The analysis of random sequential ground faults on a high phase order (six-phase) power system in phase coordinates

Abstract

High phase order transmission (HPOT) lines are considered a potential alternative to the conventional three-phase lines for the transmission of bulk power. In particular, six- and twelve-phase systems appear to be favoured for this purpose. Should HOPT prove to be economically and technically viable, the problem of fault analysis, in particular the analysis of random sequential ground faults on these systems, appears to be a complicated one. When a ground fault on a power system involves more than one terminal, the fault usually develops in sequence. This paper presents a generalized analysis of random sequential ground faults on the terminals of an initially unloaded six-phase symmetrical generator. No restriction is placed either on the sequence in which the ground fault develops or on the instants at which the various phases are grounded. Single equations from which all transient phase currents and transient terminal voltages can be calculated are given. An expression for the transient neutral current which is an important variable for any protection scheme against ground faults is also given. The method in this paper can be applied to a power system of any number of phases by suitably adjusting the summation indices in the general equations. The analysis has been done in actual phase variables. Finally, the results for an arbitrary sequential ground fault on the terminals of a fictitious six-phase generator are given.