Power Factor Improvement of Induction Motor Loads
When power factor correction capacitors are used, the
total corrective KVAR on the load side of the motor controller
should not exceed the value required to raise the no-load power
factor to unity. Corrective KVAR in excess of this value may
cause over excitation that results in high transient voltages,
currents and torques that can increase safety hazards to
personnel and possibly damage the motor or driven equipment.
Do not connect power factor correction capacitors at
motor terminals on elevator motors, multispeed motors, plugging
or joggging applications or open transition, wye-delta,
auto-transformer starting and some part-winding start motors.
If possible, capacitors should be located at position
No. 2 (see diagram, below). This does not change the current
flowing through the motor overload protectors. Capacitors should
be located at position No. 1 for applications listed in Paragraph
No. 2 above. Be sure bus power factor is not increased above 95
percent under all loading conditions to avoid over excitation.
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