What is a Soft Start Motor? What Benefits it Offers for Industrial Applications?

A soft start motor is a device which controls the acceleration of an electric motor by controlling the applied voltage. An induction motor has the ability to self-start because it works based on the interaction between the rotating magnetic field flux and rotor winding flux, high rotor current of torque is increased. A stator draws high current and at the time motor reaches to full speed, a large amount of current is drawn and this is the cause of heating it and damaging it.

Soft Starting

A soft starter is any device that reduces the torque applied to the electric motor and it generally consists of the solid-state device like thyristors that helps to control the application of supply voltage to the motor. A soft starter works on the fact the torque is proportional to the square of the starting current and that’s proportional to the applied voltage and then torque and current can be adjusted by reducing the voltage at the time of starting the motor. 

The soft starter can be used for different types of control:

• Open Control

A start voltage is applied with the time, irrespective of the speed of the motor or current drawn. In each phase of starter two SCRs are connected back to back and these SCRs are conducted initially at a delay of 180 degrees during the half wave cycle and this delay is reduced gradually with time until the applied voltage increases to the full supply voltage. This method is not relevant because it doesn’t actually control the motor acceleration.

• Closed Loop Control

In closed-loop control, the motor output speed characteristics are monitored and the starting voltage is modified accordingly to get the required response. The current in each phase is monitored and if it exceeds in certain set point then the time voltage ramp is halted. 

2 Components of Basic Soft Starter:

• Power Switches

Power switches like SCRs that need to be phase-controlled and after that, they are applied to each part of the cycle. Power switch needs to be rated at least three times more than the line voltage.

• Control Logic

Control logic is a basic component of soft starter and it helps to control the application of gate voltage to the SCR. For this, control logic uses PID controllers, microcontrollers or any other logic. It also controls the firing angle of SCR that helps to make the SCR conduct at the required part of the supply voltage cycle.

Advantages of Soft Starter

• Improved Efficiency:  The efficiency of the soft starter is improved as solid state switches are increased to the low on-state voltage.
  
  
• Controlled Startup:  The starting current can smoothly control the starting voltage and it ensures smooth starting of the motor without any jerk.
  
  
• Controlled Acceleration:  Starting motor controls the acceleration smoothly.

A soft start motor helps to eliminate the undesired side effects and it continuously controls the three-phase motors voltage supply during the startup phase. When consulting a soft start motor manufacturer for your industrial application device, make sure to research about the particular device to gain maximum advantage from that for enhanced efficiency.

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Created on Jul 8th 2019 08:09. Viewed 451 times.

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