Study On Insulation Flashover Criterion For Lightning Performance Calculation

Lightning is one of phenomena of discharge which is common in nature. In recent years, lightning stroke is one of the important causes of the accidents that occur on trans-mission lines. With the increase of voltage grade of transmission line, incidents caused by backflash can not be ignored. Therefore, exactly evaluating lightning-withstanding level of transmission line is especially important for system service and stable operation.When the first stroke of a flash terminates at the top of a tower, a wave travels down the tower and out on the overhead ground wires, making the waveshapes of the voltage across the insulation significantly differs from the standard 1.2/50μs. Research shows flash-over characteristics of insulation under non-standard waver is different from the standard wave. It's necessary to build a criterion for insulation flashover under non-standard wave.Several methods of estimating the insulation flashover are in use today. In general, these methods can be divided into those that attempt to model directly the breakdown proc-ess and those that are derived from the breakdown process. Leader progression model which used by CIGRE is one of those methods. A new criterion derived from the leader progression model is introduced here, for it based on the breakdown process. Applying this criterion, the lightning flashover performance of the insulators for 500kV and 1000kV transmission lines are calculated here, the calculation results indicate that the criterion is reasonable under non-standard wave.Also there is a model of numerical calculation of criterion model is presented, which can be easily linked to EMTP by MODELS language. And a 1000kV double-circuit trans-mission line is taken for instance to evaluate the influence of the criterion model for insula-tion flashover proposed in this thesis on the result of the calculation of lightning-withstand ability. It is obtained that the criterion model proposed in this thesis is reasonable to be used in lightning protection calculation.