WO2016030695A1

WO2016030695A1 - An oil insulated rotational drive

Info

Publication number: WO2016030695A1
Application number: PCT/GB2015/052503
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: GB201515314D0; GB201415306D0; GB2531889A; GB2531889B; EP3195340A1

Abstract

An oil insulated rotational drive comprising an oil filled cavity defined by an electrically insulating cavity wall, the cavity wall comprising first and second spaced apart end faces and a side wall extending therebetween, each end face having an aperture extending therethrough; a first rotational drive arm extending through the aperture in the first end face; a second rotational drive arm extending through the aperture in the second end face; the two arms being co-axial and arranged to rotate about a rotational axis extending along the length of the rotational drive arms; the two rotational drive arms being connected to an electrically insulating drive body arranged within the cavity and adapted to rotate about the rotational axis.

Description

AN OIL INSULATED ROTATIONAL DRIVE

The present invention relates to an oil insulated rotational drive. More particularly, but not exclusively, the present invention relates to an oil filled rotational drive comprising an oil filled cavity having an insulating drive body therein and first and second rotational drive arms connected to the insulating drive body and extending through apertures in the end walls of the cavity.

The problems of opening and closing a switch in a high voltage line (typically above 36Kv) are well known. As the switch opens there can be significant arcing between the switch contacts. In order to alleviate this problem an interrupter is used. As the switch opens an electrical arc will be drawn between the contacts which will need to be extinguished in order for the current to be switched off. Depending on the level of current to be switched an interrupter device will be required to achieve this. In the range of a few thousand volts up to 36kV (or more than 100kV in certain cases) a vacuum interrupter is used.

A typical vacuum interrupter comprises two contact disks incorporating current carrying stems which are forced together by a spring mechanism. One of the stems is connected to an interrupter drive arm which typically is in contact with the high voltage circuit. As one moves the interrupter drive arm the interrupter contact disks are driven rapidly apart so minimising the amount of time arcing can occur. A drive mechanism is required to displace the interrupter drive arm. The drive mechanism must be at earth potential so that an operator can use it without being exposed to high voltages. Typically the high voltage end of the drive mechanism is insulated from the earth end of the drive mechanism by air insulation. The drive mechanism must therefore be large to avoid electrical breakdown. It must also be very rigid. Such mechanisms tend to be heavy and therefore require large operating forces to meet the opening and closing speed requirements.

The present invention seeks to overcome the problems of the prior art.

Accordingly, the present invention provides an oil insulated rotational drive comprising an oil filled cavity defined by an electrically insulating cavity wall, the cavity wail comprising first and second spaced apart end faces and a side wall extending therebetween, each end face having an aperture extending therethrough; a first rotational drive arm extending through the aperture in the first end face; a second rotational drive arm extending through the aperture in the second end face; the two arms being co-axial and arranged to rotate about a rotational axis extending along the length of the rotational drive arms; the two rotational drive arms being connected to an electrically insulating drive body arranged within the cavity and adapted to rotate about the rotational axis.

Such rotational drives can be much smaller than traditional drive mechanisms so allowing the size of the overall apparatus to be considerably reduced. The rotational drive is simple and inexpensive to manufacture and highly reliable.

The drive body can be an epoxy or polyester glass. The drive body can be a polymer or composite material such as Kevlar.

Preferably, the ratio of the dielectric constant of the drive body to the dielectric constant of the oil is in the range 1 to 1.5, preferably 1 to 1.2, more preferably 1 to 1.1

The drive body can be a cone.

Alternatively, the drive body can be a disk.

Alternatively the drive body can be a shaft. Preferably, the disk has a plane of symmetry normal to the rotational axis, the diameter of the disk increasing from the drive shafts to the plane of symmetry.

Preferably, the surface of the drive body comprises a plurality of ridges and troughs.

Preferably, the ends of the drive arms are embedded in the drive body, the ends of the rotational drive arms being domed.

At least a portion of the outside of the cavity can be coated with a conductive layer.

At least a portion of at least one of the inside and outside of the cavity can coated with a semiconductor layer.

