Transformer Overload Sectionalizing Scheme

Provide the engineering for a new transformer overload sectionalizing scheme. The scheme was designed to provide relief of a 345kV / 138kV transformer during overload conditions. It was accomplished by the automatic isolation of one transformer from another parallel 345kV / 138kV transformer as well as transmission lines connected to an adjacent 138kV bus.


The scheme required the installation of redundant (System 1 and System 2) relaying systems utilizing the overcurrent functionality of a Schweitzer microprocessor relay for each system. The relays were set to detect an overload (overcurrent) condition of 500MVA on the transformer. When 500MVA was met or exceeded on the transformer, each system’s relay would trip a normally closed 138kV bus-tie circuit breaker and close a normally open 138kV bustie circuit breaker.

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