Electricity Generation, Transmission and Distribution Guides

The purpose of the electric transmission system is the interconnection of the #electric #energy producing #powerplants or #generating stations with the loads. A three-phase #AC system is used for most #transmission lines. The operating frequency is 60 Hz in the U.S. and 50 Hz in Europe, Australia, and part of Asia.

The three-phase system has three-phase conductors. The system voltage is defined as the #RMS voltage between the #conductors, also called line-to-line voltage. The #voltage between the phase conductor and ground, called line-to-ground voltage, is equal to the line-to-line voltage divided by the square root of three.

The generating station produces the electric energy. The #generator voltage is usually around 15 to 25 kV. This relatively low voltage is not appropriate for the transmission of energy over long distances. At the generating station, a transformer is used to increase the voltage and reduce the #current.

In Figure 1 the voltage is increased to 500 kV and an extra-high voltage (EHV) line transmits the generator-produced energy to a distant #substation.

The voltage is reduced at the 500 kV/220 kV EHV substation to the high voltage level and high voltage lines transmit the energy to high voltage substations located within cities.

At the high-voltage substation, the voltage is reduced to 69 kV. Sub-transmission lines connect the high-voltage substation to many local #distribution stations located within cities. Sub-transmission lines are frequently located along major streets.

The voltage is reduced to 12 kV at the distribution substation. Several distribution lines emanate from each distribution substation as #overhead or #underground lines. Distribution lines distribute the energy along streets and alleys.

!!! Each line supplies several step-down transformers distributed along the line.

The distribution transformer reduces the voltage to 230/115 V, which supplies houses, shopping centres, and other local loads. The large industrial plants and factories are supplied directly by a sub-transmission line or a dedicated distribution line as shown in Figure 1 above.

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