Surface discharges occurring on a porcelain bushing under DC voltage not
only causes an incipient fault condition but also can degrade the
pertinent location once the surface deposition layer or the insulation
material gets carbonized. Naturally, it becomes important to identify
and analyze the surface discharges occurring on bushing. The current
practice on analyzing surface discharges initiated under DC voltage
employs partial discharge test methods that focuses on counting the PD
events occurring over a time span. The method is sensitive but provides
no information about the possible source of fault condition. In this
context, a non-conventional, pattern based partial discharge analysis
method on understanding the characteristics of electrical discharges
occurring on the surface of a polluted bushing under DC voltage is
studied. Initially, a half-wave bridge rectifier unit that produces an
uncontrolled DC voltage is selected and employed. Later, the surface of
the polluted bushing is energized, and the signals initiated by the
surface discharges occurring on the surface contaminated bushing are
recorded. Instead of counting the PD events, the pattern manifested by
the surface discharges is correlated to the AC voltage input of the
rectifier. Once this is accomplished, the pertinent findings are
validated on an actual bushing installed in an electrostatic
precipitator unit that is applied for cleaning producer gas of a biomass
gasification plant.