Benefits of Using Soft Starter for AC Motors
Have you ever though why your motor has a shorter service life than that of others? Let us tell you, your motor may need a soft starter. Generally, the motor shall adopt a soft starter as soon as its power exceeds 20hp (15kW), otherwise it will affect the use and operation of other equipment in power grid and damage the motor. Why should the soft start controller be used? What are the benefits of using motor soft starter?
Different between Motor Full Voltage Start and Motor Soft Start
1. Lead to voltage fluctuation in power grid, affect the operation of other equipment in the same power grid
When AC motor starts directly at full voltage, the starting current will be 4-7 times of its rated current. If the motor capacity is relatively large, the starting current will cause a sharp drop in the grid voltage, and thus affecting the normal operation of other equipment in the power grid.
When using the soft starter for asynchronous motor, starting current of the motor is only 2~3 times of its rated current. As a result, voltage fluctuation of power grid is generally less than 10%, which slightly affects other equipment.
2. Affect on power grid
Affect on the power grid is mainly manifested in two aspects:
- Impact of inrush current on power grid caused by direct starting of super large motor is similar to that caused by three phase short circuit, which usually results in power oscillation and makes the power grid unstable.
- The starting current contains a large amount of higher harmonics, which may cause high frequency resonance with the power grid circuit parameters, and thus leading to faults such as malfunction of relay protection, failure of automatic control.
After using the soft starter, the motor’s starting current decreases greatly, and above affects can be completely eliminated.
3. Damage the motor’s insulation, reduce its service life
Joule heat produced by high current acts repeatedly on external insulation of the wire, which accelerates insulation aging and reduces its service life.The mechanical force produced by high current makes the wires friction with each other, which thereof reduces the insulation life.
When the high voltage switch closes, the oscillation of contacts will cause operating overvoltage on the stator winding of motor, which could be more than 5 times of the applied voltage sometimes, such a high overvoltage will cause great damage to motor insulation.
After using the soft starter, maximum current of motor would reduce by half, and the instantaneous calorific value is only about 1/4 of that under direct starting, the insulation’s service life would be greatly extended. In the soft starting, the motor voltage can be adjusted from 0, thus avoiding the damage of overvoltage.
4. Damage of electric power to motor
High current produces great impact on motor stator coil and rotor squirrel cage bar, which may lead to faults of clamping loosening, coil deformation and break of squirrel cage.
After using the soft starter, the motor’s maximum current is small, and the impact reduces greatly.
5. Damage to mechanical equipment
When the motor starts directly at a full voltage, the starting torque is about two times of the rated torque. Suddenly applying such a large torque to a stationary mechanical device will accelerate gear wear and even tooth beating, belt wear or even belt breaking, wind blade fatigue and even wind blade breaking.But if the motor is started with a soft starter, its starting torque will not exceed the rated torque, and above drawbacks can be avoided.
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