Differential Realy operation 1

[prc]

One 63/31.5/31.5 MVA 220/7/7 Kv transformer star/star/star station start up transformer was charged from 220 Kv and kept under no-load for observation.After 28 hours transformer tripped on differential with HV lines showing 43 A in all phases (all currents in phase and not 120 out of phase) and neutral CT showing 134 A.ABB RET 670 .Current started rising in all phases 75 millisecond prior to faulttripping.Transformer,on testing,seems to be OK.Relay connections etc seems OK.

What can be the reason for such a tripping?

 

[slavag]

Hi PRC.
Ufff, Dificult say something w/o set-files and configuration and test report of stability.
First reason what I see. Values what you wrote is signed on the (43x3=134A ) external earth fault and it closed via neutral of your transformer.That means, it show mistake in the setting, not taked in account I0 elimanation or Y/Yn group.
Best Regards.
Slava.
Level of current show --isn't internal fault.

 

[slavag]

Hi PRC.
Please find attached file.
Please ask commissionings guys about those parameters.
ZCcurrSubtrW1/W2/W3, I suggest someone puted W1 in off.

 

[davidbeach]

prc, can you post the relay event files, preferably in COMTRADE format?