Rockwell-automation 150 MNL/SMC DIALOG+/APP-PROD GUIDE Manual de usuario descargar pdf (Pagina 155)

8-2

Reduced Voltage Starting

Reduced Voltage

The most widely used method of electromechanical reduced voltage

starting is the autotransformer. Wye-Delta (Y-D), also referred to as

Star-Delta, is the next most popular method

Figure 8.2 Bulletin 570 Autotransformer

All forms of reduced voltage starting affect the motor current and

torque characteristics. When a reduced voltage is applied to a motor

at rest, the current drawn by the motor is reduced. In addition, the

torque produced by the motor is a factor of approximately the square

of the percentage of voltage applied.

For example, if 50% voltage is applied to the motor, a starting torque

of approximately 25% of the normal starting torque would b

produced. In the previous full voltage example, the NEMA Design B

motor had a starting torque of 180% of full load torque. With only

50% voltage applied, this would equate to approximately 45% of full

load torque. Table 5.A shows the typical relationship of voltage,

current, and torque for a NEMA Design B motor.

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Rockwell-automation 150 MNL/SMC DIALOG+/APP-PROD GUIDE Manual de usuario Pagina 155