Development of high performance screw compressor driven by direct couple high-speed motor
Shigeto Kotani(Kobe Steel, Ltd.), Shuzo Mohri(Kobe Steel, Ltd.), Masaki Matsukuma(Kobe Steel, Ltd.), Hajime Nakamura(Kobe Steel, Ltd.), Kai Nakanishi(Kobe Steel, Ltd.)

1. Outline
The screw compressor driven by direct couple 7200rpm high-speed permanent magnet motor was realized the first time in the world, and the generation source of an energy loss was eliminated thoroughly -- a new type screw compressor is overly introduced.
By coupling the motor directly with screw rotor, the new developed compressor adopted the structure of which eliminated thoroughly the generation source of energy losses, such as speed-increasing gear, shaft seal (seal mechanism), a capacity control valve, and motor bearings which were indispensable as for the conventional compressor.
Moreover, it is the high performance screw compressor with which make possible to operate at rated constant power consumption and increasing air volume (wide range control operation) in the low pressure state, and also enable effective use of energy with energy saving and in which rotating speeds control is possible for total range. Also a user's ease of using was investigated thoroughly, and abolition of starting restrictions, momentary voltage drop and power failure correspondence, and high circumference temperature correspondence were supported.

2. Details of Technology
In development, the first start is losing speed-increasing gear in order to lose the transfer loss of energy.
In order to lose speed-increasing gear, naturally, a high-speed motor is needed, and motor direct couple structure also becomes indispensable. Although the high-speed drive of a motor becomes possible by the frequency rise of a variable speed drive (VSD), it leads to the miniaturization of the motor volume accompanying improvement in the speed, but the problem of motor cooling has occurred. And, to the purpose made into couple directly with rotor of the compressor sake, it is fundamental to raising the rigidity of the shaft as resonance and an oscillating measure.
Here considered as easy explanation, first, as the resonance and oscillating measure accompanying the formation of high-speed rotation, it was coped with by the light-weight and small-size motor which is used as overhang attachment, and against the resonance which comes out high order, the vibration suppression equipment which is not in the conventional technology was newly developed, and was built-in. About the measure for cooling of motor, improvement of cooling efficiency and energy saving are simultaneously realized by adoption of other cooling way by another fan and keep power control of the fan.
Meanwhile, it is essential to the viewpoint of not only saving energy but also utilizing power effectively.
The absolute value of the power loss of a compressor becomes larger, as rated power is large. This gains in a compressor input power required for unload operation or unload loss of a motor or power of auxiliary machine, etc. as the physique of motor becomes large, and such as the 100% operation of 55kW compressor of power consumption becomes less than 73% operation (= 55kW) of 75kW compressor.
Paying attention to that the conventional compressor's power consumption is not same as rated shaft power at the time of a discharge pressure drops, and it is more effective to decease the power loss using smaller sized compressor with the time of the same output, by increasing the maximum speed and consuming rated shaft power with wide range control, it is realized raising air capacity to be 125%.
On the other hand, there is a characteristic subject in the rotating speed control model used the conventional VSD. If the control range of rotating speed is limited and separated from the range, and power consumption will become equivalent to a purge system or a suction throttle system. Also, in the case when adopt a VSD, if a loss of power where generated in the VSD is not regained by parts for another efficiency rise, power consumption will increase on the contrary.
Then, since covering the comprehensive efficiency down by the VSD, rotating speeds control for total range is possible for it by making an above-mentioned new screw rotor into direct couple structure and adopting new permanent magnet motor, new high performance screw compressor has developed and utilization became possible.
Using this new technology it has been attained about 32.2% of improvement in a performance (energy saving) as compared with the conventional ON/OFF control compressor and even if compared with the model of same rotating speeds control, attained about 5.6% in the range of all loads and about 40% in low load.

Fig. 1 Product appearance
Fig. 2 Comparison with conventional compressor and high-speed direct couple compressor
Fig. 3 Main part of high-speed IPM motor direct couple compressor
Fig. 4 Vibration suppression equipment


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