Causes Analysis of Burst Fault for 500 kV Porcelain Bushing Based on Explosion Theory

In this paper, a burst fault occurred in the normal operation of a porcelain bushing for 500 kV tank circuit breaker is considered. Based on the explosion theory, the energy range and the mechanism of the chemical and physical explosion of the porcelain bushing were calculated through the analysis of the projective kinetic energy of the porcelain block, the 3D dynamic simulation of the explosion process and the physical and chemical analysis of the ceramic fragments. On this basis, the characteristics and reasons of the explosion of porcelain bushing were systematically analyzed. The results show that the chemical explosion energy of porcelain bushing is estimated as 55–75 g TNT according to the fragmentation distance of porcelain fragments, which is much larger than the energy generated by physical explosion. Thus, the explosion could be considered as chemical explosion. From the physical and chemical analysis of the porcelain fragments and the 3D dynamic simulation results of the explosion process, it could be preliminary conclude that an intensive partial discharge in the porcelain bushing leads to the generation of a large amount of thermal energy. Meanwhile, thermal energy leads to the SF6 gas filled in bushing rapidly decomposing and expanding which generates gas shock waves and resulting in the explosion. The possible reason of explosion accident could be considered as the abnormal discharge existing in porcelain bushing.