Analysis on 2nd Main Transformer Trip Accident of a Certain Substation of the West Inner Mongolia Power Grid

Abstract

This paper mainly analyzes the causes of a 10KV line and 2nd transformer circuit breaker tripping, also analyzes the action mechanism of the relay protection. Because of the permanent phase fault at the head of the line, instantaneous over-current protection(SegmentⅠ) as its main protection of the phase fault made the 921 breaker triping, the action was selective.And the permanence of this fault led to the failure of the reclosing; Reversed the TA(current transformer) for measuring with the TA for differential protection in high voltage side of the transformer, this fault can also make the TA of the differential protection circuit quickly saturated when the external short-circuit current flowing through the TA. When the above saturation happens, a big differential current generating from differential circuit will lead to sampling error. This is the direct cause of the mal-operation of the differential protection which resulting in the 2nd transformer tripping. In response to this accident, put forward specific prevention measures.