GB2549931A

GB2549931A - High-voltage coil

Info

Publication number: GB2549931A
Application number: GB1607319.9A
Authority: GB
Inventors: Hill Graham
Original assignee: Houghton Int Electrical Services Ltd
Current assignee: Houghton Int Electrical Services Ltd
Priority date: 2016-04-27
Filing date: 2016-04-27
Publication date: 2017-11-08
Anticipated expiration: 2036-04-27
Also published as: GB2549931B

Abstract

Apparatus for use in underwater applications comprises a high-voltage coil 601 able to withstand voltages of between 3.6 and 15 kv and between 5 and 7 bars of pressure when submerged in water. The coil comprises a conductive material 602 such as copper with an insulating layer 603 covering at least part of the conductive material, the insulating layer and the high-voltage coil being encapsulated and impregnated by a layer of resin 606,moisture being removed under a vacuum and encapsulating under pressure. Further vacuum removal of moisture from the encapsulated coil to produce a void-free encapsulated surface of resin. The layer of resin thus forms a substantially void-free surface 606 which prevents water from corroding the high-voltage coil. A further pressure re-encapsulation followed by vacuum moisture removal step may be present. The insulation 603 may be two layers of tape pressed around the coil, the second partially overlaying the first. The coil may comprise subsections brazed together. The encapsulated coil is cured. A coil forming method is disclosed.

Description

High-voltage Coil CROSS REFERENCE TO RELATED APPLICATIONS This application represents the first application for a patent directed towards the invention and the subject matter. BACKGROUND OF THE INVENTION The present invention relates to an apparatus for use in underwater applications and a method of producing such an apparatus.

It is known to use high-voltage coils in electrical generators and motors in order to utilise the magnetic flux created in the coils to generate electricity. In some applications, such as in tidal renewable energy generators, the generators are placed underwater and submerged in sea water, typically at increased depths of around fifty metres.

Thus, when utilising generators in this manner, the high-voltage coils must have sufficient water resistance to enable them to function adequately for purpose. A further problem is that the coils will fail when exposed for extended periods and submerged in salty sea water. Previous proposals have included providing the coils with insulation, but in this case, when insulated in a conventional manner, the insulation around the coil cracks due to the high pressure underwater, and again the coils fail when electric current is passed therethrough, as a result of corrosion to the coils and/or breakages in the outer insulation.

BRIEF SUMMARY OF THE INVENTION

According to an aspect of the present invention, there is provided apparatus for use in underwater applications, comprising: a high-voltage coil comprising a conductive material; an insulating layer covering at least part of said conductive material; and a layer of resin which encapsulates said insulating layer and said high-voltage coil and which forms a substantially void-free surface.

According to a second aspect of the present invention, there is provided a method of producing an apparatus for use in underwater applications, comprising the steps of: winding a conductive material to form a high-voltage coil; covering at least part of said conductive material with an insulating layer; removing moisture from said insulated coil under a vacuum; encapsulating said insulated coil in resin under pressure; and further removing moisture from the encapsulated insulated coil under a vacuum to create a substantially void-free surface of resin on said insulated coil.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

Figure 1 shows part of an electromagnetic generator or motor utilising an the present invention;

Figure 2 shows a high-voltage coil in isolation;

Figure 3 shows an insulating layer being applied to the high-voltage coil of Figure 2;

Figure 4 shows a conductive material and the insulating layer being pressed together by means of a press;

Figure 5 shows a modified vacuum pressure impregnation process;

Figure 6 shows a cross sectional microscopic view of a portion of an encapsulated insulated high-voltage coil;

Figure 7 shows an insulated and resin-encapsulated high-voltage coil;

Figure 8 shows a stator housing mock-up for use with a high-voltage coil in accordance with the present invention;

Figure 9 shows two operatives lifting and positioning a high-voltage coil into the stator housing of Figure 8; and

Figure 10 shows the high-voltage coil 701 positioned in the stator housing mock-up.

DETAILED DESCRIPTION OF THE INVENTION

Figure 1

An example application utilising an apparatus for use in underwater applications is shown in Figure 1. Figure 1 illustrates part of an electromagnetic generator or motor. The electromagnetic generator comprises a stator 101 and a plurality of high-voltage coils, such as coil 102. Each coil 102 is positioned in stator housing 103 and arranged around the stator 101 to be utilised in generating electricity by means of the magnetic flux created from each of the coils. The stator also typically includes a rotor positioned through the centre to enable electricity to be generated.

