Star/Delta Starters - Danfoss VLT Pocket Manual

Star/Delta Starters: How does soft start compare
with star/delta starting?
Soft starters are much more fl exible than star/delta starters and provide
a smooth start with no risk of current or torque transients.
Star/delta starters cannot accommodate varying load conditions (e.g.
loaded or unloaded starts) and the start torque cannot be adjusted to
match motor and load characteristics. In addition, the open transition
between star and delta connection causes damaging torque and
current transients. Star/delta starters are not capable of providing soft
stop.
Star/delta starters may be cheaper than a soft starter and they may limit
the start current to a lower level than a soft starter when used on an
extremely light load. However, damaging current and torque transients
may still occur.
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40 VLT Soft Starter Pocket Guide