Computation On Power System Lightning Over-Voltage Modeling And Grounding Protection

With the development of the social economy and the demands for electricity,Extra High Voltage(EHV) transmission lines and substation become the trend ofpower system. As the pub of the power system,The trip-out event cause by lightningin EHV substation,will produce widespread blackouts, and will damage insulation ofthe main electrical equipments in the transformer substation, certainly will haveserious consequences to the power system, so it’s neccesary to provide the calculationmodel of the thunder lightning over-voltage. Lightning invasion wave caused by backstrike is the main reason of the substation lightning accidents.Transformer as the mainequipment of substation, invasion of the wave value is influenced by operation modeof substation, the area near lightning strike spot, the transmission tower, groundingresistance, power frequency voltage and distance between transformer and arrester.This thesis takes a specific500kV substation as example, according to theproduction mechanism of lightning, gives corresponding lightning over-voltage model,based on Bergron method, establish transmission lines model and various equipmentsequivalent model in the transformer substation, use international currentelectro-magnetic transient calculation program (ATP-EMTP) to simulate lightningovervoltage calculation modeling of transmission line outside of500kV substation,combined with FORTRAN program to calculate inside equipment over-voltage,finally analyzes the effect factors. The wave impedance model is used to simulate thetransmission lines tower, the shindou model is used to simulate the insulator stringflashover.In addition, to the electrodes with different shapes commonly used in groundingresistance reducing methods, the analysis formula of grounding resistance is given.Resistance of horizontal grouding net in singal-layer and double-layer soil structure isanalyzed, according to the current diffusion characteristic on the surface, Galerkin’smoment method is used to establish the micro-element division, then the calculatingmethods of self-resistance and mutual-resistance which is necessary in the calculationof resistance is provided. Aim at complex soil structure (vertical or horizontal or bothdirections), bandary element method is proposed, combined with the actual example,prove the validation effectiveness of this method.