-CT

2-CT

2-89A 2-89B

1-89L 3-89T

BUS-1 BUS-2

T/F-1

3T-CT

1-89

3

P2

P1

3P2

P1

3

P1 P2

3

P2

P1

3P2

P1

(5CT METHOD)


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LINE 1

1-89A

1-52CB

1B-CT

3-89

3-89A

3-52CB

3B-CT

2-52CB

2B-CT

2-89A 2-89B

1-89L 3-89T

BUS-1 BUS-2

T/F-1

1-89

3

P2

P1

3 P2

P1

3

P1 P2

3

P2 P1

3

P2

P1

3P2

P1

1A-CT

2A-CT

3A-CT

(6CT METHOD)


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LINE 1

1-89A

1-52CB

1-CT

3-89

3-89A

3-52CB

3-CT

2-52CB

2B-CT

2-89A 2-89B

1-89L 3-89T

BUS-1 BUS-2

T/F-1

1-89

3

P2

P1

3 P2

P1

3

P1 P2

3

P2 P1

3P2

P13P2

P1

1L-CT

2A-CT

3T-CT

(6CT METHOD)


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LINE 1

1-89A

1-52CB

1-CT

3-89

3-89A

3-52CB

3-CT

2-52CB

2B-CT

2-89A 2-89B

1-89L 3-89T

BUS-1 BUS-2

T/F-1

1-89

3P2

P1

3P2

P1

3

P1 P2

3P2

P1

3

P2 P1

3P2

P1

1L-CT

2A-CT

3T-CT

(6CT METHOD)

TYPICAL ONE & HALF BREAKER

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SYSTEM ADOPTED IN GISDS : DISCONNECTOR SWITCH, GS: GROUNDING SWITCH, CT: CURRENT TRANSFORMER, VD: VOLTAGE DIVIDER


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TYPICAL ONE & HALF BREAKERSYSTEM ADOPTED IN GIS

CT CT CT CT CT CT

1-1/2 CB SYSTEM

(SIEMENS VATECH)

VDVD

DSDSDSDSDSDS

G S

G S

G S

G S

G S

G S

G S

G S

VDVD

CB CB CB

DS : DISCONNECTOR SWITCH, GS: GROUNDING SWITCH, CT: CURRENT TRANSFORMER, VD: VOLTAGE DIVIDER

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CORE WISE

APLICATION OFCTs IN


SCHEME

CURRENT TRANSFORMER

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CURRENT TRANSFORMER CONNECTIONS IN 3CT METHOD

1 – CT 2 – CT 3 – CT

CORE – 1( PS)

BUSBAR-1

PROTECTION

2CT’s SECONDARIES ARE CONNECTED IN PARALLEL AND

CONNECTED TO MAIN PROTECTION FOR TRANSFORMER

CORE – 2( PS)

BUSBAR-1 CHECKUP

PROTECTION (SPARE)


CONNECTED TO BACKUP PROTECTION AFTER LBB/BFR

FOR TRANSFORMER

CORE – 3( 0.5 / 0.2)

SPARE METERING & ENERGY METER FOR AT/F

CORE – 4(0.5 / 0.2)

METERING & ENERGY METER FOR FEEDER SPARE

CORE – 5( PS)


CONNECTED TO MAIN-2 PROTECTION AFTER LBB/BFR FOR

FEEDER

BUSBAR-2 CHECKUP

PROTECTION (SPARE)

CORE – 6( PS)


CONNECTED TO MAIN-1 PROTECTION FOR FEEDER

BUSBAR-2

PROTECTION

CURRENT TRANSFORMER

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CURRENT TRANSFORMERCONNECTIONS IN 3CT METHOD

1 – CT 2 – CT 3 – CT

CORE – 1( PS)

BUSBAR-1

PROTECTION


CONNECTED TO MAIN PROTECTION FOR TRANSFORMER

CORE – 2( PS)

BUSBAR-1 CHECKUP

PROTECTION (SPARE)


CONNECTED TO BACKUP PROTECTION AFTER LBB/BFR

FOR TRANSFORMER

CORE – 3(0.5 / 0.2)

METERING & ENERGY METER FOR FEEDER SPARE

CORE – 4( PS)


CONNECTED TO MAIN-2 PROTECTION AFTER LBB/BFR FOR

FEEDER

BUSBAR-2 CHECKUP

PROTECTION (SPARE)

CORE – 5( PS)


CONNECTED TO MAIN-1 PROTECTION FOR FEEDER BUSBAR-2

PROTECTION

BUSHING CT

METERING

CORE (0.5 / 0.2)

NORMALLY THIS SYTEM ADOPTS, WHEN ONE SIDE LINE, OTHER SIDE AUTO

TRANSFORMER / BUS REACTOR IS PROVIDED IN A DIA OF ONE AND HALF BREAKER

SYSTEM, IF BUSHING CT METERING CORE IS AVAILABLE, THEN IT IS USED FORMETERING & ENERGY METER FOR AT/F OR BUS REACTOR.

CURRENT TRANSFORMER

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1- CT 2-BCT 2-ACT 3-CT

CORE-1(PS)

CT SECONDARY

CORE IS

CONNECTED TO

BUSBAR-1

PROTECTION

SPARE SPARE CT SECONDARY

CORE IS

CONNECTED TO

BUSBAR-2

PROTECTION

CORE-2(PS)

BUSBAR-1

CHECKUPPROTECTION

(SPARE)

SPARE SPARE BUSBAR-2

CHECKUPPROTECTION

(SPARE)

CORE-3(0.5/0.2)

2CT’s SECONDARIES ARE

CONNECTED IN PARALLEL AND

CONNECTED TO

PANEL METERS & ENERGY METER


CONNECTED IN PARALLEL AND

CONNECTED TO

PANEL METERS & ENERGY METER

CORE-4(PS)

2CT’s SECONDARIES ARECONNECTED IN PARALLEL AND

CONNECTED TO

MAIN-2 PROTECTION

AFTER LBB/BFR

2CT’s SECONDARIES ARECONNECTED IN PARALLEL AND

CONNECTED TO

BACKUP PROTECTION

AFTER LBB/BFR

CORE-5(PS)


CONNECTED

IN PARALLEL AND CONNECTED TOMAIN-1 PROTECTION


CONNECTED

IN PARALLEL AND CONNECTED TOMAIN PROTECTION

CURRENT TRANSFORMER

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CURRENT TRANSFORMER

CONNECTIONS IN 5CT METHOD

1-CT 1-LCT 2-CT 3-TCT 3-CT

CORE-1

(PS)

