Field Problems of Distance Relays with Combined Single/Double Circuit Transmission Lines

Abstract

Parallel transmission lines are characterized with a significant increase in the mutual coupling effects among the different phases of the coupled line segments raising remarkable errors for impedance-based protection equipment in particular. Owing to these situations, the total line impedance of each phase of the associated line may significantly change resulting from the mutually reflected impedances from the other phases. Thus, double line segments, when combined to single circuit ones, can significantly lead to have a deviated measured fault impedance from those parameters that are adjusted during the relaying setting stage. This may, accordingly, cause remarkable errors for distance protection algorithms in the field leading to unnecessary tripping or delayed fault clearing. In this study, the impact of the combination of single and double overhead line segments on the performance of distance relaying function is thoroughly investigated. This investigation is carried out using the Electro-Magnetic Transient Program (EMTP) using distributed parameter line modeling. The accuracy of the developed simulation is validated as compared with a recorded fault case for a 400 kV combined single/double line from the field. This corroborated the correctness and the accuracy of the constructed model. The relay enabled functions and setting are collected and realized in the MATLAB environment. This research is essential for visualizing the core of the problems of these transmission networks with distance function and can consequently help to realize a practical and reliable distance relaying for such lines.