FR2474779A1 - Rotor for high-speed asynchronous electrical machine - has material removed from teeth defined by axial slots to restrict flux path - Google Patents

Abstract

The rotor has axial grooves (2) running parallel to the generatrices of the rotor defining peripheral teeth (3). The teeth (3) each have material removed at the level of the base of the slots (2), by machining a bore through each tooth at its centre, or by machining a circular or semi-circular groove through the base of each slot (2) of larger dia. than the slot width. The machined bores or grooves provide a restriction of the flux to obtain virtual separation of the electric circuit from the magnetic circuit, so that the performance of the motor is closer to that of a motor with a smooth rotor. The motor employing this rotor can be used to drive a turbo-machine.

Description

ROTOR 1 \ ASSIF GROOVE
The present invention relates to rotary electrical machines and, more specifically, the rotor of electrical machines having a high rotational speed.

 It is known that the rotor of electrical machines operating as an asynchronous motor generally comprises two distinct parts making it possible to physically separate the electrical circuit from the magnetic circuit. However, when the rotor of such an engine has a very high speed of rotation, it becomes impossible to physically separate these two circuits because of the effects of centrifugal force. A solid steel rotor is then used, but the fact that the two circuits are intimately combined tends to reduce the performance of the machine. Axial grooves, parallel to the generatrices of the rotor, are then made at the periphery of the rotor so as to increase the reluctance by forcing the induction lines to penetrate more deeply towards the axis of the rotor. However, if the performances of a asynchronous motor with grooved solid rotor are superior to those of an asynchronous motor with smooth solid rotor, they nevertheless remain very inferior to those of a conventional motor in its range of use.

 The object of the present invention is to obviate this drawback by separating the electric circuit from the magnetic circuit in such a massive grooved rotor.

 According to the invention, the teeth, determined by the axial grooves of the rotor, are partially hollowed out at their collar, so as to create a constriction for the flow at this level and to give an essentially electrical function to the teeth. To do this, at least one channel parallel to the axis of the rotor is made at each collar.

 The invention will be better understood and several aims, advantages and characteristics thereof will appear more clearly on reading the following description of preferred embodiments given without limitation to illustrate the invention.

Figures 1,2 and 3 schematically show in half cross-section three embodiments of a grooved solid rotor according to the present invention.

 In these three figures, the rotor 1 has axial grooves 2 parallel to the generatrices of the rotor, in a known manner. These grooves determine teeth 3 at the periphery of the rotor.

 In order to create a constriction for the magnetic flux at the collar 4 of these teeth 3, the latter are partially hollowed out at this level. This recess is obtained by opening a longitudinal channel parallel to the axis of the rotor, formed at the collar 4 relative to this axis.

 According to the first embodiment shown in Figure i, a channel 5 is made longitudinally in the middle of each tooth 3. According to the second and third embodiments, respectively shown in Figures 2 and 3, the channels communicate with the grooves 2 and are made by widening the bottom of the grooves.

Figure 2, the grooves affect the shape of a tee whose small branch 6 determines the collar 4 of each tooth, while,
Figure 3, the channel 7 has a rounded shape.

 In this way, the collar 4 of each tooth constitutes a constriction for the magnetic flux, while the electrical circuit remains constituted by the crown 8 of the teeth, due to the skin effect.

 A solid grooved rotor according to the invention has the advantage of having a power factor better than that of conventional solid grooved rotors.

Although only certain embodiments of the invention have been described, it is obvious that any modification made by those skilled in the art in the same spirit would not depart from the scope of the present invention. Thus, for example, several channels can be provided, of section of different shapes.

 Obviously, the ratio of the surfaces of the section of the channel and the collar is determined in such a way that the mechanical strength of the rotor is not affected for high speeds of rotation, and that the flow entering or leaving by a tooth can pass through. normally the neck constriction when the tooth is opposite the corresponding stator pole.

 An asynchronous motor whose rotor conforms to the invention finds its application, in particular for driving turbo-machines.

Claims (4)

PEVENDICATIONS 1.- Solid grooved rotor for a rotary electrical machine, the axial grooves of which are parallel to the generatrices of said rotor, determine teeth, characterized in that said teeth are partially hollowed out at the level of their collar. 2.- Rotor according to claim 1, characterized in that at least one channel, parallel to the axis of said rotor, is formed at each collar. 3.- Rotor according to claim 2, characterized in that said channels communicate with said grooves. 4.- Rotor according to claim 3, characterized in that said grooves affect the shape of a tee whose small branch determines the collar of said teeth.