A Study on Reclosing of Asaluyeh-Isfahan 765 kV Transmission Line Considering the Effect of Neutral Reactor in Reducing Resonant Voltages

Shunt reactors are utilized on long transmission lines (in this case a 640km 765kV line) to reduce over voltages experienced under light load conditions. When the compensated line is opened to clear a fault, it is found that the open-phase voltage does not disappear. In some cases, a dangerous transient voltage with a resonant frequency between 30Hz and 55Hz can be seen which gradually reduces in magnitude. This over voltage can damage line connected equipments like shunt reactors and open circuit-breakers. This phenomenon is because of the trapped charges existing on transmission line during the dead time of secondary arc extinction. In case of high transient over voltages, we need additional equipments to reduce them. Normally, closing resistors are used to limit the over voltages. This solution is expensive and prone to failure. The proposed method is the usage of neutral reactors in the neutral of shunt reactors which is a cost effective solution. The technique is shown to reduce the resultant over voltages on the power system and allows for faster reclosing thus improving stability. In this research work, the investigation of a neutral reactor application is performed for transmission lines using transient simulation with appropriate models. The application of neutral reactors for reducing the resonant over voltages and reclosing over voltages during fault clearing is analyzed. The simulations are carried out by ATP/EMTP software and the advantages of using neutral reactors for Asaluyeh-Isfahan 765 kV transmission line are discussed.