Soft Starter

The moment a motor creates a voltage dip on the bus and other feeders begin to react is when a soft starter can be put to good use. Any time that we are selecting a soft starter, we always check to see what the driven load, starting torque requirement and allowable starting time require.

For example, a lightly loaded pump will be able to start at a much lower current than a conveyor loaded with material will; therefore, though both may have the same KVA, the conveyor will have much larger initial torque and a different ramp profile. The rating of a soft starter is determined by thermal capacity for multiple starts, and not by motor kW rating.

We utilize Schneider soft starters from the ATS22, ATS48, and ATS480 series in MCC (Motor Control Centre) panels and as stand alone motor control feeders. Bypass arrangements should be implemented such that continuous running current does not pass through the thyristor section. To ensure that nuisance tripping does not occur during the ramp up period, it is important to ensure proper protection coordination between the upstream circuit breaker and overload relay.

Control wiring has been simplified. The control wiring consists of all start/stop functions and fault feedback directing the PLC control panels, or the local push button, to control the operation of the Soft Starter. The Soft Starter should be tested at a controlled simulated motor load to validate the following parameters: current limit; acceleration ramp; deceleration mode; and kick-start function, checking for proper performance using the same parameters. It is also important to check for adequate heat dissipation from the Soft Starter enclosure due to the fact that Soft Starters will be operating at elevated temperatures for the duration of their start duty cycle.

The Soft Starter will reduce mechanical loading on couplings, limit the inrush current through the electrical supply mains, and provide smooth acceleration of the motor and will not disturb other connected loads when installed in US manufacturing facilities.