STATOR FOR AN ELECTRIC MACHINE AND METHOD FOR PRODUCTION OF SUCH A STATOR

Abstract

A stator for an electric machine having slots for receiving conductors used for generating a magnetic field; in the slots, at least two mutually parallel, adjoining conductors being provided, which are electrically insulated from one another by insulation means; the insulations means being formed at least partially by a partition inserted between the conductors. It is an object of the present invention to provide a stator, respectively a method for manufacturing such a stator, which, on the one hand, will make it possible to achieve a high fill factor and, on the other hand, to reliably prevent partial discharges. The objective is achieved by the use and/or characteristics of the partitions being a function of the particular maximum voltage potential between the mutually parallel, adjoining conductors in the slots.

Claims

1. A stator for an electric machine having: a plurality of slots for receiving conductors used for generating a magnetic field; in the slots, at least two mutually parallel, adjoining conductors are provided, which are electrically insulated from one another by insulation means; wherein the insulations means is formed at least partially by a partition inserted between the conductors, and wherein the use and/or characteristics of the partitions are/is a function of the particular maximum voltage potential between the mutually parallel, adjoining conductors in the slots.

2. The stator as recited in claim 1, wherein the partitions are preferably made of a special separating film and are always inserted when the maximum voltage potential between the adjoining conductors exceeds a specific value.

3. The stator as recited in claim 1, wherein a number of adjoining conductors in a slot is configured in at least two stacked layers; and wherein the use and/or characteristics of the partitions are/is determined by the greatest maximum potential difference of two adjoining conductors.

4. The stator as recited in claim 3, wherein the separating film optionally inserted between the layers extends over at least the two layers.

5. The stator as recited in claim 1, wherein two radially adjoining layers in a slot are constituted of at least two radially adjoining, individual conductors.

6. The stator as recited in claim 1, wherein the stator is provided with concentrated windings.

7. The stator as recited in claim 1, wherein the stator is provided with distributed windings.

8. A method for determining the use and/or characteristics of the partition for a stator in a accordance with claim 1, comprising: determining the potential differences between adjoining conductors; determining the existing theoretical partial discharge voltage that is dependent, on one or more of the following: aging, the environment, the conductor insulation, the form of the conductor or the voltage characteristic; using the partition if the calculated potential difference is above the theoretical partial discharge voltage; and not using the partition if the calculated potential difference is below the theoretical partial discharge voltage.

9. The method as recited in claim 8, wherein, if the calculated potential differences exceed the theoretical partial discharge voltage, the selection of a suitable partition depends on the magnitude of the difference between the calculated potential differences and the theoretical partial discharge voltage.

10. The method as recited in claim 8, wherein, once a partial-discharge inception voltage is established, the requisite, nominal layer thickness of the insulating material between the adjoining conductors is determined; wherein the thickness of the insulating layers of the adjoining conductors are included in the calculation of the nominal layer thickness; wherein the necessary, local, insulating layer thickness is computed from the ratio of the potential difference of two adjoining conductors and the partial-discharge inception voltage; and wherein the thickness of the insulating material of the two adjoining conductors is deducted from the computed insulating layer thickness to determine the thickness of the insulating material to be additionally inserted.

Description

BRIEF DESCRIPTION OF THE DRAWING

[0021] An exemplary embodiment of the present invention is described in greater detail in the following with reference to the drawing, in which:

[0022] FIG. 1 shows a section of a table indicating the computed potentials for the individual conductor elements (in simplified terms, often referred to as conductors) in the respective slot;

[0023] FIG. 2 shows a section of a table indicating the potential differences at this stage in each particular case between two conductors in the respective slot in accordance with FIG. 1;

[0024] FIG. 3 shows a section of a table illustrating the theoretically necessary insulating layer thicknesses for the potential differences indicated in FIG. 2;

[0025] FIG. 4 shows a section of a table in which the insulating layer thicknesses for practical use are recorded in accordance with the results in FIG. 3; and

[0026] FIG. 5 shows a section of a table that proposes which commercially available insulating materials could actually be used at which locations on the basis of the results in FIG. 4.

DETAILED DESCRIPTION

[0027] FIG. 1 shows a section of a table in which are entered the computationally determined absolute values of the potentials on the conductors in the individual slots at a specific point in time. The computation method is not described in greater detail here. In the present Application, in each particular case, the designation “conductors” means the sections of a winding that extend within a slot, along the same. In place of “conductors,” “conductor elements” could also be used.

[0028] FIG. 1 relates to a stator of a three-phase machine, for which a large amount (for example, 120) slots are provided, into which are inserted the conductors to which phases U, V, W of a three-phase current are applied. The present invention is applicable to all types of windings since the applied voltage drops across the entire line, so that different potentials prevail on the individual conductor elements.

[0029] The computations apply to all slots of the stator. In the present example, the stator has 120 slots, but may also have a larger or smaller number of slots. Thus, it is not a concentrated winding (“single-tooth winding”), but a distributed winding. The method may also be generally used for concentrated windings.

[0030] The winding of the stator in accordance with FIG. 1, which is provided for a three-phase synchronous motor, has a distinctive feature. In each of the slots, 12 conductors are stacked radially and in a plane that extends parallel to the lateral wall of the slot. Thus, within a slot, only a certain number of conductors are disposed in a stacked arrangement and not adjacently. Thus, the voltage among the individual conductors acts radially, so that the insulating means are to be inserted transversely thereto, tangentially among the conductors. Thus, in the present case, it is only conditionally possible to speak about a layer since each layer is composed of only one single conductor, and these hypothetical layers also extend in a tangential plane. Thus, for example, a potential of 86 V prevails on the radially lowermost conductor of slot 1 in “layer 1,” a potential of 516 V on the conductor in “layer 11,” and a potential of 9V in the conductor in “layer 12.” Corresponding values are apparent from the table for further slots 2 through 16.

