PROTECTION OF SERIES COMPENSATED TRANSMISSION LINES

Abstract

Series compensation is an attractive option for maximizing power transfer through existing power transmission networks. Series compensation offers considerable technical and economic advantages in long Extra-High Voltage (EHV) transmission systems. In view of the benefits offered by the series compensators, they find increasing applications. It is therefore, imperative that relevant existing transmission line protection approaches are investigated and modified in series compensated environment along with the primary system developments. Although series compensation is effective in increasing the transient stability and optimizing the power flow in the system, the protection of series compensated line is more complex than that of the uncompensated transmission lines. Series compensation can significantly modify the apparent impedance presented to the impedance based relays. In this respect, the transmission line protection in series compensated environment needs a significant modification for reliability of the power supply. The work presented in this thesis addresses the problems encountered by distance relaying scheme, when employed in series compensated transmission line. Besides fault detection, fault classification, fault zone identification and fault location estimation are main relaying tasks. An attempt has been made in this thesis to improve the performance of distance relaying scheme through improvement in all these aspects separately. A detailed analysis of the impact of series compensation on the transmission line protection has been carried out in the initial part of the thesis with up to date bibliographical survey. Based on this survey, a requirement of accurate, reliable and fast protection algorithms for the series-compensated transmission lines has thus been identified. The work presented in this thesis mainly deals with problems and their solutions for the protection of the transmission lines with mid-line series compensation. Both variants of series compensation, fixed and controllable (thyristor controlled series compensator, TCSC) are considered for this study. On the basis of the requirements identified from available literature, various techniques for fault detection, classification, fault zone identification and estimation of the fault location on the series compensated transmission line are reported in this work. All the methods developed in this thesis are single-end algorithms (based on the measurements taken at the relaying end only) without the need for data communication between two line ends. Further, in this work, a versatile and new protection algorithm is developed that can provide effective protection to uncompensated and series compensated transmission line without any modification in the methodology. iv All these algorithms were tested on a mid-line series compensated transmission line connecting a two-area system. The system model is developed using Power System Computer Aided Design (PSCAD) and measured fault data from these simulations are imported into the MATLAB platform to implement the algorithms. Upon testing, the obtained results show improvement in performance of all fault classification, fault zone identification and fault location algorithms as compared to those reported in the literature. In addition, fault classification and fault zone identification algorithms are further modified and improved for application to a TCSC compensated transmission line.