Partial discharges within power transformers and the use of ultrasonic techniques in their location

A power frequency partial discharge (PD) within the insulation structure of a power transformer (e.g. within a cavity or an inclusion) is generally regarded as being the instantaneous breakdown of a small capacitance which forms a part of the insulation capacitance as a whole. This discharge creates a short current pulse which is repeated every time the small capacitance is recharged to a level sufficient to create local breakdown. Associated with the partial discharge is an ultrasonic pulse. The author describes a technique using ultrasonic transducers to locate the pulse and hence the source of the partial discharge