Novel Diagnosis Criteria for Moisture Defect of Oil-paper Bushing Based on High Voltage Frequency Domain Dielectric Spectroscopy

As we all know, the excess moisture in oil-paper insulated bushing is the main factor that causes insulation failure, and the commonly used diagnosis method for this is the frequency domain dielectric response method. However, most of the conventional dielectric spectrum data is measured at a voltage below 200 V, which is susceptible to environmental noise interference during field testing, resulting in larger measurement errors. So this paper designs a high-voltage frequency domain dielectric spectrum measurement device for wetting degree diagnosis of oil-paper insulated bushings. Based on the self-developed measurement platform, it is found that, the dielectric spectrum data of the dry bushing model does not change significantly with the increase in voltage; while the dielectric spectrum curve of the wetting model moves up significantly. Moreover, the rate at which low-frequency dielectric loss increases with voltage is positively correlated with the moisture content in the paper. Besides, for local moisture defect conditions, traditional dielectric analyzers may not be able to provide accurate diagnostic information of insulation defects, but the high-voltage dielectric spectroscopy technology can make its unique contribution.