Novel adaptation of the critical clearing angle formula for faults on a three phase and a six phase line

Abstract

Enhanced power transfer through polyphase conversion of a transmission line, specially three to six phase, as an alternative to upgrading the conventional three phase power transmission voltage is becoming an area of growing interest in the power industry. Among others this conversion will have an impact on the system stability. While the well-known symmetrical component method has been found suitable in modeling the unsymmetrical faults of a three phase system for transient stability analysis it appeared as difficult-to-apply for six phase system. In this paper a new technique has been proposed to determine the stability in terms of critical clearing angles for both three and six phase line faults. The method has been validated by applying it first for the faults on a 132 kV three phase double circuit line of a given practical power system and comparing the results with those obtained through the symmetrical component method. Then it has been applied for the faults on the same line but considered to have been converted into a 132 kV six phase single circuit line. The method, though an approximate one, is straightforward, simpler and faster than the symmetrical component method and provides sufficiently accurate results.