An assessment of insulation condition for generator rotor windings

Shorted-turn in a generator is scarcely happened, however, it expands severe failure such as vibration increase, performance reduction and power limitation by deteriorating winding insulation of generator rotor. In this paper, we experimented shorted-turn detection test in gas turbine generator of Pyungtaek combined cycle power plant, and investigated the patterns of each results and try to extensively notify the merit of this on-line test. The on-line shorted-turn test was conducted using a permanent flux probe and on-line shorted-turn diagnosis system. The permanent flux probe installed in the generator air gap senses the field winding slot leakage flux and produces a voltage proportional to the rate of change signature unique to each field winding. We have also applied a voltage waveform analysis technique that can identify the pole location, slot number and number of shorted-turn with each slot.