Electricity – generation and distribution

Three-phase power leaves the power station via three wires (one for each phase of AC) to enter a step-up substation. Here, transformers convert the power station output to a very high voltage (155 000–765 000 V) for transmission in high-voltage power lines over long distances. High voltages are used for transmission and distribution to maintain efficiency, because power losses in the grid are related to current flow, not voltage. As electricity approaches the end user it passes a series of step-down substations, where the voltage is decreased to around 10 000 volts for distribution to substations close to the users. Here, the voltage is decreased to 240 V RMS in each of the three phases. At this substation, one limb from each phase leaving the transformer join at the star point to form a neutral and ground common to all three. The other end of the circuits for each phase are used to supply the ‘live’ to properties within range of the substation. The live entering a property is only of a single phase.

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