Digital protection scheme for distance relaying of a six-phase power system

Abstract

The objectives of this study are to investigate various algorithms for digital relaying that can be used in six-phase system and to develop a laboratory replica of six-phase system from selected three-phase double-circuit of Tenaga Nasional Berhad (TNB) network. A novel algorithm which is called bounded data uncertainties (BDU) for digital relaying is proposed. The proposed method is an enhanced least-square algorithm, which unlike classical least-square, it allows perturbations in data matrix and measurements or observations. MATLAB programs have been developed to compare the BDU with the Discrete Fourier Transform (DFT) algorithm. The results show the superiority of BDU over DFT method. An existing three-phase double-circuit line between Kuala Krai (KKRI) and Gua Musang (GMSG) substations has been selected as a case study for conversion to six-phase single-circuit system. Using the configuration line data provided by TNB, parameters of six-phase line are calculated. The calculation of parameters of line is also carried out using software package PSCAD/EMTDC. The results from MATLAB and PSCAD programs have revealed that the positive-sequence inductive reactance of six-phase single-circuit is higher than the three-phase double-circuit line. Furthermore, the results of MATLAB show that the maximum fault current occurs for phases a-b-d-f fault. Based on the maximum fault current, the necessary components have been obtained to construct the six-phase prototype. The prototype is successfully developed which resembles six-phase line of the KKRI-GMSG. The phase difference of voltages of the six-phase prototype has been successfully validated by LabVIEW software package. The prototype is unique in Malaysia and it is an invaluable tool which can be used by power utilities and graduate students to do research work in six-phase system.