Preferably the oil insulated rotational drive further comprises an interrupter drive arm connected thereto, the interrupter drive arm being connected to one of the rotational drive arms by a connector, the connector being adapted to convert rotational motion of the rotational drive arm to linear motion of the interrupter drive arm.

Preferably the interrupter drive arm is enclosed in a gas filled circuit breaker enclosure, preferably air or inert gas.

Preferably, the cavity integrally extends from the circuit breaker enclosure, one of cavity end faces being a portion of the wall of the circuit breaker enclosure.

Alternatively, a disconnector or switch is connected to one of the rotational drive arms of the oil filled rotational drive. Preferably, the oil filled rotational drive further comprises an electrical interrupter connected to the interrupter drive arm.

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 schematic form, an oil insulated rotational drive according to the invention with associated interrupter drive arm and interrupter;

Figure 2 shows an embodiment of an oil insulated rotational drive according to the invention;

Figure 3 shows an alternative embodiment of an oil insulated rotational drive according to the invention;

Figure 4 shows the oil insulated rotational drive of figure 2 along with a circuit breaker cavity and interrupter drive in end view;

Figure 5 is a pressure equalisation device for use with the oil insulated rotational drive according to the invention; and,

Figure 6 shows an oil insulated rotational drive according to the invention along with interrupter drive arm and interrupter in plan view.

Shown in figure 1 , in schematic form, is an oil insulated rotational drive 1 according to the invention along with associated interrupter drive arm 2 and interrupter 3. The interrupter 3 comprises a hollow cylinder 4 having an aperture 5 at one end and collapsible bellows 6 at the other. There is a hard vacuum within the cylinder 4. Extending through the first aperture 5 is a first stem 7 having a contact disk 8 at its end. Extending through the bellows 6 is a second stem 9 having a contact disk 10 at its end. The interrupter 3 is shown in the closed configuration with the two contact disks 8,10 abutting together.

Connected to the second stem 9 is an interrupter drive arm 2. The interrupter drive arm 2 is typically enclosed in a circuit breaker enclosure 11.The circuit breaker enclosure 1 1 is made from an insulating material, preferably a polyester composite or epoxy resin. The circuit breaker enclosure 1 is filled with air or an inert gas. Integrally extending from the wall 12 of the circuit breaker enclosure 11 is the oil insulated rotational drive 1. The oil insulated rotational drive 1 comprises a cavity 13 comprising first and second end faces 14,15 and a side wall 16 extending therebetween. The first and second end faces and side wall are an insulating material, preferably a polyester composite or epoxy resin. One of the end faces 14 is a portion of the wall 12 of the circuit breaker enclosure 11. The cavity 13 is filled with oil. A first rotational drive arm 17 extends through an aperture 18 in one end face 15. A second rotational drive arm 19 extends through an aperture 20 in the other end face 14 and connects to the interrupter drive arm 2 by a connector 21 which converts rotational motion of the second rotational drive arm 19 into linear motion of the interrupter drive arm 2. The two rotational drive arms 17,19 are coaxial and adapted to rotate about a common rotational axis 22. Arranged in the cavity 13 is an insulating drive body 23 also adapted to rotate about the rotational axis 22. The first and second rotational drive arms 17,19 are connected to the drive body 23.

In use the stems 7,9 and interrupter drive arm 2 are at high voltage. Current flows from point A through the interrupter 3, along the interrupter drive arm 2 to point B. In order to interrupt the current flow an operator rotates the first rotational drive arm 17. The drive body 23 transmits this rotational motion to the second drive arm 19 which is in turn converted to linear motion of the interrupter drive arm 2. As the interrupter drive arm 2 moves this pulls the second stem 9 so pulling the contact disks 8,10 apart halting the current flow. The motion of the second stem 9 in the interrupter 3 is highly non-linear with the second stem 9 not moving at ail until the displacement of the interrupter drive arm 2 has reached a critical level and then moving very rapidly to reduce the arcing time. Typically the connector 21 includes a spring (not shown) to maintain contact pressure and help accelerate the moving contact when the mechanism is operated. Stem 9 is connected to a flexible connector or transfer contact for the current to pass through on its way through the equipment. One rotational drive arm 19 is at high voltage. The other 17 is at earth. The full potential drop therefore appears across the rotational drive 1.

