Corona discharge prevention layer

Abstract

To provide a corona discharge prevention layer capable of mitigating an electric field and suppressing corona discharge.SOLUTION: A corona discharge prevention layer is provided in an insulation layer of a stator coil in order to prevent corona discharge in the stator coil which is stored inside of a slot of a stator core of a rotary electric machine. The corona discharge prevention layer comprises a high resistance corona discharge prevention tape which is wound around an outer periphery of the insulation layer outside of the slot and a low resistance corona discharge prevention tape which is wound around the outer periphery of the insulation layer inside and outside of the slot. The low resistance corona discharge prevention tape is wound around an outer periphery of the high resistance corona discharge prevention tape while covering an end face so as to form a clearance between the end face of the high resistance corona discharge prevention tape at the side of the stator core and the low resistance corona discharge prevention tape.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a corona discharge prevention layer applied to a stator winding for a high voltage rotating electric machine, for example, a turbine generator or a water turbine generator. [Background technology]

[0002] In recent years, there has been a trend toward higher voltage stator windings in large-capacity rotating electrical machines. Corona discharges occur at the ends of high-voltage stator windings, which can cause etching that damages the insulating layer and leads to dielectric breakdown, or ozone is generated that corrodes metals such as iron and can lead to serious accidents. Therefore, it is necessary to suppress corona discharges. To suppress corona discharges, a corona discharge prevention layer, which has the effect of alleviating the electric field, is used.

[0003] FIG. 3 is a cross-sectional view showing the structure of a conventional corona discharge prevention layer.

[0004] A stator winding 2 is housed in the slots of the stator core 1 , and a stator winding end 3 protrudes from the stator core 1 .

[0005] A typical conventional corona discharge prevention layer 11 is formed by winding a low-resistance corona discharge prevention tape 4 containing carbon on the surface of an insulating layer from the inside to the outside of the stator core 1 along the straight section of the stator winding 2, and then winding a high-resistance corona discharge prevention tape 5 containing silicon carbide and carbon so as to overlap the boundary at the end of the tape.

[0006] Since silicon carbide has an electric field-dependent resistance, when a high voltage is applied, the resistance value decreases in response to the electric field, thereby controlling the surface electric field and suppressing the occurrence of corona discharge.

[0007] In the conventional winding method, a high resistance corona discharge prevention tape 5 is wound around the step at the end boundary of the low resistance corona discharge prevention tape 4, resulting in a gap 6 being formed.

[0008] The thickness of this gap 6 is determined by the thickness of the low resistance corona discharge prevention tape 4, but the thickness of the low resistance corona discharge prevention tape 4 is about 1 / 3 to 1 / 2 the thickness of the high resistance corona discharge prevention tape 5, so the thickness of the gap 6 is very small. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] Japanese Utility Model Application Publication No. 59-145253 [Patent Document 2] Japanese Patent Application Publication No. 61-177134 Summary of the Invention [Problem to be solved by the invention]

[0010] As mentioned above, when the high resistance corona discharge prevention tape 5 is wrapped around the step at the end boundary of the low resistance corona discharge prevention tape 4, a minute gap 6 is created. This generates an electric field, which causes corona discharge.

[0011] FIG. 4 is a diagram showing the results of a simulation of the electric field generated in the gap.

[0012] The electric field applied to the gap 6 is calculated by (electric field) = (applied voltage) ÷ (gap thickness). According to this relationship, as the thickness of the gap 6 decreases, the electric field increases and corona discharge becomes more likely to occur. Therefore, by increasing the gap 6, corona discharge can be made less likely to occur.

[0013] One way to increase the gap 6 is to increase the thickness of the low-resistance corona discharge prevention tape 4. However, in this case, the cross-sectional dimensions of the straight portion of the stator winding 2 would increase, and the size of the stator core 1 that houses it would also increase.

[0014] Furthermore, if the low resistance corona discharge prevention tape 4 becomes thick, it becomes difficult for the Joule heat generated from the stator winding 2 to escape, causing the temperature of the stator winding 2 to rise, which also leads to an increase in the size of the rotating electric machine.

