Space charge injection behaviors and dielectric characteristics of nano-modified transformer oil using different surface condition electrodes

Electrodes are damaged by external forces, mechanical wear, and electrochemical corrosion during long-term operation in power systems, resulting in rough electrode surfaces. Space charge injected into the liquid by a rough electrode under a strong electric field causes electric field distortion and leads to breakdown. Moreover, the charge injection is associated with the energy barrier at the electrode-liquid interface. The combined effect mechanism of nanoparticles and electrode surface condition on the insulating characteristics of transformer oil was investigated using various surface condition aluminum plate electrodes. The breakdown voltages and space charge patterns in pure transformer oil and Al2O3 nano-modified transformer oil under impulse voltage were measured in this study through Kerr electro-optic field mapping measurement. The test results indicate that the breakdown voltage of nano-modified transformer oil depends on voltage polarity and electrode surface conditions and the charge injection shows the same mode in pure transformer oil using different surface condition electrodes, but the magnitude of charge injection differs considerably. Due to nanoparticle’s ability of shielding space charges of different polarities and the charge injection of different surface condition electrodes, they have different effects on the breakdown process of transformer oil between different surface condition electrodes. An interfacial model was formed to explore the mechanism of the effect of nanoparticles and electrode surface conditions on the insulation performance of liquid dielectrics and analyze the breakdown process using the space charge injection behaviors.