Soft starter is a motor control device that integrates motor soft start, soft stop, light load, energy saving, and multiple protection functions. The motor soft starter is not only made to start the 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

Electric soft starter is widely used in industry to improve the machine uptime, MTBF of drive systems, OEE (Overall Equipment Effectiveness), and TPM (Total Productive Maintenance) and to ensure safer & reliable equipment in the 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 Line), VFD (Variable Frequency Drive), auto transformer, and soft starter. Each method has its own specific applications and advantages. The electric motor requires a large amount of current and voltage to accelerate the speed of the motor up to a nominal speed. A soft starter is designed to limit the inrush current, voltage, and torque of an electronic motor which results in safer, smoother, and gradually speeds up the drive system. This setup is useful to protect the mechanical and electronic damage of the equipment and to extend the lifespan of the whole system. A soft starter for an induction motor can be operated either by Ethernet through PLC (RS485) or direct start/stop wiring.

Soft Starter Working Principle

Soft Starter Circuit Diagram

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 SCRs and each pair of SCRs is connected in parallel with forward & reverse bias to convert the complete Sine wave of AC supply into output when the positive & negative half cycle of the sine wave appears at the SCR terminal respectively. This whole mechanism is controlled by triggering the SCR at the gate using a 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 the motor to protect mechanical and electrical failure of the device.

Advantages of Soft Starter

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

Soft Starter 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.

Peaco Support provides a broad range of power of three-phase soft starters, including 7.5kw soft starters, 11kw soft starters, 15kw soft starters, 30kw soft starters, 75kw soft starters, 90kw soft starters, etc. The soft start contactor can be added for the soft starter as per requirements, which is the soft starter with built-in bypass (contactor). The soft starter price is competitive.

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