[0015] The present invention has been made in consideration of the above circumstances, and aims to provide a corona discharge prevention layer that can reduce the electric field and suppress corona discharge without increasing the size of the stator core or rotating electric machine. [Means for solving the problem]

[0016] The corona discharge prevention layer of the first aspect of the present invention is a corona discharge prevention layer provided on an insulating layer of a stator winding to prevent corona discharge in the stator winding housed inside the slots of a stator core of a rotating electric machine, and comprises a high-resistance corona discharge prevention tape wound around the outer periphery of the insulating layer outside the slot, and a low-resistance corona discharge prevention tape wound around the outer periphery of the insulating layer inside and outside the slot, and the low-resistance corona discharge prevention tape is wound around the outer periphery of the high-resistance corona discharge prevention tape while covering the end face so as to form a gap between the end face of the high-resistance corona discharge prevention tape on the stator core side and the low-resistance corona discharge prevention tape.

[0017] The corona discharge prevention layer of the second embodiment of the present invention is the corona discharge prevention layer of the first embodiment, in which the thickness of the high resistance corona discharge prevention tape is at least two times and at most three times the thickness of the low resistance corona discharge prevention tape.

[0018] The corona discharge prevention layer of the third aspect of the present invention is the corona discharge prevention layer of the first or second aspect, in which the outer periphery of the high-resistance corona discharge prevention tape on the stator core side is wrapped with the low-resistance corona discharge prevention tape, and the outer periphery of the high-resistance corona discharge prevention tape on the side opposite the stator core side is not wrapped with the low-resistance corona discharge prevention tape.

[0019] The corona discharge prevention layer of the fourth aspect of the present invention is the corona discharge prevention layer of the first or second aspect, in which the end face of the high-resistance corona discharge prevention tape opposite the stator core side is not covered with the low-resistance corona discharge prevention tape. Effect of the Invention

[0020] According to the corona discharge prevention layer of the present invention, it is possible to reduce the electric field and suppress corona discharge without increasing the size of the stator core or the rotating electric machine. [Brief description of the drawings]

[0021] [Figure 1] FIG. 1 is a cross-sectional view showing an example of the structure of a corona discharge prevention layer according to an embodiment of the present invention. [Diagram 2] FIG. 2 shows the results of a simulation of the electric field generated in a gap that is three times thicker than the conventional gap. [Diagram 3] FIG. 3 is a cross-sectional view showing the structure of a conventional corona discharge prevention layer. [Figure 4] FIG. 4 is a diagram showing the results of a simulation of the electric field generated in the gap. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0022] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. The drawings are schematic or conceptual, and the relationship between the thickness and width of each part, the size ratio between parts, etc. are not necessarily the same as the actual ones. Even when the same part is shown, the dimensions and ratios of each part may be different depending on the drawing. In this specification and each drawing, elements similar to those described above with respect to the previous drawings are given the same reference numerals, and detailed explanations and duplicated explanations are omitted as appropriate.

[0023] Hereinafter, the best mode for carrying out the present invention will be described with reference to the drawings.

[0024] FIG. 1 is a cross-sectional view showing an example of the structure of a corona discharge prevention layer according to an embodiment of the present invention.

[0025] That is, the corona discharge prevention layer 10 of this embodiment is provided on the insulating layer of the stator winding 2 to prevent corona discharge in the stator winding 2 housed inside the slots of the stator core 1 of a high-voltage rotating electric machine, and comprises a low-resistance corona discharge prevention tape 4 and a high-resistance corona discharge prevention tape 5.

[0026] To provide the corona discharge prevention layer 10, first, the high resistance corona discharge prevention tape 5 is wound around the insulating layer from above the insulating layer outside the slot. The thickness of the high resistance corona discharge prevention tape 5 is about two to three times the thickness of the low resistance corona discharge prevention tape 4. The position on the insulating layer where the high resistance corona discharge prevention tape 5 is wound can be the same position as the conventional corona discharge prevention layer.

[0027] Next, the low-resistance corona discharge prevention tape 4 is wound around the outer periphery of the insulating layer from the inside to the outside of the slot (from left to right in the figure). When the low-resistance corona discharge prevention tape 4 is wound from the inside to the outside of the slot, the low-resistance corona discharge prevention tape 4 reaches the high-resistance corona discharge prevention tape 5. When it reaches the high-resistance corona discharge prevention tape 5, the low-resistance corona discharge prevention tape 4 is wound around the outer periphery of the high-resistance corona discharge prevention tape 5, up to the middle of the high-resistance corona discharge prevention tape 5, without coming into contact with the end face 8 of the high-resistance corona discharge prevention tape 5 on the stator core 1 side.

