Quasi‐phase resolved partial discharge pattern analysis of surface discharges arising on the tar polluted porcelain bushing of an electrostatic precipitator unit under high voltage DC

Abstract

AbstractThis paper investigates on understanding the DC electrical discharges arising on the surface of feed‐through type indoor bushing with tar depositions. Such information not only provides diagnostic status but also characterizes the multitude of species forming tar depositions which is currently unavailable in literatures. The current practice on analyzing surface discharges initiated under DC voltage employs primitive methods that accounts for the individual discharge events over a larger span rendering it less sensitive and time consuming. The usual practice is to count the discharge events initiated under DC voltage as PD pulses and count the events, repetition rates, time of occurrence, and so forth, to estimate the severity of the fault condition. On contrary, synchronizing these discharge pulses to the phase of the AC voltage, input to the rectifier unit, manifests a pattern, which is time independent and is sensitive in revealing diagnostic status of the bushing. These objectives are initially verified on a sample extracted from a tar polluted bushing. A half‐wave bridge rectifier that produces an uncontrolled positive and negative DC voltage is selected to initiate surface discharges. Pertinent pulses are then correlated to the phase of the AC voltage input to the rectifier and a quasi‐phase resolved partial discharge pattern (QPRPD) is developed. Using this QPRPD pattern, the significance of positive and negative DC voltages applied on the surface of the polluted sample is studied and the inception of discharges events and their correlation to the defect conditions are evaluated. Following this, the pertinent findings are validated on an actual bushing installed in an electrostatic precipitator unit applied for cleaning producer gas generated in a biomass gasification plant.