Page 130 - Electrical Equipment Handbook _ Troubleshooting and Maintenance

INDUCTION MOTORS

INDUCTION MOTORS 6.19

normal. When the motor approaches the operating speed, those contacts are opened, and
contact 2 is shut, putting the full line voltage across the motor.
When the starting current is reduced proportionally to the decrease in terminal voltage,
the starting torque decreases proportionally to the square of the applied voltage. Hence, the
reduction in starting current is limited when the motor is coupled to a load.

Induction Motor Starting Circuits

Figure 6.23 illustrates a typical full-voltage or across-the-line induction motor starter cir-
cuit. The meanings of the symbols are explained in Fig. 6.24. When the start button is

FIGURE 6.23 A typical across-the-line starter for an induction motor.

FIGURE 6.24 Typical components found in induction motor control circuits.

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