BUSBAR-1PROTECTION

TEED PROT-1(BAY 1&2)



BUSBAR-2PROTECTION

CORE-2

(PS)

BUSBAR-1

CHECKUP

PROTECTION

(SPARE)

TEED PROT-2

(BAY 1&2)

TEED PROT-2

(BAY 2&3)

TEED PROT-2

(BAY 2&3)

BUSBAR-2

CHECKUP

PROTECTION

(SPARE)

CORE-3

(0.5/0.2)

SPARE METERING &

ENERGY

METER

SPARE METERING &

ENERGY

METER

SPARE

CORE-4

(PS)

TEED PROT-2

(BAY 1&2)

AFTER

LBB/BFR(1-52)

MAIN-2

PROTECTION

TEED PROT-2

(BAY 1&2)

AFTERLBB/BFR

(2-52)

BACKUP

PROTECTION

TEED PROT-2

(BAY 2&3)

AFTERLBB/BFR

(3-52)

CORE-5

(PS)

TEED PROT-1

(BAY 1&2)

MAIN-1

PROTECTION

TEED PROT-1

(BAY 1&2)

MAIN

PROTECTION

TEED PROT-1

(BAY 2&3)

Paralleling of 2Nos CTs to the Main-1/Main-2/Backup line protection is not required. This gives bettertransient response. Separate STUB protection can be connected (Nothing BUT TEED Protection).

CURRENT TRANSFORMER

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(GIS or AIS with DEAD TANK CBs)

1B-CT 1A-CT 2B-CT 2A-CT 3A-CT 3B-CT

CORE-1

(PS)

BUSBAR-1PROTECTION

2CT’s SECONDARIES

ARE CONNECTED

IN PARALLEL AND

CONNECTED TO

MAIN-1 PROTECTION

2CT’s SECONDARIES

ARE CONNECTED

IN PARALLEL AND

CONNECTED TO

MAIN-1 PROTECTION

BUSBAR-2PROTECTION

CORE-2

(PS)

BUSBAR-1

CHECKUPPROTECTION

(SPARE)

2CT’s SECONDARIES

ARE CONNECTED IN

PARALLEL AND

CONNECTED TO

MAIN-2 PROTECTION

AFTER LBB/BFR

2CT’s SECONDARIES

ARE CONNECTED IN

PARALLEL AND

CONNECTED TO

BACKUP PROTECTION

AFTER LBB/BFR

BUSBAR-2

CHECKUPPROTECTION

(SPARE)

CORE-3(0.5/0.2)

SPARE 2CT’s SECONDARIESARE CONNECTED IN

PARALLEL AND

CONNECTED TO

PANEL METERS &

ENERGY METER

2CT’s SECONDARIESARE CONNECTED IN

PARALLEL AND

CONNECTED TO

PANEL METERS &

ENERGY METER

SPARE

CURRENT TRANSFORMER

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1-CT 1L-CT 2A-CT 2B-CT 3T-CT 3-CT

CORE-1

(PS)

BUSBAR-1

PROTECTION

TEED PROT-1

(BAY 1&2)

SPARE SPARE TEED PROT-1

(BAY 2&3)

BUSBAR-2

PROTECTION

CORE-2

(PS)

BUSBAR-1

CHECKUP

PROTECTION(SPARE)

TEED PROT-2

(BAY 1&2)

SPARE SPARE TEED PROT-2

(BAY 2&3)

BUSBAR-2

CHECKUP

PROTECTION(SPARE)

CORE-3

(0.5/0.2)

SPARE METERING &

ENERGY

METER

SPARE SPARE METERING &

ENERGY

METER

SPARE

CORE-4(PS)


AFTER LBB/BFR

(1-52)

MAIN-2PROTECTION



AFTER LBB/BFR

(2-52)

BACKUPPROTECTION

TEED PROT-2(BAY 2&3)AFTER LBB/BFR

(3-52)

CORE-5

(PS)

TEED PROT-1

(BAY 1&2)

MAIN-1

PROTECTION

TEED PROT-1

(BAY 2&3)

TEED PROT-1

(BAY 1&2)

MAIN

PROTECTION

TEED PROT-1

(BAY 2&3)

CT CORES

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CT CORES

CONEECTIONDIAGRAMS IN


SCHEME

SINGLE BUS SYSTEM

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SINGLE BUS SYSTEM

1-52CB1-89 1-89L

3

1-CT

P2 P1 3

3

3

3

CORES

1 2 3 4 5

B U S B A R P R O T E

C T I O N

B U S B A R C H E C K U

P P R O T

M E T E R I N

G

M A I N - 2 / B A C K U P P R O T E C T I O N

M A I N - 1 P R O T E

C T I O N

BUS

1-CVT

3

3

3

3

1 2 3 33

3

3

3

2

1

BB-EVT

/ CVT

ONE & HALF BREAKER ( 3 CT METHOD) WITH PROTECTION SCHEME

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87BB1

87BB2

CVT

CVT

VBB1

VBB2

79

25

79

25

79

25VBB2

BF

BF

VL2 / VL1

OR VBB1

VL1 / VL2

OR VBB2

VBB1

FEEDER1 / LINE1

FEEDER2 / LINE2

87L 21M2

CVT VL2

CVT VL1

BF

VL1

BUSBAR-1

BUSBAR-2

MAIN-1

MAIN-2PROTECTION OF LINE2

(OR TRANSFORMER, IF APPLICABLE)

21M1 VL1

VL1 / VBB1

VL2 / VBB2

FOR TRANSFORMER PROTECTION &

METERING VOLTAGE SELECTION RELAYSFOR BUS-1, BUS-2& LINE ARE PROVIDED .


