Location of electrical discharges in power transformers

The discharge activity of a transformer in service may be temperature or voltage dependent or may be initiated by a switching surge or a change of tap position. These and other parameters give the impression of time dependence. Therefore, it is necessary to monitor the activity over a period of time. In order to monitor discharge activity within a transformer whilst in service the ultrasonic output of an electrical discharge is detected by an ultrasonic transducer mounted on the outside of the transformer tank. A system has been developed which utilises commercially available acoustic emission equipment and can monitor the signals from fourteen ultrasonic transducers over a period of days with a resolution of 250 nanoseconds. The author describes the system and its operation