A new variable speed drive motor for screw air compressor

A new variable speed drive motor for screw air compressor

After more than half a century of development and application, screw compressors have achieved great development in technology. Among them, the application of oil-injected screw air compressors is the fastest and most extensive. In the field of aerodynamic compressors, as a screw air compressor, which is also a positive displacement compressor, its comprehensive operating economy has been proven by facts, which is superior to the reciprocating air compressor that is used to it. Nevertheless, as the increasingly widely used screw air compressor, it still consumes a lot of energy and is still a large electricity consumer in many enterprises. Therefore, how to further improve the performance of the screw machinery, especially to reduce the operating energy consumption of the screw air compressor, is still a major subject of current research and development.

Energy saving ways of screw air compressor

Since the birth of screw machinery, the profile of the screw rotor has undergone many reforms. With the development of computer technology, people have been able to develop a variety of high-efficiency molding lines currently known. Manufacturers of screw air compressors in the world can also use the so-called third-generation high-efficiency molding line. Similarly, the research and application of the entire screw air compressor system have been roughly the same. In the short term, it is even more difficult to obtain considerable energy savings from screw machinery. At the same time, from the perspective of energy consumption, what users are more concerned about is not the energy consumption ratio of the air compressor shaft power, but the energy consumption ratio of the input power. For this reason, people pay attention to the potential of energy saving on the operation of air compressors.

On the other hand, according to the 2002 survey report of the US Department of Energy, the load rate of air compressors in various countries is almost impossible to exceed 90%. Therefore, the air compressor should run energy-saving, except when fully loaded, the input energy consumption ratio should be low, and energy-saving should be saved under partial load and no load. In this regard, higher requirements are put forward for the air volume adjustment of the screw air compressor.

Generally, there are three ways to adjust the air volume of a screw air compressor:

(1) Air intake throttle adjustment.

(2) Adjust the effective length of the rotor.

(3) Change the rotor speed adjustment.

From the perspective of energy saving, changing the rotor speed adjustment is the most effective. For this reason, people think of variable frequency motors, of course, it is more energy-efficient than other adjustment methods of fixed speed. However, because the general frequency conversion motor will cause a decrease in the power factor and efficiency of the motor when the speed is reduced, according to the test, it will reduce the gas output by 10% to 15% under the same power than the traditional air compressor. Therefore, it is not the most ideal driver. Moreover, ordinary motors cannot start and stop frequently. Here, the screw air compressor consumes 25%~30% of the no-load power. So people look forward to the emergence of a new drive motor.

A new variable speed drive motor for screw air compressor

In order to meet the energy saving in the operation of the screw air compressor, a high-efficiency variable speed drive motor must be provided. When the air compressor is running at full load, the motor can run efficiently; when the air compressor is under partial load, the motor can change its speed with the air volume and still maintain high efficiency; when the air compressor does not require a load, the motor can start, Stop, reduce energy consumption to zero. This is an HPM hybrid permanent magnet motor jointly developed by Ingersoll Rand and world-renowned electrical manufacturers.

Compared with ordinary three-phase asynchronous motors, HPM hybrid permanent magnet motors have the following differences in structure: 1) The winding of the motor stator is not integrally wound, but is divided into 8~12 groups and mounted in the stator base of the motor . 2) The silicon steel sheet of the motor rotor is inlaid with several permanent magnets. Due to the existence of permanent magnets, the electromagnetic coil on the motor stator generates a strong electromagnetic force between the stator and the rows of permanent magnets. The magnetic flux is increased by three times, so that the length of the motor can be shortened to 1/3 under the same power. . Therefore, the rotor of the motor can be omitted and suspended on any driven rotor shaft.

Compared with ordinary three-phase variable frequency motors, hybrid permanent magnet motors have the following characteristics in performance:

(1) Wide speed range. In the entire variable speed range, the efficiency and power factor of the motor are almost unchanged.

(2) The motor can start and stop without restriction. Will not increase the temperature rise of the motor and increase the current.

(3) The motor cooling effect and operation reliability are good.

