Primary Resistance Starters - Danfoss VLT Pocket Manual

Primary Resistance Starters: How does soft start
compare to primary resistance starting?
Soft starters are more fl exible and reliable than primary resistance
starters.
Primary resistance starters cannot accommodate varying load
conditions (e.g. loaded or unloaded starts) and the start torque cannot
be fi ne-tuned to match motor and load characteristics. Performance
may vary with multiple starts in close succession, because the start
profi le changes as the resistance heats up. Damaging torque and
current transients still occur at the steps between voltages, and
primary resistance starters are not capable of providing soft stop.
Primary resistance starters are large and expensive, and liquid
resistance starters require frequent maintenance.
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32 VLT Soft Starter Pocket Guide