CENTRIFUGAL COMPRESSOR AGGREGATE AND ELECTRIC MOTOR
Field of the Art
The inventions relate to refrigerating and electrical engineering, respectively, and may be used in the air-conditioning systems and refrigerating machines of household and industrial purpose.
State of the Art
Known in the art are different types of centrifugal compressor aggregates. Thus, e.g. a refrigerating compressor aggregate described in Patent US 2986905 (NKI 62-475, publ. 15.04.60) comprises two centrifugal compressor stages with impellers, diffiisers, collectors, an inlet branch pipe to the first compressor stage and an outlet branch pipe from the second compressor stage. Between the aggregate compressor stages in an electric motor, the rotor of which is mounted on a single shaft with compressor stage impellers. The electric motor utilized in this aggregate is of a considerable size, its cooling effected through the channels surrounding the stator, via which the cooling agent is fed through an additional pipeline not directly connected with the inlet and outlet compressor stage branch pipes. In the other centrifugal compressor aggregates, one of which is described in
Application WO 94/29597 (F04D 7/02, 29/04, publ. 22.02.94), the electric motor stator cooling channels are directly connected with the outlet of the first compressor stage and the inlet of the second stage. There are some seals on the rotor shaft sealing the rotor hollows of the compressor stages and the bearing fixed in the electric motor body. A high-speed brushless dc motor can be utilized as an electric motor in this aggregate. The present embodiment allows to decrease electric motor and refrigerating machine dimensions on the whole, as well as to increase the system efficiency with powers lower than 180 kW.
The most closely analogous device in the prior art is a centrifugal compressor under Patent RU 2104448 Cl (F25B 1/10, 81/02, publ. 10.02.98), the structure of which contains two centrifugal compressor stages with impellers, dif iisers, collectors, the first compressor stage inlet branch pipe and the second compressor stage inlet branch pipe, and an electric motor located between the compressor stages. The motor rotor is mounted on a single shaft with compressor stage impellers by the radial gas-dynamic bearings fixed in the body. There
are also seats on the shaft sealing the rotor hollows of the compressor stages. From the outside of the motor stator there are cooling channels. The collector of the first compressor stage is connected with the inlet of the second stage. The motor body cavity is connected from one side with the inlet branch pipe, from the other side - with the outlet branch pipe to the cooling medium body. On the stator surface facing the rotor are narrow longimdinal grooves for cooling medium passage. A cooling passage duct in the cavity of the body is formed by cooling channels made between the stator and the body, and an operiing clearance between the stator and the rotor.
A compressor aggregate of this structure is of higher reliability and small dimensions. However, in relation to imperfect cooling system structure of a high-speed electric motor the prior art compressor device possesses a comparatively low efficiency and reliability. A small operating clearance between the rotor and the stator of the electric motor, which is connected with the necessity to maintain the required value of its efficiency, and narrow grooves on the internal surface of the stator practically do not provide cooling agent vapour supply necessary for stator and rotor cooling, since with operating clearance and groove dimension, there is a non-productive energy loss ramp up. Thus, a motor cooling duct is limited only with the channels made between the stator and the internal surface of its body, by which a cooling agent flow effectively cools the external surface of the stator forming a passage duct of cooling medium. Besides, the structure of the motor rotor and stator do not allow to considerably reduce the compressor aggregate dimensions and provide an axial shaft force tradeoff.
Currently in use are high-speed valve-type or, in other terms, brushless motors. Thus, e.g. Patent US 4665331 (H02K 11/00, publ. 12.05.87) describes a high-speed motor, the structure of which includes a stator formed by flat electromagnetic windings made in the form of a constant magnet. Sush a motor, though being of small dimensions, high efficiency and manufacturability, however it does not provide a system due to a specific field of its application.
The most closely analogous device of the motor claimed is a common high-speed motor, the stator of which is formed by a magnet wire made in the form of assembly of thin electrically isolated from each other profiled ring-type steel plates and electromagnet drum winding, which has a considerable frontal bulge (Isao Takahashi et all " A Super High Speed PM Motor Drive System by a Quasi-Current Source Inverter" IEEE TRANSACΗONS OF INDUSTRY APPLICATIONS, No 3, MAY/JT NE 1994, pp. 683-689). On the internal part
of the stator of the prior art motor the profile of steel plates forms sequentially alternating in azimuth direction teeth and grooves, where the electromagnet winding is placed. There is a rotor on the motor shaft formed by a constant magnet with a dielectric bandage.
The prototype-motor tests conducted showed that a preferred efficiency, power and rotation speed of the motor rotor of the said structure can be achieved with an operating clearance value between the external surface of the rotor magnet and the internal stator surface equal to 6 mm and corresponding to an air clearance value equal to 0,5 mm. To reduce loses the bandage of the rotor is made of a material considerably resistant to whirling currents (of reinforced fibre plastics). The air clearance increase in the prototype-motor on account of using a thin non-magnetic steel bandage results in considerable increase of energy losses and decrease of rotor rotation speed. Thus, in the prototype-motor due to a small value of an air clearance the passage of cooling medium formed by the clearance between the rotor and the stator fails to be achieved.
