Soft Starters

Optimizing the operation of large power systems is the key tool that allows industrial enterprises to significantly reduce their energy operating costs. The most critical moment for any motor is its startup, when starting currents exceed the rated values by several times, causing the windings to overheat and resulting in voltage sags in the power grid. Specialized protective equipment helps prevent this. Below, we’ll explain exactly how soft starters work, how they differ from variable frequency drive systems, and what criteria to use when selecting equipment.

What are soft starters?

An industrial oft starters (PPS, soft starter) is electronic power equipment designed to limit the rate of rise of the starting current and torque in three-phase induction motors. Soft starters are closely related to other drive technologies, but they perform a more specific engineering task. While classic industrial frequency converters provide continuous control of the shaft speed throughout the entire operating cycle, a soft starters controls the motor exclusively during acceleration and deceleration.

The main feature of a soft starters is that it does not change the frequency of the voltage but only gradually increases its amplitude. This makes it a cost-effective choice for mechanisms with a constant operating speed, where there is no need to regulate the speed but it is important to eliminate dynamic start-up surges.

How soft start work

The operation of soft starters is based on phase control using thyristors connected in an anti-parallel configuration in each of the three power supply phases. At the start of the startup, the microprocessor board opens the thyristors to a minimum angle, applying a reduced voltage to the motor windings. As the rotor accelerates, this angle gradually increases, allowing the output voltage to reach the rated 100%.

As a result, the starting current is kept at a safe level. Immediately after acceleration is complete, the thyristor circuit is typically bypassed by a built-in contactor, and the motor switches to direct power from the mains. It is important to remember that a soft starters significantly reduces the starting torque; therefore, for very heavy-duty starts on high-voltage lines, it is more appropriate to use full-fledged high-voltage frequency converters drives, capable of starting motors under maximum load.

Key characteristics of soft starters

To select the right equipment, engineers analyze a set of parameters that directly affect the stability of the circuit’s operation.

Key characteristics of soft starters:

1. Rated current and power: selected with a margin of 10–20% above the electric motor’s parameters, taking into account the starting category.
2. Number of controlled phases: Industrial versions provide full three-phase control, ensuring perfect current symmetry.
3. Acceleration and stopping modes: Ability to configure the start-up using current limiting, linear voltage ramp-up, or the Kicker Start initial pulse.

Analyzing these criteria allows you to integrate the software into the overall automation system without the risk of critical failures during operation.

How to choose a soft starters for your needs?

Before purchasing a soft starters, you must clearly define the nature of the load on the motor shaft. All industrial starters are classified into classes (Class 10, 20, or 30) depending on the acceleration time. Standard devices are suitable for fans and pumps, while crushers or reciprocating compressors require heavy-duty models with high overload capacity.

Be sure to check for an integrated bypass contactor, which saves space in the control panel. If the process requires periodic speed changes or reversal during operation, a soft starters will not be sufficient. In such cases, full-featured low-voltage frequency converters are installed, which fully control frequency and speed.

Installation and configuration of soft starters

Soft starters are installed in enclosed electrical cabinets with forced ventilation, since thyristor modules generate a significant amount of heat. Power cables are connected using one of two configurations: in-line or “into the delta” of the motor windings, which allows the use of a soft starters with a lower rating.

Initial setup is performed via the built-in graphical interface. The engineer sets the basic parameters: ramp-up time from 5 to 30 seconds, initial voltage level, and starting current limit. A properly configured stop ramp smoothly reduces pressure in hydraulic systems and prevents damage to check valves in pumping stations.

Benefits of ordering soft starters from Dalgakiran

Dalgakiran Industrial offers customized engineering solutions to protect and optimize the operation of industrial drives of any complexity. We are an official partner of global manufacturers of power electronics, so the final price of a soft starters device, reactive power compensation device, and other equipment is completely transparent, competitive, and free of hidden intermediary fees.

Working with our team relieves the customer of any worries thanks to our “turnkey” project implementation. After the equipment is commissioned, we provide continuous technical support without interruptions or days off. In addition, our own network of mobile service teams guarantees the fastest possible arrival of technicians at the site for maintenance or troubleshooting in 11 regions of Ukraine.

Modern energy-saving technologies allow Ukrainian industry to remain productive and competitive, and companies know that even during the toughest challenges, everything works with Dalgakiran.

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