This is due to the increase of the magnetic force, which doubles the gap between the stator and the rotor of the motor, which greatly improves the cooling effect.

Ingersoll Rand NIRVANA screw air compressor

US Ingersoll Rand Company uses HPM hybrid permanent magnet motors to drive oil-injected and oil-free screw air compressors, and has developed a new generation of energy-saving screw air compressors of the NIRVANA series. Due to space limitations, this article only introduces the characteristics of NIRVANA oil-injected screw air compressors.

Compared with ordinary oil-injected screw air compressors, the structure of the driving part of the NIRVANA oil-injected screw air compressor is greatly simplified.

The NIRVANA oil-injected screw air compressor using HPM hybrid permanent magnet motor has a motor stator that is connected to the housing surface of the screw main engine by a flange, and the motor rotor is suspended on the shaft of the screw drive rotor. Therefore, it eliminates the need for motor bearings and seals. From the perspective of the entire transmission device, the concentricity requirements of traditional gearboxes, gears and connections are omitted. Therefore, in addition to the high transmission efficiency of the unit, users are also pleased that the maintenance of regular replacement of motor bearing grease is eliminated.

The use of HPM hybrid permanent magnet motors must save energy during operation and must rely on a complete control system. The NIRVANA air compressor has also been optimized. It integrates the variable speed control of the motor, soft start control, and the conventional operation and protection control of the air compressor, and is modularized into a low-voltage control cabinet in the chassis. It is not only convenient to operate and maintain, but also reliable in operation. Each air compressor is equivalent to 80 sets of electronic gears, which can automatically realize optimal control according to the actual gas volume and pressure of the user. When the air compressor load rate is lower than 25%, the air compressor does not need to run at no-load to consume electric energy, but can be stopped directly, reducing energy consumption to zero. Once the system pressure is lower than the set pressure, the air compressor will automatically soft start again.

In addition, the NIRVANA oil-injected screw air compressor is a little different from the ordinary frequency conversion air compressor. When the speed is reduced and the air volume is reduced, it can realize the adjustment of the fuel injection volume, which makes the flow loss smaller and more energy-saving.

The test performance of NIRVANA fuel injection screw and ordinary fuel injection screw are compared as follows. If the average load rate of the air compressor is 70% under normal conditions, the NIRVANA air compressor can reduce energy consumption by 22%-30%. Therefore, NIRVANA can be said to be the only screw air compressor with a variable speed drive in a true sense.

Energy-saving operation of multiple screw air compressors

For most users, out of consideration for gas use, multiple air compressors are often used in the compression station. From the perspective of energy-saving operation, in addition to using multiple air compressors to adjust the air load, the ideal method is to choose one of the energy-saving speed-regulating screw air compressors for partial load adjustment, which is not only the first investment The increase is not much, and the future operation is more energy-efficient. The following is an actual gas configuration.

IRN-75 is a NIRVANA adjustable-speed and energy-saving screw air compressor with an air volume of 3.7~13m3/min. For the configuration of the above-mentioned user air compressor station, the single point control pressure of the system can be set through the Ingersoll Rand IEO intelligent controller to realize automatic switching control.

In the centralized control of the compressed air system, in addition to the single-point pressure control of the system, to avoid the power loss caused by the excessive pressure band, but also to avoid the difference between the system control pressure and the actual pressure. Solan provides the IntelliFlow intelligent pressure controller to achieve, the pressure of its system control and the actual pressure fluctuation is only 0.005MPa.

The NIRVANA speed-regulating screw air compressor developed by Ingersoll Rand of the United States using HPM hybrid permanent magnet motors is indeed a major technological innovation for the energy saving of screw air compressors. Although, so far, only nearly 100 units have been put into operation in China, it is still necessary to continuously collect and accumulate operating experience. Moreover, this type of HPM hybrid permanent magnet motor is currently only developed to 160kW, and further research and development are needed. However, as a widely used screw air compressor, it is very gratifying to propose a very practical and effective operation and energy-saving attempt. We firmly believe that through continuous efforts, it will definitely bring revolutionary changes to the screw air compressor. Contribute to the improvement of human beings' increasingly scarce energy.