Electronics Principles V11

Clive W. Humphris

THREE PHASE SYSTEMS: 3-phase Generation of EMF.  

Most UK domestic consumers are fed from a 240V AC single phase supply. As we have seen this can be generated by rotating a single turn coil between two permanent magnet poles. The waveform shows that a single rotation of the coil through 180° produces the familiar sinusoidal waveform.

An alternative source of a single phase 240V can be found by tapping off a 3-phase national grid supply as we shall now explore.

When three coils are placed 120° out of phase to each other and rotated together they produce a 3-phase supply.

By convention these are coloured Red, Yellow and Blue with a fourth conductor, coloured black as a neutral connection. 3-phase supplies are used for national electricity distribution. Smaller conductors can be used, thereby saving copper. The three EMF's produced are all at the same amplitude, but displaced by 120°.

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