Why do you need a soft starter?

IMAGINE YOU are sitting in traffic. When the traffic light turns green, it’s usually a good idea to not stamp on the accelerator to reach full speed, because this may cause mechanical wear on the vehicle and could be rather inefficient, on top of being dangerous. The same is true for electronic equipment, where a slow start helps reduce energy consumption and excessive wear. This is why by using soft starters in electric motors, manufacturers can boost energy efficiency and improve the machine’s performance.

Soft starters are used to limit the initial inrush of current and provide a gradual ramp up to full speed or to stop gradually where a sudden halt may damage the connected equipment. They help reduce the mechanical stress on the motor and shaft as well as the electrodynamic stresses on the attached power cables and electrical distribution network.

Soft starters use three pairs of silicon controlled rectifiers (SCRs), one for each phase of power. Each pair of SCRs is used. They are applied gradually for the portion of each voltage phase, controlling the voltage provided to the motor and thus temporarily reducing the motor’s terminal voltage. Accordingly, current is reduced proportionally to the reduction in voltage. As torque is proportional to the square of the voltage, even a smaller reduction in voltage leads to a large reduction in torque. For instance, a 50% reduction in voltage results in a 50% reduction in current and a 75% reduction in torque.

Reduce energy consumption

Electric motors used in industry are responsible for two thirds of the entire industrial electricity consumption in the UK. The energy cost to run an electric motor over ten years is at least 30 times its original price.

Since accelerating up to the required speed needs a lot of power, the startup of motors could consume vast amounts of energy. To control the energy consumption during this period, manufacturers could consider using soft starters. With a normal start, the motor immediately starts consuming the maximum amount of energy and continues to do so for the whole operation. With soft starters, the voltage gradually rises to the maximum, leading to a smooth acceleration of the motor and coupled load. In this way, less overall energy is used.

Improve motor performance

Besides reducing energy consumption, a soft starter helps protect the motor and connected equipment from damage by providing a gradual acceleration of the drive system and thus reducing the mechanical shock associated with motors’ startup. The reduced mechanical wear on motors and other components such as belts and pulleys, gears and chains as well as couplings and bearings, could significantly extend the system’s lifetime, contributing to shorter downtime and less maintenance.

Moreover, soft starters only cost up to one-tenth of the price of high-power drives. Therefore, for applications where only the control of speed and torque during motor startup is required, a soft starter could be an economical choice. Another benefit of soft starters is that they usually take up less space than variable speed drives (VSD).

By adopting soft starters, manufacturers can boost energy efficiency while also improving motors’ performance. Owing to the colossal energy consumption of electric motors, it is necessary to apply cost-effective and energy-saving products, like soft starters, from the beginning of the operation of electric motors. EU Automation provides a large supply of automation parts for electric motors, servo drives, PLC systems, HMIs and other industrial applications.

Neil Ballinger is head of EMEA at EU Automation

www.euautomation.com/uk