RU2291542C2 - Stepped electric filed insulation system for dynamoelectric machine - Google Patents

Abstract

FIELD: electrical engineering.

SUBSTANCE: proposed invention is concerned with characteristic features of ground insulation capable of sustaining voltages higher than 4 kV, best of all 13.8 kV or higher still used for dynamoelectric machines. Machine winding insulation or conductor ground insulation has two layers. First internal layer covers conductor and has first predetermined thickness and first predetermined dielectric constant; second insulation layer has second predetermined thickness and second predetermined dielectric constant lower than that of first one. First and second insulation layers have mica paper strip, different type of mica being used for each strip with the result that pattern of electric field across ground insulation at first-to-second layer transfer point abruptly rises causing occurrence of electric field close to conductor whose strength is maximal and lower than that of known insulation systems. In this way maximal value of local electric field pattern within ground insulation reduces.

EFFECT: enhanced service life and reduced thickness of insulation.

15 cl, 7 dwg

Description

Technical field

The present invention relates to an insulation system for windings of a dynamoelectric machine, and more specifically to insulation containing inner and outer layers having different dielectric constants to create a more favorable stress distribution in the dielectric.

State of the art

Insulation systems for large dynamoelectric AC machines are constantly being developed in order to increase the voltages at which these machines operate, while minimizing the thickness of the insulating material.

In such insulation systems, mica is typically used in a variety of ways, from large flakes dispersed over the backing material to a product known as mica paper. Although the low tensile strength of mica paper is not suitable for use in such insulation systems, mica paper has a higher corona resistance, which counteracts the corona discharge occurring in high voltage windings, which tends to shorten the life of the insulation. To compensate for the low tensile strength, mica paper is bonded to fiberglass, which also tends to prevent the flaking of mica flakes from mica tape during the tape wrapping operation.

Recently, corona-resistant polyimide and composite insulation tape has been used in insulation systems. This tape has exceptional insulating properties and good crown resistance. This film can be used alone or as a substrate on a composite tape of mica paper and fiberglass. Adding improved insulation from corona-resistant tape provides an insulation system that is electrically better than standard systems.

Until now, when developing insulation systems and tapes for case insulation, the magnitude and profile of the local electric field in case insulation have not been taken into account. This electric field created in the housing insulation as a result of the high voltage applied to the conductor has a direct effect on the life of the insulation. Due to the fact that the electric field is distributed over the housing insulation, it affects the performance of the insulation system and the life of the housing insulation system.

Summary of the invention

The present invention is based on the task of developing a housing insulation system for windings of dynamoelectric machines, which takes into account the influence of a localized electric field generated in the housing insulation as a result of the voltage difference across the insulation.

In accordance with the present invention, an insulation system for windings of dynamoelectric machines is created, which allows stepwise or dramatically increasing the electric field distributed over the insulation from the inside of the insulation next to the conductor bus or conductive elements to the outer armor or the grounded insulation armor.

The term "stepwise increase" of the electric field refers to a significant change in the profile of the electric field along the cross section of the housing insulation. In accordance with the present invention, the electric field profile over the cross section of the “flat part” exhibits a sharp stepwise increase at a certain distance along the cross section compared to the flat electric field profile in the past. As for the cross section of the insulation angle, the electric field profile gradually decreases from the conductors and again sharply increases stepwise at a certain distance along the cross section of the corner.

To perform a stepwise change in the profile of the electric field of the insulation according to the invention, an insulation system is created having a dynamoelectric machine conductor that is insulated by insulation layers. The insulation comprises a first inner insulation layer and a second insulation layer external to the first inner layer. Both the first and second insulation layers have a certain thickness to obtain the corresponding insulation characteristics necessary for the insulation itself. The dielectric constant of the first inner insulation layer is greater than the second insulation layer, so that the electric field in the second insulation layer rises sharply at the junction of the first inner and second insulation layer.

It was determined that as a result of creating a relatively higher dielectric constant of the inner layer, the electric field near the conductor has a reduced value. Although the total electric field distributed over the insulation can be no less, it must be understood that the magnitude of any sudden occurrences of the electric field in the insulation layer near the conductor is reduced. Insulation is designed and developed for the weakest areas that occur at the insulation corners next to the conductors, where the largest values of the electric field are manifested. Thus, as a result of a decrease in the electric field, the requirements for the insulation thickness are reduced, i.e. it is possible to minimize it without adversely affecting the voltage that the conductors withstand, or the life of the insulation. In accordance with the present invention, it is provided that the conductors withstand voltages of the order of 4 kV or more.

