Two-terminal fault location on unsymmetrical transmission lines

The outage of a line due to a fault can be expensive, hence the fault has to be cleared as fast as possible. Digital protection relays consist of fault locators based on several methods. Due to the availability of highly accurate GPS based time references the investigation of two-terminal methods combined with signal analysis tools makes sense in the first place. The aim of this paper is to develop a two-terminal fault location algorithm based on two kinds of modeling the samples of a fault record. Derived from the coupled π-sections line model an estimation equation is developed. This equation contains time derivatives of the measured currents. To overcome this problem a frequency and a time domain approach are presented. The derivation of the voltage drops from both stations to the fault location (either in the frequency or in the time domain) allows the calculation of the fault location via the least squares method. A simulation model serves for testing the algorithm. Different scenarios e. g. several fault locations, fault resistances and fault types allow a detailed investigation. Furthermore identified i. e. uncertain line parameters are used to calculate the fault location as well as the influence of inexact time synchronisation is investigated.