In an example application, the stator 101 forms part of an electromagnetic generator used in a tidal renewable energy generator. In further applications, the stator forms part of any underwater submerged motors or generators. In this particular example, the stator is used at a depth of around fifty metres (50m) under sea water and is typically subjected to around five bar (5 bar). Standard currently available high-voltage coils cannot be used in this application as they are known to fracture under the high pressure and corrode due to the presence of salt water. Thus, the present invention provides a solution which is pressure resistant and corrosion resistant to enable it to be utilised in such conditions.

Simulated laboratory tests have indicated that the present invention is able to withstand pressures of at least seven bar (7 bar) for periods of seven continuous days in salt water making them suitable for this kind of application.

Figure 2 A high-voltage coil 201 is shown in isolation in Figure 2. High-voltage coil 201 comprises a conductive material 202, which, in the embodiment, comprises copper.

In the embodiment, coil 201 comprises a plurality of subsections 203 which are substantially similar to each other and each comprise copper. Coil 201 further comprises connecting wires or connectors, such as connecting wire 204 which extends from coil 201. in the example shown in Figure 1, these connecting wires are connected to an electrical circuit to enable a current to be passed therethrough to produce the magnetic flux through the coils and therefore stator or motor.

Each subsection 203 is manufactured in a substantially conventional manner whereby conductive material comprising copper is provided and wound into a hollow elliptic cylinder in the shape shown Figure 2. The conductive material is wound by a number of turns to provide a dimension which is suitable to enable the coil to fit into the stator housing, as will be described further in Figures 8 to 10.

It is appreciated that, in alternative embodiments, other shape formations are utilised instead of the hollow elliptic cylinder. For example, in one embodiment, a hollow diamond shaped arrangement is used. In further embodiments, other suitable shape formations are utilised.

In the embodiment, coil 201 comprises four subsections, 203A, 203B, 203C and 203D. Once each subsection has been wound, they are aligned and suitably attached to form a single coil. In order to maintain the four subsections as a single coil, each of the subsections are brazed at one end, as indicated at 205, to hold the subsections together and provide continuous conduction throughout the coils. To maintain a consistent resistance throughout, it is often preferable to have a plurality of subsections as this avoids variations in the circumference of the coil as it is wound. In this example, additionally, each individual subsection has a mass of around ten kilograms (10 kg) each, meaning that for handling purposes, it is more suitable to use a plurality of subsections having a mass of ten kilograms (10 kg) each than a forty kilogram (40 kg) coil.

The conductive material making up each of the subsections is available in various forms. In some embodiments, the conductive material comprises bare copper, however, in alternative embodiments, the conductive material comprises copper including a coating. In one embodiment, the conductive material is Grade II enamel copper which comprises copper having an enamel coating. For the connecting wires, the enamel coating is removed to enable a clean connection.

Figure 3

Once coil 201 has been formed into the embodiment of Figure 2, an insulating layer is applied to the coil in the manner shown in Figure 3.

An operative applies an insulating layer 301 to coil 201. Insulating layer 301 comprises an electrical insulator which is suitable for underwater applications. In the embodiment, insulating layer 302 is an epoxy resin based tape. In a specific embodiment, the insulating layer 301 comprises a partially cured epoxy tape such as stage B epoxy tape.

In the embodiment, the insulating layer 301 is applied as a first layer onto the conductive material 201. A second layer is then applied in the same manner such that the second layer partially overlays the first layer. A third layer is then applied which partially overlays the second layer such that each subsequent layer overlays the previously applied layer. This provides an improved join and reduces any gaps in the insulating layer as the most recently applied layer always covers the previously applied one. In an embodiment, the overlap of the layers is around fifty percent (50%).

In an embodiment, the number of layers of insulation is three or four layers which are suitable for withstanding an application where the voltage applied to the coils is substantially three point six kilovolts (3.6 kV). In an alternative embodiment, the voltage applied to the coils in use is substantially six point four kilovolts (6.4 kV) and the number of layers is typically four or five layers. In a further embodiment, the voltage applied to the coils in use is substantially thirteen point eight kilovolts (13.8 kV) and the number of layers is typically eight or nine layers. In further embodiments, the number of layers of insulation is configured to withstand a voltage range of up to fifteen kilovolts (15 kV).

Following the application of the insulating layer 301, in an embodiment, a further layer of semi-conductive coating is applied, such as that known as Electrodag.

Figure 4

On completion of the layering process described in Figure 3, the conductive material and insulating layer are pressed together by means of a hot press 401.

High-voltage coil 402 comprises a conductive material and an insulating layer substantially similar to that described in previous Figures 2 and 3. In Figure 4, a process known as consolidation is completed whereby the conductive material now covered by the insulating layer is placed inside press 401 with heat and pressure being applied to the coil 402 to form an insulated coil ready for further processing in the manner described in Figure 5.

