Discover the Different Types of Soft Starters for Your Motors

Soft starters have various types. All versions of the soft starter enable loaded motors to be started smoothly. But there are some differences between them. Let’s go step by step and check the types of soft starters used in the industry.

Types of Soft starters

There are different styles of soft starters that control the motor in different ways and offer different features. Some soft starter types are:

1-phase controlled soft starter

When the terms 1-phase, 2-phase, or 3-phase ‘controlled soft starter’ are used, it refers to the number of sets of thyristors that are being used. 1 phase-controlled device has thyristors only in 1 phase.

The remaining phases are directly connected from line to load. 1 phase-controlled device reduces torque shock at the start but does not reduce start current. Also known as torque controllers, these devices must be used in conjunction with a direct online starter.

2-phase controlled soft starter

2 phase-controlled devices have thyristors in 2 phases. The remaining phase is directly connected from line to load. These devices eliminate torque transients and reduce motor start current. The first thing noted when starting a 3-phase motor with a 2-phase controlled soft starter is that the currents in the phases are not equal. Typically, the controlled phases have approximately 30-50% lower current relative to the uncontrolled. When a compact and cost-effective solution is required 2 phase-controlled soft starters can be used. 2-phase soft starters can’t be used with an inside delta connection.

3-phase controlled soft starter

These devices control all three phases, providing the optimum in soft start control. Three-phase control should be used for severe starting situations. In 3-phase controlled soft starters, all three phases will have 2 thyristors/phase. Here 3 phase current will be fully balanced when compared to 2-phase controlled devices. 3-phase soft starters can be connected inside delta.

In-line connected soft starter

An in-line connection is the most common and also the easiest way to connect the soft starter. It’s also called direct connection. All three phases are connected in series with the overload relay, the main contactor, and other devices. The selected devices for an inline connection must be chosen to cope with the full-rated motor current. The motor itself can either be star-connected or delta-connected.

Inside delta connected soft starter

The inside delta connection makes it possible to place the soft starter in the delta circuit and allows for a very easy replacement of existing star-delta starters. When the soft starter is inside delta it will only be exposed to 58% of the Inline current. Therefore, it is possible to downsize the devices to achieve a more cost-effective solution.

A direct connection requires less output wiring than an inside delta connection, which requires double the wiring. On the other hand, the inside delta connection requires a smaller cross-section. Because of this, an inside delta connection will normally be a less expensive option for short distances, when considering the soft starter + motor + wiring.

A motor used for an Inside Delta connection must be able to delta-connect during a continuous run. In the USA and some other countries, a special six-wire motor has to be ordered for this type of connection.

Potentiometer-type soft starter

Potentiometer- type soft starters are generally basic soft starters. The set-up of the soft starter can easily be done and confirmed using marked potentiometers on the front.

Displayed type soft starter

Displayed type soft starters are advanced soft starters. The display and the button keypad make it easy to take advantage of all the advanced functionality in the soft starter. The display is used for several purposes such as programming the soft starter, i.e. setting up inputs and outputs, protection functions, warning levels, Fieldbus communication, etc. The display will also provide all the necessary information both during ramping and continuous operation.

Class 10 type soft starter – Normal start

The involved moment of inertia or flywheel mass is the size of the flywheel, connected to the motor axis. An application with a small moment of inertia is usually called a normal start. A normal start has a small moment of inertia and a short starting time. Normally OL class 10 is used. Examples of applications are pumps, compressors, bow thrusters, and short conveyor belts. You can select the soft starter size according to the motor kW ratings.

Class 30 type soft starter – Heavy-duty start

An application with a big moment of inertia is called a heavy-duty start. The heavy-duty start has a big moment of inertia and a long starting time. Normally OL class 30 is used. Examples of applications are fans, crushers, mills, and long conveyor belts. You can select a soft starter one size larger compared to the motor kW ratings.