Statistical law for parameters of very fast transient overvoltage in UHV substations

Abstract

Very fast transient overvoltage (VFTO) generated by switching of disconnector in UHV substations may exceed the lightning impulse withstand voltage (LIWV), which is a serious threat to the electric power system. In this paper, five UHV substations in operation or under construction have been modeled in EMTP-ATP, and four operation modes are considered in VFTO simulation. Statistical law of characteristic parameters, such as maximum amplitude and first-peak gradient, etc. is analyzed by smoothing kernel density estimation method. The result shows that the statistical law of the characteristic parameters presents concentrated distribution when the bus is uncharged. The maximum amplitude appearing in ninety percent probability reaches 2.5p.u., which may surpass the LIWV, and the first-peak gradient is 5.85kV/ns. While the bus is charged, the statistical law shows dispersed, in which the maximum amplitude as well as the first-peak gradient reaches 2.01p.u. and 9.68kV/ns respectively.