RU195701U1 - PERMANENT MAGNET ELECTRIC MACHINE - Google Patents

Abstract

The utility model relates to electrical engineering and is an electric machine with excitation by permanent magnets and field damping in case of emergency overspeed, designed to generate alternating voltage and power supply. Various constructions of electric machines are known from the prior art, including those using permanent magnets to excite EMF in its output windings to power the load with alternating current. The use of permanent magnets as a replacement for the pole windings provides an improvement in the mass and dimensions of the electric machine as a whole. The efficiency also increases, the losses on the excitation of the magnetic field are reduced. The only fundamental drawback of such solutions is the impossibility of damping the field, that is, the generator continues to induce EMF in the windings, while the mechanical rotation of the electric machine continues. This also means that it is impossible to relieve voltage from a mechanically rotating electric machine until it stops completely in the event of a short circuit in its own windings. This drawback leads to the possibility of serious irreversible damage to the stator, up to the ignition and release of toxic substances, which threatens the safety of staff. The proposed solution describes a permanent magnet generator that combines the advantages of excitation from permanent magnets, but at the same time provides the possibility of damping the field of excitation of permanent magnets and thus removing the EMF from the output windings. This is achieved by closing the magnetic flux of permanent magnets, bypassing the magnetic circuit of an electric machine. The achieved technical result of the solution is the appearance of overvoltage protection in case of emergency exceeding the rotation speed by damping the excitation of a mechanically rotating electric machine with permanent magnets.

Description

The technical field to which the utility model belongs. The utility model relates to electrical engineering and is an electric machine with permanent magnet excitation, designed to generate alternating voltage and load power.

The prior art. The prior art unipolar current generator [RF patent for the invention No. 2518461] containing a rotating rotor and a fixed stator. As a rotor rotating in a perpendicular magnetic field, a stacked disk of metal plates (disk sectors) separated by dielectric spacers with sliding contacts on the axis of rotation of the disk is used. The poles of a rotating constant or alternating magnetic field are used as a fixed stator, and the number of sectors of the rotor is equal to the number of stator poles or more, and the stator poles of a rotating magnetic field can be created by rotating magnets, or electromagnets, or fixed windings with a magnetic circuit inside, in which a rotating constant or variable field. The number of rotating poles can be 2 or more, subject to the condition that the directions of the EMF created by the diametrically arranged poles in the rotor are aligned, and the adjacent poles (along the perimeter) create alternating directions of the diametrical polarity of the EMF on the rotor.

The disadvantages of this solution include the presence of a sliding contact device (current collectors), which reduces reliability, as well as the lack of protection against exceeding the output voltage by the allowable limit in case of emergency exceeding the rotation speed.

Also known is a synchronous electric machine [Kopylov I.P. Design of electrical machines. M .: Yurayt, 2014], containing a multi-pole rotor, and equipped with a stator located in its grooves of a three-phase winding. In this case, an electric winding receiving power from the contact rings of the rotor, or permanent magnets, can be used as the excitation of the poles of the rotor. In both versions, the magnetic poles of the rotor have alternating polarity “north” and “south”, at each pole there is a pole tip with side edges parallel to the longitudinal axis of the pole.

This decision is taken as the main prototype, the closest in its technical essence.

The disadvantages of this solution include the lack of protection against exceeding the output voltage by the permissible limit in case of emergency exceeding the nominal rotation speed (hijacking) when using magnets as rotor poles.

Disclosure of a utility model. The prior art various designs of electrical machines, including those using permanent magnets to excite the emf in their output windings to power the load with alternating current. The use of permanent magnets as a substitute for the pole windings provides an improvement in the mass and dimensions of the electric machine as a whole. The efficiency also increases, the losses on the excitation of the magnetic field are reduced. The only fundamental drawback of such solutions is the impossibility of damping the field, that is, the generator continues to induce EMF in the windings, while the mechanical rotation of the electric machine continues. This also means that it is impossible to relieve voltage from a mechanically rotating electric machine until it stops completely in the event of a short circuit in its own windings. This drawback leads to the possibility of serious irreversible damage to the stator, up to the fire and release of toxic substances, which threatens the safety of maintenance personnel. This drawback applies to the technical solution adopted for the main prototype.

In the claimed solution, it is proposed to use pole inserts made of magnetic material as shunting magnetic poles of the jumper. In this case, the magnetic flux of permanent magnets is closed between adjacent poles of the rotor having alternating polarity, directly bypassing the stator teeth. This is facilitated by the presence of an air gap between the teeth of the stator and rotor, which reaches 3-4 millimeters in powerful machines. The magnetic flux of the poles is always closed along the shortest path with a minimum resistance [1, 2]. Since the radius of the back of the stator slots is larger than the radius along the outer part of the rotor poles, and also taking into account the presence of an air gap and the length of the stator teeth, the magnetic field lines will be closed directly from the pole to the rotor pole, passing through the pole insert. In this case, the induced EMF will be absent in the stator windings, since the slew rate of the magnetic field induction dB / dt will be zero.

To do this, it is necessary to ensure the closure of the lateral edges of the pole tips of adjacent poles with each other, with a minimum air gap and the shortest path length of the magnetic flux.

The figure 1 shows a top view of a pole insert having a trapezoidal cross-sectional shape (tapering up), and two through holes for the guide pins. The pole insert must be fixed in the transverse plane, for which it is mounted on the pins, limiting its movement in the lateral direction. The tapered edges of the illustrated pole insert are designed to facilitate retraction between the pole pieces, with the smallest possible air gap. This avoids jamming it, as would happen when retracting the pole inserts with edges that are parallel to the axis of the pole. In this case, the cross section of the pole inserts should be identical to the gaps between the pole pieces.

