Impact of distribution line insulated tower head and cross arms on lightning surges in 10 kV substations

In order to reduce the lightning trip-out rate, a kind of insulated tower head and cross arms are used in 10kV overhead distribution lines, which may lead to the increase of lightning surge amplitude and create hazards to the equipment in substations. It's crucial to analyze the insulation coordination of 10kV substations under such condition. In this paper, an EMTP model for a 10kV distribution line and substation is developed. The lightning surges and influence factors on mean time between failure (MTBF) of substation are analyzed. The results show that overvoltage on equipment of substation are greatly increased and the MTBF of main transformer and surge arrester are reduced and below the allowable limit after the use of insulated tower head and cross arms. The MTBF of main transformer are greatly influenced by the front time of lightning current, the peak current distribution and the pole grounding resistance. An additional arrester at the incoming line and the increase of absorption energy of arrester are adopted as the effective countermeasures to improve the insulation coordination of such 10kV substation.