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Fundamentals of Electricity

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Distribution System

The purpose of the distribution system is to distribute the electricity to each customer's residence, business, or industrial plant. It is primarily composed of the distribution substation and distribution feeders, but also contains many other pieces of equipment including reclosers, sectionalizers, fuses and capacitors.

Step-Down Transformer PictureElectricity is "stepped down" from a high to low voltage by transformers located at the distribution substation. These transformers are just the reverse of those which increased the voltage at the generating station. Electricity enters the primary side coil with the larger number of windings and leaves from the secondary coil with the smaller number of windings. The electricity is reduced to a lower distribution level voltage, usually less than 39,000 volts, and distributed on three phase lines. There are a wide variety of three phase distribution line types and voltages supplied by electric utilities across the country. A very common three phase distribution line voltage is 12,000 volts or 12 kV.

Distribution Transformers PictureThe distribution line supplies the final step down transformer at the customer location where the voltage is stepped down or lowered to the service voltage for the customer's electrical system. Then the electricity flows through the service drop to the electrical meter at the service to be measured for billing purposes.