When operating high-voltage air compressors, one of the key challenges is managing the high starting current, which can cause strain on both the motor and the power grid. To alleviate this issue, several techniques are used to reduce the starting current while maintaining efficient operation. Below, we will explore five common methods used by high-voltage air compressor manufacturers to minimize starting current, including series resistance, auto-transformer, direct start, frequency converter, and star-delta decompression starting.
1. Starting with Series Resistance
One of the most popular ways to reduce starting current is by using series resistance. In this method, resistances are connected in series with the stator winding circuit during the start-up phase. As current flows through the circuit, a voltage drop occurs across the resistors, which reduces the voltage supplied to the stator winding. This controlled voltage reduction helps in limiting the starting current while allowing the motor to gradually ramp up to full speed. This technique, known as tripping starting, is especially effective in reducing the initial surge of current.
2. Auto-Transformer Starting
Another method involves the use of auto-transformers. These devices offer multi-tap pressure reduction, allowing the motor to start at different load levels. This method not only reduces the starting current but also provides a higher starting torque, making it suitable for larger capacity motors. The adjustable winding taps can reduce voltage by up to 80%, meaning the motor can start with 64% of the torque of direct starting. Auto-transformer starting is commonly used for high-load applications where strong initial torque is needed without putting excessive strain on the electrical system.
High-Voltage Air Compressors
3. Direct Start
Direct starting is the simplest method, where the stator winding is directly connected to the power supply at the motor’s rated voltage. While this method provides a large starting torque and quick start-up time, it also results in a higher current draw, which can strain the power grid. Direct starting is typically used for motors under 1 megawatt and when the power supply grid can handle the load. This method is fast and easy, but it should only be used where the grid capacity can support the large initial current.
4. Frequency Converter Starting
A frequency converter is a modern motor control solution that regulates both speed and torque by adjusting the frequency of the incoming power supply. This method allows for gradual acceleration, making it ideal for applications requiring precise speed control. While frequency converters are effective at reducing starting current, they are more expensive and require advanced maintenance due to the complexity of power electronics and microcomputer technology involved. Frequency converter start-up is commonly found in high-performance environments where motor speed must be adjusted frequently.
High-Voltage Air Compressors
High-Voltage Air Compressors5. Star-Delta Decompression Starting
Star-delta decompression is another effective technique for reducing the starting current of high-voltage air compressors. In this method, the stator winding is initially connected in a star configuration, which reduces the voltage applied to each phase by a factor of √3. Once the motor reaches a certain speed, the configuration is switched to delta. This switch ensures full voltage operation while keeping the starting current manageable. Star-delta starting is well-suited for motors with no-load or light-load conditions during start-up. Moreover, it provides the additional benefit of energy savings when the motor operates at light loads since the motor can run in star mode, improving efficiency.
Conclusion
Reducing the starting current of high-voltage air compressors is essential for minimizing the impact on the power grid and ensuring the longevity of the equipment. Techniques like series resistance, auto-transformer starting, direct starting, frequency converters, and star-delta decompression provide various ways to manage the current effectively. Each method offers its own advantages and is best suited to specific operational requirements. By choosing the appropriate starting method, businesses can optimize their compressor performance while protecting their electrical infrastructure.
How to Properly Use a 25 HP Screw Compressor
How to use oil-free air compressors correctly to extend their life
