A Calculation of Potential Distribution Caused by Static Electrification Owing to Oil Flow in a Oil-Paper Insulation System and it's Application to Partial Discharge Phenomena in Oil

Electrostatic charging in transformer oils. Testing and assessment

“…Higaki et al [89] reported results of measurements of ECT in a model with mineral oils flowing through a long pressboard pipe. They later reported similar measurements for perfluorocarbon liquid (PFC-B).…”

“…Pipe system with charge relaxation tank [89] kraft paper, PET, PTFE) pipe inside. The internal diameter of the insulating pipe was 12 m m and the length was 10 m. The liquid electrified in the pipe flowed into the charge relaxation tank.…”

“…Higaki et al [89] utilized another type of duct structure for studying transformer oils. A cross section of the duct which consisted of four coaxial layers of cylindrical pressboard separated by insulating spacers and two inner and outer copper tube electrodes is shown in Figure 11.…”

“…Aging of oil results in the presence of oxidation products influencing ECT levels [go], It was demonstrated [5,33,53,81,82,89], that an increase in the degree of aging causes transformer oil to change ECT. Severe oxidative aging caused ECT to rise [go] in uninhibited oils.…”

Charge density enhancement due to recirculatory flow

“…One proposed scenario is that the flowing oil carries charge from the ducts through the transformer windings up to the header region above the windings where the charge can accumulate. When the transformer is energized, the applied ac field is superimposed on the dc field associated with the volume space charge and the total field may exceed the breakdown strength of the dielectric insulation between the windings [4,51. Another sequence of events that can lead to the electrification failure of a transformer begins with charge accumulating on the surface of the solid insulation in the plenum or entrance region to the winding ducts [6,7].…”