transformer protection

Please consider Differential Protection for the transformer.

hi,

For delta side we should connect CTs in resudal mode & in star CTs should in restricated E/F mode ( One CT in Neutral).

REF will work only for Trafo. internal fault only

Hope it will help

tadagids

Two different froms of protection shall be considered:

1)as already mentioned, to read the residual current in the neutral of the transformer

2)to connec a differential protection in a connection named earth differntial protection. In this kind of connection, the relay will be connected in the neutral connectionto earth of the phase current transformers and the other side to the current transformer connected to the wye of the power transformer.

If you only use the regular differential protection, this will not be able to detect a phase to ground fault.

Your neutral is grounded through resistor to limit ground to earth fault current. To protect your down stream network, you should use GFCI " Ground fault current protector". This is used in two different ways. (1) If your distribution is 3ph, 4 wire system, all 3 phases and neutral are passed through one CT. CT functions as resultant current detector and which is zero at all the time except ground fault. Normally, settings are in the range of 4ma to limit touch voltages to safe level. (2) The another method is using one CT on grounding conductor. Whenever there is a ground fault on down stream distribution, ground current will return path through grounding resistor and back to transformer. In this case, CT will detect fault and trip breaker.

I think this is enough for your question.

Overall Differential protection normally used for >5MVA trafo. Use 51N on upstream line side, 51NT at neutral as standby to 51N and co-ordinate. 64R (REF) for trafo internal fault. This is a bit conservative design and used in many power stations in India.