A soft starter has different characteristics to the other starting methods. It has thyristors in the main circuit, and the motor voltage is regulated with a printed circuit board.It can control the current flow to motor more efficient and stability.
The soft starter makes use of the fact that when the motor voltage is low during start, the starting current and starting torque is also low.This type of motor starting is common used for air-condition and chiller system because it can reduce starting current in rush and can made a compressor more life span.
How a soft stater operation ?
- During the first part of the start the voltage to the motor is so low that it is only able to adjust the play between the gear wheels or stretching driving belts or chains etc. In other words,eliminating unnecessary jerks during the start.
- Gradually, the voltage and the torque increase so that the machinery starts to accelerate.
- One of the benefits with this starting method is the possibility to adjust the torque to the exact need, whether the application is loaded or not.
- In principle the full starting torque is available, but with the big difference that the starting procedure is much more forgiving to the driven machinery, with lower maintenance costs as a result.
- Another feature of the soft starter is the softstop function, which is very useful when stopping pumps where the problem is water hammering in the pipe system at direct stop as for star-delta starter and direct-on-line starter.
- The soft stop function can also be used when stopping conveyor belts to prevent material from damage when the belts stop too quickly
For more detail information,please refer to MOTOR CONTROL HANDBOOKS :