[0028] In other words, the outer periphery of the high resistivity corona discharge prevention tape 5 on the stator core 1 side is wrapped with the low resistivity corona discharge prevention tape 4, but the outer periphery of the high resistivity corona discharge prevention tape 5 on the opposite side to the stator core 1 side is not wrapped with the low resistivity corona discharge prevention tape 4. Therefore, the end face 9 of the high resistivity corona discharge prevention tape 5 on the opposite side to the stator core 1 side is not covered with the low resistivity corona discharge prevention tape 4.

[0029] Thus, the corona discharge prevention layer 10 differs from the conventional corona discharge prevention layer shown in FIG. 3 in that the winding order of the low resistance corona discharge prevention tape 4 and the high resistance corona discharge prevention tape 5 is reversed.

[0030] As a result, a gap 7 is formed between the end surface 8 and the low resistance corona discharge prevention tape 4, that is, at the step where the low resistance corona discharge prevention tape 4 and the high resistance corona discharge prevention tape 5 overlap.

[0031] The thickness of this gap 7 is determined by the thickness of the high resistance corona discharge prevention tape 5 that has been wrapped previously, and is therefore about 2 to 3 times thicker than the thickness of gap 6, which was previously determined by the low resistance corona discharge prevention tape 4.

[0032] FIG. 2 shows the results of a simulation of the electric field generated in a gap that is three times thicker than the conventional gap.

[0033] In Fig. 2, the electric field value of 100% corresponds to the maximum electric field value of corona discharge occurring when the thickness of gap 6 is the conventional corona discharge prevention layer shown in Fig. 1. According to the corona discharge prevention layer 10 of this embodiment, the thickness of gap 7 is three times the thickness of gap 6 in the conventional corona discharge prevention layer, so that the electric field value due to corona discharge can be suppressed to 75% compared to the conventional technology.

[0034] As described above, according to the corona discharge prevention layer 10 of the embodiment of the present invention, by switching the winding order of the low resistance corona discharge prevention tape 4 and the high resistance corona discharge prevention tape 5 wound around the insulating layer of the stator winding 2, it is possible to enlarge the gap 7 at the step where the two corona discharge prevention tapes 4, 5 overlap. This makes it possible to reduce the electric field and suppress corona discharges without increasing the size of the stator core 1 or the rotating electric machine.

[0035] Although some embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These embodiments can be implemented in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their modifications are included in the scope of the invention and its equivalents described in the claims, as well as in the scope and spirit of the invention. [Explanation of symbols]

[0036] 1 Stator core 2 Stator Winding 3 Stator winding end 4. Low resistance corona discharge prevention tape 5. High resistance corona discharge prevention tape 6 Gap (conventional technology) 7 Gap (present invention) 8 End face (stator core side) 9 End face (opposite side to the stator core) 10 Corona discharge prevention layer (present invention) 11 Corona discharge prevention layer (prior art)

Claims

1. A corona discharge prevention layer provided on an insulating layer of a stator winding in order to prevent corona discharge in the stator winding housed inside a slot of a stator core of a rotating electric machine, comprising: a high resistance corona discharge prevention tape wound around the outer periphery of the insulating layer outside the slot; a low resistance corona discharge prevention tape wound around the outer periphery of the insulating layer inside and outside the slot; A corona discharge prevention layer is formed by wrapping the low-resistance corona discharge prevention tape around the outer periphery of the high-resistance corona discharge prevention tape while covering the end face so as to form a gap between the end face of the high-resistance corona discharge prevention tape on the stator core side and the low-resistance corona discharge prevention tape.

2. 2. The corona discharge prevention layer according to claim 1, wherein the thickness of said high resistance corona discharge prevention tape is at least two times and at most three times the thickness of said low resistance corona discharge prevention tape.

3. 3. The corona discharge prevention layer according to claim 1, wherein the outer periphery of the high-resistance corona discharge prevention tape on the stator core side is wrapped with the low-resistance corona discharge prevention tape, and the outer periphery of the high-resistance corona discharge prevention tape on the opposite side to the stator core side is not wrapped with the low-resistance corona discharge prevention tape.

4. 3. The corona discharge prevention layer according to claim 1, wherein an end face of said high-resistance corona discharge prevention tape opposite said stator core side is not covered with said low-resistance corona discharge prevention tape.

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