30 | Danfoss Drives · DKDD.PB.551.A1.02
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
line
x 0.8 x motor no load current
1000
Power factor correction: Can power factor correction
be used with soft starters?
Thermal capacity, also called “maximum locked rotor time” or
“maximum DOL start time”, describes the maximum time a motor
can run at locked rotor current from cold. This information is
usually available from the motor datasheet.
The MCD 202 overload protection can be set to match the motors
thermal capability using the motors locked rotor time (cold).
Motor thermal capacity: What is it?
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