Surge analysis for lightning strike on overhead lines of wind farm

Abstract

The overhead line in wind farm is vulnerable to lightning strikes at a high risk. The lightning surge would propagate along the line and damage the equipment in substation. In this work, the mathematical models for transmission tower, overhead lines, power transformer and wind farm substation have been developed in the environment of EMTP, especially the wind turbine converter and step up transformer models. The transients in the case of back flashover and shielding failure are analysed. The influences of radial and cross-shaped connections of wind turbine topology on the wave reflection and refraction have been investigated. The performance of surge arrester, not only the protection area but also the absorbed energy under lightning overvoltage is also computed. The wind farm substation is divided into multi zones and the transient response at different nodes is obtained. It indicates that the characteristics and propagation for surge under lightning strike on overhead line are completely different from direct lightning strike on wind turbine receptor. The capacitance between the high and low voltage side of step up transformer plays a key role in system transients. Compared with back flashover, the overvoltage caused by shielding failure is relatively small; the cross-shaped scheme is preferred and would benefit the lightning protection; the absorbed energy of arresters under a high lightning current is a major consideration.