Soft starter versus VSD Control
Soft Starters:-
Used for fixed speed application. Not suitable for speed/torque control during running. Motor speed is controlled during starting by applying a reduced voltage, which increases until full voltage is reached.
The main benefit of this unit is that eliminates the starting inrush current which occurs with D.O.L starting of motors. (Sudden torque).
Saves energy by eliminating the inrush current. Improves the life of the motor & the driven machine by gradual application of torque. Once the full speed is achieved the by-pass contactor may be used to disconnect soft start unit and connect the motor to main supply.
Why VSD?
Used for simple process control:-
In most process there may be a need for controlling a variable of the process. This variable may need to be kept constant or be changed according to a pre-set pattern. variables such as:- Speed, Pressure, temperature ,flow, etc. Reduce fan noise. Enable operation above motor base speed.
Energy control a saving:-
Reduction of running costs by reducing the power wasted, tuning the motor speed to the load demand. Motors running at full speed but half load waste energy and increase running costs.
Replacing mechanical controls such as dampers, valves & throttling. Reducing maintenance costs by replacing mechanical controls. Improving motor and machine life expectancy by reducing shock loads and mechanical stress.