Summary of the Invention
The inventions patented are aimed at higher efficiency and operation reliability of a centrifugal compressor aggregate and a motor, as its structural member, on account of an optimum cooling process of the rotor and stator organized with a structural optimum from energy loss viewpoint, as well the aggregate dimension reduction and its axial shaft force tradeoff on account of axial motor dimension decrease.
Achieving the said technical results is provided by the fact that in a centrifugal compressor aggregate containing two centrifugal compressor stages with impellers, diffiisers, collectors, the first compressor stage inlet branch pipe and the second compressor stage outlet branch pipe, a motor placed between the compressor stages, the rotor of which is on a single shaft with compressor stage impellers, bearings fixed in the aggregate body, and seals made on the shaft sealing the rotor hollows of the compressor stages, with cooling channels formed on the external side of the stator, the first compressor stage collector connected with the second stage outlet, the motor body cavity connected from one side with the inlet branch pipe, from the other side - with a branch pipe of cooling medium outlet, which is connected with the second compressor stage inlet, a passage cooling duct in the cavity of the body formed by cooling channels made between the stator and the body, and an air clearance between the stator and the rotor, according to the present invention, the first stage collector
connected with the second stage inlet directly through the cavity of the motor body, the stator made of laminated magnet wire of a torroidal shape with ring-type winding, the rotor formed by at least a single constant magnet with a bandage of a material resisting to whirling current passage, the value of an radial air clearance between the rotor and the stator equal to not less than 1 ,5 mm. A preferred air clearance between the rotor and the stator is 2 mm.
It is preferred also to use gas-dynamic bearings in the compressor aggregate. The magnet wire of the motor stator is preferably made of pressed powder by a powder metallurgy method.
In the preferred embodiment the stator magnet wire is the assembly of thin ferrite or electroengineering steel rings, electrically isolated from each other. It is preferred that a constant magnet of the rotor be made of a high electric resistance material. Magnetoplast can be used as such material.
The rotor is preferably made in the form of the assembly of electrically isolated from each other ring-type constant magnets. The rotor bandage can be made of carbon plastics.
The above said technical results are also provided by the fact that in the motor containing the stator formed by a magnet wire, made in the form of the assembly of thin electrically isolated from each other rings, and electromagnet winding, and a rotor mounted on the shaft, formed by at least a single constant magnet with a bandage of a material suppressing whirling current passage, according to this invention, the stator is made in the torroidal form, a ring-type winding used as the stator winding, the rotor made in the form of the assembly of electrically isolated from each other constant magnets in the shape of thin rings of a high electric resistance material, the air clearance between the stator and the rotor, the value of which amounts to not less than 1,5 mm, forming a cooling, passage duct of the motor. The air clearance value between the stator and the rotor preferably amounts to 2 mm.
The motor stator magnet wire is preferably made of pressed powder by a powder metallurgy method.
In a preferred embodiment a stator magnet wire is made in the form of the assembly of thin ferrile rings or electroengineering steel rings. In a preferred embodiment the rotor is made of magnetoplast.
The rotor bandage of the motor may be made of carbon plastics, which suppresses whirling current passage.
Brief Description of the Drawings
Hereinafter the inventions are described with reference to a specific embodiment illustrated in the accompanying drawings, wherein: Fig. 1 is a longitudinal section of the compressor aggregate made according to the present invention,
Fig. 2 is a transverse section of the compressor aggregate in Fig. 1.
Preferred Embodiment of the Invention
A centrifugal compressor aggregate has a body 1, in which by the aid of bearing boards 2 and 3 and positioriing screws 4 and 5 the gas-dynamic bearings 6 and 7 are fixed, a gimball 8 supporting thrust bearings 9 and 10. A centrifugal compressor has two compressor stages. The cantilevers of the shaft 11 support the impellers of the first 12 and the second 13 compressor stages. At the working medium outlet from the impellers 12 and 13 the diffiisers (diffuser devices) 14 and 15 are installed, respectively, which are connected with collectors 16 and 17.
To ensure a minimum overflow of cooling agent between the first and the second stages the labirynth seals 18 and 19 are provided, made at the end portions of the shaft 11 and sealing the rotor hollows of the compressor stages. The body 1 has a first compressor stage inlet branch pipe 20 and a second compressor stage outlet branch pipe 21. Between the compressor stages is a high-speed electric motor, the rotor 22 of which is fixed on a single shaft 11 with impellers 12 and 13 of the aggregate.
The stator of the electric motor is made in the form of an imbricated magnet wire 23 of a torroidal shape of presented powder by a powder metallurgy method, with an electromagnetic ring-type winding 24. In the other embodiment (not shown in the drawing) the stator magnet wire is made in the form of assembly of thin ferrile or electroengineering steel rings, electrically isolated from each other. The rotor 22 of the electric motor is made in the form of the assembly of electrically isolated from each other ring-type constant magnets 25 made of magnetoplast, with a bandage 26 of carbon plastics suppressing the whirling current passage. Along the edge of the rotor are balance rings 27. The stator of the electric motor is fixed inside the body 1 in the casing 28, in which there are longitudinal cooling channels 29.
