Motor soft starter

One of the main drawbacks of squirrel-cage induction motors is their high inrush currents. And if theoretically the methods for reducing them have been well developed for quite some time, then almost all of these developments (using starting resistors and reactors, switching from a star to a triangle, using thyristor voltage regulators, etc.) were used very rarely.

Everything has changed dramatically in our time, because thanks to the progress of power electronics and microprocessor technology, compact, convenient and efficient have appeared on the market soft starters for electric motors (soft starters).

Soft starters of induction motors are devices that significantly increase the life of electric motors and actuators operating from the shaft of this motor. When the supply voltage is applied in the usual way, processes occur that destroy the electric motor.

Starting current and voltage on the motor windings, at the time of transients, significantly exceed the permissible values. This leads to wear and breakdown of the insulation of the windings, "burning" of the contacts, significantly reduces the service life of the bearings, both the motor itself and the devices "sitting" on the motor shaft.

To provide the necessary starting power, it is necessary to increase the rated power of the supplying electric networks, which leads to a significant increase in the cost of equipment and the cost of electricity.

In addition, the "subsidence" of the supply voltage at the time of starting the electric motor - can lead to damage to equipment used from the same power sources, the same "subsidence" causes serious damage to the power supply equipment, reduces its service life.

At the time of start-up, the electric motor is a serious source of electromagnetic interference, disrupting the operation of electronic equipment powered from the same electrical networks, or located in close proximity to the engine.

If an emergency occurs and the engine overheats or burns out, then, as a result of heating, the parameters of the transformer steel change so that the rated power of the repaired engine can decrease by up to 30%, as a result, this electric motor will be unusable in the same place.

The soft starter of electric motors combines the functions of a soft start and braking, protection of mechanisms and electric motors, as well as communication with automation systems.

Soft start using soft starter is realized by a slow rise in voltage to smoothly accelerate the engine and reduce starting currents. Adjustable parameters are usually the initial voltage, acceleration time and braking time of the motor. A very small value of the initial voltage can greatly reduce the starting torque of the motor, so it is usually set to 30-60% of the nominal voltage.

When starting the voltage, it jumps up to the set value of the initial voltage, and then gradually rises to the nominal value over the specified acceleration time. At the same time, the electric engine will smoothly and quickly accelerate to rated speed.

The use of soft starters allows to reduce the starting “surge” of current to minimum values, reduces the number of relays used and contactorscircuit breakers. Provides reliable protection for electric motors from emergency overload, overheating, jamming, phase failure, reduces the level of electromagnetic interference.

Soft starters for electric motors are easy to install, install and operate.

Example wiring diagram for a soft starter motor

When choosing a soft starter, consider the following:

1. Electric motor current. It is necessary to choose a soft starter at the full load current of the motor, which should not exceed the maximum load current of the soft starter.

2. The maximum number of starts per hour. Usually it is limited to a soft starter. It is necessary that the number of starts per hour of the electric motor does not exceed this parameter.

3. Mains voltage. Each soft starter is designed to operate at a specific voltage. The power supply voltage must correspond to the rated value of the soft starter.