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Energy Saving Transformation of Soft Start Air Compressor

22kw30hp Rotary Screw Air Compressor

The main classification of soft starters

1. According to voltage classification: high voltage soft starter, low voltage soft starter;

2. Classification according to medium: solid state soft starter, liquid resistance soft starter;

3. According to the control principle: electronic soft starter, electromagnetic soft starter;

4. According to the operation mode: online soft starter, bypass soft starter;

5. According to the load: standard soft starter, heavy-duty soft starter.

How does the soft starter realize light-load energy saving?

The cage-type asynchronous motor is an inductive load. During operation, the current in the stator coil winding lags behind the voltage. If the working voltage of the motor is constant, the power factor is low when it is under light load, and the power factor is high when it is under heavy load. The soft starter can realize the purpose of energy saving at light load by reducing the motor terminal voltage, improving the power factor, reducing the copper consumption and iron consumption of the motor at light load; when the load is heavy, increasing the motor terminal voltage to ensure the normal operation of the motor .

22kw30hp Rotary Screw Air Compressor

 What occasions are soft starters suitable for?

In principle, cage-type asynchronous motors are suitable for various applications that do not require speed regulation. The current application range is AC 380V (or 660V), and the motor power ranges from several kilowatts to 800kW. The soft starter is especially suitable for various pump loads or fan loads, where soft start and soft stop are required. Also for variable load conditions, the motor is in light-load operation for a long time, and only in a short-term or momentary heavy-load situation, the application of a soft starter has the effect of light-load energy saving.

The frequency converter is a device that transforms the power frequency power supply (50Hz or 60Hz) into AC power supply of various frequencies to realize the variable speed operation of the motor. Among them, the control circuit completes the control of the main circuit, the rectification circuit converts the alternating current into direct current, the direct current intermediate circuit smoothes and filters the output of the rectification circuit, and the inverter circuit inverts the direct current into alternating current. For inverters that require a lot of calculations, such as vector control inverters, sometimes a CPU for torque calculation and some corresponding circuits are needed.

Benefits of Soft Starter Motors

With the development of my country’s economy, more and more motors are used, and the starting method of the motor has been paid more and more attention by people. Generally speaking, when the power of the motor exceeds 30KW, the motor soft starter cabinet should be used, otherwise it will seriously affect the use and operation of other equipment in the power grid and damage the motor itself.

22kw30hp Rotary Screw Air Compressor

Harmfulness of direct full-voltage starting of motors and benefits of motor soft starter cabinets

1. Cause voltage fluctuations in the power grid and affect the operation of other equipment in the same power grid

When the AC motor is started directly at full voltage, the starting current will reach 4 to 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 same grid.

When the motor uses a soft starter cabinet, 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 power grid

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

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

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

When the motor is started with a soft starter cabinet, the starting current is greatly reduced, and the above effects can be completely eliminated.

22kw30hp Rotary Screw Air Compressor

3. Damage the motor insulation and reduce the life of the motor

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

②The mechanical force generated by the high current makes the wires rub against each other and reduces the insulation life.

③When the high-voltage switch is closed, the shaking phenomenon of the contact will generate an operating overvoltage on the motor stator winding, sometimes reaching more than 5 times the applied voltage, such a high overvoltage will cause great damage to the motor insulation.

When the motor uses a soft starter cabinet, the maximum current is reduced by about half, and the instantaneous heat generation is only about 1/4 of the straight start, 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 high current produces a great impact on the stator coil of the motor and the cage bars of the rotor, which will cause faults such as loose clamping, deformation of the coil, and breakage of the cage bars.

When the soft starter cabinet is used for the motor, the impact force is greatly reduced due to the small maximum current.

22kw30hp Rotary Screw Air Compressor

5. Damage to mechanical equipment

The starting torque of the full pressure direct start is about twice the rated torque. Such a large torque is suddenly added to the stationary mechanical equipment, which will accelerate the wear of the gears or even the teeth, accelerate the wear of the belt or even break the belt, and accelerate the wind blade. Fatigue or even broken wind blades and so on.

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

The benefits of using soft start for air compressors

1. Reduce maintenance

In the traditional star-delta starting mode, during the starting process of the motor, a large current will pass through the contactor when it is closed and disconnected, resulting in a reduction in the life of the contactor.

Use the soft starter to control the main motor of the unit, and control or limit the starting current of the motor through the control of the gate trigger control circuit of the thyristor SCR.

2. Increase system reliability

The traditional star-delta starting method can realize overload, underload and phase sequence protection only through the combination of components, which causes troublesome wiring and high failure rate. System reliability is poor.

In short, the soft start of the air compressor can greatly reduce the starting current of the air compressor, avoiding the impact and damage to the equipment caused by the excessive starting current when the air compressor is started; according to the demand for compressed air, the motor can be precisely matched Power avoids waste; at the same time, the pressure stability can be guaranteed by the production process of gas equipment.

Sollant Focus on Energy Saving

Sollant group

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