Modeling lightning as a voltage source and as a current source — A comparison analysis with an ATP insulation coordination study in a 500 kV air-insulated substation

Lightning electromagnetic transient simulations using Alternative Transients Program — ATP were carried out in a 500 kV air-insulated substation owned by Chesf, an utility company from Brazil. Two modeling approaches were analyzed. In the first approach, lightning was modeled by a voltage source entering the substation and the lightning struck Transmission Line (TL), substation equipment, and busbar were modeled in a single-phase basis. The second modeling approach accounts for three-phase models of substation components, as well as, lightning hit TL tower surge impedance, grounding system and, insulator string withstand models. Preliminary results have showed that modeling lightning surge as a voltage source originates overvoltages that exceed the maximum permissible voltage. Depending on lightning current parameters and waveshape, different results are observed in the current source modeling method. Both modeling approaches have great impact on station insulation coordination and care must be taken when deciding which one should be used.