A Modern Approach to Differential Partial Discharge Diagnosis on Instrument Transformer

In this article, a new approach to measuring differential electrical partial discharge is presented. A computer-controlled measuring bridge is combined with a digital partial discharge measuring system. Partial discharge signals decoupled with two conventional measuring impedances, are balanced and subtracted within the measuring bridge. Since partial discharge events occur as differential-mode signals within the circuit, while disturbances from the voltage source or from ground occur as common-mode signals, the difference interpretation of the signals can lead to an improvement in the signal-to-interference ratio. The measuring bridge and the acquisition unit of the measuring system are battery operated and are controlled via fiber optics. Therefore, the measuring device itself shows a low sensitivity to interference. In addition, the setup can be combined with a power loss factor measuring system. A combined measurement and test can thus be carried out. Since the measuring bridge is computer-controlled, the measurement data are used for the semiautomatic parameterization of the measuring bridge. The parameters of the bridge are calculated according to the frequency setting of the partial discharge filter. This method demonstrably leads to a user-friendly and time-saving workflow. Using the described approach, efficient noise suppression of partial discharge measurements can also be achieved in asymmetrical structures.