Parameter identification of unsymmetrical transmission lines using accurately re-synchronised fault records

Abstract

Today transmission lines are protected by installing protection relays at their terminating stations. If a fault appears, the protection relays of the faulty line as well as of adjacent lines react and record measurement data. Until today these records are often unexploited. The purpose of this work is to analyse these records with the goal to identify equipment parameters in particular to estimate parameters of unsymmetrical transmission lines by using time-varying phasors. Due to the characteristic of the assumed line model only synchronously sampled fault data of two terminating stations can be used for this type of identification. It is commonly assumed in the field of signal processing of disturbance records (e. g. calculation of fault distance with multi-terminal signals) to use synchronised relays as signal sources. In practise this is not always the case. GPS-synchronised fault data are a minority compared with unsynchronised. This paper presents a novel method for re-synchronising unsynchronised fault data with time differences up to seconds. The proposed re-synchronisation method is divided into two stages. The pre-synchronisation uses segment borders to synchronise disturbance records of similar sequences. The second stage precisely synchronises the fault data belonging to two sides of an overhead transmission line by taking into account the characteristics of a simple line model.