The soft starter is a motor control device that integrates motor soft start, soft stop, light load, energy saving and multiple protection functions. It is not only make to  start motor smoothly without any adverse impact during the whole starting process, but also can adjust the parameters during the starting process such as current limit value, starting time, etc., according to the characteristics of the motor load.

The Importance of Soft Starter

Soft starter is widely used in industry to improve the machine Uptime, MTBF of drive system, OEE (Overall equipment effectiveness), TPM (Total productive maintenance) and to ensure safer & reliable equipment in workplace.

Most of the failure of equipment occurs due to sudden shock during ramping up & down the drive system with high voltage, current, frequency and torque. To avoid this, there are various methods to start the electric motor such as DOL (Direct on Line), VFD (Variable Frequency Drive), auto transformer and soft starter. Each method has its own specific applications and advantages. Electric motor requires large amount of current and voltage to accelerate the speed of motor up to nominal speed. A soft starter is designed to limit the inrush current, voltage and torque of electronic motor which results in safer, smoother and gradually speeds up the drive system. This setup is useful to protect the mechanically and electronically damage of the equipment and to extend the lifespan of the whole system. A soft starter can be operated either by Ethernet through PLC (RS485) or direct start/stop wiring. 

Soft Starter Working Principle


As shown in the soft circuit diagram–S1, the main components of a soft starter are TRIAC or SCR and logical gate. There are TRIACs or SCR and each pair of SCR is connected in parallel with forward & reverse biased to convert the complete Sine wave of AC supply into output when the positive & negative half cycle of sine wave appears at the SCR terminal respectively. This whole mechanism is controlled by triggering the SCR at gate using pulse.

When an internal pulse is applied to its gate. It permits current to flow to the motor. The pulses are generated based on the set ramp up and ramp down time. Therefore, the current is allowed slowly to the motors to gain its nominal speed with gradual torque. As shown in graph-S2, voltage ramps up and ramps down gradually with time during the start and stop of motor to protect mechanical and electrical failure of device.

Advantages of Soft Starter

  • Smooth and uniform starting of motor by gradual acceleration of the drive system which insists to developing the jerk while running the motor in initial stage.
  • Power factor correction is facilitated by avoiding the excessive current and voltage drawn by the motor in starting stage.
  • Enhance the safe working condition and build Eco-Friendly system.
  • It evidences the milestone of system by increasing the life span.
  • It is suitable for all types of induction motors.
  • Soft starter is economical and compact in size.
  • Avoid undesirable mechanical and electrical effects on the process.

Application

Soft starter has wide applications. It can be used for dust collectors, pumps, conveyor belts, milling machines, compressors, fans, mixers and other industrial machines.