Research On Over-voltage Calculation And Insulation Coordination Of 500kV EHV Substation

The development of extra high voltage (EHV) transmission and the importance of EHV systems are firstly introduced. The meanings of insulation coordination and protecting the EHV substation from over-voltage caused by lightning strike and operation are also introduced. At the same time, the methods of calculation of the over-voltage are introduced. The merits and the demerits of these methods, and the factors that should be taken into account in the calculation are also pointed out.The model of transmission lines is established and the parameters of the model are calculated. The counter-flashing time and the potential of the transmission lines after counter-flashover are calculated by the current distribution method. The amplitude of the voltage of the lightning wave is calculated when it transmits to the substation, considering the refraction and the distortion along the transmission lines. The over-voltage of the electric apparatus and the current of the arrester are calculated. By making analysis of the amplitude and the gradient of the lightning wave, the mode that the substation works, the electric distance between the arrester and its protected apparatus, the entry capacitance of the apparatus, and the U-I characteristic of MOA, how these factors influence the over-voltage of the apparatus is known. The equated circuit for the breakers closing is established. The over-voltage caused by the reactor switching on the unloaded transmission lines is calculated. In the end, some methods to ameliorate the insulation coordination are suggested, and some deficiencies of the paper are pointed out.