Tripping of transformer due to abnormal noise during re-commissioning – An experience

In India, bulk power is transmitted from one grid to another through 400 kV AC lines. The 400 kV-class transformer, installed in 400kV sub station, plays a vital role in delivering power to the various utilities. Outage of any 400kV class transformer will lead to disruption of power flow. It is, therefore, very much essential that the operation of transformer is reliable and trouble-free. A 315 MVA 400/220/33 kV transformer, first commissioned in January 1991, was operating satisfactorily till 2001. High concentration of fault gases was observed in DGA result of October 2001. Details of DGA result monitored from October to December 2001 are given.