Time to think for ehv cb interlocks
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1. The document discusses issues with existing EHV circuit breaker closing interlocks and proposes additional logic to improve safety. 2. Case studies describe instances where circuit breakers closed unexpectedly due to failures in the closing interlock circuits, posing dangers to equipment and the power system. 3. To address this, the authors propose adding a normally open contact in the negative side of the closing coil circuit. Additional logic would prevent the contact from unexpectedly closing, while allowing operators to override if needed. This aims to cut power to the closing coil if the interlock circuits fail.
Time to think for ehv cb interlocks
- 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 D 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 D 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 D oble Engineering
- 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 D 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 D 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 D 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