S&C Trans-Rupters
S&C Trans-Rupters
(OP)
Our Main Substation transformers (15MVA, 69kV/12.47kV)have S&C Trans-Rupters with overcurrent protection on the 69kV side. What would be the best placement for the CTs used with the overcurrent relays: on the line side of the Trans-rupters or on the load side of the Transrupters.






RE: S&C Trans-Rupters
RE: S&C Trans-Rupters
That said, it is all too common that transformer protection is done using just the CTs on the transformer bushing because there is no place to put CTs on the line side of the interrupting device. But where it is at all practical to do so, CTs should always be placed such that the interrupting device is in the zone of protection.
RE: S&C Trans-Rupters
CT just defines the zone you want to protect. As it is in case of Transrupter self powered relay is used the Ct is used as supply source and will be after breaker
RE: S&C Trans-Rupters
RE: S&C Trans-Rupters
However, if you use the transformer BCT's, the zone of protection will not include the high side transformer bushings. But I would presume the high side (line) is protected by a distance, or over current type of protection.
Consiter this: The cost of a breaker with BCT's isen't that much more than a transrupter with an added free standing CT. So if your goal is to cut cost, use the transformer BCT's with the transrupter. However, if your goal is to reduce outages, install breakers.
RE: S&C Trans-Rupters
The only protection that the Trans-Rupters now have are the protective relays at the Utility substation where our two 69kV lines are fed from; that is why I think Mr. Beach is strictly correct: The interrupting device should be in the zone of protection. Why subject the interrupting device to fault currents waiting for the Utility protection to kick in?
RE: S&C Trans-Rupters
If the fault is temporary, having the separate CTs will result in an unnecessary trip of the Trans-Rupter. If the fault is permanent, not having the CTs will result in an unnecessary permanent trip of the line.