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This paper proposes a method to localize multiple partial discharge (PD) sources in air-insulated substation by using radio frequency (RF) antenna sensors combining with clustering algorithm, which solves the problem that multiple PD or interference sources are difficult to localize in air-insulated substation (AIS). Our research group made four omnidirectional RF antenna sensors, the detection frequency band was 250 MHz-3 GHz, the voltage standing wave ratio (VSWR) of the RF antenna in the detection frequency band was less than 2, which meets the detection requirements. The scenes of multiple PD sources in AIS were simulated in the laboratory, the time difference of arrival (TDOA) was collected through four RF antennas, and the clustering effects of K-means and Two Step algorithms were compared. Based on the normal distribution characteristics of TDOAs and the better Two Step algorithm, a $3\sigma $ -Two Step algorithm was proposed to process TDOAs and output the centers of TDOAs. Newton iterative algorithm was used to solve the localization equations. The results show that the average localization error of two PD sources was 0.21 m and that of three PD sources was 0.45 m. The PD localization tests were carried out in an actual AIS in China, the proposed method localized a corona discharge on a post insulator and a corona discharge on a disconnector. Through the verifications with an ultraviolet camera, it was obtained that the localization errors at each position were within the range of 0.6-2 m. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Diffraction of Ultra-High-Frequency (UHF) electromagnetic waves generated by partial discharges (PDs) inside a transformer will decrease the amplitude when passing through the winding and delay the arrival time of initial wave at the UHF sensors installed on the internal wall of the tank. It may be difficult to locate PDs inside the winding based on detection of UHF signals. To study the feasibility of locating PDs inside the winding using UHF methods, the propagation of UHF wave through windings was simulated by the XFDTD software and the cause of arrival time delay was analyzed by a geometric model. Experiments were carried out on a 220 kV oil-immersed transformer to test the measurement sensitivity and the location accuracy of UHF method for PDs inside windings. The theoretical research results indicated that the UHF wave passed through windings along broken lines, and the propagation time from the PD source to UHF sensors was compared to the time of wave travelling along a straight line. It was found that the arrival time delay caused by diffraction was less than 1ns. The experimental results showed that PDs about 500 pC inside the windings could be detected and located. The amplitude of the UHF signal decreased by about 18 dB, the errors of time difference measurements were less than 0.5 ns, and the location errors were less than 0.1 m. [ABSTRACT FROM AUTHOR]