WO2016030698A1

WO2016030698A1 - An oil insulated connector

Info

Publication number: WO2016030698A1
Application number: PCT/GB2015/052509
Authority: WO
Inventors: Martin Snell
Original assignee: Martin Snell
Priority date: 2014-08-29
Filing date: 2015-08-28
Publication date: 2016-03-03
Also published as: GB201415305D0; GB201515327D0; GB2531890B; GB2531890A

Abstract

An oil insulated connector for connecting module housings together, the connector comprising first and second spaced apart electrically insulating end faces at least partially defining a cavity therebetween; each end face having an aperture extending therethrough for receiving an electrical conductor; the cavity being filled with an electrically insulating oil

Description

An oil insulated connector

The present invention relates to an oil insulated connector. More particularly, but not exclusively, the present invention relates to an oil insulated connector comprising first and second spaced apart electrically insulating end faces at least partially defining a cavity therebetween, each end face having an aperture extending therethrough, the cavity being filled with an electrically insulating oil.

High voltage systems are typically encased in an electrically insulating housing for safety reasons. It is not practical to produce one large moulded housing and then insert all the components (conductors, switches, drives etc) in through the open end. The housing is therefore produced as a series of modules which are connected together. The connections between the modules must be at least as resistant to electrical breakdown as the modules themselves.

The equipment housings themselves may be incorporated into earthed steel cubicles or tanks in such a way that the sealed insulated housings provide the main insulation to earth and between phases but the equipment may still be designed as the metal enclosed type.

Typically the modules are connected together by flanges. The space between the flanges is filled with a grease or adhesive It can be very difficult to totally fill the space with such a material. Typically air bubbles are trapped in the space, these voids provide a much weaker breakdown path. Also the high electric field within the void may lead to discharge which can cause electrical breakdown.

The oil insulated connector according to the invention seeks to overcome the problems of the prior art.

Accordingly, in a first aspect, the present invention provides an oil insulated connector for connecting module housings together, the connector comprising first and second spaced apart electrically insulating end faces at least partially defining a cavity therebetween; each end face having an aperture extending therethrough for receiving an electrical conductor; the cavity being filled with an electrically insulating oil

The oil filled connector according to the invention is simple to assemble. Any bubbles which form within the oil tend to move to a point remote from the apertures so reducing the risk of electrical breakdown.

The arrangement and profiles will be arranged such that any bubbles within the oil will be diverted by gravity into the regions of low electrical stress to avoid the onset of any discharges.

Preferably, the first and second end faces are connected together to define the cavity.

Preferably the first and second end faces are connected together to define a toroidal oil filled cavity, the apertures extending through the centre of the toroid.

The oil insulated connector can further comprise a side wall extending between the first and second end faces to define the cavity.

The side wail can integrally extend from one of the end faces.

Preferably an electrical conductor extends through the first and second apertures.

Alternatively a first electrical conductor extends at least partially into the aperture in the first end face and a second electrical conductor extends at least partially into the aperture in the second end face, the two electrical conductors being connected together within the oil filled cavity.

Preferably at least one of the electrical conductors forms an oil tight seal with one of the apertures.

Preferably the oil insulated connector further comprises an intermediate connector arranged within the oil filled cavity and in sealing engagement with at least one of the apertures, the first and second electrical conductors being connected to the intermediate connector.

Preferably the cavity defining side of at least one of the end faces comprises a plurality of ridges and grooves.

Preferably the oil insulated connector further comprises a pressure equalisation mechanism connected between the oil filled cavity and a gas filled volume, the pressure equalisation mechanism being adapted to maintain the oil pressure in the oil filled cavity substantially equal to the gas pressure in the gas filled volume.

The present invention will now be described by way of example only and not in any limitative sense with reference to the accompanying drawings in which

Figure 1 shows, in cross section, a first embodiment of an oil insulated connector according to the invention;

Figure 2 shows, in cross section, a further embodiment of an oil insulated connector according to the invention; Figure 3 shows, in cross section a further embodiment of an oil insulated connector according to the invention;

Figure 4 shows, in cross section a further embodiment of an oil insulated connector according to the invention;

Figure 5 shows, in cross section, a further embodiment of an oil insulated connector according to the invention;

Figure 6 shows, in cross section, a further embodiment of an oil insulated connector according to the invention; and,

Figure 7 shows, in cross section, a pressure equalisation mechanism for use with an oil insulated connector according to the invention.

