What is the motor speed of the screw air compressor

Screw air compressor motor speed according to the type of equipment and application scenarios there are differences, the following is a detailed answer:

1. speed range standard

1. national Standards
   according to GB/T standard, screw air compressor motor speed is divided into two gears:
   • 2-pole motor: The synchronous speed is 3000rpm, and the actual air compressor electronic control system is usually nominal 2960rpm (allowing 3% error).
   • 4-pole motor: Synchronous speed 1500rpm, actual nominal 1480rpm (allowable error of 3%).
2. Load adjustment range
   • no-load speed: Maintain 75%-85% of the rated voltage, that is, 2220-2520rpm(2 poles) or 1110-1275rpm(4 poles).
   • Load speed: Dynamically adjusted according to the pressure demand, with a minimum of not less than 75% of the rated voltage speed (2220rpm/1110rpm) and a maximum of not more than 110% of the rated voltage speed (3256rpm/1628rpm).

2. fixed frequency vs variable frequency speed characteristics

case: A 37kW variable frequency screw machine has a rotating speed of 900rpm at 50% load, saving about 35% of energy. The rotating speed is 1480rpm at full load.

Influencing factors of 3. speed

1. core Parameter Association
   • pressure and speed: For every 10% increase in speed, the exhaust pressure increases by about 7% (compression ratio design needs to be matched).
   • Flow and speed: The speed is proportional to the volume flow, but is limited by the exhaust temperature (usually ≤ 100°C).
2. Energy efficiency balance
   • speed too high: Increase bearing wear (shorten life by about 40%) and lubricating oil consumption (increase by 15%-20%).
   • Speed too low: May cause insufficient lubrication (recommended minimum speed ≥ 800rpm).
3. Environmental Adaptability
   • high temperature environment: The speed needs to be reduced to avoid over-temperature of the exhaust gas, for example, at an ambient temperature of 40°C, it is recommended that the speed does not exceed 1200rpm.
   • high altitude area: The air density decreases, and the speed needs to be increased to compensate for the pressure loss (the speed increases by 5%-8% for every 1000m elevation).

4. speed monitoring and maintenance

1. real-time detection
   • check the speed through the control panel (most models support digital display or APP remote monitoring).
   • Abnormal alarm: an alarm will be triggered when the speed deviates from the set value by ± 5%.
2. Maintenance recommendations
   • lubrication inspection when the rotating speed is> 1200rpm, the lubricating oil replacement cycle should be shortened (normal 8000 hours vs high rotating speed 6000 hours).
   • Bearing maintenance: Check the radial clearance of the bearing every 2 years, and replace it if it exceeds 0.15mm.

5. special scene speed optimization

• two-stage compression: The speed of the first stage is 20%-30% higher than that of the secondary stage, and the compression ratio of all stages is balanced.
• waste heat recovery: The rotating speed is controlled at 1000-1200rpm to improve the heat exchange efficiency (the oil temperature is 1 ℃ per liter, and the recovered heat is increased by 0.8).

Conclusion: The speed of the screw air compressor motor should be set according to the load, environment and energy efficiency. The fixed frequency machine is suitable for stable working conditions, and the frequency converter can achieve 25%-40% energy saving effect through speed adjustment. It is suggested to combine the pressure sensor and frequency converter algorithm to realize the dynamic optimization of the speed.