In alternative embodiments of the present invention, the insulation may comprise more than two layers applied to each other in the form of successive layers, where each subsequent layer has a dielectric constant that is less than that of the previous insulation layer.

Preferably, the insulation system of the present invention can be used as housing insulation for conductors in a winding of a dynamoelectric machine withstanding voltages of 4 kV or more. In the case where the voltage is about 13.8 kV, the thickness of the casing insulation is about 3.2 mm.

In accordance with a preferred embodiment of the present invention, a body insulation is provided for a conductor of a dynamoelectric machine, which has a stepped profile of the electric field along the body insulation. Housing insulation comprises a first inner insulation layer and a second outer insulation layer. The first inner insulation layer is applied to the conductor and has a first predetermined thickness and a first predetermined dielectric constant. A second outer insulation layer is applied to the first inner insulation layer and a transition is formed between them. The second outer insulation layer has a second predetermined thickness and a second predetermined dielectric constant, the second dielectric constant being less than the first dielectric constant of the first inner insulation layer. In this case, a stepwise increase in the electric field is formed in the casing insulation at the junction of the first inner and second outer insulation layers.

Brief Description of the Drawings

The invention is further explained in the description of the preferred embodiments with reference to the accompanying drawings, in which:

figure 1 depicts a cross section of a known stator bus for a large dynamoelectric AC machine;

figure 2 depicts a cross section of a known stator winding coil for a large dynamoelectric machine AC;

figa depicts an insulation system for a stator bus according to the invention;

3B shows an insulation system for a stator winding coil (another embodiment) according to the invention;

figure 4 depicts schematically the arrangement of the cross sections of the angle and the flat part for profiles of the electric field according to the invention;

Fig. 5 is a diagram of a profile of an electric field of a body insulation of a stator tire according to the invention;

6 depicts a profile diagram of the electric field of the casing insulation of the stator bus according to the invention.

Description of preferred embodiments of the invention

The known bus 10 (figure 1) of the stator for a large dynamoelectric AC machine contains many insulated conductors 12, which are isolated from each other by insulation 14.

Conductors 12 are formed into a group after deposition of insulation on them 14. The upper and lower surfaces of the group of conductors are filled with insulating material 13, which serves as a filler and prevents movement. A group of insulated conductors 12 is then wrapped with housing insulation material 16. The number of layers of insulating tape forming the insulation is from 7 to 16 layers of mica tape wound in a half-overlap depending on the level of operating voltage, to which the conductors 12 are exposed.

For high voltage, i.e. for voltages above 4000 V and preferably 13.8 kV, the preferred housing insulation 16 is a composite miklement layer containing a corona-resistant polyimide connected to a mica-type paper tape. Mikalenta provides a layer of effective insulation and, due to its resistance to corona discharge, has a long service life. The mica paper composite materials and tapes used in these hybrid systems contain a high percentage of partially cured resin (resin enriched), which may or may not contain corona-resistant material. The wrapped tire is heated and compressed in an autoclave or press to temporarily melt the resin in order to remove air and eliminate voids. The tire being machined is heated and pressurized so that the resin contained in the insulation goes into a gel state, connecting the entire insulation system together. The surface of the cured tire can then be coated with appropriate materials to form an equipotential surface during operation of the machine.

A cured tire made using these tapes functions well within the design parameters of the machine for a predetermined period of time.

Figure 2 shows a cross section of a known coil 10b. In this example, copper cores 12b (six shown) are grouped together so that although they are separated from each other by insulation 14b, six cores grouped in a turn must be isolated from other turns of the coil 10b using turn insulation 15b. The turn assembly is ultimately covered by case insulation 16b.

3A shows a cross section of a stator tire insulated according to the invention. In the described embodiment, the bundle of wires consists of individual conductors 22, separated by insulation 24 of the core. Several layers of the composite tape are then wound onto a wire bundle. Each layer of composite tape contains a first inner layer 26 of insulating tape and a second layer 28 of insulating tape. Each tape layer 26, 28 has a predetermined thickness and a different dielectric constant. In particular, the dielectric constant of the first inner layer is greater than the dielectric constant of the outermost layer. According to an embodiment of the invention, additional third or fourth layers of tape with reduced dielectric constant may be used.

