Poly means many (more than one) and phase means windings or circuits, each of them having a single alternating voltage of the same magnitude and frequency. Hence, a polyphase system is essentially a combination of two or more voltages having same magnitude and frequency, but displaced from one another by equal electrical angle. This angular displacement between the adjacent voltages is called phase difference and depends upon the number of phases.
However, the abovementioned relation does not hold good for two-phase system, where the voltages are displaced by 90° electrical. Thus, an AC system having a group of (two or more than two) equal voltages of same frequency arranged to have equal phase difference between them is called a polyphase system.
The polyphase system may be two-phase system, three-phase system, or six-phase system. However, for all practical purposes, three-phase system is invariably employed. Therefore, whenever a polyphase system is mentioned, we mean by that a three-phase system unless stated otherwise.
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