Why does a high-power motor initiate a recovery soft start

Update:13 Oct 2021

When we are purchasing high-power motors, the general motor manufacturer asks about the start-up method of the high-power motors to ensure that the high-power electrical performance recovery meets the start-up method to start operation.

Because when the high-power motor is started directly at full voltage, the starting current will instantly reach 4 to 7 times the rated current, and when the capacity of the high-power motor is relatively large, the current directly started by the high-power motor will cause the grid voltage to sharpen Decrease, affecting the normal operation of other equipment on the same power grid.

In soft start, the starting current is generally 2 to 3 times the rated current, and the grid voltage fluctuation rate is generally within 10%, which has little impact on other equipment.

Other full-voltage starting will damage the insulation of high-power motors and reduce the service life of the motor; ①The heat generated by the large current is repeatedly impregnated into the outer insulation of the wire, which accelerates the aging of the insulation and reduces the life. ②The machine force generated by the large current causes the wires to rub against each other, which reduces the insulation life. ③When the high-voltage switch is closed, the chattering of the contacts will cause overvoltages on the motor stator windings, sometimes reaching more than 5 times the applied voltage. Such high overvoltages will cause great damage to the motor insulation. When soft-starting, the maximum current drops by about half, and the instantaneous fever is only about 1/4 of straight-up, and the insulation life will be greatly delayed. When soft-starting, the motor terminal voltage can be adjusted from zero, which can completely avoid over-voltage damage.

Full-voltage start will cause damage to the machinery and equipment. The large current will cause great attack on the motor stator coil and rotor squirrel cage bar, which will cause the clamping looseness, coil deformation, squirrel cage bar breakage and other obstacles. During soft start, the attack power is greatly reduced due to the small maximum current. The starting torque at full-pressure direct starting is about twice the rated torque. Such a large moment is suddenly added to stationary machinery and equipment, which will accelerate gear wear or even toothing, accelerate belt wear and even break the belt, and speed up the fan blades. Tired and even broken wind leaves and so on.

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