The inner and outer layers of insulation may contain layers of a half-lap-wound tape consisting of a composite material, such as mica paper, deposited on a glass tape substrate, forming a layer 28. A corresponding resin impregnating material is present in the mica paper. This standard tape can withstand high voltage.

The casing insulation containing layers 26 and 28 may be subjected to pressure curing or an autoclave curing process to remove voids in the insulation layers 26 and 28 and transfer the resin to a gel state.

Appropriate surface coatings may be applied to the insulation layer 28 before or after curing.

FIG. 3B shows a composite housing insulation for a coil 20 consisting of three turns. In this case, the copper conductors 22b are surrounded by insulation 24b. Coil insulation 25b is applied to each coil, and an initial layer of casing insulation 26b is applied containing the same components as layer 26 in FIG. 3A. Finally, a layer of outer shell insulation 28b is applied. With the exception of coil insulation 25b, the insulation systems in FIGS. 3A and 3B are very similar.

Figure 4 shows a simplified diagram of a conductor 25 containing an inner layer 26 of housing insulation and a second outer layer 28 of housing insulation, also referred to as the first and second layers 26, 28. The first layer 26 has a dielectric constant that is greater than the dielectric constant of the second layer 28. Testing showed that the inner insulation layer 26 had a dielectric constant of 6.5. The dielectric constant of the second, more outer insulation layer 28 is 4.2. The predefined layer thickness was 0.096 inches or slightly less than 2.5 mm. The electric field profiles were determined at an angle of 40, and on a flat part 42. The measurement results are shown in diagram form in Fig.6. Figure 5 presents the insulation diagram in figure 1.

Figure 5 shows that the profile of the electric field at angle 40 decreases in the form of a curvilinear decline, defined by curve 55, starting at about 4200 V / mm, and gradually decreases to a thickness of 3 mm for this conductor insulation material. On the flat part, the potential electric field is stable at about 2600 V / mm. This is shown by curve 50.

Therefore, in the insulation shown in FIG. 1, the weakest section is at the corner next to the conductor, where the electric field is maximum, and therefore, the insulation has its weakest section. The diagram in FIG. 6 is compared with the diagram in FIG. 5. The thickness of the two insulation systems 26 and 28 is shown. In diagram 65, the maximum electric field is 4000 V / mm, compared to 4200 V / mm in FIG. 5. The profile of the electric field, however, gradually decreases along the curve to the steep step 68, where a second insulation layer is formed at this junction between the layers 26 and 28. After that, the electric field again decreases in the form of a curvilinear decline. As for the electric field profile on the distribution layer of the flat part 42, it is shown at 60 and can be compared with the profile 50. The distribution of the electric field next to the conductor is less for both the flat and the curved parts 42 and 40 and has a stepped increase denoted by 68, and more than curves 50 and 55, respectively. The present invention provides a reduction in the maximum value of the electric field that the housing insulation must withstand.

The electric field profile shown in FIG. 6 is intended for winding stator tires, and this electric field profile has a step-like function at the junction of the first and second insulation layers for stator winding coils. This shape can be repeated by adding subsequent layers of insulation having a lower dielectric constant in each subsequent layer.

In addition, the thickness of the insulation system is significantly reduced compared to that used in the prior art. Reducing the thickness of the insulation leads to savings in material costs.

As shown in FIGS. 3A and 3B, subsequent insulation layers 80 and 82 are shown in dashed lines and sequentially applied to layer 28 (FIG. 3A) and layer 28b (FIG. 3B). These successive layers 80, 82, if used, have decreasing dielectric constants for each layer located further from the coil insulation 24 or the shell insulation layers 26, 28.

It is further provided that the inner and outer layers of insulation used in the present invention may comprise two tapes made of different types of mica having different dielectric constants depending on the choice of mica for a tape of mica paper. The mica papers selected for these tapes are such that the difference in permittivity inherent in the mica itself contributes to the overall resulting permittivity of each tape. Thus, numerous tapes with different dielectric constants can be used based on the same basic structure and chemical composition of the tape. The most common type of mica is muscovite, which has a dielectric constant in the range of 6 to 8. Another type of mica is phlogopite, which has a dielectric constant in the range of 5 to 6. There are many different types of mica pairs from which you can select useful material pairs. . Mica can be selected from the following: anandite, annite, biotite, bitite, boromuscovite, celadonite, chernichite, clintonite, ephesite, ferriannite, glauconite, hendrixite, cinositalite, lepidolite, masutomilite, muscovite, nanpingite, paragonite, politonolithonite, robitolitonite, robitolithonite, robitolithonite, robitolithonite , siderophyllite, sodium phlogopite, teniolite, vermiculate, vonesite and cynvaldite.

