WO2002089295A1 - Electrical machine - Google Patents

Abstract

The invention relates to a salient pole synchronous machine comprising a stator and a rotor, which form an air gap between them. The stator or the rotor have pole shoes that support field windings. The invention is characterized by the following feature: the pole shoes are, when viewed in an axially vertical section, structured so that the air gap enlarges in the rotational direction of the rotor.

Description

 Electrical machine

The invention relates to an electrical machine, in particular a salient pole machine.

Such machines have a stator and a rotor. Pole shoes are assigned to the rotor. The pole pieces carry a field winding to generate a magnetic field in the air gap. Armature windings are provided in the fixed stator.

The contour of the pole shoes in a salient pole machine is generally designed in such a way that an almost sinusoidal induction curve prevails in the air gap when idling.

It is known that the induction at nominal load (= active load) is greater than at idle. Under load, however, tooth and rotor pole saturation in the area of circumferential force formation must be expected. This leads to increased losses in the stator winding and to the so-called lion heart losses with the tooth relief field as the cause. Due to the saturation, the calculation of the excitation current is also subject to uncertainties.

The invention has for its object to design a salient pole machine in such a way that the aforementioned lion heart losses are reduced or avoided, and that the required excitation current can be calculated more precisely.

This object is solved by the features of claim 1. Accordingly, the pole shoes - seen in an axis-perpendicular section - are designed in such a way that the air gap increases in the direction of rotation of the rotor. The maximum value is therefore on the force application side.

The inventor recognized the following: During the transition from idling to the nominal load, a significant increase in the induction occurs on one side of the pole shoe, as seen in the direction of rotation of the rotor. This is the side of the pole shoe on which the torque-generating force acts. However, if the pole piece is designed asymmetrically in accordance with the invention so that the air gap - seen in the circumferential direction of the rotor - widens on one side, the induction above the salient pole piece is made more uniform. As a result, about half of the torque is already formed from the magnetic force - more precisely from its tangential component.

One could compare the measure according to the invention mentioned with the wing adjustment of wind rotors. Analogously, it could be considered to make the poles or their geometric configuration changeable and to adapt them to the respective load. However, this is generally not necessary, since many electrical machines run at constant nominal loads, for example generators from hydropower plants. Therefore, the pole shoe shape can be designed from the outset in such a way that the optimum induction results at nominal load.

The invention has another advantage. Since the amplitude of the voltage lies approximately in the center of the pole, ie in the main magnetic axis, the stability improves. The excitation winding is no longer exclusively in the magnetic longitudinal axis of the pole piece.

The invention can also be used in hydropower plants with pump turbines. In motor operation, the direction of rotation is reversed compared to generator operation. However, what is not reversed is the direction of the torque, which is determined solely by the asymmetrical pole shoes according to the invention.

So far, the idea of asymmetrical pole pieces could not arise because the expert only had to see disadvantages. The problem only appeared when the machines were used more and more, i.e. with higher induction operation. In fact, the behavior of a machine with asymmetrical pole pieces is less favorable when idling, because the voltage curve becomes less favorable due to the asymmetry and because lion heart losses occur during idling. It is crucial, however, that the losses are minimized at nominal load and thus the operation is optimal. One could speak of a load case-optimized shape in the asymmetrical pole shoe shape according to the invention.

In summary, the invention provides the following advantages:

(1) The lion heart losses (longitudinal field losses) in the stator development are almost completely eliminated at nominal load.

(2) The current-dependent losses in the pole shoe surface due to finite number of uses also decrease significantly at nominal load.

(3) The pole horns are relieved of extreme saturation at nominal load; this allows the excitation current to be calculated more precisely.

(4) The static and dynamic stability are greater at nominal load than with conventional pole pieces with the same excitation current.

(5) The field curve at nominal load can be adapted to the ideal shape.

(6) Generators according to the invention can also be used in pump turbines, regardless of the change in the direction of rotation.

The invention and the prior art are explained in more detail with reference to the drawing. The following is shown in detail:

Figure 1 illustrates an asymmetrical pole piece with associated

Induction chart.

Figure 2 illustrates a conventional pole piece with associated

Induction chart. FIG. 3 illustrates the course of the losses in the stator winding through the tooth relief field over the load, specifically for inventive and conventional pole pieces.

Figure 4 is a performance diagram showing the static and dynamic stability in asymmetric and conventional pole pieces.

Claims

claims

1. salient pole synchronous machine;

1.1 with a stator and a rotor, which form an air gap between them;

1.2 the stator or the rotor have pole shoes;

1.3 the pole pieces have field windings;

1.4 the pole shoes are - seen in a section perpendicular to the axis - designed such that the air gap increases in the direction of rotation of the rotor.