Why Do Air Compressors Adopt Soft Starters?
I. Main Classification of Soft Starters
Classified by voltage: High-voltage soft starters, Low-voltage soft starters
Classified by medium: Solid-state soft starters, Liquid resistance soft starters
Classified by control principle: Electronic soft starters, Electromagnetic soft starters
Classified by operation mode: Online soft starters, Bypass soft starters
Classified by load type: Standard-duty soft starters, Heavy-duty soft starters
II. How Do Soft Starters Achieve Energy Saving Under Light Load?
Squirrel-cage asynchronous motors are inductive loads. During operation, the current in the stator winding lags behind the voltage. Given constant motor operating voltage, the power factor is low under light load and high under heavy load.
Under light-load conditions, the soft starter reduces the terminal voltage of the motor to improve the power factor and cut down copper loss and iron loss of the motor, thereby realizing energy saving under light load. When the load becomes heavy, it raises the motor terminal voltage to guarantee normal motor operation.
III. Applicable Scenarios of Soft Starters
In principle, soft starters are applicable to all scenarios adopting squirrel-cage asynchronous motors without speed regulation requirements. Currently, they are applied for 380 V AC (660 V AC optional), with motor power ranging from several kilowatts to 800 kW.
Soft starters are especially suitable for pump loads and fan loads requiring soft start and soft stop. For variable load conditions where the motor runs under light load for a long time and only bears heavy load briefly or momentarily, the soft starter can deliver light-load energy-saving benefits.
A frequency converter is equipment that converts power frequency power supply (50 Hz or 60 Hz) into AC power supplies of various frequencies to realize variable-speed operation of motors. The control circuit controls the main circuit; the rectifier circuit converts alternating current into direct current; the DC intermediate circuit smoothes and filters the output of the rectifier circuit; the inverter circuit converts direct current back into alternating current. For frequency converters requiring massive computation such as vector control inverters, a CPU for torque calculation and corresponding circuits are sometimes required.
IV. Advantages of Adopting Soft Start for Air Compressors
1. Reduced Maintenance
For traditional star-delta starting, huge current passes through contactors during motor startup when contactors close and open, shortening the service life of contactors.
When a soft starter is adopted to control the main motor of the unit, the gate trigger control circuit of silicon controlled rectifiers (SCRs) controls and limits the motor starting current.
2. Improved System Reliability
Traditional star-delta starting realizes overload, underload and phase sequence protection via component combinations, leading to complicated wiring, high failure rate and poor system reliability.
In summary, soft start for air compressors can greatly reduce the starting current, avoiding impact and damage to equipment caused by excessive starting current during compressor startup. The motor power can be accurately matched according to compressed air demand to prevent energy waste. Meanwhile, stable pressure ensures the production process of gas-consuming equipment, which greatly facilitates enterprises’ product quality control.
Classified by voltage: High-voltage soft starters, Low-voltage soft starters
Classified by medium: Solid-state soft starters, Liquid resistance soft starters
Classified by control principle: Electronic soft starters, Electromagnetic soft starters
Classified by operation mode: Online soft starters, Bypass soft starters
Classified by load type: Standard-duty soft starters, Heavy-duty soft starters
II. How Do Soft Starters Achieve Energy Saving Under Light Load?
Squirrel-cage asynchronous motors are inductive loads. During operation, the current in the stator winding lags behind the voltage. Given constant motor operating voltage, the power factor is low under light load and high under heavy load.
Under light-load conditions, the soft starter reduces the terminal voltage of the motor to improve the power factor and cut down copper loss and iron loss of the motor, thereby realizing energy saving under light load. When the load becomes heavy, it raises the motor terminal voltage to guarantee normal motor operation.
III. Applicable Scenarios of Soft Starters
In principle, soft starters are applicable to all scenarios adopting squirrel-cage asynchronous motors without speed regulation requirements. Currently, they are applied for 380 V AC (660 V AC optional), with motor power ranging from several kilowatts to 800 kW.
Soft starters are especially suitable for pump loads and fan loads requiring soft start and soft stop. For variable load conditions where the motor runs under light load for a long time and only bears heavy load briefly or momentarily, the soft starter can deliver light-load energy-saving benefits.
A frequency converter is equipment that converts power frequency power supply (50 Hz or 60 Hz) into AC power supplies of various frequencies to realize variable-speed operation of motors. The control circuit controls the main circuit; the rectifier circuit converts alternating current into direct current; the DC intermediate circuit smoothes and filters the output of the rectifier circuit; the inverter circuit converts direct current back into alternating current. For frequency converters requiring massive computation such as vector control inverters, a CPU for torque calculation and corresponding circuits are sometimes required.
IV. Advantages of Adopting Soft Start for Air Compressors
1. Reduced Maintenance
For traditional star-delta starting, huge current passes through contactors during motor startup when contactors close and open, shortening the service life of contactors.
When a soft starter is adopted to control the main motor of the unit, the gate trigger control circuit of silicon controlled rectifiers (SCRs) controls and limits the motor starting current.
2. Improved System Reliability
Traditional star-delta starting realizes overload, underload and phase sequence protection via component combinations, leading to complicated wiring, high failure rate and poor system reliability.
In summary, soft start for air compressors can greatly reduce the starting current, avoiding impact and damage to equipment caused by excessive starting current during compressor startup. The motor power can be accurately matched according to compressed air demand to prevent energy waste. Meanwhile, stable pressure ensures the production process of gas-consuming equipment, which greatly facilitates enterprises’ product quality control.
