SPAJ 140C Relay Tripping

Dear Friend

Primary current & surge current of 500 kVA transformer is twice that of 250 kVA transformer, assuming even the transformer % impedance is same for both.

Thus pls. check current settings of the relay. I donot know anything about SPAJ 140 relay & hence cannot comment on its suitablity for 500 kVA transformer.

Thanks and regards

Ashok Toshniwal, Bangalore, India

Two possibilities:

- magnetizing inrush current is doubled -> instant tripping after transformer is powered.

- your load amperage has risen -> overcurrent relay tripping is set too low

Solution: Check your overcurrent relay settings to correspond new transformer.

As stated in one of the replies; all of the primary current dynamics would double when replacing a 250KVA unit with a 500KVA unit. If your relay settings have been changed accordingly and verified by testing to be correct (including the time curve) then you need to look at the many other probable causes.

Have you tried energizing the transformer without the secondary connected to eliminate the possibility of excessive secondary loading?

Are you sure that the time curve is adequate for meeting the inrush demand?

Have you performed a Turn-to-Turn Ratio (TTR) Test on the transformer to verify the windings?

Have you performed a Doble and/or HyPot test on both the primary and secondary winding to check for faults other than grounds?

Reputable electrical testing vendors also have the capability of performing a surge test on your equipment that will identify any shorting between winding conductors and phase-to-phase faults. The cost is very reasonable when compared to unit replacement and it will establish a good "basepoint" for future testing reference.

I suspect that the relay just needs adjusting to accommodate your new transformer. Your transformer may have a higher leakage than your previous unit. See http://www.abb.com/product/db0003db004281/c12573e700330419c225695f003ae92b.aspx for a list of literature for this relay. You might find the answer to your problem here.