FI119458B - Arrangements for cooling an electric machine - Google Patents

Description

119458

SYSTEM FOR COOLING THE ELECTRICAL MACHINE

The invention relates to an arrangement for cooling an electric machine according to the preamble of claim 1.

The electrical machine generates heat during operation, which must be removed from the machine. One commonly used cooling nozzle is air cooling, in which a fan is fitted to the shaft of the machine to blow air through the electrical machine. If necessary, the cooling air is directed by special air ducts to the targets with the highest cooling rate. Such objects include, for example, winding ends. If the outdoor air flow rate is not sufficient, the cooling is enhanced by heat exchangers, whereby the cooling air is cooled. The temperature difference between the cooling air and the parts to be cooled in the electric machine is then increased, which results in more efficient cooling.

The simplest solution is a fan directly connected to the shaft of the electrical machine, which rotates at the same speed as the electrical machine itself. In speed-controlled drives, the fan speed drops as well as the machine rotation speed, resulting in a reduction in cooling power at speeds lower than the rated speed. At the same time, however, the need for cooling power may remain unchanged or even increase compared to unregulated speed. In slow-rotating and heavy-duty electrical machines, a fan directly connected to the drive shaft of the machine is not an adequate solution even at rated speed and rated load • · · * ... ·. In order to keep the operating temperature of the machine within the set limits, • · · * ... * 20 additional cooling must be developed, for example, with heat exchangers or separate fans.

• · • · · · · · *; ***; Permanent magnet motors with fractured coil are preferred electric motors for applications requiring slow rotation speeds. Also, the internal air circulation required to cool these slow engines will decrease as the rotation speed decreases. Solutions have been proposed in which an electric fan is provided with a second rotor rotating the fan, which is coaxial with the drive shaft and has a higher rotation speed than the drive shaft. This increases the flow rate of the cooling air and thus enhances the efficiency of the *; *; cooling.

* 1 * For example, GB 948013 discloses a solution that utilizes the sliding speed of an off-road engine. In the publication, some of the rotor short-circuiting rods are used as "stator" of 30 · fan motors. The fan rotor is supported by bearings on the drive shaft rotor so that the fan can rotate at a different speed than the drive shaft.

2,119,458

GB 2139011 proposes a solution for an asynchronous machine in which one end of the drive shaft is supported by the bearings of the fan motor to the other end plate of the electric machine. The drive motor is controlled over a wide speed range while the fan motor speed varies relatively little.

According to the prior art, the speed of the rotor rotating the fan is higher than that of the actual drive motor. This is accomplished by either adjusting or constructing the motor driving the fan differently from the drive motor. In practice, such arrangements always require additional components such as additional bearings and windings and additional space requirements.

An object of the invention is to provide an inexpensive and efficient air cooling for an electric machine, in which a motor driving a fan is provided on the same axis as the drive machine. To accomplish this, the arrangement for cooling an electrical machine according to the invention is known from the features of the characterizing part of claim 1. Certain particular embodiments of the invention are characterized by the features defined in the dependent claims.

With the solution of the invention, the cooling means of the electrical machine form a unitary and compact structure with the electrical machine. Compared to the basic solution, in which the fan ... is directly connected to the drive shaft of the electrical machine, the present solution requires only a · · IV. ' auxiliary rotor rotating the fan and its bearing on the drive shaft of the electric machine. In the longitudinal * ·. • I ·, 20 direction, the fan takes up the same space as the above basic solution. At the same time, the solution of · · ·, ··· according to the invention provides sufficient cooling power for applications where it was previously required. . ·. non-propulsion radiator solutions.

The invention will now be described in detail with reference to an embodiment of the drawings, in which: Figure 1 illustrates an embodiment of the invention. electric machine, • * • ♦ · • · · l. '. Fig. 2 is a cross-sectional view of a machine according to the invention at the drive rotor. Fig. 3 is a cross-sectional view of a machine according to the invention at the auxiliary rotor.

3, 119458

A sectional view of an electrical machine according to one embodiment of the invention is shown in Figure 1. The body structure 2 of the electrical machine surrounds a plate pack of stator 4 made of magnetically conductive plates. The stator has grooves in which the windings are fitted. The coil ends 14 of the coils project from each end of the stator outside the plate pack 5. At the ends of the electrical machine are bearing shields 12 which are attached to the stator body structure 2. In the center of the shields 12 are bearings 10 which support the drive shaft 8 of the electrical machine, which is known to be connected to the working machine used by the electrical machine. On the inside of the stator 4 is mounted on the drive shaft 8 a rotor 6 of an electrical machine, which in this embodiment is made of an iron core with permanent magnets magnetizing 10 electrical machines on its surface. The electric machine is a slow-speed motor with a high number of poles and a constant breaking winding, as will be described in more detail below.

