RU2320064C1 - Synchronous electrical machine rotor - Google Patents

Abstract

FIELD: electrical engineering; electrical machines.

SUBSTANCE: proposed synchronous machine rotor mounts permanent magnets, nonmagnetic inserts, butt-end locking rings, and binding sleeve. Novelty is that permanent magnets are split into segments separated by nonmagnetic inserts and that locking rings are made of low-resistance material, for instance copper. Proposed electrical machine can run as synchronous generator or as motor, if necessary, while setting up desired starting torque.

EFFECT: improved damping and starting characteristics, simplified design, and enhanced reliability of rotor due to minimized quantity of its components.

1 cl, 2 dwg

Description

The invention relates to the field of electrical engineering, in particular to electrical machines, and is intended to expand the scope of synchronous generators.

It is known that synchronous machines, like other types of electric machines, have the property of reversibility, i.e. a synchronous machine designed to operate in generator mode can operate as an engine and vice versa. However, a synchronous motor accelerates to an angular speed close to synchronous, either due to an additional accelerating motor, or due to its own asynchronous moment that appears when the armature winding of the motor is turned on, and for synchronous motors designed for asynchronous start-up, a specially calculated rotor is placed on the rotor starting winding. The traditional constructive solution is that in the lined rotor magnetic circuit grooves are stamped, into which the starting winding rods are laid, at the ends the rods are closed by arcs. [A.V. Ivanov-Smolensky. Electric cars .: Textbook for universities. - M .: Energy, 1980. - 928 p., Ill.]. In a synchronous machine with permanent magnet excitation, such a solution is also realized [for example, I.V.Smolyanov, V.P. Kolesnikov, N.N. Farkhullin, I.I. Vasilchenko and V.D. Bartenev. A.S. No. 663032. Synchronous motor. Bulletin No. 18, 1979]. The design, which includes both permanent magnets and starter winding rods, is quite complex and unreliable. There are opportunities to create a starting moment by inducing currents in the structural elements of the machine - in the rotor barrel, in metal wedges, in bandages. In the invention [application No. 55-23019 (Japan) Synchronous electric motor with a magnetic rotor. Publication 1980.20.06. No. 7-57] (prototype) a design is proposed that includes a permanent magnet in the form of a hollow glass, which is fixed from the end sides by locking rings. Damping and protective glasses are put on the outer surface of the magnet, the damping glass is made of materials with low electrical resistance, which ensures the damping effect.

The disadvantage of this design is the presence of two glasses made of various materials. For high-speed synchronous machines, this option is unacceptable, because with large centrifugal forces, this can lead to a gap between the cylinders and loss of machine performance due to vibration.

The task of expanding the scope of application of high-speed synchronous generators can be solved by improving the damping and starting parameters of the rotor.

In the present invention, the structural elements (Fig. 1) are radially magnetized segmented permanent magnets (1), separated by non-magnetic inserts (2), end locking rings (3) and one retaining ring (4). A distinctive design feature is that the locking rings are made of a material with low electrical resistance, and the retaining ring is made of non-magnetic steel.

The proposed design does not require an additional accelerating motor, does not require a special starting winding and allows the synchronous generator to be launched due to its own asynchronous moment.

To start the proposed synchronous machine, the stator winding is connected to the network with a given voltage U _c and frequency f _c , the currents flowing through the winding form a magnetic field rotating at a speed ω _c = 2πf _s . This magnetic field will induce currents in the retaining cylinder, which, being closed through the locking rings, form short-circuited circuits. The currents have a slip frequency sω _с = ω _с -ω, i.e. frequency, which is determined by the difference between the rotational speeds of the stator magnetic field ω _s and the rotor speed ω. As a result of the interaction of currents induced in the short-circuited circuits of the rotor with the rotating magnetic field of the stator, an electromagnetic moment of the same nature as in asynchronous ones will act on the rotor, and the machine will have an asynchronous electromagnetic moment. The magnitude of the asynchronous electromagnetic moment depends on the active and inductive resistances of the short-circuited circuits created on the rotor by a retaining cylinder and locking rings.

Since the synchronous machine has electromagnetic excitation from permanent magnets, the start-up occurs when the excitation is constantly on, i.e. the magnet flux induces in the stator winding the EMF changing with frequency f _E = (1-s) f _c . Under the influence of this EMF in the circuit, the stator winding - the power source flows a current having a frequency different from the network frequency. As a result of the interaction of the excitation field with the induced currents, a braking moment is formed, which is similar in nature to the braking moment of the generator during a short circuit. In order for the engine to gain speed close to synchronous, the value of the asynchronous moment must be greater than the braking one. The transition from sub-synchronous speed to synchronous occurs due to the action of the synchronizing moment for a very short period of time. The synchronizing moment is due to the interaction of the field of magnets with the field of the armature and acts on the rotor during the entire start time. The average value of the synchronizing moment per revolution at a rotor speed other than synchronous is zero.

Starting qualities of the proposed design are estimated by calculation. From the theory of calculation of electric machines it is known that the active resistance of a short-circuited ring depends on its average diameter and cross section. By varying the geometrical dimensions of the locking ring, it is possible to achieve the desired value of the active resistance and the given starting qualities of the machine. It should be noted that the inductive resistances of the locking ring can also be calculated, however, their values are very small and do not significantly affect the starting characteristics of the machine. By virtue of symmetry, both active and inductive resistances along the longitudinal d and along the transverse q axes are equal to:

r _ddk = r _dqk x _ddk = x _dqk

To calculate the active and inductive resistances of the retaining cylinder, you can use the recommendations [L.R. Neumann. Surface effect in ferromagnetic bodies. - M .: Gosenergoizdat, 1948.], assuming the magnetic permeability μ _e = μ ₀

where l, u is the length and perimeter of the retaining cylinder;

- круговая частота;

- circular frequency;

γ is the specific conductivity of the material;

μ _e = μ ₀ - magnetic permeability.

Figure 2 shows the results of the calculation of the starting characteristics of the synchronous generator 5.0 MW, 12000 min ^-1 , made according to the proposed design. Here 1 is the asynchronous moment, 2 is the braking torque, 3 is the total starting torque. The maximum value of the starting torque is M _max = 4.08 M _N , the sliding moment is equal to unity, M _{s = 1.0} = 0.278 M _N. For comparison, the same generator with a starting winding (14 rods with a diameter of 10 mm) has values of the moments M _max = 2.59 M _H and M _{s = 1.0} = 0.174 M _H.

Thus, the proposed design provides starting characteristics of a synchronous machine and the generator can work in engine mode, creating the necessary starting moment. The proposed design is simple and reliable, because contains the minimum required number of elements.

Claims (1)

A rotor of a synchronous electric machine containing permanent magnets fixed on the end faces by locking rings and a retaining ring, characterized in that the permanent magnets are segmented and separated by non-magnetic inserts, and the locking rings are made of a material with low electrical resistance, for example, copper.

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