Power Factor Correction - Danfoss VLT Pocket Manual

Power factor correction: Can power factor correction
be used with soft starters?
Power factor correction (PFC) capacitors can be used with soft starters,
provided they are switched in using a dedicated contactor when the
motor is running at full speed. PFC must always be installed on the
input side of the soft starter; connecting PFC capacitors to the output
of a soft starter causes resonance between the inductance of the motor
and the power factor capacitance, resulting in severe overvoltage and
equipment failure.
The contactor should be AC6 rated for the motor full load current.
PFC capacitors can be sized using the following formula:
_
kVA (Cap) = √ 3 x V x 0.8 x motor no load current
line
1000
®
VLT Soft Starter Pocket Guide 31