an off load but energized 11/0.4 KV, 1250 KVA T/F has a power factor of 0.65(capacitive)..!! why is it so, though T/F being an inductive device ??

4 Answers  

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what is a diffrence between MCCB, RCCB, MCB, & ELCB ? what is rated current e.g. on motor name plate indicated that is rated curent? what is full load current? If we run D.C. motor with mechanical coupling and we measure voltage on terminal it shows voltage or not ? same in AC also possible ?

5 Answers   Reliance,

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Tell me about Tesla.

1 Answers   Tata Power,

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HT and LT cables can be laid on same cable tray

1 Answers  

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Why strting torqe high in inducation motor?

0 Answers  

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i have 60Hz motor, can i run it at 50Hz power supply ???

2 Answers  

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Explain the operation of grid connected central solar inverter ?

0 Answers  

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The loads are connected with phase and ground then why current flow as the loads ?

0 Answers  

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sir i am apearing for nic exam.i dont know exam pattern.can you please send me some model papers

0 Answers  

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what is high tension ? specify the range?

3 Answers  

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why any inductive load need free wheeling diode?

4 Answers   Essar,

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RELAY 1. REF RELAY : • OPERATION WITH CT CURRENT FLOW DIRECTION. • WHY REF RELAY WHEN DIFFERENTIAL RELAY IS THERE. • REF RELAY STABILITY CHECK BY PRIMARY INJECTION – WHICH POINT FOR CUR RENT INJECTION. • WHY REF RELAY NEED STABILISING RESISTOR. IF RESISTOR SHORTED OR BYPASSED, WHAT WILL HAPPEN. • WHICH TYPE OF RELAY FOR REF, HIGH IMPEDANCE OR LOW IMPEDANCE. • IF NEUTRAL CT IS NOT CONNECTED IN THE CIRCUIT, WHAT WILL HAPPEN. • REF PROTECTION ACTS ON WHICH OF FOLLOWING: SINGLE PH. TO E/F; PH-PH TO E/F; THREE PH. TO E/F. 2. DISTANCE RELAY : • BASIC PRINCIPLE AND TYPES • SWITCHED MODE PROTECTION – WHY IS IT CALLED SO. • SCHEMES USED • WHY ZONE-1 SET AT 80% • SETTING RANGE FOR ZONE-2 AND ZONE-3 • HOW SINGLE PHASE TO GROUND FAULT MEASUREMENT IS DONE. • 3. WHAT IS POLARITY. CT LOCATION IF INTERCHANGED WHAT WILL HAPPEN. 4. SOLKOR RELAY: 1. WHY SOLKOR IS USED. 2. CIRCUIT DIAGRAM OF SOLKOR RELAY 3. DIFFERENT PARTS OF RELAY 4. HOW IT WORKS. 5. EXPLAIN BY VECTOR DIGRAM. 6. WHAT ADVANTAGE FOR USING SUMMATION TR. 7. DIFFERENCE BETWEEN R & RF WITH CIRCUIT. 8. ADJUSTMENT OF PADDING RESISTANCE. 9. WHAT IS LEAKAGE CURRENT AND HOW TO MEASURE. 10. WHAT HAPPEN IF LINK IS LEFT OPEN. 11. 5KV/15KV INSULATION TR. ARE USED IN WHICH SYSTEM. 12. WHAT PRECAUTION TAKEN DURING TESTING. Relay Page 1 of 5 13. PROCEDURE BEFORE TESTING AND AFTER NORMALISATION. 14. HOW RELAY IS TESTED IN LIVE CONDITION. 15. RANGE OF SPILL CURRENT ANS SETTING OF RELAY 16. IF MEASURED CURRENT IS 5MILLI AMPS, CAN RELAY OPERATE. 17. EACH FAULT APPROXIMATE VALUE OF PICK UP. 18. WHAT IS THE REASON SOLKOR-R MODE PILOT SHORTED CONDITION RELAY CURRENT PRESENT. 19. AFTER SHUTDOWN, WHY NEED TO OPEN SOLKOR PILOT, IF NOT WHAT WILL HAPPEN. 20. AFTER NORMALISING WHAT CURRENT TO BE MEASURED, WHAT IS ACCEPTABLE LIMIT. 21. WHAT HAPPENS IF PILOT OPENS FROM RELAY, WHEN FEEDER IS LOADED. 22. CAN WE USE THIS RELAY AS O/C OR E/F RELAY. 23. ANY RELAY OTHER THAN PILOT CABLE TYPE. 24. IF FEEDER TRIPS ON SOLKOR, WHAT TO DO. 25. WHAT HAPPENS IF PILOT POLARITY REVERSE. 