How to Diagnose and Analyze Faults of 500kV Power Transformer

Abstract: A short circuit fault of 500kV transformer is detected. An in-depth investigation into transformer transportation, installation and operation status is carried out. Moreover, Field fault diagnosis and simulation test have been conduced to conclude that short circuit fault occurs in the internal transformer. Hanging-cover inspection after returning to the factory confirms that the fault is turn-to-turn short circuit of low-voltage side, which is directly caused by water in transformer oil.   

Key words:  500kV voltage grade, power transformer, fault diagnosis, investigation and analysis    

Introduction

Failure of main transformer in 500kV substation will pose a great threat to safe operation of power grid, causing severe consequences. It is relatively difficult to diagnose the fault and takes longer time to maintain. The model of 500kV main transformer in some substation is ODFPSZ-250MVA/500kV. The test object is single-phase self-coupling transformer with  non-directed oil-forced cooling. Rated voltage is 525/230±9×1.33%/63kV. It was produced in August 2005, and was put into use in March 2006. On June 9 2012, there was something wrong with W-phase of this transformer. Main transformer heavy gas action occurred; the breaker of primary side operated with that of secondary side; main transformer stopped operating. When the transformer broke down, light gas protection of main transformer also sent out alarm signal.