Permanent magnet motors have now become firmly established in the automotive industry in particular. But they are also growing in significance in the compressed air industry as they greatly improve efficiency. There are many reasons for this. Compared to conventional three-phase asynchronous motors, there is no electricity in the rotor of permanent magnet motors. No energy is required to generate a magnetic field as it is permanently available. Which means virtually no energy losses and consequently improved efficiency.
Compressors with a direct drive lend themselves particularly to use with a permanent magnet motor. Permanent magnet motors come into their own where there are frequent changes between low and high speeds. Compressors with variable speed can individually regulate the free air delivery and thus optimally adapt to the respective requirement. Permanent magnet motors cannot be used in compressors that operate at a constant speed and thus produce a fixed amount of compressed air. That‘s why Boge initially focused on the 5.5 to 11 kW power range of its frequency-controlled screw compressors with direct drive. In this performance class, the compressed air specialist replaced the asynchronous motors with permanent magnet motors and noticed a particularly potent impact on efficiency and the adjustment range in numerous studies and field tests.
Increased free air delivery
In addition to reduced energy consumption, permanent magnet motors also increase the free air delivery. This improved efficiency compared to asynchronous motors ensures that more power is generated at the motor shaft with a steady power consumption. The compressor can then convert this increased power to additional free air delivery while compensating for even extreme fluctuations in consumption. This means that when the compressed air requirement is low, the compressor does not idle and then the next minute switch back to full-load operation. Avoiding such load changes reduces the wear and tear of the relevant components. It also further reduces energy consumption as inefficient idling is preventable. Thus the compressor only needs energy when compressed air is actually required. Thanks to the wide adjustment range, the compressor reliably delivers compressed air when both large and small amounts are being consumed. Selecting the suitable airend with the appropriate speed range in conjunction with an adjustable permanent magnet motor can result in an adjustment range from 17 to 100 % for example with the Boge C14 PM screw compressor with 11 kW motor power.
Compact design retained
The permanent magnet motor does not come at the expense of compactness, which means the original housing design has been retained. The motor and compressor unit are still spatially separated. „This design is tried-and-tested,“ says Frank Hilbrink, product manager at Boge. „Because the compressor structure makes maintenance much easier.“ The motor and airend can be maintained separately. Any repair work or component replacements can be carried out quickly and easily without having to replace the entire drive train. Easy access to the individual components helps with maintenance. Sound-insulating panels can be easily removed, and the filter can also be changed without long tooling times.
Boge‘s direct drive screw compressors are extremely sturdy and low maintenance. They offer high availability and reliable operation. Compared with direct drive compressors, a compressor with belt drive requires more regular maintenance and is often out of action for the duration of the maintenance. This adds to costs. Furthermore, the belt is susceptible to dust and polluted surrounding air. This causes unwanted friction between the pulley and the belt, resulting in further wear and tear. The tension generated by the belt exerts forces on the motor and airend, which can shorten the service life of the bearing and shaft. The new models from the C-series with permanent magnet motor are not only typically reliable, they are also quiet. The sound pressure level of the airend is effectively deadened by components made of flake graphite casting. An extra deflection of the cooling air further reduces noise. The sound pressure level can be lowered by another 3 dB(A) with the optional super sound insulation. This is achieved by installing additional sound traps where the cooling air enters and exits.
Boge‘s screw compressors from the C-series with permanent motor are available with different controls. Even the standard base control enables standalone operation as a complete compressed air station. The optional focus control 2.0 allows up to four compressors to be integrated. The control monitors the entire system and offers flexible and convenient adjustment to the local situation and demand. „Encouraged by the excellent results in terms of efficiency in the low power range, we are going to look at other power ranges in the future,“ explains Frank Hilbrink. „At present, tests with other series are already underway so that we will be able to offer customers an even wider portfolio of compressors with permanent magnet motors.“ The compressed air specialist intends to fully utilise the advantages of combining the efficient motor and smart compressor technology in order to continue to optimally fulfil the quality standards of different industries.
Boge Kompressoren Otto Boge GmbH & Co. KG, Bielefeld