26. WHAT HAPPENS WHEN CT SHORTED AT ONE END. 27. WHAT HAPPENS IF PILOT SHORTED – STATUS OF RELAY 28. WHAT HAPPENS TO RELAY ,IF POWER CABLE GETS OPEN. 29. WHAT HAPPEN IF PADDING RESISTOR IS SHORTED AT ONE END. 5. TR. DIFFERENTIAL: 1. CIRCUIT DIAGRAM 2. DIRECTION OF FAULT CURRENT. 3. WHEN THE FAULT IS IN ZONE AND OUT OF ZONE. 4. CT CONNECTION IN PY. AND SY. SIDE. 5. BIAS SETTING AND BIAS CURRENT. 6. WHICH BIAS SETTING USED IN TRS. FOR HIGHER TAPS. 7. PURPOSE OF RESTRAINING BIAS COIL. 8. WHY BIASING REQUIRED. 9. EXPLAIN IPCT, FOR EXAMPLE, DYN10 VECTOR GROUP. WHY MATCHING TR. USED. 10. WHY NEED 2ND HARMONIC BLOCKING DURING INRUSH. 11. WHICH HARMONIC IS MORE 2ND OR 3RD. 12. HOW TO AVOID FALSE TRIPPING IN DIFF. PROTECTION WHEN INRUSH CURRENT FLOW DURING TR. IS ENERGISED. Relay Page2 of5 6. DIRECTIONAL RELAY: 1. CIRCUIT FOR USE OF DIRECTIONAL PROTECTION SYSTEM. 2. WORKING ZONE / NON-WORKING ZONE. 3. HOW THE CORRECT DIRECTION OF FLOW OF CURRENT IS DETERMINED. 4. CT & PT CONNECTION DIAGRAM. 5. SETTING OF PHASE & EARTH FAULT ANGLE AND OPERATING REGION. 6. WHICH DIRECTION IT IS PROTECTING. 7. WHAT PROTECTION AVAILABLE FOR POWER TR. 8. WHY CT CONNECTION IS STAR, IF TR. WINDING IS DELTA. 9. DIFFERENCE BETWEEN REF AND DIFF. RELAY 10. WHERE IS O/C & E/F RELAY CONNECTED EITHER HV SIDE OR LV SIDE AND HOW E/F RELAY WORKS IF TR. WINDING IS DELTA CONNECTED. 11. IN DELTA WINDING OF TR., IF ONE WINDING IS CUT AND NOT EARTHED, WHICH PROTECTION WILL ACT. 12. IF DIFF. & REF RELAY ARE NOT WORKING, WHAT IS BACK UP PROTECTION IN TR. 13. WHAT IS PURPOSE OF NGR AND HOW STANDBY E/F RELAY WORKING, TESTING PRECAUTIONS IF COMMON NGR IS USED. 14. WHAT IS PROTECTIVE ZONE OF STANDBY E/F RELAY. 15. WHAT ARE PROTECTION AVAILABLE FOR FEEDER. 16. AFTER TR. IS NORMALISED, WHAT CURRENT TO BE MEASURED. 17. BUSBAR PROTECTION: a. BASIC PRINCIPLE AND DIAGRAM WITH CURRENT DIRECTION. b. WHY OVER LAPPING CT’S REQUIRED, IF NOT WHAT WILL BE THE EFFECT. c. WHY CT SUPERVISION REQUIRED, HOW TRIPPING IS AVOIDED, WHAT IS CT SUPERVISION SETTING VALUE. d. HIGH IMPEDANCE & LOW IMPEDANCE TYPE e. TEST PROCEDURE(STEP BY STEP) f. AFTER NORMALISING, SPILL CURRENT VALUE AND LIMIT. Relay Page3of5 18. CIRCUIT BREAKER FAILURE – FUNCTION, WHY NEEDED, HOW TRIPPING ARRANGEMENT. 19. WHY INSTANTANEOUS ELEMENT IS NOT USED IN THE NETWORK. 20. WHEN FEEDER IS LIVE AND BY MISTAKE LINE EARTH SWITCH IS CLOSED, WHICH RELAY OPERATES – O/C OR E/F. 21. DURING TR. SWITCHING ON, IF DIFF. RELAY IS BLOCKED BY 2ND HARMONICS, WHAT ARE THE OTHER PROTECTION IN SERVICE. 22. WHICH OF FOLLOWING PROTECTION OPERATES FAST, WHEN 11KV CABLE COMPARTMENT GET FLASH OVER: CABLE DIFFERENTIAL; OVERCURRENT & EARTH FAULT; ARC PROTECTION. 23. WHICH PROTECTION OPERATES WHEN ANY ONE OF THE OHL PHASE IS CUT AND HANGING, NOT TOUCHED WITH EARTH. 24. WHAT ARE DIFFERENT TTB ALARMS – HOW YOU KNOW THERE IS ANY ALARM. 25. WHAT IS CIRCULATING CURRENT AND HOW IT WILL COME. 26. IF ONE TR. TRIPPED ON DIFF. RELAY WHAT YOU WILL DO. 27. IF SUB-STATION TRIP ON BUSBAR PROTECTION, HOW YOU WILL RESTORE. 28. WHAT IS CT SATURATION. HOW IT IS CARRIED OUT. 29. D.C EARTH FAULT – HOW YOU WILL FIND OUT. Relay Page 4 of5 30. PILOT WIRE SUPERVISION – HOW IT WORKS 31. IN 11KV SWITCHGEAR DBB SCHEME, ONE E/F RELAY IS FAULTY IN ONE FEEDER AND THERE IS NO SPARE FEEDER – HOW YOU WILL NORMALISE THE FEEDER. 32. WHICH PROTECTION IS USED FOR LONG CABLE FEEDER 33. DIFFERENCE BETWEEN TRAFO. DIFF. AND CABLE DIFF. PROTECTION. 34. WHAT TYPE CHARACTERISTIC AVAILABLE FOR O/C AND E/F RELAY. 35. WHAT IS THE DIFFERENCE BETWEEN STATIC AND ELECTRO- MECHANICAL O/C RELAYS. 36. WHAT IS DEAD ZONE 37. HOW TRIPPING OF OTHER ZONE AVOIDED WHEN BUS SECTION CB IN OPEN CONDITION FOR DEAD ZONE FAULT. 38. IF OUT OF STEP ALARM COMES WHILE ALL TR. IN SAME TAP POSITION, WHAT YOU WILL DO. 39. WHAT YOU WILL DO IF AN 11KV FEEDER FAILED TO TRIP ON: O/C or E/F or SOLKOR. HOW YOU RESTORE THE SUPPLY. Relay Page 5 of5

2 Answers   KSEB, Siemens,

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