The collector 16 of the first compressor stage is connected with the second compressor stage directly through the body of the electric motor and pipeline 30 with the outlet of the second stage. The cavity of the electric motor body is connected, from one side, through the first compressor stage, with the inlet branch pipe 20, from the other side - with the branch pipe 31 of cooling medium outlet, which is connected with the second compressor stage inlet through pipeline 30.
A cooling passage duct in the cavity of the motor body is formed by cooling channels 29 made between the stator and the body, and a radial air learance between the stator and the rotor, the value of which amounts to 2 mm. It should be noted that in the motor structure proposed with the increase of an air clearance in comparision with a prototype the air clearance between the rotor and the stator remains the previous one, close to 6 mm.
A centrifugal compressor aggregate and an electric motor, as a part of its structure, function in the following manner.
Before starting a compressor aggregate a static frequency converter (not shown in the drawing) is started and rotor 22 of a high-speed motor is accelerated from a stationary state up to operating rotation frequency separating from the surfaces of gas-dynamic bearings 6 and 7. The cooling agent vapours from the refrigerating system evaporator (not shown in the drawing) enter the inlet branch pipe 20 of the compressor aggregate and, accordingly, the first compressor stage. With high-speed impeller 12 rotation of the first compression stage the cooling agent vapours are fed under the excessive pressure through a diffuser (diffuser device) 14 into the collector 16, from which they pass to the cavity of the motor body and then through a cooling duct, formed by an air clearance between the stator and the rotor and longitudinal cooling channels 29, to the branch pipe 31 of the cooling medium outlet. As a result of cooling agent circulation through a sufficiently wide annular channel between the rotor and the stator, with keeping a high motor efficiency, the effective cooling of their opposite surfaces takes place. From the outside the stator of the motor is cooled on account of cooling agent vapour passage through longitudinal channels 29. Besides, the cooling agent vapours passing through the internal cavity of the motor body cool the bearings 6 and 7 and the shaft 11 together with the rotor 22 being in thermal contact. After the cooling agent feed through the cooling motor duct their vapours enter the second compressor stage inlet through the branch pipe 31 of cooling medium outlet and the pipeline 30. With the impeller 13 rotation the cooling agent vapours are compressed and fed through a diffuser (diffuser device) 15 into the collector 17, and then they enter a cooling system of the refrigerating plant
through a branch pipe 21.
To decrease the motor mass and dimensions its rotor 22 is made active in the form of the assembly of constant magnets 25. However, at high rotation speeds there arise energy losses which, firstly, decreases the aggregate efficiency and, secondly, the refrigerating plant efficiency decreases on the whole due to a cooling agent temperature increase. Utilization of constant magnets made of magnetoplast possessing the highest electric resistance to whirling currents is preferred in comparison with cast or extruded constant magnets. The most active resistance of the rotor is achieved with its embodiment in the form of a constant magnet assembly made of magnetoplast in the shape of thin rings 25 electrically isolated from each other.
To provide the rotor 22 strength a carbon fibre bandage 26 is mounted on the rotor at high rotation speeds. This embodiment of the bandage allows to decrease the losses connected with whirling current occurrence.
Utilization of the electric winding 24 of the ring-type motor stator allows to reduce a frontal bulge and, accordingly, the axial motor dimension in comparison with drum windings, which is the most advantageous for "short" machines, to which number the motor patented is related, which is used in a refrigerating centrifugal compressor.
Thus, in the motor patented simultaneously with the axial rotor length decrease the active winding resistance is managed to be lowered and, consequently, the copper volume decreased and increase the motor efficiency increased on account of thermal energy loss decrease.
On account of utilization in the aggregate patented and the motor, of the stator with a smooth active zone (teeth-free) a thermal loss decrease is ensured connected with whirling current appearance in the high-speed motor stator. Though a smooth ring-shape stator of a high-speed motor will have a large diameter in comparison with the classical stators with teeth and grooves, where the motor windings are placed, however, in centrifugal compressor aggregates, in which the longitudinal motor dimension is essential, the operation efficiency increases on account of thermal loss decrease and perfection of motor cooling conditions.
Besides, a smooth stator has a higher manufacturability and less cost, since in this case the magnet wire has a simple annular (grooves- and teeth-free) shape, the electromagnet winding placed directly on the smooth (grooves-free) cylindrical surfaces of the magnet wire. The most preferred embodiment of the stator magnet wire is of ferrite rings, since in this case magnet wire losses decrease.
The knowledge of particular embodiments of a compressor aggregate and an electric motor, as its structural member, is the evidence of a possibility to solve the problems set up and achieve a technical result.
Industrial Application
A centrifugal compressor aggregate and an electric motor manufactured according to the invention may, accordingly, be used in the air conditioning systems and refrigerating systems of household and industrial application.