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87BB1

87BB2

CVT

CVT

VBB1

VBB2

79

25

79

25VBB2

BF

BF

VL2 / VL1

OR VBB1

VL1 / VL2

OR VBB2

VBB1

FEEDER1 / LINE1

FEEDER2 / LINE2

87L 21M2

CVT VL2

CVT VL1

BF

VL1

BUSBAR-1

BUSBAR-2

MAIN-1

MAIN-2PROTECTION OF LINE2


21M1 VL1

79

25VL1 / VBB1

VL2 / VBB2




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87BB1

87BB2

CVT

CVT

VBB1

VBB279

25VBB2

BF

BFVL2 / VL1

OR VBB1

79

25

VL1 / VL2

OR VBB2

VBB1

FEEDER1 / LINE1

FEEDER2 / LINE2

87L 21M2

CVT VL2

CVT VL1

BF

VL1

BUSBAR-1

BUSBAR-2

MAIN-1

MAIN-2

PROTECTION OF LINE2


21M1 VL1

79

25VL1 / VBB1

VL2 / VBB2




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87BB1

87BB2

CVT

CVT

VBB1

VBB2

79

25

79

25

79

25VBB2

BF

BF

VL2 / VL1

OR VBB1

VL1 / VL2

OR VBB2

VBB1

FEEDER1 / LINE1

FEEDER2 / LINE2

CVT VL2

CVT VL1

BF

87L 21M2

VL1

BUSBAR-1

BUSBAR-2

MAIN-1

MAIN-2

PROTECTION OF LINE2


21M1 VL1

VL1 / VBB1

VL2 / VBB2

87 TD1 HZ

87 TD2 LZ

87 TD1 HZ

87 TD2 LZ

.

.




7/26/2019 1431928792session II Ct & Vt


87BB1

87BB2

CVT

CVT

VBB1

VBB2

79

25

79

25VBB2

BF

BF

VL2 / VL1

OR VBB1

VL1 / VL2

OR VBB2

VBB1

FEEDER1 / LINE1

FEEDER2 / LINE2

CVT VL2

CVT VL1

BF

87L 21M2

VL1

BUSBAR-1

BUSBAR-2

MAIN-1

MAIN-2

PROTECTION OF LINE2


21M1 VL1

79

25VL1 / VBB1

VL2 / VBB2

87 TD1 HZ

87 TD2 LZ

87 TD1 HZ

87 TD2 LZ

.

.




7/26/2019 1431928792session II Ct & Vt


87BB1

87BB2

CVT

CVT

VBB1

VBB2

79

25

BF

BF

79

25VBB2

VL2 / VL1

OR VBB1

VL1 / VL2

OR VBB2

VBB1

FEEDER1 / LINE1

FEEDER2 / LINE2

CVT VL2

CVT VL1

BF

87L 21M2

VL1

BUSBAR-1

BUSBAR-2

MAIN-1

MAIN-2

PROTECTION OF LINE2


21M1 VL1

79

25VL1 / VBB1

VL2 / VBB2

87 TD1 HZ

87 TD2 LZ

87 TD1 HZ

87 TD2 LZ



COMPARISION BETWEEN DIFFERENT CT METHODS

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CTPURPOSE

3 CTMETHOD

4 CTMETHOD

6 CT (S)METHOD

5 CTMETHOD

6 CT (T1)METHOD

6 CT (T2)METHOD

BUSBAR &

BUSBAR

CHECKUP

PROTECTION

1 CT 1 CT 1B CT 1 CT 1 CT 1 CT

ABOVE FOR BUS-1 & BELOW FOR BUS-2

3 CT 3 CT 3B CT 3 CT 3 CT 3 CT

MAIN-1

MAIN-2

PROTECTION

&

METERING

1 - CT & 2 - CT 1 CT & 2 B - CT 1 A – CT & 2 B – CT 1 L - CT 1 L - CT 1 L - CT

ABOVE CT SECONDARIES ARE CONNECTED PARALLEL FOR FEEDER-1

BELOW CT SECONDARIES ARE CONNECTED PARALLEL FOR FEEDER-2

ABOVE FOR FEEDER-1

BELOW FOR FEEDER-2

3 - CT & 2 – CT 3 - CT & 2 A - CT 3 A - CT & 2 A - CT 3 L - CT 3 L - CT 3 L – CT

ADDITIONAL

PROTECTION

AVAILABLE

STUB-1 & STUB-2 PROTECTIONFOR LINE & AT/F

TEED-1 & TEED-2 PROTECTIONFOR LINE & AT/F

STUB-1 & STUB-2 PROTECTION IS A NORMALLY INBUILT

PROTECTION FOR MAIN-1 & MAIN-2 RELAYS, IN CASE OF LATEST

NUMERICAL RELAYS. STUB PROTECTION WORKS WHEN LINE

ISOLATOR OPEN CONDITION ONLY.

TEED–1 IS NORMALLY HIGH IMPEDENCE DIFFERENTIAL RELAY &

TEED-2 IS NORMALLY LOW IMPEDENCE DIFFERENTIAL RELAY.

THESE ARE NOT INBUILT FUNCTIONS OF MAIN-1 & MAIN-2

RELAYS.

BLINDZONE

A FAULT BETWEEN CIRCUIT BREAKERS AND CT (END FAULT) MAY THEN STILL BE FED FROM ONE SIDE

EVEN WHEN THE BREAKER HAS BEEN OPENED. CONSEQUENTLY, FINAL FAULT CLEARING BY CASCADEDTRIPPING HAS TO BE ACCEPTED IN THIS CASE. THIS SITUATION LBB/BFR OPERATES AND TIME TAKEN TOCLEAR FAULT IS ABOUT 300 mSECs. THIS IS BLIND ZONE AREA.

ADVANTAGES

MINIMUM CT

METHOD. REDUCING

THE COST OF CTs

TIE CB BLIND ZONE

AREA IS TAKEN

CARE.

MAIN CB & TIE CB

BLIND ZONE AREA IS

TAKEN CARE

BLIND ZONE FOR

MAIN CB & TIE CB

TIE CB BLIND ZONE

AREA IS TAKEN CARE

TIE CB BLIND ZONE

AREA IS TAKEN CARE

WHEN THE FAULT IS TAKEN PLACE BETWEEN THE MAIN

CB, TIE CB & LINE ISOLATOR, DURING SERVICE ONLY,DISTANCE SCHEME SHOULD TAKE CARE.

WHEN THE FAULT IS TAKEN PLACE BETWEEN THE MAIN CB, TIE CB &

LINE ISOLATOR DURING SERVICE ONLY, TEED PROTECTION INADDITION TO DISTANCE SCHEME SHOULD TAKE CARE.