[0031] What is important at this stage for a potential partial discharging between two (radially) adjoining conductors, however, is not the absolute potential on the individual conductors, rather the potential difference therebetween. These potential differences are noted in FIG. 2 as the differences between the individual potentials prevailing on the adjacent conductors. FIG. 2 refers to FIG. 1 and has an analogous structure. Thus, when conductor 12 has a potential of 9 V and conductor 11 a potential of 516 V in slot 1, a potential difference of 507 V prevails therebetween. A corresponding value is entered in FIG. 2 for the intermediate space, layer 11-12. The remaining values for slots 1 through 16 and layer-to-layer intermediate spaces for layer 1-2 to layer 11-12 are entered in FIG. 2. Since the insulating layers of two adjoining conductors alone suffice to prevent a partial discharge at a potential difference of 248 V; in terms of additional insulating means, it is only necessary to consider potential differences from FIG. 2 that are greater than 248 V.

[0032] The nominal layer thickness is determined from a theoretical consideration, namely which partial-discharge inception voltage (PD) is to be achieved. This value is derived from the boundary conditions of the system (voltage level, aging, environment, inverter clocking, etc.).

[0033] If the insulation system is subject to a low voltage load (in the case of stacked conductors having small potential differences), less insulating material leads to the same result. This means that 250 μm layer thickness (wire enamel+partition) is needed in this example to observe the partial discharge voltage at maximum voltage. Depending on the potential difference, a greater or smaller partition thickness is then needed; in many cases, the enamel layer thickness suffices (partition thickness <0).

[0034] In the present exemplary embodiment, it is assumed at this stage that the nominal insulating layer thickness between live conductors (including the enamel) should be altogether 250 μm (micrometers). By convention, the nominal layer thickness (wire enamel+partition) of 250 μm assumed in the present case certainly suffices to reliably prevent a partial discharge up until a potential difference of 248 V. Thus, if a considered potential difference is below 248 V, there is no need to insert an additional insulating means or a corresponding film.

[0035] It is possible to compute the voltage between two conductors, starting at which a partition is used, for example, from the ratio of the thickness of the enamel layer to the total thickness of the layer, multiplied by the maximum voltage, thus, for example, 2×60 μm/250 μm×516 V˜248 V.

[0036] In FIG. 3, it is computed at this stage, at which potential differences derived from FIG. 2, additional insulating means, respectively an appropriate film must be inserted. The assumption is based, for example, on the necessity of providing an insulating layer of a total of 250 μm under the prevailing boundary conditions for a maximum voltage (for example, 516 V). 2×60 μm may then be deducted from this insulating layer, for example, since the insulating layers of the two adjoining conductors already include this amount. Thus, with regard to the theoretically necessary insulating layer thickness, a value of 507 V/516 V×250 μm-2×60 μm˜126 μm is derived for layer 11-12 of slot 1. The further values in the table according to FIG. 3 are computed analogously.

[0037] In terms of the use or avoidance of additional insulating means, the computational results derived from FIG. 3 are analyzed at this stage in FIG. 4. If the values computed in accordance with the method described further above in connection with FIG. 3 are positive, it is then necessary to insert an insulating film there having at least the computed thickness, while in the case of negative, computed values, the insulating layers of the two corresponding conductors alone suffice for avoiding a partial discharge. Accordingly, an additional insulating layer having thickness 0 μm is formally noted for the mentioned negative values.

[0038] Thus, for all values below 0, the thickness of the enamel layer suffices to reach the requisite partial-discharge inception voltage. For this reason, there is no need to use a partition for additional insulation. All values >0 are rounded up to the next possible material layer thickness (the insulating material is only manufactured in specific layer thicknesses) to ensure that at least the theoretically required layer thickness is reached. In addition, the thickness totals of all of the insulating films used in the particular slot are entered underneath the columns associated with the slots in the table in FIG. 4.

[0039] The values in FIG. 5 assume that two standardized insulating films having carrier thicknesses of 80 μm and 130 μm are commercially available, and the thickness of the bonding agent is 50 μm; however, the bonding agent being considered with respect to integrity, namely, in terms of elongation and spacing, but not in terms of the insulation effect. Therefore, a film is used, whose thickness is not smaller than that of the insulating layer computed in connection with FIG. 4. In practical terms, this means that a 130 μm thick film is used for all insulating layer thicknesses computed in accordance with FIG. 4 that are greater than 80 μm and smaller than 130 μm, and a 80 μm thick film is used for insulating layer thicknesses smaller than 80 μm. With regard to the actual thickness of these films, the thickness of the bonding agent is also to be added thereto in each particular case. The material thicknesses of 180 μm, respectively 130 μm indicated in FIG. 5 are thereby arrived at.

[0040] For reasons of manufacturing economics, only two film thicknesses are used. To the extent that they are commercially available and reasonably manageable in the manufacturing process, it is self-evident that the films to be inserted may be adapted to the reduced thicknesses computed for layers 9-10 and 8-9.

[0041] Also provided in FIG. 5 below the columns associated with the individual slots is the sum of the material thicknesses and the number of partitions to be inserted. The commercially available Nomex 410 film and acrylate bonding agents are indicated exemplarily as the materials used.