Study on Development Characteristics of Partial Discharge in Oil-Pressboard Insulation under Constant DC Voltage

The converter transformer is the core equipment of HVDC transmission system, valve-side winding which needs to withstand DC voltage. Partial discharge one main threats safe operation transformer, yet characteristics partial development oil-pressboard insulations under constant voltage are insufficiently understood. In order better understand insulation and provide deeper theoretical support for diagnosis transformers, including time-varying tendency magnitude repetition rate in positive negative were studied. results indicate that a needle-plane model has three stages: intensive discharging stage, silent-burst breakdown stage. Throughout all stages, first decrease increase afterwards. At appears form “cluster” with very large rate. Each cluster exists tens seconds but at long interval each other. Further analysis shows repeated accumulation dissipation free charges on surface pressboard cause above phenomena. Negative easy accumulate difficult dissipate same amplitude compared charges, leading weaker actual electric field needle tip thus discharges lower longer interval.