Unit Substation

The main substation supplies power to many unit substations. Each of the unit substations is designed to reduce the voltage to some lower value. One such substations is shown as transformer T3. This transformer reduces power voltage from 13.8 kV to 440 volts.

440 Volt System

Notice two motors are supplied with 440 ac power voltage through the breakers B7 and B8. Most of the electric motors in an industrial plant are rated at 440 volt. Some are rated at 2300 volts as well. 13.8kV motors which we discussed earlier are extremely rare.

110 Volt System

The 440 volt bus supplies power to transformer T4. The purpose of the transformer T4 is to reduce the power voltage from 440 volt to 110 volt. The 110 volt system is designed to supply power for lights and other low voltage devices.