This article describes how a drastic failure of a machine is caused by insulation collapse which results heavy interruption as well as losses. The stable operation of a generator mainly depends upon the stator winding insulation. In past, various testing and repairing techniques have been applied in order to analyze the insulation life. However, in this context, a complete stator windings insulation analysis have been carried out by testing and monitoring techniques such as insulation resistance, di-electric absorption ratio, polarization index before repair and after rehabilitation work, ac & dc high voltage, dc resistance test of winding coils, as well as surface potential test, no-load test and short circuit test. It basically reflected the insulation life of stator winding and helped to take remedial measures. This research techniques will pave the way to overcome such failure in machine and recommended the interval based tests for safety purpose.