Propagation and localisation of partial discharge in transformer bushing based on ultra-high frequency technique

As an essential component of power transformers, the detection and diagnosis of incipient partial discharge (PD) activities of bushings are of great significance. A 35-kV oil-impregnated paper (OIP) bushing is investigated. The bushing is modelled by coaxial theory and electromagnetic (EM) simulation. As the paths of PD-induced ultra-high frequency (UHF) signal propagating in the bushing are OIPs and oil gap, small attenuation during signal propagation is seen. Since OIP is composed of heterogeneous media compared with pure oil, there will be relatively less UHF signal leakage from OIPs, whereas more leakage from the oil gap. This leakage provides the possibility of non-contact detection outside the bushing by UHF method. PD measurements with UHF method are carried out on the bushing. Then, the minimum energy method is used to extract time-difference-of-arrival (TDOA), and Chan algorithm is adopted to locate points of UHF signal radiation. High accuracy locating with a small error of 15 cm has been achieved. The contactless UHF method-based tests have demonstrated the effectiveness of online monitoring and locating of bushing PD.