Research on Fault Diagnosis of Oil-Paper Insulated Bushing Based on Frequency Domain Dielectric Spectrum

As an important component of power transformer, transformer bushing cause thirty percent of transformer accidents. It is difficult to find defects in transformer bushing in advance because of the lack of on-site inspection methods. Frequency domain dielectric spectroscopy is widely used in the field of insulation evaluation of electrical equipment because of its frequency bandwidth and rich information. However, the frequency domain dielectric spectroscopy in the inspection of oil-paper insulated transformer bushing is affected by lacking substation test case and diagnostic criteria. In this paper, a dielectric response model of the transformer bushing is established to reveal the different defect types corresponding to the test curves in different frequency bands. In the low frequency band which is less than 0.0lHz, it is reflecting the water content of bushing. In the middle frequency band which is between 0.0lHz to 100Hz, it is reflecting the aging of bushing. Several cases of substation bushing defects detected by frequency domain dielectric spectroscopy have verified the above results. It is difficult to propose uniform fault diagnosis criteria for the frequency domain dielectric spectrum of transformer bushing which is affected by the structure and type. Based on a large number of substation case studies, a defect diagnosis criterion based on Fréchet similarity method is proposed in this paper, which is universal for different structures and different types of bushing.