Harmfulness of air compressor motor direct full pressure start and the benefits of motor soft start cabinet

With the development of my country's economy, the application of motors is increasing, and people's attention is paid to the starting method of motors. Generally speaking, the motor soft start cabinet should be used when the motor power exceeds 30KW, otherwise it will seriously affect the operation of other equipment in the power grid and damage the motor itself.

   The hazards of direct full-voltage starting of the air compressor motor and the benefits of the motor soft start cabinet:

   1. Cause voltage fluctuations in the power grid, affecting the operation of other equipment on the same power grid

   When the AC motor is started directly at full voltage, the starting current will reach 4-7 times the rated current. When the capacity of the motor is relatively large, the starting current will cause a sharp drop in the grid voltage and affect the normal operation of other equipment on the grid.

   When using a soft-start cabinet for motors, the starting current is generally 2 to 3 times the rated current, and the grid voltage fluctuation rate is generally within 10%, which has very little impact on other equipment.

  2. Impact on the power grid

   The impact on the power grid is mainly manifested in two aspects:

  ① The impact of the large current directly started by the super-large motor on the power grid is almost similar to the impact of a three-phase short circuit on the power grid, which often causes power oscillations and destabilizes the power grid.

  ②The starting current contains a large number of high-order harmonics, which will cause high-frequency resonance with the power grid circuit parameters, causing malfunctions such as relay protection malfunction and automatic control failure.

   The starting current is greatly reduced when the soft-start cabinet for the motor starts, and the above influence can be completely eliminated.

  3, damage the motor insulation and reduce the motor life

  ①The Joule heat generated by the large current repeatedly acts on the outer insulation of the wire, which accelerates the aging of the insulation and reduces its life.

  ②The mechanical force generated by the large current causes the wires to rub against each other, reducing the insulation life.

  ③ When the high-voltage switch is closed, the vibration of the contacts will produce operating 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 using a soft-start cabinet for a motor, the maximum current is reduced by about half, and the instantaneous heat generation is only about 1/4 of the straight-up, and the insulation life will be greatly extended; the motor terminal voltage can be adjusted from zero during soft-start, which can completely avoid overvoltage damage.

  4, the damage of electric power to the motor

   The large current produces a great impact on the motor stator coil and rotor squirrel cage bar, which will cause the clamping loose, the coil deformation, and the squirrel cage bar breakage.

   When using a soft-start cabinet for motors, the impact force is greatly reduced due to the small maximum current.

   5. Damage to machinery and equipment

The starting torque at full-pressure direct starting is about twice the rated torque. Sudden addition of such a large torque to stationary mechanical equipment will accelerate gear wear or even toothing, accelerate belt wear, and even break the belt and accelerate the fan blades. Fatigue or even break the wind leaf and so on.

  The starting torque of the soft starter cabinet for the motor will not exceed the rated torque, and the above drawbacks can be completely overcome.