Identification of simultaneously active PD sources using passive comparison of UHF signals

This paper reports on the development of UHF sensor arrays for partial discharge (PD) detection and location within high voltage electrical components such as power transformers and switchgear. The technique outlined is based on the linear combination of signals radiated from the discharge site and measured at each array element. Since the arrival times and signal characteristics at each respective array element are dependent on the position of the PD within the system under test, a passive linear combination of signals has the potential to provide some information unique to the PD location. By this means it should be possible to identify whether multiple PD sources are simultaneously active within the system. The performance of two arrays - a monopole array and a new double spiral array - was compared by plotting the energy of the combined signals from the array elements at various positions within a test tank. A contact discharge test cell provided a repeatable source of PD. It was found that greater variation in the sum and difference channels between array elements occurs when the monopole array is used. It is therefore more likely that the presence of multiple PD sources can be successfully identified using this configuration. Advantage of the technique include its ability to be implemented using relatively inexpensive hardware and that subsequent analysis of PD data by conventional means would not be hampered by the superposition of data from than one PD source.