400KV C T INFORMATION

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400KV C.T. INFORMATION

3 3 U

3 U

3 U

3

1S11S21S3

2S12S22S3

3 S 1

3 S 2

3 S 3

3 S 4

5S1

5S25S35S4

4S14S24S34S4

P1 P2

P1 P2

3 U

3 S 1

3 S 2

3 S 3

3 S 4

EYE BOLT

DESIGN

HAIR

PIN /U SHAPE

DESIGN

DEAD TANK DESIGN

PRIMARY CONNECTIONS : P1 – P2

CURRENT RATING : 2000 AMPS

CORES CLASS PURPOSE

SECONDARY CONNECTIONS

CURRENT RATING : 1A

2000/ 1A 1000/ 1A 500/ 1A

CORE-1 PS

BUSBAR

PROTECTION 1S1 – 1S3

1S1 – 1S2

1S2 – 1S3

__

CORE-2 PS

BUSBAR

CHECKUP

PROTECTION

2S1 – 2S32S1 – 2S2

2S2 – 2S3__

CORE-3 0.5 / 0.2 METERING 3S1 – 3S4 3S1–

3S33S4 – 3S2 3S1–

3S23S4 – 3S3

CORE-4 PSMAIN-2

PROTECTION4S1 – 4S4

4S1 – 4S3

4S4 – 4S2

4S1 – 4S2

4S4 – 4S3

CORE-5 PSMAIN-1

PROTECTION5S1 – 5S4

5S1 – 5S3

5S4 – 5S2

5S1 – 5S2

5S4 – 5S3

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CT PARAMETERS

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1. Top cover

2. Oil level indicator

3. Oil expansion device4. Metal box LV screen and cores

5. Bar-type or wound type primary

6. Paper-oil insulation

7. Porcelain insulator

8. LV screens

9. Secondary terminal box10. Base

Current Transformers (Paper/Oil) up to 765 kV

Eye Bolt Design

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Eye Bolt Design

IT range

Primary conductor (1,2 or 4 turns)

Primary steel pipe

Paper insulation

Secondary cores

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1. Dome

2. Nitrogen filling valve

3. Primary terminal4. Collar


6. Primary conductor with

insulation

7. Adaptor cylinder

8. Secondary cores9. Base

10. Oil drain plug


Hair-Pin design

7/26/2019 1431928792session II Ct & Vt


1. Oil filling plug

2. Dome

3. Nitrogen filling valve4. Collar

5. Primary terminal


7. Insulated primary

8. Cover plate for tank

9. Tank10. Secondary cores


Eye bolt design

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FUNDAMENTALS

WHAT IS CT?

WHEN IS CT REQUIRED ?

WHY IS CT REQUIRED?

HOW IS CT CONNECTED?

WHERE IS CT CONNECTED?

WHICH CT IS CONNECTED?

7/26/2019 1431928792session II Ct & Vt


WHAT IS CT?

IT’S AN INSTRUMENT TRANSFORMER

WHICH TRANSFORMS CURRENT FROMONE LEVEL TO ANOTHER LEVEL SUCH AS

1000/1 (CT RATIO) i.e. TRANSFORMS

CURRENT OF THE LEVEL OF 1000 AMPS

INTO CURRENT OF 1 AMP LEVEL.

back

7/26/2019 1431928792session II Ct & Vt


WHEN IS CT REQUIRED ?

ELECTRICAL SYSTEMS IN WHICH LARGE

AMOUNT OF CURRENT ( TO THE TUNE OF

100AMPS OR MORE) FLOWS , DIRECTMEASUREMENT OF THAT CURRENT IS

NOT POSSIBLE AS DEVICES USED FOR

MEASUREMENT OF CURRENT ARE NOT

DESIGNED TO HANDLE SUCH HUGE

AMOUNT OF CURRENT.

back

7/26/2019 1431928792session II Ct & Vt


WHY IS CT REQUIRED?

THE SYSTEM WHICH CARRIES CURRENTMEANS THERE IS A SOURCE WHICHINJECTS THE CURRENT INTO THE SYSTEM

AND THERE IS A LOAD WHICH CONSUMESTHE CURRENT (OR POWER/ENERGY).SUCHA SYSTEM HAS TWO BASICREQUIREMENTS:

METERING OF ENERGY SOURCED ORCONSUMED.

PROTECTION OF THE ELECTRICALSYSTEM FROM FAULTS AND

DISTURBANCES. back

7/26/2019 1431928792session II Ct & Vt


HOW IS CT CONNECTED?

CT HAS A PRIMARY AND ONE OR MORE

SECONDARY WINDINGS. SECONDARY

WINDING IS WOUND AROUND THE

MAGNETIC CORE. METERING AND

PROTECTION DEVICES ARE CONNECTED

TO THE SECONDARIES OF THE CT.

7/26/2019 1431928792session II Ct & Vt


HOW IS CT CONNECTED?contd

M/R

PRIMARY

Ip

Ψ

Is

back

P1

P2

S1

S2

7/26/2019 1431928792session II Ct & Vt


WHERE IS CT CONNECTED?

FOR METERING AND PROTECTION OF

A FEEDER, CT IS CONNECTED AT THE

BEGINNING OF THE FEEDER.

WHERE IS CT

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WHERE IS CT

CONNECTED? contd

Power Station to be protected

back

Unit

protUnit

prot

Non-

unit

prot

meter meter prot meterDist

prot

One prim one sec

One prim two or more sec

7/26/2019 1431928792session II Ct & Vt


WHICH CT IS CONNECTED?

METERING: IF WE WANT TO MEASURECURRENT FOR METERING PURPOSE, WEDESIRE THAT:

WHATEVER CURRENT WE MEASURE,THAT SHOULD BE VERY ACCURATE ASTHE METERED DATA MAY BE USED FORTARIFF PURPOSE i.e. MONEY EXCHANGE

IS INVOLVED AMONG VARIOUS PARTIES.MOREOVER, THE DATA IS USED FORDECISION MAKING SUCH AS DECISIONON RAISING/LOWERING OF POWER

OUTPUT etc.

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WHICH CT IS CONNECTED?Contd meter ing

WHAT IS INACCURACY?

THE SECONDARY CURRENT WHICH WEGET IS NOT TRUE REFLECTION OF ITSPRIMARY CURRENT. FOR EXAMPLE, FOR ACT WITH CT RATIO OF 1000/1AMPS, IF WEGET 0.99 AMPS IN SECONDARY LEADINGPRIMARY CURRENT BY 15 MINUTES FOR

PRIMARY CURRENT OF 1000AMPS, SO THECT HAS RATIO ERROR OF (0.99-1)/1 x 100=-1% AND PHASE ERROR OF 15 MINUTES.

