Outer corona protection and electrical machine

Abstract

The invention relates to outer corona protection, having an insulating material or an insulating system, the insulation system which is electrically conductive in layers and exhibits hydrophobic material wound in the form of a strip, in which a PTFE-containing material is arranged between the internal outer corona protection winding (110) and external outer corona protection material (200), wherein an electrically conductive insulating material, which exhibits hydrophobic material, which forms a strip, and in which carbon has been incorporated as electrically conductive material into the hydrophobic material.

Description

[0001] Description

[0002] External corona protection and an electrical machine

[0003] The invention relates to an external corona shield and an electrical machine.

[0004] Potential control enables the minimization of electrical voltages (potential differences) in rotating machines, such as generators or high-voltage motors, whereby the occurrence of partial and / or glow discharges can be reduced or completely avoided.

[0005] In rotating electrical machines, the reliability of the insulation system is crucial for their operational safety. The insulation system's job is to permanently insulate electrical conductors (wires, coils, bars) from each other and from the stator core or the environment. The external potential control system is responsible for establishing electrical contact between the stator core, which is at earth potential, and the outside of the main insulation. This ensures that no partial discharges occur in cavities near the boundary layer between the insulation and the core.

[0006] A distinction must be made here

[0007] • External corona shielding (AGS) for generator winding bars, which were manufactured according to individual bar production (AGS-E)

[0008] • External corona shielding (AGS) for generator winding bars manufactured using the GVPI process (AGS-G).

[0009] In the case of fully impregnated stator windings (Global Vacuum Pressure Impregnation GVPI), the entire laminated core is impregnated and cured together with a fully installed winding. This means that the winding is bonded so tightly in the slots of the laminated core that the different expansion coefficients of copper, iron and insulation lead to high thermo-mechanical stresses between copper, insulation and iron. This stress can lead to the interfaces tearing open after a certain number of thermal cycles (starts and stops of the generator). To prevent the gaps from being subject to an electrical potential difference and the partial discharges igniting there from destroying the insulation, outer corona protection (OCP) is used. This is shown in Figure 1 as a double-layer external corona protection, as used for potential control in machines processed using G-VPI.An insulating base winding 70 made of fine mica tape is applied over the current-carrying Roebel rod made of copper conductors 40, which smoothes and enlarges the edge radii of the thin copper conductors 40.

[0010] A first graphite-containing conductive fleece strip 100 is wound over this, which is connected to the high-voltage potential of the copper partial conductor 40 at only one point via a contact strip 130.

[0011] Only then is the main insulation 160 made of fine mica glass wound. Instead of the copper conductors, the first conductive fleece strip 100 now forms the high-voltage electrode. It is permanently bonded to the main insulation. The main insulation 160 is followed by the inner external corona protection wrap 110 made of a state-of-the-art material (conductive, flexible strip, in particular from the Krempel company), an outermost separating strip 190', and an outer external corona protection wrap 200. An external corona protection strip 140, which is woven into the outermost separating strip 190', connects the inner 110 and outer 200 external corona protection wraps.

[0012] The thermomechanical stresses that arise between the copper conductor assembly and the insulation during generator startup and shutdown can, after a certain period of operation, lead to local detachment of the insulation sleeve from the conductor, without the dreaded partial discharges igniting in the resulting gaps. The area of ​​delamination is potential-free because the high-voltage potential has been transferred to the conductive fleece that has baked onto the main insulation. This IPS design at the highly stressed inner interface between conductor and insulation allows decades of peak-load operation of turbogenerators without noticeable partial discharge aging.

[0013] It is therefore an object of the invention to solve the above-mentioned problems.

[0014] The object is achieved by an external corona shield according to claim 1 and an electrical machine according to claim 15.

[0015] The subclaims list further advantageous measures which can be combined as desired to achieve further advantages.

[0016] It shows :

[0017] Figure 1 shows an external potential control of a generator winding bar according to the prior art,

[0018] Figure 2 shows an external potential control according to the invention and

[0019] Figure 3 shows a generator.

[0020] The figures and the description represent only exemplary embodiments of the invention.

[0021] The invention consists in using hydrophobic material, PTFE (Teflon) as insulation, in particular for such a high-voltage insulation system, wherein the insulation system is designed to be electrically conductive in layers.

[0022] The high voltage insulation system can be a simple system or a more complex system as shown in Figure 1 .

[0023] The invention is explained only by way of example using PTFE as an example of a hydrophobic material. Preferably, the hydrophobic material or PTFE is already electrically conductive. The PTFE is then a composite material. This preferably occurs during the production of the material, in particular by mixing in electrically conductive material, such as graphite or carbon black, e.g., by extrusion during production.

[0024] A preferred band has a thickness of < 100pm, in particular from 40pm to 60pm.

