ABSTRACT
This chapter presents a general representation of power systems and their sequence networks. Typical simultaneous unbalances that occur in a power system are a broken conductor falling to ground and faults occurring in different parts of the system at the same time. Since the sequence connections for the unbalances are different either in type or location, it is necessary to isolate one from the other. If one side is ungrounded, it will be seen that the zero-sequence network is open. The calculation for a phase-to-ground fault on one of the phases of the delta is complicated by two sets of unbalances: the unbalance of the ground and the unbalance of the ground fault. The techniques of calculating unbalances such as an open phase with and without a simultaneous shunt fault have been presented with a number of examples. In general, series and simultaneous unbalance calculations are more tedious unless they are programmed in the computer fault study.
