Study on the joint time-frequency characteristics of the ultra-wideband partial discharge signals of the generator bars

The characteristics of the ultra-wideband partial discharge of both the stator bar of 300 MW turbo-generator out of service and the stator bar of 780 kW electromotor out of service are studied by using the developed ultra-wideband partial discharge detecting system. With the help of the joint time-frequency analyzing technique, the time-frequency characteristics of these samples are qualitatively analyzed. The results show that a partial discharge signal includes many impulses on which there are many small pulses, and the high energy density area of the partial discharge signal of the bars moves to the higher frequency after aging. The characteristic peaks of the straight part and R part nearly appear in the same place. The new method is proved useful for evaluating the insulating remnant life.