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A Soft Starter is a device that starts motors with reduced power supplied at start-up. Reducing the power reduces potentially damaging electrical and mechanical shocks on the system.

As the name implies, starters “start” motors. They can also stop, reverse, accelerate and protect them. Whether it’s a small fan, or piece of mining equipment, electric motor are often the driving force behind them. Electric motors consume 60% to 70% of all energy used in the United States

Soft Starters are a combination of a controller and overload protection.

CONTROLLERS – turns electric current to the motor on and off. A contactor is a controller that is controlled by an electromagnet.

OVERLOAD PROTECTION – protects a motor from drawing too much current and “burning out” from overheating. The overload relay is the motor overload protection used in soft starters. It limits the time the overload current is drawn and protects the motor from overheating.

Soft Starters place a device called a reduced voltage starter, or soft starter, between the motor and the incoming utility line to regulate the amount of current fed to the motor. Soft Starters enable the AC induction motor to speed up in smaller, resulting in less current drawn than with a traditional motor starter. Due to decreased voltage, torque is also reduced resulting in a soft, or easy start. Soft Starters are used on all types of AC and DC motors. They are most commonly used with the AC squirrel cage induction motor because of its simplicity, ruggedness and reliability.

Why Soft Starters are Needed

To avoid overloading the power distribution system

To avoid unnecessary wear and tear on equipment by reducing starting torque

A typical NEMA design B motor can draw six to eight times its full load operating current when it’s first started. If the utility’s power distribution network is loaded to capacity, the current inrush from starting up large motors can result in anything from flickering lights to brownouts. It can also result in nuisance tripping of circuit breakers and protective devices on the system. Many utilities impose limits on the amount of power customers can draw at any one time, enabling a balance in their distribution system. Reducing voltage to motor terminals at startup reduces the current surge.

Types of Soft Starters

There are five main varieties of Soft Starters:

Primary Resistor

Auto Transformer

Part Winding

Wye Delta

Solid State