Abnormal Voltage Conditions Produced by Open Conductors on 3-Phase Circuits Using Shunt Capacitors [includes discussion]

Undesired voltages often accompanied by phase reversal have been experienced1,2 on distribution systems after the opening of 1- or 2-phase conductors. The mere opening of phase conductors on a 3-phase system will not necessarily result in undesirable voltages and phase reversal, but certain combinations of open conductors and unbalanced circuit impedances3 or open conductors and balanced impedances containing inductive and capacitive reactance4,5 can result in undesirable voltage conditions. In the latter, previous studies have not included simultaneously the effect of system load and of the transformer non-linear magnetizing characteristic upon these abnormal voltages. The results in this paper include the combined effect and are therefore more applicable to a wider range of system conditions. Specifically, these phenomena were investigated with regard to the grounded-wye or 4-wire distribution system containing floating wye or delta-connected capacitor banks for kilovar supply, because it is the most common circuit arrangement occurring in practice. However, it is recognized that many other configurations may result in the same phenomena. It is the purpose of this paper to define the nature of the phenomena and under what conditions they may be obtained, including the effect of capacitor size, transformer magnetizing characteristics, magnitude of load, and load power factor. This study was made largely on systems in miniature on the transient network analyzer.