Auto-Transformer Starters - Danfoss VLT Pocket Manual

Auto-Transformer Starters: How does soft start
compare to auto-transformer starting?
Soft starters are much more fl exible than auto-transformer starters and
provide a much smoother start, generally at a lower cost.
Auto-transformer starters cannot accommodate varying load
conditions (e.g. loaded or unloaded starts) and the start torque cannot
be freely adjusted to match motor and load characteristics. Damaging
torque and current transients still occur at the steps between voltages,
and auto-transformer starters are not capable of providing soft stop.
Auto-transformer starters are large and expensive, especially if high
start frequency is required.
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14 VLT Soft Starter Pocket Guide