Compensation of impedance measurement error due to arcing

Abstract

Arcing is a phenomenon which is closely related to short circuits in electrical systems. The nature of arcing can be different but, in any case, there is no universal mathematical model to describe arcing. In a general approach arcing is described with a non-linear, but only resistive voltage-current characteristic. Based on this assumption the distance protection is using the R-reach of the characteristic to cover the arc impedance. For the impedance-based fault location a similar approach applies. If the arc is only resistive, the reactance measurement used for the fault location is not influenced. This paper presents two real cases where impedance measurement errors due to arcing can heavily influence the behaviour of distance protection and impedance-based fault location. In the first example the fault locator estimates a location with an unacceptable measurement error. This happens after a successful trip of the line differential protection on a 400kV line with single side infeed only. The arcing impacts the voltage measurement in magnitude and phase angle which finally leads to the incorrect estimation of the fault location. The second example is about distance protection applied to a medium voltage cable. Due to the arcing a fault in zone 1 is measured to be outside of zone 1 for a long time. After approximately 170 ms the characteristic of the arc is changing which enables the distance protection to measure the fault in zone 1 and send a trip command to clear the fault. The paper analyses the two cases in detail and suggests a method how to improve the impedance measurement for distance protection and fault location in such cases of arcing.