PAPER PRESENTED AT DOBLE CONFERENCE

1. TIME TO THINK FOR EXTRA CLOSING
INTERLOCK FOR EHV CIRCUIT BREAKERS
12th IndiaDoble Power Forum, 2014,
Vadodara, Gujarat, INDIA 1
12th IndiaDoble Power Forum, 2014
Niraj Agrawal & Chetan Shete
ADANI POWER LIMITED , TIRORA
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oble
Engineering

2. PRESENT SITUATION
• FOLLOWING ARE COVERED IN EHV CB
CLOSING INTERLOCK
1. TRIP CIRCUIT SUPERVISION
2. LOCKOUT RELAY RESET
3. ALL PROTECTION RELAY RESET
4. SF6 LEVEL OK & SPRING IS CHARGED
5. BOTH DC HEATHY
6. AC SUPPLY OK
7. PDR NOR OPERATED
8. ADJACENT ISOLATOR CLOSED.
12th IndiaDoble Power Forum, 2014,
Vadodara, Gujarat, INDIA 2
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oble
Engineering

3. CASE STUDY-1
• ON 4TH JULY 2013 , CB OF 400KV WARORA-
TIRORA LINE CLOSED & OPENED > 20 TIMES.
1. 400KV WARORA – TIRORA LINE HAND TRIPED FROM TIRORA END .
2. 400KV TIE & MAIN CB AT WARORA OPENED SUCCESFULLY BUT MAIN
CB CLOSED FREQUENTLY SUBSEQUENT TO OPENING OF CB POLES.
3. RESULTING IN FREQUENT CHARGING OF OPEN-ENDED LINE FOR TWO
PHASES ( R & B).
4. FLICKRING OF LIGHTS & CHARGING –DISCHARGING SOUND WAS
NOTED.
5. OVERVOLTAGE STAGES TRIGGRED NO OF TIMES ..DANGER TO EHV
EQUIPMENTS.
12th IndiaDoble Power Forum, 2014,
Vadodara, Gujarat, INDIA 3
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oble
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4. CASE STUDY-1
• FINDINGS.
1. MOISTURE INGRESS IN MECHANISM BOX , SPRING CHARGE LIMIT
SWITCH OF Y -POLE.
2. CB CLOSE INTERLOCK & CB HEALTHY CONTACTS GOT SHORTED DUE TO
MOISTURE INGRESS. RESULTING IN FAILURE OF CLOSING COIL , DUE
TO CONTINEOUS DC POSITIVE TO COIL.
3. CONTROL CIRCUITARY IS RESPONSIBLE FOR FREQUENT CLOSE /OPEN
OPERATION OF CB AFTER SHORTING OF CONTACTS.
4. CB POLES WERE OPENING ON PDR & AGAIN CLOSING FOR ONLY TWO
PHASES (R &B).
5. CONTINUES UNTILL MANUAL DC OFF BY OPERATOR.
12th IndiaDoble Power Forum, 2014,
Vadodara, Gujarat, INDIA 4
D
oble
Engineering

5. CASE STUDY-2
• ON 17TH JAN 2014 , 400KV CB OF GT#3
CLOSED ON FAULT.
1. GT#3 , 400KV CB TRIPPED ON FAILURE OF B-PHASE GT HV BUSHING .
2. ALL CONTROL CABLES FROM NEAR BY TRENCHES BURNT DUE OIL
SPILLAGE & FIRE.
3. 400KV MAIN CB CLOSED ON FAULT DUE TO SHORTING OF CLOSING
COMMAND CONTROL CABLE.
4. RESULTING IN MORE DANGEROUS CONDITION FOR SYSTEM.
12th IndiaDoble Power Forum, 2014,
Vadodara, Gujarat, INDIA 5
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oble
Engineering

6. WHAT CAN BE DONE ?
1. SEGREGATE AUXILLIARY CONTACTS RELATING TO CB CLOSING CIRCUIT
APART FROM OTHER CONTACTS CARRYING DC +VE SUPLY.
2. ROUTE CB CLOSING CIRCUIT CABLES AWAY FROM GT AREA .
ABOVE SOLUTIONS ARE NOT 100% FULL PROOF , CAN WE CUT CLOSING
CIRCUIT AT TWO POINTS 1. +VE SIDE ( USUALLY DONE) 2. –VE SIDE
(INTENDED) ?.....
12th IndiaDoble Power Forum, 2014,
Vadodara, Gujarat, INDIA 6
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oble
Engineering

7. PROPOSED INTERLOCK IN CB CLOSING
CIRCUIT
12th IndiaDoble Power Forum, 2014,
Vadodara, Gujarat, INDIA 7
BCU OUTPUT
CONTACT TO CUT
NEGATIVE OF
CLOSING COIL
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oble
Engineering

8. LOGIC FOR CB CLOSING CIRCUIT
PROPOSED INTERLOCK
12th IndiaDoble Power Forum, 2014,
Vadodara, Gujarat, INDIA 8
Reset Logic
(Except Line)
Reset Logic for Lines.
( Considering Auto
Reclose Operation)
D
oble
Engineering

9. PROPOSED INTERLOCK IN CLOSING
CIRCUIT
12th IndiaDoble Power Forum, 2014,
Vadodara, Gujarat, INDIA 9
Possibility of unwanted SET –ON of Negative
Break contact for closing circuit is as follows
1. Restarting of BCU/IED/ SAS Server
a. Normally Open contact is used .
b. All inputs for logic are normally in reset condition (No internally
inverted signal is used), so possibility of closing of contact during
restarting of IED/BCU/SAS server is NIL.
2. SET & RESET control for same is given to Shift
engineer through OWS ( Operating work station ) ,
which helps during on time change in decision of
closing of circuit breaker.
D
oble
Engineering

10. 12th IndiaDoble Power Forum, 2014,
Vadodara, Gujarat, INDIA 10
THANKSD
oble
Engineering