Dual three phase transformation for comprehensive fault analysis of a six phase system

Recently there has been a growing interest in the concept of six phase transmission as an alternative to the upgradation of a line, to increase the power transfer capability within the existing right of way. In this work the six phase system is treated as two mutually coupled three phase systems and a transformation called dual three phase transformation (DTPT) is proposed for the analysis of a six phase system compared to earlier works on this subject. This method has reduced the number of significant combinations to 13, by choosing appropriate reference phases and renaming of the conductors, compared to 23 groups. The DTPT sequence networks are obtained in terms of the familiar three phase sequence components avoiding the use of complex ratio or phase shifting transformers, mutual inductances and the results completely agree with the results of fault analysis using the phase coordinate method. In a companion paper titled “Transposition of a six phase transmission line” it has been established that in the case of conversion of an existing double circuit three phase transmission line into a six phase line, a three barrel transposition somethat similar to the transposition of a double circuit line is sufficient, in which case there is mutual coupling only between the two zero sequence components of the two mutually coupled three phase systems which constitute the six phase system.