How Soft starter works?

A soft starter is another form of reduced voltage starter for A.C. induction motors. The soft starter is similar to a primary resistance or primary reactance starter in that it is in series with the supply to the motor. (Three wire or standard connection) The current into the starter equals the current out. The soft starter employs solid state devices to control the current flow and therefore the voltage applied to the motor. In theory, soft starters can be connected in series with the line voltage applied to the motor, or can be connected inside the delta loop of a delta connected motor, controlling the voltage applied to each winding.

SCRs

Most soft starters are made from solid-state switches known as silicon-controlled rectifiers, or SCRs. They have a simple job: regulate voltage so the motor first is given a low-voltage surge, which ramps up as the motor starts to turn, saving on wear and tear and often helping electronic components to last longer. The switches turn on in rapid succession to let more and more voltage through.

Phase Designs

Soft starters vary for different phases. A single-phase unit controls starting torque but does not really affect the current much, which makes it difficult to help motors with frequent cycling. Two-phase starters offer more protection but typically are used with a thermal switch to help protect the motor. Three-phase starters control all three phases of the common motor and offer much more complete protection.

Loop Options

Soft starters can be open-loop or closed-loop. Open-loop units have no feedback, so they control voltage only according to a preset voltage setting. If the motor does not match that setting, the soft starter might not operate correctly. Closed-loop versions offer a feedback loop that allows the starter to determine how it needs to protect the motor.

We, at KMIC, provide softstarters from all leading brands ABB, Siemens, Schneider, Alan Bradley, L&T Yashkawa etc. Feel free to contact us for any inquiries for soft starters.