On the right side of the rotor of the electric machine, in Fig. 1, auxiliary rotor 16 is mounted which rotates a fan 20 directly attached thereto. The auxiliary rotor 16 is supported on shaft 8 by bearings 18 and thus rotates with respect to both stator 4 and rotor 6 of electric machine. The fan 20 directs cooling air to the coil ends 14 and the stator 4 and rotor 6 as is known in connection with air cooling of electrical machines. On the left side of the rotor of the electric machine in Fig. 2, a second auxiliary rotor 16 'and a second fan 20' are mounted. One of the auxiliary rotors 16 'is also mounted on shaft 8 by a bearing 18' and the other fan lt 20 20 'thus operates in substantially the same manner as the fan 20 mounted on one end of the electric machine. : in axial direction. The auxiliary rotor 16 may be of the same construction as the rotor 6 in which it is made of an iron core, for example, a cast iron core having an outer surface:.:. · Permanent magnets are glued. The auxiliary rotors may be disc-shaped in appearance.

25 The electrical machine is either directly connected to the mains with an input frequency of generally 50 Hz, or; ; *: In controlled mode via frequency converter, the input frequency varies within the adjustment range.

• t ·: * * *; The alternating current supplied to the stator winding of the electric machine generates a magnet • · ·. ···. a path whose frequency corresponds to the voltage supply frequency. This main magnetic flux closes • · · *, ···. through the stator, the air gap of the machine and the rotor, and by means of which the power of the machine is produced.

• · · 30 The speed of rotation of an alternating electrical machine is known to depend on the number of hubs in the machine.

• · • · »* ... When a two-pole motor rotates at 3,000 rpm at 50 Hertz feed rate, for example, a 30-pole motor at the same frequency is only 200 rpm.

4, 119458

One advantageous solution for slow use is the so-called. low-constant (constant q <l) permanent magnet motor. The motor winding is simple and it is easy to make a corresponding large number of poles in the rotor, for example by gluing magnets to the surface of a solid-iron rotor. The stator winding is made of so-called. An example of a low constant number fracture winding is an electrical machine having a pole number of 2p = 34, a phase number of m = 3 and the number of stator grooves Ql = 36. Then the constant number q = Ql / (2 * p * m) = 36 / (34 * 3) = 6/17. The main field is 34-pole and rotates at 176 rpm at a 50 Hz input frequency. In addition to the main field, the fractured constant winding generates a number of subharmonic fields which also close through the magnetic circuits of the stator and rotor 10. In particular, the 34-pole Main field generates magnetic fields that are 2, 4, 6, and 8 poles. When an auxiliary rotor having a pole number of 2, for example, is mounted on the drive rotor shaft, the corresponding subharmonic component of the main flow causes a torque to the auxiliary rotor and rotates it at 3000 rpm. The peripheral speed of the internal fan attached to the auxiliary rotor increases sufficiently that it is sufficient to cool the electrical machine.

15 A two-pole auxiliary rotor is advantageous because of the highest rotation speed. On the other hand, other subharmonic fields that rotate faster than the field of the electrical machine are also available in the manner of the invention, because the rotor auxiliary rotor attached to them rotates faster than the drive rotor. (The magnitude and intensity of the subharmonic fields is a machine-specific feature, and therefore, each application must determine which 20 is the most useful auxiliary rotor hub number.) V, ϊ and air intakes).

In Fig. 1, an auxiliary rotor or auxiliary rotor is mounted on both sides of an electric machine drive. töroottoria. The control of the cooling air inside the electrical machine is carried out in accordance with your * · 25 rated electrical cooling unit. Thus, the electrical machine may have one or two fans per application:: *: one or two fans. The airflow of the fans can be directed in from both ends and • «: ***: out of the center of the electrical machine. Or with fans mounted at opposite ends, the cooling air flow can be used to direct • • ·, ··· from one outlet to the other and inside the electrical machine. air is directed to the most heat generating sites. The control of the cooling air can be performed by methods known per se, such as internal cooling ducts.

