Remote detecting and locating partial discharge in bushings by using wideband RF antenna array

It is bushing that performs an essential function in power transformer. Since the existing on-line partial discharge (PD) test methods for bushings require the current from the test tap, it is difficult to be applied to in-service bushings, especially to some old bushings without voltage taps. In order to detect PDs without changing grounding circuit, a novel non-contacting on-line approach to detecting and locating PDs in bushings using time delay of arrival (TDOA) of radio frequency (RF) antenna array signals is proposed in this paper. Based on a real 126 kV oil-impregnated paper (OIP) condenser bushing, four typical PD defect models were made, which were suspended discharge on bushing's top cap, poor connection in bushing tap, surface discharge on oil-side porcelain insulator and suspended discharge near the oil-side grading ring. The detection and location of PDs induced by these defects were carried out and different features were obtained. For the defects of suspended discharge on bushing's top cap and poor connection in bushing tap, this approach gives good location accuracy and the error is less than 20 cm. For the defects inside the bushing housing, the RF signals generated from PDs still can be detected and located, but the calculated location results are all focused around the bottom of the air-side porcelain insulator. In order to reveal the test results, the propagation of electromagnetic (EM) waves in the bushing housing was simulated, which indicated that the coaxial gap between the condenser core and the fixing flange allows various modes of EM waves to propagate with a attenuation from 40 to 60 dB. In the on-site tour-inspection tests, a real PD fault in an 110kV cable terminal bushing was located in a substation, which verified the availability and effectiveness of this approach.