[0025] The width of the band is adjusted accordingly and can preferably be up to 3 cm wide.

[0026] The proportion of carbon or graphite, in particular carbon black, in the hydrophobic material, in particular in Teflon, is 2 wt.% to 30 wt.%, in particular at least 8 wt.% graphite or carbon black.

[0027] The proportions of graphite or carbon black are adjusted so that a surface resistance after application is < 1000 kΩcm / cm, in particular at least 2 kΩcm / cm, most especially at most 50 kΩcm / cm.

[0028] The proportions of graphite or carbon black are also adjusted so that the specific volume resistivity is < 50MΩcm, in particular at least 0.1MΩcm.

[0029] However, it is also possible to subsequently apply an electrically conductive coating to a fabric, fiber, fabric, membrane or film.

[0030] The fabric is preferably formed from fibers which comprise the electrically conductive insulating material, in particular PTFE.

[0031] This fabric is preferably in strip form and is wound onto the surface to be insulated (see Figure 2). A perforated tape (in fabric form or similar), a perforated membrane, or a perforated scrim (scrim as known from textile technology) can also be used, i.e., through-holes are introduced into the tape, the fabric, the membrane (which is already porous), or the scrim.

[0032] Preferably, the high-voltage insulation system in the external corona shield comprises fibers or a fabric made of PTFE, wherein, in order to achieve electrical conductivity, an electrically conductive material, preferably graphite, is also present between the structures forming the fabric.

[0033] The AGS in the high voltage insulation system in Figure 2 preferably comprises a fabric made of PTFE , which is constructed so that the fabric has pores which can be infiltrated by the method described above .

[0034] The basic structure and functionality of the current AGS system according to Figure 1 should remain unchanged, with the exception of the omission of the external corona shielding tape 140 and the replacement of the split mica with the PTFE-containing material according to the invention. Furthermore, the external corona shielding wrap 200 in Figure 2 can preferably be omitted.

[0035] This results in the following advantages:

[0036] • Good impregnation properties as it is a porous fabric and can therefore be applied before curing.

[0037] • Unchanged resistance before and after impregnation, since the conductivity comes from fibers and not from particles as in the AGS tape. (These have a different resistance value compared to the initial value due to the plastic matrix surrounding the particles after impregnation.) The objectives for the AGS-G according to the invention are:

[0038] • simplified application / cost reduction

[0039] • Reduced layer thickness of the double AGS due to thinner alternative

[0040] The approach for the inventive AGS-G is:

[0041] • Reduction of the layer thickness by using a separating layer that achieves a defined mechanical decoupling without changing the electrical resistance. This is to be achieved by replacing the double layer of split mica with hydrophobic fabrics. This can be a Teflon fabric in particular. The structure is as follows:

[0042] An improvement is achieved according to the invention by using electrically conductive fabric 190 made of PTFE, since this facilitates the "weaving" of the external corona protection strip 140 (Fig.

[0043] 1 ) unnecessary . This would enable a reduction in layer thickness and manufacturing costs ( Fig . 2 ) .

[0044] The inventive design of an innovative external potential control for use in the GVPI process enables an insulation system that corresponds to the current state of the art in terms of properties, but has the following advantages:

[0045] • Determination of TE freedom after curing

[0046] • comparable loss factors after performing temperature cycle tests for accelerated thermomechanical loading

[0047] • comparable electrical endurance under operating voltage load and at increased voltage load

[0048] • comparable electrical endurance under operating voltage load and under increased voltage load after exposure to different temperature cycles. These tests were carried out on generator winding bars with the following design:

[0049] • Aluminium profiles with a length of approximately 1.5 m and dimensions of 1 cm x 5 cm

[0050] • Number of mica layers 8 + 1 layer IPS for a nominal voltage of 13.8 kV

[0051] • Number of generator winding bars per collective : 6 .

[0052] This made it possible to reduce the layer thickness of the current AGS from approximately 450pm to approximately 100pm.

[0053] Figure 3 shows an example of a generator as an electrical machine.