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CURRENT OR RATIO ERROR AS PER IEC IS:

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NOW SECOND QUERY WHICH COMES IN

MIND IS WHY AT ALL CTS ARE

INACCURATE?

THE CULPRIT IS CORE LOSS AND

MAGNETISING CURRENT, WHICH

INTRODUCES RATIO AS WELL AS PHASE

ERROR.

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THE INTSRUMENT CONNECTED TO THESECONDARY ESPECIALLY ANALOGINDICATING METER SHOULD NOT GET

DAMAGED DURING PRIMARY FAULTCONDITION.

FOR THIS INSTRUMENT SECURITYFACTOR (FS) IS DEFINED WHICH IS RATIOOF MINIMUM PRIMARY CURRENT AT

WHICH COMPOSITE ERROR OF THE CT (ATRATED BURDEN) IS EQUAL TO ORGREATER THAN 10% OF RATED PRIMARYCURRENT.

THE TYPICAL VALUES ARE 5,10 etc.

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WHICH CT IS CONNECTED?contd

IEC60044-1 HAS LAID DOWN STANDARDS ON

THIS:

25 25 25

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FOR ACHIEVING ABOVE, A CT IS

CHOSEN HAVING VERY HIGHPERMEABILITY AND HIGH

REMANENCE

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THE ABOVE CT PARAMETERS ARE

THEREFORE SPECIFIED AS FOR

EXAMPLE: CTR:1000/1,0.2FS5 ,30VA

etc.

IN NTPC, WE TYPICALLY SPECIFY,

CTR: 2000/1, 0.2,FS 5, 20VA

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PROTECTION CLASS:

HERE, MAIN REQUIREMENT IS ABILITY OFCT TO FAITHFULLY TRANSFORM THEPRIMARY CURRENT DURING FAULTCONDITION.

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WHICH CT IS CONNECTED?Contd p rotection PR

DURING FAULT CONDITION, VALUE OFPRIMARY CURRENT MAY BE 10 TO 20 TIMESTHE RATED PRIMARY CURRENT.

PROTECTIVE RELAY BURDEN ISCONNECTED TO THE CT SECONDARY. ATSUCH HIGH LEVEL OF PRIMARY CURRENT,IF CT IS NOT PROPERLY DESIGNED, IT MAYSATURATE AND RELAY WILL RECEIVE

VERY LESS CURRENT AND, THEREFORE,DOES NOT TAKE RIGHT DECISION.

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FOR NON-UNIT TYPE PROTECTION SUCHAS O/C TYPE OF PROTECTION, CLASS PR TYPE CTs ARE USED.

THE PARAMETERS THAT ARE DEFINEDFOR THE CT ARE:

STANDARD ACCURACY LIMITFACTOR(SALF):

= RATED ACC. LIMIT PRIMARY CURR.

RATED CURRENT

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WHEREAS, RATED ACCURACY LIMITPRIMARY CURRENT IS THE VALUE OF

THE PRIMARY CURRENT UPTO WHICHCT WILL COMPLY WITH THEREQUIREMENT OF COMPOSITE ERROR.

STANDARD VALUES OF SALF ARE5,10,15,20,30

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THEREFORE SPECIFIED AS FOREXAMPLE: CTR:1000/1, 5PR20 @

30VA etc.

IN NTPC, FOR GENERATORPROTECTION WE TYPICALLY

SPECIFIY CTR 10000A/5A,5PR20 @

75VA

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WHICH CT IS CONNECTED?Contd protect ion

FOR UNIT TYPE PROTECTION:

HERE , REQUIREMENTS ARE RATHERSTRINGENT AS WE COMPARE CURRENTOF TWO OR MORE CTS AND RELY ON THETHEIR MUTUAL FAITHFULL-NESS .MOREOVER, OUR AIM IS THAT THE

PROTECTION MUST BE STABLE FOR EVENWORST THROUGH FAULT AND FASTACTING FOR INTERNAL FAULT.

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WHICH CT IS CONNECTED?Contd protect ion PX

FOR THIS PX CLASS OF CTs ARE

NEEDED (THESE CTs ARE SIMILAR IN

ALL RESPECTS TO CLASS PS OF IS-2705 AND CLASS-X OF BS-3938 WITH

SOME ADDITIONAL FEATURES)

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THE PARAMETERS WHICH ARE DEFINED

IN THIS CT ARE:

KNEE POINT VOLTAGE (KPV):

That minimum sinusoidal voltage (r.m.s.) at rated

power frequency when applied to the secondary

terminals of the transformer, all the terminals

being open-circuited, which when increased by10% causes the r.m.s. exciting current to increase

by no more than 50%.

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FOR WORST THROUGH FAULT, CTs

SHOULD NOT GET SATURATED.WHEN ONE

OF THE CTs GETS SATURATED, LARGE

AMOUNT OF CURRENT MAY FLOW

THROUGH DIFFERENTIAL CIRCUIT AND

RESULT IN OPERATION OF

RELAY.HOWEVER, IF RELAY IS SETABOVE THIS VALUE

i.e. Iset= Ifx (Rct+2xRl),

Rstab

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WHICH CT IS CONNECTED?contd protect ion PX

MAGNETISING CURRENT AT KPV OR%AGE THEREOF:

TWO OR MORE CTs USED FOR UNITPROTECTION SHOULD WORK LIKE CLONEBROTHERS i.e. FOR THROUGH FAULTCONDITION, THE SPILL CURRENTSHOULD BE IDEALLY ZERO. BUTPRACTICALLY, THIS IS NOT THE CASE.

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WHICH CT IS CONNECTED?contd protect ion PX

IF TWO CTs HAVE DIFFERENTMAGNETISING CURRENT AND HIGH

LEAKAGE REACTANCE, IT WILLINTRODUCE HIGH CURRENT AS WELL ASPHASE ERROR.THUS, RESULTANTCURRENT OF THESE CT SECONDARIESMAY LEAD TO HIGH SPILL(DIFFERENTIAL)

CURRENT DURING THROUGH FAULT.THISMAY LEAD TO PROTECTION OPERATIONDURING THROUGH FAULT.

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CT DC RESISTANCE AT 75 deg C(Rct):

THIS VALUE IS VERY IMPORTANT FROM

THE POINT OF VIEW OF KPVCALCULATION AS IT IS ONE OF THE

LIMITING FACTORS TO THIS. THEREFORE,

IT IS DEFINED.

