Electrical Power Systems Technology

Operational Power Control Systems 435

apply full voltage to the motor. Notice that a step-down transformer is used

for applying voltage to the control portion of the circuit. This is a commonly

used technique for reducing the voltage applied to the relay coils.

Primary Reactor Starting—Another method, similar to primary re-

sistance starting, is called the primary reactor starting method. Reactors

(coils) are used in place of resistors, since they consume smaller amounts

of power from the AC source. Usually, this method is more appropriate for

large motors that are rated at 600 volts.

Autotransformer Starting—A utotransformer starting is another

method used to start electric motors. This method employs one or more

autotransformers to control the voltage that is applied to a motor. The auto-

transformers used are ordinarily tapped to provide a range of starting-cur-

Figure 16-11. Full-voltage starting circuit for a three-phase motor (Courtesy

Furnas Electric Co.)