The pole inserts and pole tips of the proposed solution should be made of magnetic (i.e., ferromagnetic) material, which ensures efficient transfer of the flux of pole magnets, and shunting of the magnetic flux of the poles of the rotor magnets using pole inserts between the mentioned poles.

To ensure that completely coinciding with the pole inserts of the air gaps between adjacent magnetic poles of the rotor, the pole pieces are made with symmetrically beveled side edges, expanding to the outer part of the rotor.

The figure 2 shows the cross section of the rotor of the claimed solution in the initial state (the electric machine is stopped or rotates at rated speed, the protection against exceeding the speed (hijacking) is not triggered). The stator of the proposed solution in figure 2 is not shown, as it is well described in the educational literature on electric machines, and is known from the prior art. A three-phase winding is laid in the grooves of the stator, in which the variable EMF is induced, with a frequency proportional to the rotational speed of the rotor of the electric machine. The change in polarity of the half-waves of the EMF of the stator winding is due to the alternation of the polarity of the poles of the rotor magnets. When changing the rotor speed, there is not only a change in the frequency of the EMF induced in the stator winding, but also a change in its amplitude. The reason for this is an increase in the steepness of the change in the magnetic flux dB / dt with an increase in the rotor speed [1]. Thus, in an emergency, when the rotation speed of the electric machine is significantly exceeded - there is also an increase in the EMF of the stator winding, reaching many times the nominal level. In this case, the field of permanent magnets cannot be extinguished by the removal of current, as in conventional electric machines with windings at the poles of the rotor. The only way to protect the supplied load, as well as the windings of the electric machine itself, is to short-circuit (bypass) the magnetic flux of the poles to each other, bypassing the stator.

For this purpose, the claimed solution uses pole inserts that close the magnetic flux of the magnets of the rotor poles through itself. In the actuated (attracted) state, the pole inserts are held in place by the magnetic flux passing through them - this avoids the "bounce" and incomplete operation.

The figure 3 shows a cross section of the rotor of the claimed solution in the worked state (pole inserts are drawn). It can be seen from the figure that the pole inserts occupy the air gap between the edges of the pole tips of the rotor pole magnets. The pole inserts are connected by a spring to the rotor shaft, and in the initial state (until the nominal rotor speed is exceeded), the compression force of the spring draws the pole inserts closer to the rotor shaft. The rods limit the deviation of the pole inserts in the transverse axis, ensuring their accurate retraction into the openings between adjacent pole pieces.

When the rotor of the electric machine rotates, the springs shown in Figure 3 begin to stretch by centrifugal forces acting on the pole inserts outside the rotor, which causes them to move. The tensile force of the springs must be selected so that the retraction of the pole inserts occurs when the nominal rotation speed is significantly exceeded.

As the pole inserts approach the pole pieces, ponderomotive forces of the magnetic field begin to act on them, which speeds up the process of retracting the pole inserts. In the activated state, the pole inserts close the magnetic flux of the rotor poles. Returning to the initial state is possible by installing temporary plates.

The presented solution is simple and therefore industrially applicable, providing protection of the stator windings and the supplied load against overvoltage accompanying the excess of the nominal rotational speed of the rotor of an electric machine with excitation by permanent magnets (theft).

The proposed technical solution is new, having the following fundamental differences from the main prototype:

- the rotor is equipped with pole inserts having a trapezoidal section;

- in each pole insert there are two through holes for the guide pins;

- pole inserts are mounted on guide pins;

- pole inserts are attached by springs to the rotor shaft, and have free movement along the pins;

- the pole pieces mounted on the magnets have edges that expand to the outside of the rotor;

- openings between adjacent pole pieces coincide with the shape and size of the pole inserts.

Thus, the entire set of essential features of the utility model is previously unknown and leads to a new technical result - providing overvoltage protection in the event of an emergency excess of the rotor speed of an electric machine.

A brief description of the drawings. The figure 1 shows a top view of the pole insert of an electric machine with permanent magnets. The figure 2 shows a cross section of the rotor of an electric machine with permanent magnets when the protection against theft. Here 1 is a magnet, 2 is a pole piece, 3 is a rotor shaft, 4 is a spring, 5 is a pole insert, 6 is a non-magnetic pin. The figure 3 shows a cross section of the rotor of an electric machine with permanent magnets when the protection against theft in terms of rotation speed has been activated.

List of used literature.

1. Kopylov I.P. Design of electrical machines. M: Yurait, 2014.

2. Stelting G., Beiss A. Electric machines. M .: Energoatomizdat, 2015.

Claims (1)

An electric machine containing a fixed stator with a three-phase output winding laid in its grooves, as well as a rotor with permanent magnets, the poles of which are alternated, and a pole piece made of magnetic material is installed outside each magnet, and characterized in that the rotor is equipped with pole inserts made of magnetic material, having the shape of a trapezoid in cross section, in an amount equal to the number of poles of the rotor, the pole pieces have beveled edges that expand to the outer part of the rotor, the removed pole inserts completely coincide with the openings between the edges of the adjacent pole pieces, each pole insert has two through holes for the pins, the pins are attached to the rotor shaft in pairs between adjacent magnets, the pole inserts are mounted on the pins along which they are moved, and are fixed by springs to the rotor shaft with such a tensile force that said pole inserts are drawn into the openings between the edges of adjacent pole pieces when the permissible rotor speed is exceeded.

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