TURN RATIO ERROR: LIMITED TO 0.25%.

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THEREFORE SPECIFIED AS FOR

EXAMPLE:CTR: 1000/1 ,PX , KPV=1000V,

Ie=30mAmp @ KPV/2, Rct< 5OHMS @75

deg C etc. (TYPICAL TO NTPC)

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Current Transformers

Causes of Failure andMonitoring/Maintenance

CT Failure and remedial action

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Generally failures can happen due to the following reasons

• Opening of C terminal (used for tan delta and

capacitance measurement) when CTs are in energisation. This

leads to very high voltages resulting in failure.


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Remedial actions in CT at site to avoid failures

• Tangent delta and Capacitance measurement from the C terminal at periodic

intervals every years or during shutdown.

• Dissolved gas analysis of oil taken out from CT alteast once in ten years.

• Thermo vision scanning of CTs of rating 132kV ( or above).

Multiple Chopped Impulse test

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Multiple Chopped Impulse test

Application of 100 chopped impulses of negative polarity

on CTs of ratings above 300kV. These impulses will be

applied at the rate of one impulse per minute. The test

Voltage shall be 60% of the rated lightning impulse voltage

Before the test and three days after the test the dissolved

gas analysis of oil taken from CT will be carried out.Analysis

procedure and fault diagnosis shall be as per IEC 60599.

As per IEC 60044-1 ( 2002)

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Special test

A. Thermal Stability test :

This involves simultaneous application of rated voltage

(1.1Um/Sqrt3) and rated simultaneous current (1.2,1.5 etc)

by using a synthetic test circuit.Capacitance, tangent delta,

secondary resistance and temperature of primary terminal

are recorded until stable values are acquired.

This test demonstrates the insulation capacity (healthiness) under energised

conditions.

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Special test

B. Temperature coefficient test:

The CT is heated in a oven to approximately 90Deg C. The tan delta is

measured at ambient, 80 and 90 deg C at voltages of 0.3,0.7,1.0 and1.1Um/Sqrt3.

This test demonstrates the healthiness at high extreme temperature conditions.


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Type Tests

IEC 600 44-1a) short-time current tests

b) temperature rise test

c) lightning impulse test

d) switching impulse test

e) wet test for outdoor type transformers

f) determination of errors

Current Transformer

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Routine testsCEI 600 44-1

CEI 60-1

Routine tests

The following tests apply to each individual transformers:

a) verification of terminal markings

b) power-frequency withstand test on primary windingc) partial discharge measurement

d) power-frequency withstand test on secondary windings

e) power-frequency withstand tests, between sections

f) inter-turn overvoltage testg) determination of errors

The order of the tests is not standardized, but determination of

errors shall be performed after the other tests.

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VT PARAMETERS

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FUNDAMENTALS

WHAT IS VT?

WHEN IS VT REQUIRED ?

WHY IS VT REQUIRED?

HOW IS VT CONNECTED?

WHERE IS VT CONNECTED?

WHICH VT IS CONNECTED?

7/26/2019 1431928792session II Ct & Vt


1. Oil level indicator (optional)

2. Expansion device

3. Capacitor units

4. Insulating oil5. Porcelain insulator

6. Sealing

7. Electromagnetic unit

8. Low voltage terminals box/

HF terminal

9. Series inductance

10. Medium voltage transformer

11. Damping circuit againstferroresonance effects

Capacitor Voltage Transformers (Paper/Film/Oil) up to 765 kV

1

2

3

4

5

7

8

9

11

6

10

7/26/2019 1431928792session II Ct & Vt


Capacitor stack

Inductive VT

7/26/2019 1431928792session II Ct & Vt


CCV 72.5 to 765 kV

Capacitor elements

Capacitor column

Insulating oil

Insulator flange

Secondary terminal box

Inductance

MV Transformer

Oil expansion device

Damping circuit

7/26/2019 1431928792session II Ct & Vt


WHAT IS VT?

IT’S AN INSTRUMENT TRANSFORMER

WHICH TRANSFORMS VOLTAGE FROM

ONE LEVEL TO ANOTHER LEVEL SUCH AS400KV/√3:110V/√3 (VT RATIO) i.e.

TRANSFORMS VOLTAGE OF THE LEVEL OF

400KV/√3 INTO VOLTAGE OF 110V/√3

LEVEL.

back

7/26/2019 1431928792session II Ct & Vt


WHEN IS VT REQUIRED ?

ELECTRICAL SYSTEM WHICH HASHIGH LEVEL OF VOLTAGE ( TO THE

TUNE OF 3.3KV OR MORE) , DIRECTMEASUREMENT OF THAT VOLTAGEIS NOT POSSIBLE AS DEVICES USEDFOR MEASUREMENT OF VOLTAGEARE NOT DESIGNED TO HANDLESUCH HIGH LEVEL OF VOLTAGE.

back

7/26/2019 1431928792session II Ct & Vt


WHY IS VT REQUIRED?

THE SYSTEM WHICH CARRIES VOLTAGEAND CURRENT MEANS THERE IS ASOURCE WHICH INJECTS THE POWER INTO

THE SYSTEM AND THERE IS A LOADWHICH CONSUMES POWER/ENERGY.SUCHA SYSTEM HAS TWO BASICREQUIREMENTS:

METERING OF ENERGY SOURCED OR

CONSUMED.PROTECTION OF THE ELECTRICAL

SYSTEM FROM FAULTS ANDDISTURBANCES.

7/26/2019 1431928792session II Ct & Vt


WHY IS VT REQUIRED?Contd

FAULTS CAN BE MANY KINDS. SOMEFAULTS SUCH AS O/C CAN BE DETECTEDSOLELY ON CURRENT MEASUREMENT,

BUT CURRENT DOES NOT PROVIDEDISCRETION ABOUT NATURE ANDLOCATION OF THE FAULT. FOR HIGHLYINTERCONNECTED ELECTRICAL SYSTEMCARRYING HUGE AMOUNT OF POWER,

SUB-SYSTEM ISOLATION SELECTIVITY ISIMMENSLY DESIRABLE.

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VT HAS A PRIMARY AND ONE OR MORE

SECONDARY WINDINGS.

METERING AND PROTECTION DEVICES

ARE CONNECTED TO THE SECONDARIES

OF THE VT.


