Two-phase co-ordinates of a four-phase network

SUBSTITUTION of variables (voltage, current, impedance, and so forth) in order to simplify solution of problems on polyphase networks is a well-established practice. A polyphase network may be regarded as several single-phase networks which are coupled to one another in many places and all of which contain power sources. Simplification of network problems results from the replacement of the original phase networks by an equal number of single-phase substitute networks which are not coupled to one another or are coupled in fewer places or in a simpler manner than the phase networks, and which, preferably, have fewer power sources. In these substitute networks, the substitute currents and voltages exist.