Power transformer is one of the critical equipment in power system. The transformer insulation diagnosis can be done by winding resistance test, dissipation factor test, dielectric absorption index, polarization index and through core insulation test. 765/400 kV, single phase, Inter connecting Transformer, 500 MVA, have fed fault current of 16 kA for 50 ms to 400 kV side due to fault in transmission line during lighting. After occurrence of fault, identification of incipient fault inside transformer has been done through DGA analysis. Many times, incipient faults were identified through DGA analysis. This paper highlights one of our experience in saving 765/400 kV, 500MVA power transformer from a major failure by carrying DGA analysis immediately after feeding high fault current.