22 | Danfoss Drives · DKDD.PB.551.A1.02
Soft starters can be used with ying loads (motors that are already
rotating), without any special wiring or conguration.
As a general rule, the faster the motor is rotating in the forward
direction, the shorter the start time will be.
If the motor is rotating in the reverse direction, it will be slowed to
a standstill before accelerating in the forward direction. In this case
allow for the extended start time when rating the soft starter.
Flying Loads: Are soft starters suitable for use
with a ying load?
Harmonics: Are harmonics an issue for
soft starter applications?
Harmonics are voltages and currents that create unwanted heating
in motors, cables and other equipment. Harmonics may also
disrupt operation of other electrical and electronic equipment.
Soft starters generate very low levels of harmonics, only during
starting or soft stopping. According to IEC 60947-4-2 (8.3.2.1.1),
“harmonic emissions are of short duration during starting, and
there are no signicant emissions in the FULL-ON state”. No special
considerations or ltering are required for soft start applications.
All MCD soft starters comply with the EMC directive on
radiofrequency emissions and immunity.
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