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ANANDANRCR
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Join Date: Mar 2014
Posts: 19

Station Transformer, 220kV / 6.9kV - Tripping

05/05/2014 12:09 AM

RESPECTED FRIENDS,

WE HAVE INSTALLED 50 MVA 220 KV / 6.9 KV STATION TRANSFORMER WHICH HAS 2 WINDINGS IN LV SIDE AND LV1 6.9 SIDE BREAKER HAS TRIPPED DUE TO NEUTRAL DISPLACEMENT RELAY ACTION BECAUSE OF 6.9 KV CABLE FAILURE . WE HAVE TR. DIFFERENTIAL RELAY PROTECTION ALSO FOR THIS TRANSFORMER . OUR QUESTION IS WHY ONLY NEUTRAL DISPLACMENT RELY IS ACTING AND WHY NOT TR. DIFFL. RELAY.

PLEASE REPLY EARLY

WITH REGARDS
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lyn
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#1

Re: STATION TRANSFORMER , 220 kV /6.9 kV - TRIPPING

05/05/2014 12:16 AM

WHY DID THE CABLE FAIL?
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ANANDANRCR
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Join Date: Mar 2014
Posts: 19
#5
In reply to #1

Re: STATION TRANSFORMER , 220 kV /6.9 kV - TRIPPING

05/05/2014 6:02 AM

SIR,

BECAUSE THE CABLE TRENCH AND CABLE TRAYS WERE DAMAGED...
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lyn
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#8
In reply to #5

Re: STATION TRANSFORMER , 220 kV /6.9 kV - TRIPPING

05/05/2014 10:21 AM

i GIVE UP!

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RAMConsult
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Engineering Fields - Power Engineering - New Member

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#2

Re: STATION TRANSFORMER , 220 kV /6.9 kV - TRIPPING

05/05/2014 12:24 AM

Was the fault inside the transformer? Why would you expect the transformer differential relay to act on a fault that is outside of its protective zone?

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ANANDANRCR
Active Contributor

Join Date: Mar 2014
Posts: 19
#3
In reply to #2

Re: STATION TRANSFORMER , 220 kV /6.9 kV - TRIPPING

05/05/2014 5:58 AM

Sir,

THE FAULT IS NOT INSIDE THE 220 Kv/ 6.9 kV TRANSFORMER, BUT IT IS IN THE CABLES FROM TRANSFORMERS LV SIDE TO SWITCHGEAR AND DIFF CT'S ARE COVERING TRANSFORMER AND ALSO CALBES. PL. CLARIFY HOW DIFF RELAY NOT OPERATING...?

WITH REGARDS..
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RAMConsult
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#7
In reply to #3

Re: STATION TRANSFORMER , 220 kV /6.9 kV - TRIPPING

05/05/2014 10:08 AM

Are the settings coordinated? Look at the pickup times and settings for each relay and report back.

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TonyS
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#4

Re: STATION TRANSFORMER , 220 kV /6.9 kV - TRIPPING

05/05/2014 6:02 AM

The facts seem to point to some shorted windings in the transformer caused by the cable failure.
You've two faults to sort out.

Good luck.

PLEASE DON'T SHOUT!

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DmanEng
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Join Date: Apr 2011
Location: KCM, chingola; copperbelt; zambia; southern africa.
Posts: 75
#6

Re: STATION TRANSFORMER , 220 kV /6.9 kV - TRIPPING

05/05/2014 6:45 AM

how can you have it trip on differential when you have neutral earth composater? differential just compares the current value between the loads and incomer. if you want it to be tripping at the same time and faults, then change the plug settings and the relays should be using same CT ratios or inter trip of some kind. as far is understand the systems to operate, it will be giving new sense trips, because in differential the toralance is high, while in neutral earth its very minimal.

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ANANDANRCR (2); DmanEng (1); lyn (2); RAMConsult (2); TonyS (1)

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