Shown in figure 1 is a first embodiment of an oil insulated connector 1 according to the invention. The oil insulated connector 1 comprises first and second electrically insulating end faces 2,3. The end faces 2,3 extend integrally from adjacent modules 4,5 as shown. The defining wails of the modules 4,5 are also electrically insulating. The end faces 2,3 are axially symmetric about the axis A. The insulating material is typically a polymeric, e!astomeric or composite material. Typical examples include epoxy resin, glass filled thermoset composite, epoxy glass or EPDM rubber.

The first and second end faces 2,3 are spaced apart to define a toroidal cavity 6 therebetween as shown. The cavity 6 is filled with an electrically insulating oil. The end faces 2,3 are held together by screws 7. The cavity 6 is sealed by means of seals 8.

Extending through each of the end faces 2,3 is an aperture 9. An electrical conductor 10 extends from one module 4, through the two apertures 9 and into the other module 5. Shown in figure 2 is a further embodiment of an oil insulted connector 1 according to the invention. The oil insulated connector 1 comprises first and second spaced apart electrically insulating end faces 2,3. The two end faces 2,3 are each end faces of adjacent modules 4,5. The two end faces 2,3 are connected together as shown to define a cavity 6. The cavity 6 is filled with an electrically insulating oil.

Arranged in a first end face 2 is a first aperture 11. Extending from one module 4 through the first aperture 11 and into the oil filled cavity 6 is a first electrical conductor 12. The electrical conductor 12 is moulded into the engagement with the first aperture 11 , preventing the oil from leaking from the oil filled cavity 6, through the first aperture 11 and into the first module 4.

Arranged in the second end face 3 is a second aperture 13. Arranged in the oil filled cavity 6 is an intermediate connector 14 having recesses in both ends as shown. One end of the intermediate connector 14 is in sealing engagement with the second aperture 13, again preventing the oil from escaping from the oii filled cavity 6 via the second aperture 13. The first electrical conductor 12 is push fit into connection with the recess in the first end of the intermediate connector 14. A second electrical conductor 15 in the second module 5 is push fit into connection with the second recess in the second end of the intermediate connector 14.

It is important to note that the only seal required is the seal 16 between the first and second end faces 2,3. Sufficient force can be applied to this seal 16 by means of a screw 17 adjacent to the seal 16. No further seals proximate to the electrical conductors 12.15 are required.

Shown in figure 3 is a further embodiment of an oil insulated connector 1 according to the invention in cross section. The connector 1 comprises first and second end faces 2,3 each having an aperture 11 ,13 therein. The two end faces 2,3 are each end faces of adjacent modules 4,5. A side face 18 integrally extends from the second end face 3 to the first end face 2. The side face 18 is a portion of the defining wall of the module 5. The first end face 2 is urged into engagement with the side face 18 by means of a screw 17. The screw 17 compresses a seal 16 preventing oil from leaking from the oil filled cavity 6 through the join between the two faces 2,3.

One end face 2 is convex. The other end face 3 is concave. This results in a bowl shaped oil filled cavity 6. This shape maximises the distance between the apertures 11 ,13 and the side wall 18, so reducing the risk of electrical discharge along the inner surface of an end face 2,3 and through the join between side face 18 and second end face 3.

A first electrical conductor 12 extends from the first module 4 and into the first aperture 11. The end of the first conductor 12 comprises a recess 19. Both the inner and outer faces of the recess 19 are threaded. The outer thread of the recess 19 is threaded into engagement with the first aperture 11 producing an oil tight seal between the two.

A second electrical conductor 15 extends from the second module 5 through the second aperture 13 and into threaded engagement with the inner threaded face of the recess 19 of the first electrical conductor 12.

Shown in figure 4 is a variant of the oil insulated connector 1 of figure 3. In this embodiment both of the end faces 2,3 are separate plates which are urged into engagement with the side face by screws. The side face 18 of the connector 1 is formed by portions of the adjacent modules 4,5. Such an embodiment is useful when the adjacent modules 4,5 do not have pre-formed end walls which can act as end wall of the connector 1.

