Modelling of HVDC wall bushing flashover in nonuniform rain

The authors present the first mathematical model to provide necessary and sufficient conditions for flashover of a high voltage direct current (HVDC) wall bushing under nonuniform rain. The suggested mechanism is initiated by streamer bridging of the dry zone. The findings of the model have been satisfactorily compared with previous experiments and field observations and can account for the following aspects of the flashover mechanism: critical dry zone length, polarity effect, specific leakage path, wet layer conductance per unit leakage length, and the DC system voltage