Implementation of leader development models in ATP-EMTP Using a type-94 circuit component

Evaluation of the dielectric strength of transmission line insulation subjected to fast-front overvoltages is of major importance for the insulation coordination of overhead lines and the connected substations. Among models proposed in literature for the prediction of the dielectric behavior of air gaps and insulators, leader development models have a greater physical significance. In this study several leader development models are implemented in a new model in ATP-EMTP using MODELS simulation language. The new model is solved simultaneously with the rest of simulated system interacting with it as a circuit element; this is accomplished by using the model with a type-94 circuit component. The developed model is verified against literature data referring to breakdown of long air gaps. Shielding failure and backflashover simulations are conducted for a 150 kV and a 400 kV overhead transmission line to demonstrate the effects of modeling of the predischarge current flowing during leader propagation phase on the estimated critical currents.