Effect of injected charge on the electrification of oil flowing past the surface of composite polymers

The factors affecting oil-flow electrification (OFE) in large forced oil-cooled electric power apparatus are experimentally investigated using a closed cycle model, and a coaxial test section comprising a charge injector. The streaming and leakage currents are measured to investigate the impact of injected charge on OFE interfaced with composite polymers. The results reveal that the magnitude and polarity of the injected charge, and the type of composite polymer and its impregnation resin, if it exits, cause evident qualitative as well as quantitative changes in the measured currents. Cellulose-based materials give the highest leakage current. For other composite polymers, the higher the number ofketonic carbonyls and/or delocalized states in the aromatic moieties, the higher is the leakage current, and hence the lower is the streaming current. Underflow conditions, the leakage current is lower than that under a stationary condition, but the trend is reversed at high temperature, especially for the HVDC case. Under HVAC, the streaming current shows polarity reversal from negative to positive on increasing the oil temperature and/or voltage. For HVDC application, the streaming current is significantly reduced by calendering the outermost layer of the composite polymer, using fine glass as a backing material instead of using glass fabric, and impregnating the composite polymer with highly dipolar epoxy resin.