A system for the detection and location of partial discharges using X-rays

A measuring system has been designed which has an enhanced ability to detect partial discharges (PDs) and locate their origin in large epoxy castings. The enhancement is primarily based on the application of X-rays during high voltage testing, which reduces the apparent inception voltage and increases the pulse repetition rate. A high PD signal-to-noise ratio is achieved by using a combination of several techniques, including; a differential (balanced bridge) measuring scheme: detecting PD in the GHz frequency range; use of a lossy transmission line between the power supply and the test specimen to attenuate external noise; and modulation of the X-ray beam. The PD sites are located by scanning the X-ray beam. The system can test 138-kV-class epoxy spacers used in gas-insulated switchgear (GIS). Test voltages up to 500 kV can be achieved with a reliable PD sensitivity of less than 0.1 pC in a typical industrial environment.<>