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°. Three phase colours have since been changed. Phase 1. from Red to Brown, Phase 2. Yellow to Black, Phase 3. Blue to Grey and Neutral Black to Blue. As these are much more difficult to read on screen, we have kept the old ones in our diagrams. TEST YOUR UNDERSTANDING: Three phase systems are more applicable to the study of electrical heavy-duty engineering than electronics. Nevertheless an appreciation of what is occurring between the electricity generation plant and the end user is helpful. Follow each of the topics and leave it at that for now!
