A New Approach to the Study of Simultaneous Unbalances [includes discussion]

A new method of studying simultaneous unbalances with the aid of a network calculator is discussed. Such unbalances may occur in power systems when faults involve more than one circuit of a double-circuit line; when the line-to-ground or line-to-line faults are accompanied by open conductors; when simultaneous faults occur at more than one location, as can result from overvoltages due to one fault causing insulation breakdown at some point removed from the original fault; and from faults which involve two or more circuits of different voltage levels, as sometimes occur when subtransmission and primary distribution circuits are carried on the same pole structures. The method enables one to include the general case of Z1≠Z2, with only conventional passive network calculator impedances and 1-to-1 ratio transformers being required. No negative impedances, mutual impedances between networks, or "imaginary" turn-ratio transformers are required, even for cases involving wyedelta transformations between the unbalances. Applications to conditions of simultaneous faults and open conductors are discussed.