Figure 5

Once the insulated coil of Figure 4 has been sufficiently consolidated and prepared in the manner of Figures 2 to 4, the coil is processed further as described in the process of Figure 5.

At step 501, the insulated coil is prepared and consolidated such that part of the conductive material at least is covered with an insulating layer. This step is substantially similar to that as previously described.

Once prepared, at step 502 the coil is introduced into a tank suitable for Vacuum Pressure Impregnation (VPI) processing. While this process is used in cases of highly porous materials, the present invention utilises a modified process which enables a substantially void-free surface to be created on the high-voltage coil which enables the coils to be waterproof, even in high pressure underwater applications.

The coil is introduced into the tank at atmospheric pressure (approximately one bar (1 bar)) and, at step 503, the pressure is reduced to substantially between two hundred and three hundred millibars (200 to 300 mbar). Under this reduced pressure, or high vacuum, at step 504, any residual moisture and air is removed from the insulated coil.

At step 505, the insulated coil is immersed in resin while still operating under the high vacuum of step 504. The resin is introduced at a higher rate than conventional processes which prevents bubbles or blisters in the final encapsulated coil.

The pressure is then raised at step 506 to a lower vacuum which allows the insulated coil to be encapsulated in the resin. This pressure at this step is typically around five hundred millibars (500 mbar). The insulated coil is maintained in this way for a period of time, typically around an hour to allow the resin to enter into any cavities or cracks in the coil and to further remove moisture from the encapsulated insulated coil.

The change in pressure between steps 504 and 506 forces the resin into any cavities and/or cracks in the material, and, by maintaining the insulated coil in situ for an increased period of time further allows the final coil to be substantially waterproof. The process also leads to the encapsulated coil having a substantially void-free surface of resin on the insulated coil and substantially seals the resin surface to protect the inner coil.

At step 507, the resin-encapsulated insulated coil is cured in an oven to harden the resin. Once hardened, the thickness of the coil is checked to ensure it is suitable for the stator before substantially repeating the process described in steps 502 to 507.

Figure 6

In Figure 6, a cross sectional diagrammatic microscopic view of a portion of an encapsulated insulated coil 601 is shown having been subjected to the process described in Figure 5.

High-voltage coil 601 comprises a conductive material 602 with an insulating layer 603. Insulating layer 603 includes a plurality of cracks, such as crack 604. When used in standard applications, such as in air, the resistance of the insulating layer is typically sufficient for use. However, once this is submerged in water, the resistance reduces due to the presence of the cracks to as much as one thousand times less the resistance due to water being present in the cracks.

If the high-voltage coil is subjected to the process previously described in Figure 5, and in accordance with the present invention, the resin layers 605 create a substantially smooth lacquer-type void-free surface 606 which prevents water from entering the cracks or voids. In addition, the varied vacuum of the process described in Figure 5 also allows resin to enter the cracks 604 in manufacture such that the cracks are filled with resin rather than water. Thus, even if damage occurs to the resin layer 606, water is still unable to enter the cracks due to the resin therein. In this way, the resistance remains consistent even when used in underwater applications.

Test results in relation to the present application have shown that, for a five thousand volts (5000 v) Megger Insulation Resistance (IR) test, the resistance achievable is in the region of two hundred gigaohms (200 ΘΩ) under seven bars (7 bar) of pressure in salt water without a resistance drop.

In an embodiment, if the values reached on the Megger IR test are less than two hundred gigaohms (200 GQ), an application of a spray varnish is added to the outer surface of the high-voltage coil. The spray varnish is low viscosity and air drying and provides extra protection to the outer resin surface and cracks 604 from water.

Figure 7

An insulated and resin-encapsulated high-voltage coil is shown in Figure 7. High-voltage coil 701 comprises a conductive material, such as copper, and has an insulating layer 702 which covers at least part of high-voltage coil 701. The insulating layer is further encapsulated by a layer of resin to form a substantially void-free surface 703 across the coil.

Coil 701 includes connecting wires 704 which are substantially similar to those shown in Figure 2. Additionally, underneath the void-free surface 703 and insulating layer 702, it is appreciated that coil 701 is substantially similar to coil 201 of Figure 2.

Figure 8 A stator housing 801 which is suitable for use with the high-voltage coil described herein is shown in isolation in Figure 8.

Stator housing 801 is substantially cuboid in shape having sides 802, 803, 804, 805, 806 and 807. Extending along the length of housing 801 between sides 804 and 805 are two slots 808 and 809 which are configured to receive a high-voltage coil as will be described further in Figures 9 and 10.

