Quantifying the Gas Generation Rate at the PD Evolution Stages in an Oil-Paper Insulating System

Abstract

Partial discharge (PD) in oil-paper insulation would destroy the hydrocarbons of insulating oil, and therefore generate characteristic gases (e.g., H₂, CH_4, and C₂H₂) for fault diagnosis. Modeling the quantitative relationship and elucidating the reaction mechanism of gas generation rates at PD evolution stages plays a significant role in accurately evaluating fault severity. In this work, we present experimental detection methods for dissolved gas and free gas from surface discharge in an oil-paper insulating system. The evolution of discharge characteristic parameters and gas generation rates across varying discharge stages is investigated, and mathematical models and critical thresholds for gas generation rates in relation to discharge amplitude and discharge energy are proposed. The correlations between gas generation and surface discharge intensity are further elucidated. The results reveal that no gas was generated at a low discharge amplitude, with initial gas generation occurring at thresholds of 420 pC and 1.6 J/h, followed by an exponential increase with increasing discharge severity. Furthermore, the quantitative analysis reveals that the gas generation rate follows an S-shaped correlation with the discharge energy while demonstrating a linear relationship with the discharge amplitude. The errors of the verification experiments for the quantitative relationships are less than 15%. Owing to distinct reaction mechanisms and energy requirements, severe PDs promote the conversion of generated C₂H₆ and C₂H₄–C₂H₂ and H₂, which are primary indicators for dissolved gas analysis (DGAs) and free gas analysis during severe discharge, respectively.