The high-voltage insulators on a high-speed train roof are subjected to both the normal single-phase power frequency 27.5 k V AC voltage from traction substation and the frequent overvoltage shocks. The overvoltage will affect the surface electric field distribution of the insulator

and the effect gets worse when the insulator surface is contaminated or generates drying band

which may harm safe operation of the system. This paper analyzes the effects of phase overvoltage and lightning induced overvoltage on potential and electric field distribution of the contaminated insulators with different contamination degree. The results show that: the single-point electric field intensity of the insulator is directly proportional to overvoltage amplitude; the electrice field distribution along the surface of a clean insulator is independant to overvoltage frequency; and no matter whether or not the drying band exists on the surface of a contaminated insulator

the electric field exhibits more obvious capacitive feature as the harmonic frequency increases

but the electric field with pure resistative or pure capacitative feature keeps unchanged as the conductivity of contamination changes.This study may offer a theoretical basis for further research of overvoltage effect on insulator surface electric field on high-speed train roof.