Parameter identification of unsymmetrical transmission lines

Today transmission lines are protected by 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 objective 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. This paper presents a theory for the identification of transmission line parameters based on time-varying phasors. By assuming equal admittances at both ends of a pi-section model it is possible to calculate the currents through the line using the measured currents of the fault records. Afterwards the line parameters are estimated using the least squares method. It is shown that only measurements including transients can be used for the identification. The proposed approach is verified in two steps. At first fault records are generated by simulating a line model and after that real measurements on a three phase dynamic network model are used for a verification of the algorithm.