Shown in figure 2 is an embodiment of an oil insulated rotational drive 1 according to the invention. The rotational drive 1 comprises an oil filled cavity 13. The cavity 13 comprises first and second end faces 14,15 and a side wall 16 extending therebetween. In this embodiment the first end face 14 is an integral part of a circuit breaker enclosure 1. The side walls 16 of the cavity 13 extending between the first and second end faces 14,15 also integrally extend from the circuit breaker enclosure 11. The second end face 15 is a separate plate which is bolted to the side walls 16. A seal 24 makes the joint between end face 15 and side walls 6 oil tight.

The cavity 13 is filled with oil. Any insulating oil could be employed however a low flammability oil such as a natural or synthetic ester or silicone oil is to be preferred. The oil typically has a permittivity in the range 3 to 3.5. Further arranged in the cavity 13 is a drive body 23. This is typically an epoxy or polyester glass, typically having a permittivity in the range 3.5 to 4. Typically the drive body 23 takes up the majority of the space in the cavity 13 reducing the amount of oil required. In this embodiment the drive body 23 is a disk. Connected to the drive body 23 and extending through apertures 18,20 in the end faces 14,15 are first and second rotational drive arms 17,19. Seals 25 between the cavity 13 and the rotational drive arms 17,19 make the cavity 13 oil tight.

The disk 23 has a plane of symmetry 26 normal to the rotational axis 22. The diameter of the disk 23 increases from the rotational drive arms 17,19 towards the plane of symmetry 26. As mentioned above, the full potential drop appears across the two rotational drive arms 17,19. One way in which the rotational drive 1 may fail is by an electrical discharge between the two rotational drive arms 17,19 which travels along the outer face of the rotational body 23. By shaping the rotational body 23 in this way the length of the discharge path is maximised for a given size of rotational body 23, reducing the risk of discharge.

Electric field lines tend to gather at discontinuities or corners of the drive body 23. There is a risk of electrical breakdown at such points. In order to minimise the risk of such breakdown the dielectric permittivity of the drive body 23 and the oil are chosen to match as closely as possible. Preferably the ratio of the dielectric constant of the drive body 23 to the dielectric constant of the oil is in the range 1 to 1.5, preferably 1 to 1.2, more preferably 1 to 1.1

The irregular shape of the cavity 13 may also cause the field lines to cluster at points within the cavity 13. Again, these may cause electrical breakdown within the cavity 13. In order to minimise this risk at least a portion of the outside of the cavity 13 can be coated with an electrically conducting layer to alter the pattern of field lines within the cavity 13. Additionally or alternatively at least a portion of the inside of the cavity 13 can be coated with a semiconducting layer to achieve the same result.

There is also a risk of electrical breakdown through the drive body 23 from one rotational drive arm 19 to the other 17. The rotational drive arms 17,19 are embedded in the drive body 23 and the ends of the drive arms 17, 19 are rounded as shown to reduce the concentration of field lines.

In order for the drive body 23 to be able to transmit the high rotational forces required for operating the device the ends of the rotational drive arms 17,19 are shaped to enhance adhesion between the arms 17,19 and the drive body 23 and to transmit the load evenly into the drive body 23.

Shown in figure 3 is an alternative embodiment of an oil insulated rotational drive 1 according to the invention. This embodiment is similar to that of figure 2 except in this embodiment the drive body 23 is conical and the cavity 13 is shaped to match. The outer surface of the drive body 23 comprises a plurality of peaks 27a and troughs 27b to increase the length of the discharge path.

A further potential cause of electrical breakdown in the cavity 13 of the rotational drive 1 is air gaps or bubbles at the top of the cavity 13. In order to minimise air gaps the wall of the cavity 13 can comprise a valve (not shown) though which the cavity 13 can be pumped down to vacuum. Oil can then be drawn into the cavity 13 though the valve under the vacuum action of the cavity 13. A reservoir of oil (not shown) may also be connected to the cavity 13 by a pipe, in use the cavity 13 is preferably oriented so that any bubbles within the cavity 13 rise up to the pipe and into the reservoir, keeping the cavity 13 completely filled with oil.

