Performance Analysis Of Lightning Overvoltage On GIS Substation

A lightning surge overvoltage is a dominant factor to determine the insulation level of a substation. It is very hard to observe the lightning overvoltage experimentally, and thus a numerical simulation has been adopted to investigate it. EMTP has been widely used since the 1970s with increasing usage of digital computer. For insulation co-ordination in transmission lines and substation equipments, it is necessary to accurately predict the lightning surge overvoltage that occurs in power system. The magnitude and waveshape of this overvoltage arriving at the terminating transformer is greatly affected by the use of the arrester at the terminating transformer. The thesis mainly focuses on the following aspects:First, three typical kinds of transient model for transmission line are studied in this thesis. They areπmodel, constant parameter model and Marti model.πmodel is a line model which transforms line parameters into parallel admittance matrix and parallel series impedance matrix. It is the most stable model and with very high accurate in the very short line. Also, it may use very small step time for delta-t. Constant parameter model is characterized by resistance, inductance, capacitance, conductivity and other line parameters will not change with the frequency. Marti model consider the increasing resistance in the range of high frequency. It has very good dumping during the simulation.πmodel in 1 MHz is suggested in this thesis.Second, lightning protection of transmission line and substation in power system are analyzed from theoretically. There are direct lightning overvoltage and lightning induced overvoltage on transmission line, and the first one does more harm to transmission line. Lightning on substation can case the overvoltage of direct lightning and lightning incoming surge. Insulation coordination of Electric Equipment which is the cooperation of transformer insulation levels and arrester protection level is studied.At last, a lightning performance of a transmission line using the ATP-EMTP program is presented. Adequate possible models involved in the simulation are suggested, including transmission line, tower, flashover, GIS bus, arrestor, transformer, cable, and so on. This paper presents the method of a lightning surge analysis applied to the UHV and EHV system rationalized insulation design and coordination. Overvoltage due to external lightning strikes is studied for the 220kV GIS (gas insulated switchgear) substation.This paper suggests further work to be done based on discussions of applicable limits and problems of the recommended models.