Improvements in Revealing differential Transformer to protect against internal faults

摘要

A transformer differential relay which includes apparatus for speeding up the detection of a power transformer internal fault condition to initiate breaker action which interrupts current through the transformer is disclosed. Presently, conventional transformer differential relays include a unit for each phase of the power transformer for detecting a potential internal fault in a respective transformer phase winding and for generating a signal to operate a set of breakers. This breaker operation is inhibited for current inrush conditions of the transformer. However, a processing time is associated with the detection of such a current inrush condition. Accordingly, the breaker operating signal must be delayed for at least this processing time in order for the inhibition to be effectuated. For the case in which there is no current inrush condition, the breakers remain delayed in operation from the inception of a true internal fault. The aforementioned speed-up apparatus circumvents this time delay in breaker operation and renders breaker initiation for detected internal faults with response times on the order of 3-5 milliseconds. In addition, the speed-up apparatus is inhibited from responding to potential internal fault conditions which may arise from initial inrush or recovery inrush current conditions or an external fault condition with severe current transformer saturation.