Although a preferred embodiment relates to case insulation, the coil insulation 24 (FIG. 3A) surrounding the conductor 22 may comprise a first inner insulation layer and a second, more outer layer may comprise a case insulation layer 26, provided that the second layer 26 has a smaller dielectric constant than layer 24.

Claims (15)

1. The insulation element of the winding for a dynamoelectric machine, containing a first inner insulation layer deposited on the conductor and having a first predetermined thickness and a first predetermined dielectric constant, a second insulation layer deposited on the first inner insulation layer and having a second predetermined thickness and a second predetermined dielectric constant, the second dielectric constant being less than the first dielectric constant, characterized in that the first inner insulation layer and the second insulation layer comprise a mica paper tape, the mica for each tape being a different type of mica. 2. The insulation of the winding element according to claim 1, characterized in that each first inner and second insulation layers contain several layers of wrapped or overlapping insulating tape. 3. The insulation of the winding element according to claim 2, characterized in that the first inner and second layers of insulation contain material resistant to corona discharge. 4. The insulation of the winding element according to claim 1, characterized in that the first insulation layer is a layer of coil insulation applied to each conductor of a plurality of conductors forming the winding, and the second insulation layer is a layer of casing insulation applied to the first insulation layer of the plurality conductors. 5. The insulation of the winding element according to claim 4, characterized in that it further comprises at least one additional insulation layer deposited sequentially on the second insulation layer and having a dielectric constant that is less than that of the previously applied insulation layer. 6. The insulation of the winding element according to claim 1, characterized in that it further comprises at least one subsequent insulation layer deposited sequentially on the second insulation layer and having a dielectric constant that is less than that of the previously applied insulation layer. 7. The insulation of the winding element according to claim 1, characterized in that the mica for each tape is selected from the group consisting of anandite, annite, biotite, bitite, boromuscovite, celadonite, chernichite, clintonite, ephesite, ferriannite, glauconite, hendrixite, cinositalite, lepidolite, masutomilite, muscovite, nanpingite, paragonite, phlogopite, polyolithionite, prismatic, roscolite, siderophyllite, sodium phlogopite, teniolite, vermiculate, vonesite and cynvaldite. 8. Case insulation for the conductor of a dynamoelectric machine having a stepped electric field across the case insulation and containing a first inner insulation layer deposited on the conductor and having a first predetermined thickness and a first predetermined dielectric constant, a second insulation layer deposited on the first inner insulation layer, forming a transition with it and having a second predetermined thickness and a second predetermined dielectric constant, the second dielectric constant being less than the first dielectric constant, and forms a stepwise increase in the electric field in the housing insulation in place the transition of the first inner and second layers of insulation, characterized in that the first inner and second layers of insulation contain a tape of mica paper, and the mica for each tape is a mica of a different type. 9. Case insulation according to claim 8, characterized in that each of the first inner and second layers of insulation of the body insulation contains several layers of wrapped or overlapping insulation tape. 10. Case insulation according to claim 9, characterized in that the first inner and second layers of insulation are impregnated with a resin that contains particles of corona-resistant material. 11. Housing insulation according to claim 9, characterized in that it further comprises at least one additional insulation layer applied sequentially to the second insulation layer, each subsequent insulation layer having a dielectric constant that is less than that of the earlier applied insulation layer. 12. Case insulation according to claim 9, characterized in that the winding is designed to withstand voltages above 4 kV. 13. Case insulation according to item 12, wherein the winding is designed to withstand voltages equal to at least 13.8 kV. 14. Case insulation according to claim 9, characterized in that the insulation thickness is less than 3.2 mm 15. Case insulation according to claim 8, characterized in that the mica for each tape is selected from the group consisting of anandite, annite, biotite, bitite, boromuscovite, celadonite, chernichite, clintonite, ephesite, ferriannite, glauconite, hendrixite, cinositalite, lepidolite , masutomilite, muscovite, nanpingite, paragonite, phlogopite, poly lithithionite, priceworkite, roscolite, siderophyllite, sodium phlogopite, teniolite, vermiculate, vonesite and cynvaldite.

Images