This embodiment further comprises a pressure equalisation mechanism 20 connected between the oil filled cavity 6 and a gas filled volume (in this case the adjacent module 5). The pressure equalisation mechanism 20 keeps the oil pressure in the oil fi!!ed cavity 6 equal to the gas pressure in the gas filled volume. In use the oil in the oil filled cavity 6 becomes warm. Because it cannot expand the oil pressure rises and the oil may force its way out into the adjacent modules 4,5 through the apertures 11 ,13 in the end faces 2,3. Similarly, as the oil cools its pressure drops and air may be pulled into the oil filled cavity 6. As previously mentioned, bubbles within the oil can cause electrical breakdown. The pressure equalisation mechanism 20 prevents this from happening.

Shown in figure 5 is a further embodiment of an oil insulated connector 1 according to the invention. In this embodiment the first end face 2 is the end face of an adjacent module 4. The second end face 3 is a separate plate which is connected to the wall 18 of a second adjacent module 5. A portion of the wall of the second adjacent module 5 forms the side face 18 extending between the first and second end faces 2,3. The side face 18 is connected to the first end face 2 by means of a metal flange 21.

Extending through the metal flange 21 is an oil fill aperture 22. The cavity 6 is filled with oil through this aperture 22. In use the connector 1 is typically oriented such that any bubbles in the oil float up to and then out of the aperture 22 so that the cavity 6 is completely filled with oil.

Arranged within the cavity 6 is an intermediate connector 14 which has been described previously. This intermediate connector 14 however has a thin disk 23 which extends substantially normal to the axis of symmetry. In use the electrical conductors 12.15 become hot. This heat is transferred to the disk 23 and then in to the oil. Convection within the oil transfers this heat to the side face 18 and then into the surrounding atmosphere. Additional cooling can be provided by using a system of embedded heat pipes to transfer excess heat away from the flanges.

Shown in figure 6 is a further embodiment of an oil insulated connector 1 according to the invention. In this embodiment the first end face 2 is shaped as a finger having a first aperture 11 which extends along its length. A first electrical conductor 12 extends along the length of the finger 2 through the aperture 11 and extends from the end of the finger 2. The outer surface of the finger 2 comprises a plurality of ridges and troughs.

The second end face 3 has an aperture 13 extending therethrough. An intermediate connector 14 is moulded into the second aperture 13 as shown. A side face 18 extends integrally from the second end face 3 and defines a recess into which the finger 2 is received as shown. The end of the first conductor 12 which extends beyond the finger 2 is push fit into electrical contact with the intermediate connector 4. The finger 2 is connected to the side face 18 by means of a metal flange 21. The small gap between the finger 2 and the side wall 18 is the oil filled cavity 6. The ridges and grooves on the outside of the finger 2 maximise the discharge path between the first eiectricai conductor 12 and the metal flange 21 though the oil, so minimising the risk of electrical discharge.

Shown in figure 7 is a pressure equalisation mechanism 20 for keeping the pressure in the oil filled cavity 6 equal to the pressure in a gas filled cavity. The pressure equalisation mechanism 20 comprises a set of bellows 30. The bellows 30 are divided into two portions 31 ,32 by means of a dividing plate 33. One of the two portions 31 ,32 is in fluid communication with the oil filled cavity 6 by means of a pipe 34 and is filled with oil. The other portion 32 is in fluid communication with the gas filled cavity by means of a further pipe 35 and is filled with the gas.

If the pressure in the oil filled cavity 6 rises this is transmitted to the bellows 30. The dividing plate 33 moves effectively increasing the volume of the oil filled cavity 6 until the pressure in the oil filled cavity 6 is again equal to that in the gas filled cavity. Typically sensors 36 are employed to monitor the position of the dividing plate 33. If the dividing plate 33 moves too far from its equilibrium position this may indicate a leak in the oil filled cavity 6.

A multi stage alarm may be provided which will give a warning on loss of a small volume of oil but can initiate an eiectricai isolation of the equipment on a large or sudden change of movement.

A spring 37 may be provided to provide a residual positive pressure in the oil filled cavity 6 thus avoiding the danger of air being drawn into the cavity 6. A measurement indicating an apparent significant increase in the volume of oil would indicate a potential leak of air into the cavity 6. The insulated housings themselves may be ventilated to atmosphere via a breather valve containing a desiccant material.

Alternatively the housings may be designed so that they can be air or gas tight. If required they may be filled with air or gas at an elevated pressure to increase the dielectric withstand capacity within the housings.

