The process of creeping discharge-caused damage on oil/pressboard insulation

Abstract

This paper presents experimental research on creeping discharge by using cylinder-plate electrode configurations under AC voltages. The process of creeping discharge-caused damage on the oil/pressboard insulation was studied. First, the electric field distribution was achieved by Multiphysics software simulation. Afterwards, the phenomena that occurred in the entire damage process, such as "white smoke", "white mark", and "black mark", were recorded and analyzed. Furthermore, the micromorphology of the oil-impregnated pressboard was observed via scanning electron microscope (SEM). Finally, the inner mechanism of the damage to the oil/pressboard insulation was explored according to the phenomena and the SEM morphologies. Results showed that during damage processes, the high electrical field strength (nearly 25.853 MV/m) at the weak-link point between the cylinder electrode and the pressboard directly caused the incipient discharge. The cavity, moisture, impurity, solid particle, and formation of a gaseous channel all contributed to the development of the damage. The "white smoke" consisted of gases that stemmed from the ionization of oil and evaporation of moisture. The "white mark" was the gas channel and pressboard carbonization was caused by discharge and high temperature, both of which were also the main causes of the emergence of "black mark". SEM images revealed that the pressboard successively experienced "white solid", "crack", and "pitting", which changed its surface roughness. The distorted electric field caused by gases, solid particles, and pitting further damaged the oil/pressboard. The pitting evolved into the starting point of the electrical trees and gradually led to the final breakdown.

Experimental Investigations Performed on Surface Discharges at oil-pressboard Interface: An Overview

“…These PDs are stable only for a short duration but creates rapidly growing carbon traces. The carbon deposited on the pressboard increases with the temperature [53]. At the initial stage of application of high voltage, the carbon trace is almost invisible.…”

Active Dielectric Window: A New Concept of Combined Acoustic Emission and Electromagnetic Partial Discharge Detector for Power Transformers

“…An electrode system (Figure 18a), in which the creeping discharges were generated on a pressboard sample with a diameter of 100 mm and a height of 3 mm, was placed in the oil-filled transformer tank (Figure 18b). These types of discharges were selected due to the fact that together with turn-to-turn discharges, they are the most dangerous defects that typically result in catastrophic failures at normal operating conditions [41][42][43][44][45]. An electrode system (Figure 18a), in which the creeping discharges were generated on a pressboard sample with a diameter of 100 mm and a height of 3 mm, was placed in the oil-filled transformer tank (Figure 18b).…”