Distribution grid refers to the final stage of the electrical grid in which electricity is distributed to homes, industry, and other end use products. Distribution is the process of reducing power to safe customer-usable levels, and delivering the electric power to the grid. The power level is reduced by step-down transformers, which lower the voltage of the electricity from dangerous levels (over 1 kV) to safer levels (100 - 400 V). The entire distribution grid includes lines, poles, transformers, and switching and protection circuits that deliver safe electrical power.
Substations are located throughout the whole electrical grid, from the power plants all the way to the distribution grid. The ones near the power plant contain the transformers that step-up the electricity in order to reduce energy loss over its transmission, the ones before subtransmission lines step-down the electricity to lower voltages, and distribution stations connect the subtransmission lines to distribution lines.
The distribution grid uses overhead and underground subtransmission power lines which operate between 26 kV and 69 kV. These connect to the distribution substations that distribute the power to where it is needed via lower voltage distribution lines (2.4 - 33 kV), shown in Figure 1. These lines lead to transformers that step-down the electricity while also preventing circuit overloads from affecting voltages at other points on the grid. The transformers used for distribution can be seen on poles for overhead lines (Figure 1), or on the ground for underground lines, called pads (Figure 2).
Distribution stations are either built within buildings or outdoors, but always in an enclosed area. The design of these stations depends on economic, environmental, legal and social factors.
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