Figures 2 and 3 illustrate the operation of the solution according to the invention in an electrical machine magnetized with permanent magnets and wherein the fan rotor auxiliary rotor is also magnetized with permanent magnets. Where applicable, the same reference numerals as in FIG. 1 are used in FIGS. 2 and 3. FIG. 2 illustrates an axial half-section of a 34-pole electrical machine at the stator 4 and the rotor 6 of the machine. For clarity of presentation, the stator winding wall and teeth are not described in the cross-section.

5 On the outer surface of the rotor, i. fixed magnets 26 and 28, 34 of which are embodiments of Fig. 2, are mounted on the surface facing the air gap 22. The permanent magnets 26 are magnetized so that the outer periphery of the rotor has alternately an S-pole of the permanent magnet 26 and an N-terminal 28 of the permanent magnet towards the air gap 22. The main magnetic field induced by the stator winding (not shown in Fig. 2) is illustrated by the dashed lines 24 which close through the stator 410 and the rotor 6. The flows close through adjacent counterclockwise and clockwise poles, whereby the flow direction follows the arrows of the lining lines 24. At a feed rate of 50 Hz, this 34-pole machine has a rotation speed of approximately 176 rpm.

Figure 3 is a cross-sectional view of the auxiliary rotor 16. A permanent magnet 30 is attached to the peripheral surface of the auxiliary rotor, i.e. to the peripheral surface of the air gap 22. through the back of the auxiliary rotor 16 and through the air gap and the permanent magnet 30. Corresponding to the permanent magnet 30, an opposite permanent magnet is mounted on the second peripheral half of the auxiliary rotor. Although in Fig. 3, the permanent magnet -: [**: 20] is shown as a single piece, it may consist of several rotor exteriors ((: circumferentially parallel permanent magnet pieces magnetized in the same direction • a ϊ, ϊ, ϊ). the auxiliary rotor is configured as a bipolar, but equally, the auxiliary rotor may be four, six, or eight pole in connection with the 34-pole machine of Figure 2. Likewise, the auxiliary rotor may have any number of poles that corresponds to the actual electrical power. ... * 25 subharmonic fields of the magnetic field of the coil motor.

•: *; The invention has been described above with reference to an embodiment thereof. However, the disclosure is not to be construed as limiting the scope of the patent, but the implementation of the invention may vary within the scope of the following claims.

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Claims (8)

An apparatus for cooling an electric motor, the electric motor comprising a stator (4), the pole of which the electric motor is substantially large and whose rotor (6) is mounted on the drive shaft (8) of the electric motor, whereby in the electric motor an actuator is operated on the stator and the rotor. a main magnetic field, and together with which the rotor (6) of the motor on the same shaft (8) substantially inside the stator (4) of the motor is placed an auxiliary rotor (16, 16 '), which is arranged to rotate in relation to the stator (4) of the electric motor. drive shaft (8) and whose pole number is substantially smaller than the electric motor's pole number, characterized in that on the electric motor's stator (6) is arranged to operate at least one subharmonic magnetic field induced by the stator winding and arranged to operate at least on the auxiliary motor (16). , 16 '), wherein the subharmonic magnetic field is arranged to rotate the auxiliary rotor (16,16') and the fan (20) arranged on the auxiliary rotor. 2. A device according to claim 1, characterized in that the locking speed q of the electric motor is less than 1. 3. A device according to claim 1 or 2, characterized in that the pole number of the electric motor is greater than 20 and the pole number of the auxiliary motor is not more than 8. A device according to any of claims 1-3, characterized in that the electric motor; '* *; the pole number is 34 and the pole number of the helper protector is a maximum of 8. • · · • · • · Device according to any of claims 1-4, characterized in that the auxiliary motor • t ·, ·· * 4 (16) is arranged and stored at the first end of the drive shaft (8). ·· * • · A device according to any of claims 1-4, characterized in that two auxiliary rotors (16, 16 ') arranged in the first and second ends of the drive shaft (8) are arranged in the electric motor φ · · • · ** ·· *. • · • ·· Device according to any of claims 1-6, characterized in that the electric motor is: magnetized with permanent magnets (26,28). • · * 1 Device according to any one of claims 1-7, characterized in that the auxiliary rotor (16,16 ') of the electric motor (16,16') is magnetized with permanent magnets (30). • *