The profile of the drive body 23 is such that air bubbles cannot get trapped during filling or in service. Drive body profiles may differ depending upon the intended orientation of the rotational drive in use.

Any oil feed tubes to the oil insulated rotational drive 1 are preferably arranged such that the oil can be purged through the system during initial filling or following long service to remove any build up of contaminants or aging products.

Shown in figure 4 is the oil filled rotational drive 1 of figure 2 along with the circuit breaker enclosure 11 and interrupter drive arm 2 in end view. The circuit breaker enclosure 11 is at earth whilst the interrupter drive arm 2 is at high voltage. The circuit breaker enclosure 11 is therefore filled with air or an inert gas such as nitrogen to reduce the risk of arcing between circuit breaker enclosure 11 and interrupter drive arm 2. The gas may be under pressure. The seal 25 between the rotational drive arm 19 and enclosure 1 is designed to prevent leakage of oil from the cavity 13 to the circuit breaker enclosure 11 and gas from the circuit breaker enclosure 1 1 to the cavity 13.

The circuit breaker enclosure 11 has an aperture 28 in its wall opposite where the rotational drive arm 19 enters the circuit breaker enclosure 19. The aperture 28 is used for maintenance of the device. When the aperture 28 is not being used it is covered with a transparent cover plate 29. A second transparent cover plate 30 is arranged spaced apart from the first 29 and filled with oil to reduce the risk of electrical discharge through the plates 29,30. As both plates 29,30 are transparent an operator can view the rotational drive arm 19 and interrupter drive arm 2 in the circuit breaker enclosure 11 in use.

The rotational drive arm 19 is connected to the interrupter drive arm 2 by a connection means 21. In this embodiment the connection means 21 is a rocking linear drive which is known in the field of mechanical engineering and the operation will not be described in detail. The rocking linear drive converts rational motion of the rotational drive arm 19 to linear motion of the actuator drive arm 2 in and out of the page.

In order to prevent oil leaking from the cavity 13 into the circuit breaker enclosure 11 or gas from the circuit breaker enclosure 11 leaking into the cavity 13 it is desirable to maintain the pressure of the gas and the oil at substantially the same level. During operation the oil can become hot but cannot expand due to the surrounding cavity 13. The oil pressure can vary significantly during operation of the device. Figure 5 shows a pressure equalisation device

40 adapted to solve this problem. The device 40 comprises a hollow tube 41 having a side wall defined by bellows 45. One end of the tube 41 is in fluid communication with the circuit breaker enclosure 1 by means of a pipe 43 of small diameter. The opposite end of the tube

41 is in fluid communication with the oil filled cavity 13 by a plurality of pipes 42.

Arranged within the tube 41 is a dividing plate 44 connected to the bellows 45. Provided the pressure on both sides of the dividing plate 44 is the same the dividing plate 44 will be located half way along the tube 41. If the pressure on one side of the tube 41 changes then the plate 44 will move along the tube 41 until again the pressures are equal. The tube 41 may comprise a further biasing spring 46 urging the dividing plate 44 towards the oil filled side of the tube 41 so maintaining a slight overpressure in the oil compared to the gas. The tube wall may further comprise an end stop 47 restricting the range of motion of the dividing plate 44 and preventing the oil pressure going negative with respect to the gas pressure. The device 40 may further comprise position sensors 48 for measuring the position of the dividing plate 44 in the tube 41. If the dividing plate 44 moves too far with respect to its typical range of equilibrium positions then this may indicate a leak on either the gas or oil side.

Using a bellows type arrangement ensures that the insulating oil is separated from atmosphere and is therefore not susceptible to contamination by absorption of ambient moisture. No breather system is required. Shown in figure 6 is the oil insulated rotational drive 1 in combination with the interrupter drive arm 2 and interrupter 3 in plan view. The interrupter drive arm 2 is connected to the interrupter 3 so that rotation of the oil insulated rotational drive 1 indirectly activates the interrupter 3. In this embodiment the interrupter 3 is arranged in the circuit breaker assembly enclosure 11. The modular form of the entire assembly has a number of advantages over known systems -

Firstly, the three main components (interrupter 3, circuit breaker enclosure 11 and rotational drive 1) are sealed. Only puncture through a solid moulding or insulating oil will cause the assembly to fail.