It would normally be expected that the pressure of all the gas zones within a single switchboard circuit or stand alone circuit breaker would be interconnected so one pressure balancing and leak detection module would be required.

The pipework connecting the oil filled cavities 6 may be arranged such that the oil can be circulated by a pump during fifling or re-filling to purge any contamination or degradation products in the oil.

General design considerations apply to all of the embodiments described above. The cavity 6 is preferably of cylindrical form with the high voltage components located on the longitudinal axis.

Where openings or joints are required between insulating parts (typically first and second end faces 2,3 and side face 18) these are typically sealed by a homogeneous void free layer of adhesive of sufficient width to withstand the electrical potential it is exposed to.

The minimum distance through the oil between parts at different potentials must be adequate to avoid creating field potentials causing electrical breakdown of the insulating oil.

The minimum distance across insulating surfaces in contact with the oil between parts at different potentials must be sufficient to avoid creating field potentials capable of causing electrical breakdown of the insulating oil In embodiments which employ an electrically conducting connecting flange 21 the flange 21 may be at a floating potential. In this case the oil insulation is only required to withstand the very high electrical stresses adjacent to the live parts. In such cases the clearances in the oii may be reduced with a commensurate increase in external clearances to avoid external ionisation and discharge.

Alternatively, the connecting flange 21 may be maintained at earth potential. In this case the rest of the enclosure will still need to be constructed of insulating material and appropriate distances to adjacent equipment maintained to avoid ionisation and discharge.

Where required the external surfaces of any electrically insulating parts may be coated with an electrically conductive layer. Normally this conductive layer will be maintained at or close to earth potential such that the high voltage appears largely across the thickness of the insulating parts. In this cased clearance to adjacent parts to avoid externa! discharge should not be required.

Where metal flanges 21 are incorporated at earth or near earth potential then these can be linked capacitively with high voltage components thus providing a point of connection for suitable high frequency monitoring equipment which may be used to measure the onset of any discharges within the equipment.

Where appropriate the flanges 21 may also be used to sense the presence of high voltage on the conductors, thereby indicating the system is energised.

The oil filled cavity 6 may contain one or more insulating spacers reducing the amount of oil required.

The oil filled cavity 6 may include a circumferential current measuring device such as a current transformer, hall effect device or Rogowski coils. At least a portion of the inside or outside of the cavity 6 may be coated with a conductive layer for electrical stress control purposes.

At least a portion of the inside or outside of the oil filled cavity 6 may be coated with a semi- conductive layer for electrical stress control.

At least a portion of the outside of the cavity 6 may be connected close to or at earth potential.

Claims

An oil insulated connector as claimed in claim 1 , wherein the first and second end faces are connected together to define the cavity.

An oil insulated connector as claimed in claim 2, wherein the first and second end faces are connected together to define a toroidal oil filled cavity, the apertures extending through the centre of the toroid.

An oil insulated connector as claimed in claim 1 , further comprising a side wall extending between the first and second end faces to define the cavity.

An oil insulated connector as claimed in claim 4, wherein the side wall integrally extends from one of the end faces.

An oil insulated connector as claimed in any one of claims 1 to 5, wherein an electrical conductor extends through the first and second apertures.

An oil insulated connector as claimed in any one of claims 1 to 5, wherein a first electrical conductor extends at least partially into the aperture in the first end face and a second electrical conductor extends at least partially into the aperture in the second end face, the two electrical conductors being connected together within the oil filled cavity.

8. An oil insulated connector as claimed in either of claims 6 or 7, wherein at least one of the electrical conductors forms an oil tight seal with one of the apertures.

9. An oil insulated connector as claimed in claim 7, further comprising an intermediate connector arranged within the oil filled cavity and in sealing engagement with at least one of the apertures, the first and second electrical conductors being connected to the intermediate connector.

10. An oil insulated connector as claimed in any one of claims 1 to 9, wherein the cavity defining side of at least one of the end faces comprises a plurality of ridges and grooves.

11. An oil insulated connector as claimed in any one of claims 1 to 10, further comprising a pressure equalisation mechanism connected between the oil filled cavity and a gas filled volume, the pressure equalisation mechanism being adapted to maintain the oil pressure in the oil filled cavity substantially equal to the gas pressure in the gas filled volume.

12. An oil insulated connector substantially as hereinbefore described.