Development of a continuous on-line partial discharge monitoring system for medium voltage motors

There is an apparent need to provide continuous, as opposed to periodic, on-line PD monitoring for medium voltage motors because the time-to-failure from the appearance of relatively low PD activity may be much shorter than for high voltage machines. From the cost-benefit perspective, two developments have made the prospect of developing such a tool attractive. First, utilities are operating in an increasingly competitive market. Thus, the loss of a medium voltage motor running, for example, a boiler feed pump, can lead to the loss of a generator with the adverse financial consequences which ensue. For process industries, which tend to have lower redundancy than utilities, the consequences of motor failure can often result in complete loss of production. Second, rapid developments in the electronics industry now permit construction of inexpensive instruments which have the speed and processing power necessary to implement a continuous, reliable and cost effective PD monitoring device. The paper describes the development of such a device and its application on medium voltage motors.