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HOW IS VT CONNECTED?contd

M

P

P

INDUCTIVE VOLTAGE TRANSFORMER


7/26/2019 1431928792session II Ct & Vt


HOW IS VT CONNECTED?contd

back

M

P

P

CAPACITIVE VOLTAGE TRANSFORMER

7/26/2019 1431928792session II Ct & Vt


WHERE IS VT CONNECTED?

FOR METERING AND PROTECTION OF A

FEEDER, VT IS CONNECTED AT THEBEGINING OF THE FEEDER.

WHERE IS VT

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WHERE IS VT

CONNECTED? contd

Power Station to be protected

back

7/26/2019 1431928792session II Ct & Vt



AS STATED FOR CT, WE NEED IT FOR

METERING: VOLTAGE MEASUREMENT,ENERGY, POWER MEASUREMENT.

PROTECTION: FOR DISTANCE

PROTECTION, O/V,U/V, O/F AND U/FPROTECTIONS, FIELD FAILURE, OVER-FLUXING,etc.


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WHICH VT IS CONNECTED?contd

FOR METERING VTs WE NEED HIGHACCURACY IN THE VOLTAGEMEASUREMENT DURING STABLE

CONDITIONS i.e 80% TO 120% OF NOMINALSYSTEM VOLTAGE WITH BURDENS FROM25% TO 100% OF RATED BURDEN ATPOWER FACTOR OF 0.8 . IN VTs ALSO AS IN

CTs, RATIO AS WELL AS PHASE ERRORSARE THERE.


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WHICH VT IS CONNECTED?Contd meter ing

IEC 60044-2 AND 60044-5 DEFINES THIS AS :

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WHICH VT IS CONNECTED?contd protect ion

IEC 60044-2 AND 60044-5 DEFINES THIS AS :

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Capacitor Voltage

Transformer

Causes of Failure andMonitoring/Maintenance

Capacitor Voltage Transformers

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p g

Monitoring and maintenance

Causes of Failure

Due to Ferroresonance caused by primary/secondary disturbances

Oil leak at sealing points leading to ingress of moisture and

degradation of capacitor

Monitoring

Capacitance and tangent measurement using the tan delta kit at

periodic intervals or whenever there is a shut down

Using thermovision camera especially for 220kV to detect any high

temperature abnormalities IR check on secondary

To check the resistance of the damping wdg externally and also the

condition of the Lightning arrester in the sec terminal box

Capacitor Voltage Transformer

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Definitions

Element Pack

(or pack)

Pile of elements : ± 10 to 25 kV


D fi i i

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Definitions

Assembly of elements in an

insulating container: ± 245 kV.Can be connected to a HV line

Capacitor Unit

(or unit)

HV Power line

Ground


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Definitions

Capacitor STACK

(or stack)

Assembly of elements to reach

higher voltage levels : ± 800 kV

HV Power line

Ground

In general, the term

CAPACITOR

stands for a capacitor element

as well as a capacitor stack.

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Magnetic Transformer

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Lµ = Inductance equivalent to magnetic losses of the magnetic circuit.

R w = Resistance equivalent to the watt losses of the magnetic circuit.

Lfs = Secondary leakage inductance of the magnetic VT.

Rs = Resistance of the secondary winding

g

Ce La Lfs Ra Rs

Lμ Rw Zc Us U’P = Vp . C1 k . (C1+C2)

Equivalent Diagram

Capacitor Voltage TransformerCapacitor Elements

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Capacitor Elements All Paper Dielectric design Mixed dielectric design

Paper PPR film + paper

Copper tabs for

connection

Aluminum foil

folded for contact

with next element

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Damping Circuit

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Short-circuit at zero crossing

Primary voltage

Secondary voltage

t

Vs

Vi

t

Damping CircuitPrimary Short Circuit & Transient Response

Capacitor Voltage TransformerDamping Circuit

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Short-circuit at zero crossing

Primary voltage

Secondary voltage

t

Vs

Vi

t

5%

10%

Secondary error

t

0 100 200 300 [ms]

Necessary to add a damping circuit

20 msIEC 186

error limits

IEC today :

max 10% after 20ms

Primary Short Circuit & Transient Response

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R R-L-C R-L-RHow to solve transient problems :

• High

burden

• jeopardize

accuracy

• Efficient

• Easy to design

• Expensive

• Efficient

• Sophisticated design

• Economical


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150200

Tension primaire

Primary Voltage

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-200

-100

0

100

200

3 0 0

3 5 0

4 0 0

4 5 0

5 0 0

5 5 0

6 0 0

Tension secondaireSecondary Voltage

-2

-1

0

1

2

3

4

5

6

7

3 0 0

3 5 0

4 0 0

4 5 0

5 0 0

5 5 0

6 0 0

% Erreur secondaire (transitoi re)% error at secondary

R-L-RR-L-R

-200-150

-100-50

050

100150

3 0 0

3 5 0

4 0 0

4 5 0

5 0 0

5 5 0

6 0 0

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Transformers

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Routine tests (IEC 60044-5)Routine tests

The following tests apply to each individual transformer:

a) Verification of terminal markings

b) Power-frequency withstand tests on primary windings

c) Partial discharge measurementd) Power-frequency withstand tests on secondary

windings

e) Power-frequency withstand tests between sections

f) Determination of errors.

G) Ferroresonance test

h) Sealing test

Voltage transformersProtection accuracy classes

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Protection accuracy classesIEC 600 44-2

Accuracy classes (Protection)

Maximum error in % of VP

- Voltage between 5 % and f T x VNP

- Burden between 25% and 100% of SN

- Maximum error doubled for VNP=2%

Accuracy

class

Voltage

(ratio)

error

Phase

displacement

[minutes]Cl 3P

3 %

120

Cl 6P

6 %

24O


T t t (IEC 60044 5)

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Type tests (IEC 60044-5)

a) Temperature-rise test

b) Short-circuit withstand capability test

c) Lightning impulse test

d) Switching impulse test

e) Wet test for outdoor type transformers

f) Determination of errors.

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Condition Monitoring

and FailureInvestigations of

Instrument

Transformers

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Live Tank CTs

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CT Design

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g

Core Material –

The main aim is togive high accuracy with low

saturation factor.