[0054] According to Figure 3, a rotary machine arrangement, in particular a generator arrangement 2, extends along a longitudinal axis 3 from an end region 6 on the turbine side to an end region 8 on the exciter side. The generator arrangement 2 has a housing 10. A cooling device 12 is arranged in the turbine-side end region 6. In particular, two coolers 16 and a compressor in the form of a fan 18 with a fan hub 20 are arranged in a cooler head 14, which is part of the housing 11. The fan hub 20 sits on a rotor 22, which extends along the longitudinal axis 3 through the generator arrangement 2. The actual generator region 23 is arranged following the cooling device 12 in the direction of the longitudinal axis 3. In this region, the rotor 22 is surrounded by a stator 24, forming an air gap 26. The stator 24 has a stator winding with a turbine-side stator winding head 28A and with an excitation-side stator winding head 28B.A so-called laminated core 30 is arranged between the two stator winding overhangs 28A, 28B. Analogous to the stator 24, the rotor 22 has a turbine-side rotor winding overhang 32A and a field-side rotor winding overhang 32B. Due to the high power density typical of turbogenerators, cooling of the generator arrangement 2 in the generator area 23 is necessary. The stator winding overhangs 28A, 28B and the rotor winding overhangs 32A, 32B have a particularly high cooling requirement. To cool the generator area 23, this area has a cooling system 34 which is supplied with cooling gas from the cooling device 12. The cooling system 34 has a number of cooling gas channels 36A, 48, via which the cooling gas is circulated. A first cooling gas channel 36A extends in the axial direction and is arranged between the stator 24 and the housing 10. A second cooling gas channel 36B is formed by the air gap 26.Further cooling gas channels 36C extending in the axial direction lead through the laminated core 30. A cooling gas channel 36D leads through the rotor 22 to cool it. The cooling gas flow in the generator region 23 and in the cooling device 12 is indicated by arrows, with the dashed arrows indicating the flow path of the cold cooling gas and the solid arrows indicating the flow path of the heated cooling gas (hot gas).

[0055] To cool the stator winding overhangs 28A, 28B, the cooling gas flow coming from the coolers 16 is split in the turbine-side end region 6. One partial flow is used to cool the turbine-side stator winding overhang 28A and the other partial flow is passed on via the cooling gas duct 36A to the exciter-side stator winding overhang 28B and split again. One part is used to cool the stator winding overhang 28B and from there flows back as hot gas via the air gap 26. The other part is passed through the cooling gas ducts 36C of the laminated core 30 and exits in the turbine-side end region 6 as hot gas and is fed to the coolers 16. To cool the rotor winding overhangs 32A, 32B, cooling gas is introduced into the cooling gas duct 36D of the rotor 22 from both the turbine-side end region 6 and the exciter-side end region 8.A partial flow of the cooling gas flows through the respective rotor winding heads 32A, 32B and is then directed into the air gap 26 as hot gas and supplied to the coolers 16. The remaining

[0056] Partial flow is guided further through the rotor 22 in the cooling gas channel 36D, in such a way that the cooling gas flows from the two rotor winding heads 32A, 32B towards each other and approximately in the middle area 38 of the generator area 23 into the

[0057] air gap 26 is passed.

Claims

Patent claims 1. External corona shielding, comprising an insulation material or an insulation system, the layered electrically conductive insulation system, in particular high-voltage system, which comprises PTFE, which is wound in tape form, in which a PTFE-containing material is arranged between the inner external corona shielding winding (110) and the outer external corona shielding material (200), wherein an electrically conductive insulation material comprises PTFE, in particular consists thereof, which forms a tape, and in which carbon is mixed into the PTFE as an electrically conductive material.

2. External corona shielding according to claim 1, comprising fibers.

3. External corona shielding according to claim 2, wherein the fibers comprise, and in particular consist of, electrically conductive PTFE fibers.

4. External corona shielding according to one or more of claims 1, 2 or 3, which comprises a fabric (5) made of electrically conductive PTFE.

5. External corona shielding according to one or more of claims 1 to 4, which is a membrane.

6. External corona shielding according to one or more of claims 1, 2 or 3, which is a scrim.

7. External corona shielding according to one or more of the preceding claims, which comprises a perforated band made of electrically conductive PTFE by admixture of carbon.

8. External corona shielding according to one or more of claims 1 to 8, in which carbon is distributed as an electrically conductive material between the fibers, the fabric, the membrane or the fabric structure.

9. External corona shielding according to one or more of the preceding claims, in which the PTFE, the fiber, the fabric, the membrane, the scrim or the tape are coated with an electrically conductive layer.

10. External corona shielding according to one or more of the preceding claims 6 to 9, which has pores which are in particular infiltrable.

11. External corona shielding according to one or more of claims 1 to 10, wherein the electrically conductive material is carbon in the form of graphite or soot.

12. External corona shielding according to claim 11, in which the proportion of graphite or carbon black is 2% by weight to 30% by weight, in particular at least 8% by weight of graphite or carbon black.

13. External corona shielding according to one or more of claims 1 to 12, wherein the strip has a thickness of < 100pm, in particular from 40pm to 60pm and / or the width of the strip is up to 3cm.

14. External corona shielding according to one or more of claims 1 to 13, in which the proportions of carbon, in particular graphite or soot, are adjusted so that a surface resistance is < 1000 kΩcm / cm, in particular at least 2 kΩcm / cm, very particularly at most 50 kΩcm / cm, and / or the specific volume resistance is < 50 kΩcm, in particular at least 0 kΩcm.

15. Electrical machine with an external corona shield according to one or more of the preceding claims 1 to 14, in particular a generator.

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