Saturday , May 28 2022

Applications and Types of Soft Starters

Something that we don’t pay much attention to when using machinery and other pieces of equipment is the way they turn on. Turning them on can be as simple as pushing a button. While this simple action is often overlooked, it is one of the most crucial operations of every machine and device. Behind this seemingly simple operation, there’s a component called a starter that helps make it happen. But people have also been trying to incorporate a different type of starter to change the startup method of their machine or device, known as a soft starter. A soft starter is a separate device that allows you to reduce the strain on the motor of a machine by controlling the voltage sent to the motor. The soft starter gradually and slowly sends the voltage to the motor which allows the machine to start up in a smooth fashion rather than in a sudden burst of power. But why is a soft starter used in the first place?

Why We Use Soft Starter?

setup soft starter


Improves Lifespan

Since a soft starter makes for a smooth power-up transition, it contributes to prolonging the lifespan of a machine as well as its components. Soft starters for motors help prevent jerks, especially when it comes to phase 3 control starters. This also helps reduce the maintenance requirements of certain components. For this reason, starters are often used in the cement industries, steel industries, textile industries, and sugar plants.

Reduces Weakening

A significant role of every soft starter is to make the startup of every machine gradual so that it prevents the weakening of electrical equipment. Be it mechanical, electrical or thermal, all switchgear, motors, and transformers will stay safe and last longer, too. This is important, especially for machines in the power sector, water supply schemes and in various process control applications.

Fewer Losses

A built-in feature that all soft starters for motors come with is power factor correction. This self-monitoring feature is capable of making the motor operate at a lower load than usual. This is done because the relative reactive component of current that is drawn by the motor comes at an excessive level due to power loss. This is where the power factor correlation feature helps prevent major current losses. For this reason, tool applications, paper and pulp, as well as rubber and plastic production need machines with a soft starter.

What Soft Starter Should You Choose?

close-up of emotron soft starter


Primary Resistor

The primary resistor soft starter motor was developed back in the early 1900s. This is a simple device with a straightforward operation that has a resistor for each phase of its three phases. These soft starters offer smooth starts, two-point acceleration and only one step of resistance. Primary resistor starters are able to send about 70% of the line voltage to the motor’s terminals. They may be the oldest starters, but they are still pretty reliable.

Part Winding

A part winding soft starter unit has the motor windings divided into two or more sets. These winding sets are separate from each other despite being intended for parallel operation. Part winding starters are compatible with dual voltage motors.

Auto Transformer

An auto transformer starter utilises a more effective method of soft starting which is preferred over the one that a primary resistor soft starter uses. Instead of using resistors, an auto transformer uses what are known as taps on the transformer windings to help control the input sent to the motor. This makes them more flexible since they allow different levels of currents to be sent to the motor. The taps auto transformers use are able to provide 80%, 65%, or at least 50% of the line voltage. This variability depends on the number of taps that happen when a machine is being turned on.


The Wye-Delta starter is a peculiar soft starter motor that looks like the letter “Y” when seen from above and it uses three coil windings. These windings are wound with six leads for both delta and wye connections. This type of “Y” connection allows for an in-line voltage to be applied to a larger winding which reduces the current.

A Wye-Delta starter provides a motor around 33% of its normal starting torque and around 58% of its normal starting voltage. Further, it switches from its wye configuration to a delta configuration in order to send the proper amount of voltage without making it seem abrupt. This is when the motor must be disconnected and then reconnected.

Solid State

For people that want to utilise the latest technology when it comes to soft starters, a solid-state unit is your best bet. Why? Because solid-state starters do not use mechanical components, but rather electrical ones. Out of the many electrical components a solid-state starter uses, the SCT, or silicon control rectifier, is the main one. This component helps control everything, including the motor voltage, current and torque. The SCR can also switch heavy currents quickly. This makes solid-state starters far more reliable and accurate since there are fewer moving components and more electrical signals.