A Microcomputer Based Approach for Identification and Selective Control of Uhv Lines Operating Under Mixed Faults.

Abstract

This dissertation investigates a methodology for the application of microcomputer based technology to improve the performance of a network of transmission lines. The improvement is achieved by means of microcomputer based identification and selective control of faulted and unfaulted phases and lines of an interconnected network of transmission lines operating under mixed fault conditions. In this approach, faults are isolated through the disconnection of a minimum number of fault-involved phases. The performance analysis of transmission lines under connected and isolated faults is carried out. Analytical expressions for residual fault currents and recovery voltages for selective control applications are developed. The UHV lines ranging from 345 to 1500 kv have been simulated on the digital computer, and the maximum permissible line lengths with and without inductive compensation are specified. Electromagnetic and electrostatic field effects of isolated faults on differential relaying algorithms are analyzed. A model to investigate transient stability regions resulting from the selective control application to power systems is developed. An open air, non-linear, time-varying residual fault arc is modeled as a circuit element; with the use of the state space approach, minimum switching times are computed. Using only one instantaneous sample from each phase of a line, the expressions for fault detection, classification, phase selection, and zone discrimination are developed. A set of expressions for distance, differential, and directional protection is developed. Based on traveling wave theory, a set of expressions for high speed protection of transmission lines is developed. For faster response time these expressions can be implemented on state-of-the-art microcomputers. Using discrete Fourier series and least squares curve fitting techniques, recursive and non-recursive digital filter expressions in multiple coordinates are developed. As an example, a typical implementation of a microcomputer based system for fault identification and selective control of a double circuit line is proposed.