A Novel Fabry-Perot Sensor Mounted on External Surface of Transformers for Partial Discharge Detection

The extrinsic Fabry-Perot interferemeter (EFPI) sensor for the detection of partial discharge (PD) in power transformers was mounted inside the oil, to receive the mechanic wave by diagram. This would limit the application. Especially, in gas insulated switches (GIS), the high frequency acoustic wave could propagate effectively in the solid of the shell tank instead of inside gas in which high frequency acoustic wave was attenuated fast. This paper proposes a novel method to detect partial discharge (PD) in power transformers using an extrinsic Fabry-Perot interferemeter (EFPI) sensor. An EFPI sensor was creatively designed to mount on the outside steel surface of the oil tank inside which partial discharge happened in oil dielectrics. Results of finite element simulation method (FEM) predicate that the vibration of diagram was excited by the frame stress, which was generated by PD caused acoustic wave propagated in steel of the tank. Main resonance frequency of the surface mounted sensor was 108 kHz by experiment which agreed well with the simulating result. Experimental study also shown that under 90pC and 120pC PD levels have the similar sensitivity of the newly designed sensor with the earlier one used in insulation oil was gained.