Secondly, an earthed rotational drive 1 can be used in close proximity to the high voltage parts of the assembly reducing space requirements and improving mechanical integrity.

Thirdly, the connections between the individual main components of the assembly are straightforward.

Each of the main components 1 , 2, 3 is a controlled environment which avoids the problems of condensation in electrically stressed regions which can lead to discharge problems and failures.

In all of the above embodiments the oil insulated rotational drive 1 is shown connected to an interrupter drive arm 2 which is in turn connected to an interrupter 3. The oil insulated rotational drive 1 has applications in other areas. For example, it could be used to drive disconnectors or switches. Typically disconnectors and switches are used in applications where the need to interrupt high currents is not necessary but insulated drives are still required. As in the higher voltage fields these are typically air insulated which are large and heavy.

Claims

An oil insulated rotational drive comprising an oil filled cavity defined by an electrically insulating cavity wall, the cavity wall comprising first and second spaced apart end faces and a side wall extending therebetween, each end face having an aperture extending therethrough; a first rotational drive arm extending through the aperture in the first end face; a second rotational drive arm extending through the aperture in the second end face; the two arms being co-axiai and arranged to rotate about a rotational axis extending along the length of the rotational drive arms; the two rotational drive arms being connected to an electrically insulating drive body arranged within the cavity and adapted to rotate about the rotational axis.

An oil insulated rotational drive as claimed in claim 1 , wherein the drive body is an epoxy or polyester glass.

An oil insulated rotational drive as claimed in either of claims 1 or 2, wherein the ratio of the dielectric constant of the drive body to the dielectric constant of the oil is in the range 1 to 1.5, preferably 1 to 1.2, more preferably 1 to 1.1

An oil insulated rotational drive as claimed in any one of claims 1 to 3, wherein the drive body is a cone.

An oil insulated rotational drive as claimed in any one of claims 1 to 3, wherein the drive body is a disk.

An oil insulated rotational drive as claimed in any one of claims 1 to 3, wherein the drive body is a shaft.

7. An oil insulated rotational drive as claimed in claim 5, wherein the disk has a plane of symmetry normal to the rotational axis, the diameter of the disk increasing from the drive shafts to the plane of symmetry.

8. An oil insulated rotational drive as claimed in any one of claims 1 to 7, wherein the surface of the drive body comprises a plurality of ridges and troughs.

9. An oil insulated rotational drive as claimed in any one of claims 1 to 8, wherein the ends of the drive arms are embedded in the drive body, the ends of the rotational drive arms being domed.

10. An oil insulated rotational drive as claimed in any one of claims 1 to 9, wherein at least a portion of the outside of the cavity is coated with a conductive layer.

1 1. An oil insulated rotational drive as claimed in any one of claims 1 to 10, wherein at least a portion of at least one of the inside and outside of the cavity is coated with a semiconductor layer.

12. An oil insulated rotational drive as claimed in any one of claims 1 to 1 1 , further comprising an interrupter drive arm connected thereto, the interrupter drive arm being connected to one of the rotational drive arms by a connector, the connector being adapted to convert rotational motion of the rotational drive arm to linear motion of the interrupter drive arm.

13. An oil insulated rotational drive as claimed in claim 12, wherein the interrupter drive arm is enclosed in a gas filled circuit breaker enclosure, preferably air or inert gas.

An oil insulated rotational drive as claimed in claim 13, wherein the cavity integrally extends from the circuit breaker enclosure, one of cavity end faces being a portion of the wall of the circuit breaker enclosure.

15. An oil filled rotational drive as claimed in any one of claims 12 to 14, further comprising an electrical interrupter connected to the interrupter drive arm.

An oil filled rotational drive as claimed in any one of claims 1 to 11 comprising a circuit breaker or switch connected thereto, the circuit breaker or switch being connected to one of the rotational drive arms.

An oil insulated rotational drive substantially as hereinbefore described.