Research On The Induced Overvoltages In Electric Transmission Lines By Directly Lightning Striking On Tower

Lightning-induced overvoltage is a major cause of outages in power systems. In this dissertation, the author studies the induced overvoltages across the insulator string caused by directly lightning striking on the tower. With the voltage upgrading in the power system, the formula in the Regulation is no more appropriate. Therefore, it needs to deduce a more flexible formula for maximal voltage and function for wave shape of lightning-induced overvoltage.In the dissertation, the author theoretically analyzes the calculation methods of the lightning-induced overvoltages, such as Regulation Method, Loop Voltage Method, and Field Cancellation Method. And based on the Field Cancellation Method, the author deduces the Quasi-steady Induced Charge Method to calculate the lightning-induced overvoltages with the consideration of the dart leaders effect. It is known that the length of leader is one of the important facts influencing the induced overvoltages. Simulation software is developed based on the Quasi-steady Induced Charge Method. It can calculate induced overvoltages under different towers structure and lightning strokes.Further, the dissertation discusses the effects of the following parameters on the peak value of induced overvoltage and on the wave shape of the induced voltage: propagation velocity, length of upward leader, lightning current peak value, the ground-resistance. With the resultant data, the author deduces the peak value formula and the wave shape function of the lightning-induced overvoltage by curve fitting. The formula and function can be used to calculate the lightning induced overvoltage individually or be embedded in the EMTP-ATP program to calculate the lightning surge overvoltage.