Top side 806 and front and rear sides 805 and 804 respectively, therefore provide an open aperture to allow positioning of the high-voltage coil therein.

It is appreciated that, in the application described in Figure 8, the stator housing comprises several stator housings similar to stator housing 801, but which form a single housing arranged in a cylindrical stator arrangement. Typically, however, the high-voltage coils are positioned within two slots in a housing for use.

Figure 9

In order to prevent additional cracks or voids arising in the high-voltage coil 701, when positioning into the housing 801, coil 701 is carefully lifted by two operatives in the manner shown in Figure 9.

As previously described in Figure 2, each of the subsections of which the high-voltage coil 701 comprises has a mass of around ten kilograms (10 kg), meaning the high-voltage coil as a whole has a mass of around forty kilograms (40kg). Thus, the cantilever forces induced in the high-voltage coil when lifted can lead to cracks in the void-free surface. For this reason, the coil is typically lifted by two operatives into housing 801. Thus, high-voltage coil 701 is positioned in housing 801 as will be shown further in Figure 10.

Figure 10

High-voltage coil 701 is shown positioned in stator housing 801 in Figure 10. A first portion 1001 of high-voltage coil 701 has been received in slot 808 of housing 801 and a second portion 1002 has been received in slot 809 of housing 801. In this way, high-voltage coil 801 fits securely in position ready for use.

Connecting wires 704 extrude from housing 801 to enable connection to an electrical circuit so as to provide a current to high-voltage coil 801 to enable a magnetic flux to power a generator. In the embodiment, connecting wires 704 are also able to withstand high pressure underwater environments and are also encapsulated in resin and suitable insulating layers in a substantially similar manner to the rest of high-voltage coil 701.

Claims

CLAIMS The invention claimed is:

1. Apparatus for use in underwater applications, comprising: a high-voltage coil comprising a conductive material; an insulating layer covering at least part of said conductive material; and a layer of resin which encapsulates said insulating layer and said high-voltage coil and which forms a substantially void-free surface.

2. The apparatus of claim 1, wherein said apparatus further comprises a stator housing in which said high-voltage coil is positioned.

3. The apparatus of claim 2, wherein said stator housing comprises two slots in which a first slot receives a first portion of said high-voltage coil and a second slot receives a second portion of said high-voltage coil.

4. The apparatus of any one of claims 1 to 3, wherein said high-voltage coil comprises a plurality of subsections.

5. The apparatus of claim 4, wherein each said subsection comprises copper.

6. The apparatus of any preceding claim, wherein said insulating layer comprises epoxy resin.

7. The apparatus of claim 6, wherein said epoxy resin is in the form of partially cured tape.

8. The apparatus of any preceding claim, wherein said high voltage coil further comprises connecting wires extending from said coil.

9. The apparatus of any preceding claim, wherein said high-voltage coil is configured to withstand between 5 and 7 bars of pressure when submerged in water.

10. An electromagnetic generator comprising the apparatus of claim 1.

11. A method of producing an apparatus for use in underwater applications, comprising the steps of: winding a conductive material to form a high-voltage coil; covering at least part of said conductive material with an insulating layer; removing moisture from said insulated coil under a vacuum; encapsulating said insulated coil in resin under pressure; and further removing moisture from the encapsulated insulated coil under a vacuum to create a substantially void-free surface of resin on said insulated coil.

12. The method of claim 11, further comprising the step of: pressing said conductive material and insulating layer together to form an insulated coil.

13. The method of claim 11 or claim 12, further comprising the step of: curing said encapsulated insulated coil.

14. The method of any of claims 11 to 13, wherein said method further comprising repeating the steps of: removing moisture from said insulated coil under a vacuum; encapsulating said insulated coil in resin under pressure; and further removing moisture from the encapsulated insulated coil under a vacuum.

15. The method of any of claims 11 to 14, wherein said high-voltage coil comprises a plurality of subsections.

16. The method of claim 15, said method comprising the steps of: aligning each said subsection; and brazing each said subsection at a first end to form said high-voltage coil.

17. The method of any of claims 11 to 16, wherein said step of covering at least part of said conductive material comprises the steps of: applying a first layer of tape onto said conductive material; and applying a second layer of tape to partially overlay said first layer of tape.

18. The method of any of claims 11 to 17, further comprising the step of: positioning said high-voltage coil in a stator housing.

19. Apparatus for use in underwater applications as described herein with reference to the accompanying Figures.

20. A method of producing an apparatus for use in underwater applications as described herein with reference to the accompanying Figures.