Moisture State Diagnostic Analysis for Epoxy-Resin Impregnated Paper Bushings Based on High-Voltage Dielectric Spectroscopy

The valve-side bushings of converter transformers play a critical role in the connection between converter transformers and valve halls. The epoxy-resin impregnated paper (ERIP) as the main insulation form of valve-side bushings determines their safety and reliability in power energy transmission. However, the valve-side bushings operate in extremely harsh environment of the coupled electrical, thermal, mechanical, and ambient stresses. Notably, the moisture as strong polar substances poses a significant impact on accelerating the degradation and increasing the failure risk for ERIP insulation systems. Therefore, this study investigates the influence analysis of moisture states on the insulation characteristics of ERIP bushings based on high-voltage dielectric spectroscopy. Firstly, the preparation method of ERIP bushings with different moisture states and the high-voltage dielectric spectroscopy measurement setup are analyzed. Subsequently, the influence behaviors of different moisture states and measurement voltages on dielectric spectroscopy are discussed for ERIP bushings. Finally, the diagnostic method and its potential challenges for ERIP bushings are discussed. This study provides a solid basis for diagnostic and assessment of moisture state in ERIP bushings.