Moeller - Basics of drives engineering - Soft starters (electronic motor start)

Soft starters (electronic motor start) [t-head1-pg]

The characteristic curves for DOL and star-delta starting show sudden current and torque changes, which have a number of negative effects, especially at medium and high motor ratings:

High mechanical machine loads

Rapid wear

Increased servicing costs

High supply costs from the power supply companies (peak current calculation)

High mains and generator load

Voltage dips with a negative effect in other consumers

The ideal scenario of a smooth torque build-up and a controlled current reduction in the starting phase is made possible by the electronic soft starter. Providing infinitely variable control of the three-phase motor’s supply voltage in the starting phase, it matches the motor to the load behaviour of the driven machine and accelerates it smoothly. This avoids mechanical jolting and suppresses current peaks. Soft starters present an electronic alternative to the conventional star-delta switch.

Features of the soft starters [t-head3]

For low- to high-power three-phase motors

No current peaks

Zero maintenance

Reduced adjustable starting torque