Power transformer 2

[redlinej]

Hi guys,
The power pant that I work at have two outgoing feeder,which feeds two power transformer 11 KV to 69 KV. The 11 KV breaker that feeding these transformer are interlock, so at no time both of they cannot be in service at the same time.which I understand because of recirculating current and protection issue, however I recently visited a power plant that have two power transformer same voltage but they are in parallel.This this is confusing to me for protection issue and recirculating current problem.can some one explain how this is possible.

 

[mgtrp]

Often, the two transformers and associated cables etc are near enough to the same in impedance and ratio, and the impedance is large enough, that any mismatch current is relatively small and therefore insignificant. Another concern that sometimes prevents parallelling is that having both feeders in service would result in fault currents that exceed the rating of the switchgear.

 

[tinfoil]

Have a read through
Link

 

[redlinej]

Thanks Mgtrp and Tinfoil for the info.