Investigation of Neutral Reactor Performance in Reducing Secondary Arc Current

The majority of transmission-line faults are temporary short circuits. The short circuit arc is usually self-extinguishing after opening the transmission-line circuit breakers. High-speed reclosure of transmission-line circuit breakers can improve system stability. As the voltage level increases, arc deionization time increases as well, endangering system stability. Application of automatic single-phase reclosing makes it possible to increase system stability even for extremely high voltage transmission lines. Automatic single-phase reclosing is used to clear single-phase-to–ground faults, which are about 80% of the transient faults. In order to have successful fast reclosing, different methods are used to extinguish the arc. One of the common methods is to use a single-phase reactor in the neutral of shunt reactor, when transmission line is compensated with shunt reactors. As of now, the effect and parameters of this neutral reactor are usually determined based on the steady-state analysis without exact system and arc modeling. In this research work, the investigation of a neutral reactor application is performed for transposed and untransposed transmission lines using transient simulation with appropriate models. Then, guidelines for selecting the appropriate amount for the neutral reactor are proposed.

I. Introduction

In extra–and ultra-high voltage (EHV, UHV) transmission lines, three phase reclosing system could only be used when it is very fast. Reclosing time is set based on arc deionization period in air gap between phase conductor and tower body [1]. For high-voltage transmission systems, short circuit capacity of the system usually increases as system voltage increases. The higher short circuit power results in higher short circuit current and higher ionization of the related arc. It results in higher arc extinction time so that the air gap at the fault point would be deionized before reclosing could be performed [2]. This necessitates that reclosing would be performed after some time delay. However, this delay contradicts with the lower stability margin of higher voltage systems. Therefore, application of three phase reclosing might become a nonpractical solution for EHV and UHV systems.