Observation and analysis of residual voltage of SPD connecting to overhead line

Residual voltage of SPD connecting to overhead line is closely related to earth potential rise at the grounding terminal of SPD. Characteristics of the SPD residual voltage caused by natural lightning and artificially triggered lightning were analyzed in this paper, and the results show that: (1) In case of the natural lightning, the earth potential can be regard as zero, and the voltage difference between the two terminals of the SPD comes from the induced voltage on overhead line. (2) When the distance from the grounding point of SPD to the earth grid of triggered lightning is within 30 m, the earth potential can not be regard as zero. The voltage difference between the two terminals of the SPD comes mainly from the induced voltage on overhead line for return strokes, but from the earth potential rise for some weak processes. The influence of the earth potential rise should not be ignored. (3) When the grounding point of SPD is very close to the earth grid of triggered lightning, the voltage difference between the two terminals of the SPD comes mainly from the earth potential rise. The SPD residual voltage exhibits the characteristics of polarity reversal, and then the current from the ground to the SPD. The duration of the SPD residual voltage may be up to the order of millisecond in case that long continuous current (LCC) occur following return stroke may cause harm to the SPD.