A power-system computer is described that combines an analogue computer for the representation of the synchronous generator with a network analyser for the representation of the transmission network. These two forms of computer are coupled to give an overall representation that facilitates the study of the transient performance of a synchronous power system in unbalanced fault conditions.In the studies described, the system represented is that of a synchronous generator connected to an infinite busbar through a double-circuit transmission line, one circuit of which is subjected to a series of unbalanced and balanced faults. Studies of the effect of fault type, fault resistance, system neutral earthing and single-phase autoreclosing are included. For purposes of comparison, and in view of their ubiquity on a modern power system, automatic-voltage-regulator and speed-governor representation are included in some of the studies.