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  • IEC 60034-31:2009

  • 15 –

2/1554/CD

5.7

Power Factor

1

Efficiency [%]

150kW

15kW

1,1kW

0,9

0,8

0,7

0,6

0,5

0,4

0,3

  • 0

    0,25

0,5

0,75

1

P/PN

1,25

Figure 4

Typical power factor versus load curve bands for 2- and 4-pole three-phase, cage-induction motors

The total motor load in a facility is usually a major factor in determining the system power factor. Low system power factor results in increased losses in the distribution system. Induction motors inherently cause a lagging system power factor. The power factor of an induction motor decreases as the load decreases. Rated-load power factor increases with an increase in the power rating of the motor. A number of induction motors, all operating at light load, can cause the electrical system to have a low power factor. The power factor of induction motors at rated load is lower for low-speed motors than for high-speed motors.

A small increase in voltage (less than 10 percent) above rated voltage will decrease the power factor, and a small decrease in voltage (less than 10 percent) below rated voltage will improve the power factor of an induction motor. However, other performance characteristics may be adversely affected by such a change in voltage and operation as close as possible to the rating-plate voltage and power rating is recommended.

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