Core Material is made of CRGO

Silicon steel

For very low loss characteristics, µ

material (Alloy of Ni-Fe) is used

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CT accuraciesAs per IEC-60044(1)

Metering Core – ±0.2 or 0.5% atrated Currents

Protection Cores –

±

1% at ratedcurrent

Accuracies as per IEC-60044-1

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p

Class 5% of

rated I

20% of

rated I

100% of

rated I

120% of

rated I

0.2 0.75 0.35 0.2 0.2

0.5 1.5 0.75 0.5 0.5

Protection Cores

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Protection Cores

Class Current Error at

rated Primary

Current

Composite Error at

rated accuracy limit

Primary Current

5P ±1% ±5%

10P ±3% ±10%

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Ph A l E

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Phase Angle Error

The difference in Phase between

the Primary and Secondary

current vectors

i

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Knee Point Voltage

10% increase in Voltage will lead to

30% or more increase in Current.

Insulation Levels

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Insulation Levels

For Windings having Um greater than

300kV, the rated insulation level is

determined by rated switching and

lightning impulse withstand voltage

For voltages < 300kV, insulation levels

are decided by lightning impulse and

power-frequency withstand voltages

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CT Insulation

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GSTg Mode of Measurement

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g

Here measurement is done for CHE

as L is guarded

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Negative Tan delta

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Negative Tan delta

Negative tan delta may result if there is

shunt to ground in between the points of

measurement

Heavily polluted porcelain exterior surface

or porcelain internal surface contamination

may result in negative tan delta reading

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Negative Tan Delta

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g

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CT FAILURES

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Primary Insulation failure

due to moisture entry

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due to moisture entry

Violent failure due to arcing

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g

CT under Flames

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Burnt CT

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Puncturing of Paper Insulation

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g p

Depression and wrinkles in paper

wrapping

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wrapping

Wrinkles in Paper

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Sharp edges on primary

conductor

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conductor

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CVT Construction Details

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There are 280 – 300 elements inC1 & C2

C1 will be about 260 to 280

elements

C2 will be 15 to 20 elements

Ratio of C1/ C2 is about 20

400/ 20 = 20kV (Tap Voltage)

Compensating Reactor

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Compensating Reactor

Compensating Reactor is provided

to compensate for the phase

displacement in Capacitor elements

ωL = 1/ω (C1+C2)

L = 1/ ω

2 (C1+C2)

Ferro Resonance

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Ferro resonance in CVTs is due to the

Capacitance in Voltage Divider in series with

the inductance of the Transformer and series

reactor. This circuit is brought to resonanceby various disturbances in the network that

may saturate the iron core of the transformer,

over heat electro magnetic unit and lead toinsulation breakdown.

Ferro Resonance Circuit

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Ferro resonance circuit is provided in

CVT Secondary to suppress Ferro

resonance oscillations

There can be active or passive Ferro

resonance circuits

It can be RLC circuit (ABB make CVTs)

or RL circuit (CGL, BHEL CVTs)

CVT VA Ratings VA ratings for core 1 core 2 and core 3 are

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VA ratings for core-1, core-2 and core-3 are

generally 200VA, 200VA and 100VArespectively.

CVT accuracies are guaranteed if connected

burdens are within 25% to 100% of therated burdens

In POWERGRID, with static meters andstatic/ numerical relays, connected burdensare 10 to 20 VA in each core which are verylow as compared to rated burdens.

CVT Secondary Voltage

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CVT Secondary Voltage v = k * V * C1/ (C1+C2)

V – Primary Voltage

k – Secondary Transformation ratio

Note:

Puncturing of C1 – Secondary Voltage will increase

Puncturing of C2 – Secondary Voltage will decrease


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Secondary Voltage

measurement

Capacitance and Tan delta

measurement of stacks

Secondary Voltage measurement

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Periodic measurement to be carried out. In caseof doubt, simultaneous measurement to be

carried out with another feeder/ Bus CVT.

For 400kV CVTs puncturing of one Capacitorelement in C1 side is likely to increase Secondary

Voltage by about 0.35 – 0.45% (0.22 – 0.28V)

Failure of one Capacitor element in C2 side islikely to decrease Secondary Voltage by 5 – 6%

(3.2 – 3.8V)

Capacitance and Tan delta

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p

measurement of stacks

Change in Capacitance value

above 6%, CVT need to bereplaced

Tan delta values more than 0.003

from pre-commissioning value

needs replacement

Reasons for Failure of CVTs

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WRINKLES ON ALUMINUM FOIL

POOR SOLDERING QUALITY

POOR QUALITY OF PAPER (LOCAL SOURCE)

PINHOLES IN BELLOWS

SNAPPING OF BELLOW CONNECTION

OVERHEATING OF DAMPING RESISTOR

SHORTING OF TRANSFORMER CORES

FAILURES OF FR CIRCUIT COMPONENTS

RUSTING OF COUPLING BOLTS (BETWEENFLANGE AND EMU TANK)

RUSTING OF FLANGE

Reasons for Failure of CVTs …

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LOOSENESS OF CORE BOLTS SNAPPING OF CONNECTION BETWEEN

PRIMARY WINDING AND COMPENSATINGREACTOR

FAILURE OF VARISTORS PROVIDED INSECONDARY

ENTRY OF MOISTURE IN CAPACITORSTACKS

MOISTURE ENTRY DUE TO POOR GASKETQUALITY

CVT Failures

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Failure of Bellow

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Rusting of Coupling bolt

and moisture entry

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and moisture entry

Rusting of flange

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Rusting of EMU Tank

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Capacitive Voltage Transformers

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0

1

2

3

4

1 9 9 4

1 9 9 5

1 9 9 6

1 9 9 7

1 9 9 8

1 9 9 9

2 0 0 0

2 0 0 1

2 0 0 2

2 0 0 3

2 0 0 4

2 0 0 5

2 0 0 6

YEAR

% a

g e p e r

y e a r

In last 4-1/2 yrs, newly commissioned CVTs failed 40 nos.

Old CVTs failed- 101 nos.

Secondary Voltage measurement Norms

Sr.

N

Drift in Sec.

Voltage

Condition of CVT Measurement

Frequency

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No. Voltage Frequency

1 Upto ±0.5 Volts Healthy Six monthly

2 ±0.5 to ±0.8 Volts Needs monitoring Three monthly

3 +0.8 to +1.2 Volts Needs close

monitoring4 +1.2 to +2.0 Volts Needs close

monitoring

15 days

5 Above +2.0 volts Alarming/ critical Needs replacement

6 -0.8 to -4.0 volts Needs closemonitoring 15 days

7 Less than -4.0 volts Alarming Needs replacement

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