GB2168198A

GB2168198A - Terminating vacuum switches

Info

Publication number: GB2168198A
Application number: GB08528239A
Authority: GB
Inventors: John Leyton Davenport; Henry Spillman Wood
Original assignee: Associated Electrical Industries Ltd
Current assignee: Associated Electrical Industries Ltd
Priority date: 1984-11-21
Filing date: 1985-11-15
Publication date: 1986-06-11
Also published as: GB8429431D0; GB8528239D0; AU5021385A

Abstract

A vacuum switch 1 is mounted within a sealed enclosure 4 containing an insulating fluid, with conducting leads 8,38 to the switch contacts 2,3 extending through insulating bushings 9 supported by the enclosure wall, the movable contact 3 being connected to the respective conducting lead 38 by a coupling 34 which permits transfer of current to take place between the contact and lead whilst allowing opening and closing movement of the contact. The coupling comprises a cage of sprung fingers engaging over the bulbous ends of the lead 38 and a contact stub 32. The contact 3 is moved by a shaft 27 projecting from the enclosure 4 and linked to the contact lead 3.3 through a spring 29 and telescopic section 30. <IMAGE>

Description

SPECIFICATION Circuit Breakers This invention relates to circuit breakers of the kind employing vacuum switches, that is to say devices comprising a pair of separable contacts contained within a sealed evacuated envelope, one of said contacts being fixed in position within the envelope and the other being supported by a flexible part of the envelope wall so that it can be moved into and out of engagement with the fixed contact.

In accordance with the invention such a circuit breaker incorporates a vacuum switch mounted within a sealed enclosure of a generally cylindrical form containing an insulating fluid, conducting leads to the vacuum switch contacts extend through insulating bushings supported by the enclosure wall, and the movable contact is connected to the respective conducting lead by a coupling which permits transfer of current to take place between the contact and the lead whilst allowing the opening and closing movement of the contact.

The enclosure is conveniently of a generally cylindrical shape with the envelope of the vacuum switch supported substantially coaxially within it, the conducting lead to the fixed contact preferably extending in an axial direction through an end of the enclosure, and the lead to the movable contact extending transversely through the side of the enclosure.

The coupling between the movable contact and the respective conducting lead, in such a case, conveniently comprises a cylinder having longitudinal slots extending into it from each end so as to provide a plurality of spring fingers, a projection extending transversely from a conducting member carried by the external part of the stem of the contact or an extension thereof, extending into one end of the cylinder, and the conducting lead extending into the opposite end of the cylinder, the spring fingers bearing resiliently against the projection and lead respectively. This permits the cylinder to tilt with respect to both the projection and lead whilst retaining resilient engagement therewith, thereby ensuring adequate current transfer between the lead and at the same time allowing the contact to be moved between its open and closed positions.

Actuation of the movable contact is conveniently achieved by a rotatable shaft extending into the enclosure transverse to the direction of movement of the contact through a suitable gas- and liquid-tight bearing, the shaft being coupled to an extension of the contact stem through a coupling means arranged to produce a linear movement of the contact on rotation of the shaft.

The coupling means conveniently incorporates a telescopic section held in the extended position by compression springs, which allow a degree of overmovement of the rotatable shaft, following the closure of the contacts, thereby allowing a known pressure to be applied to the contacts.

A transparent window is conveniently placed in a part of the casing through which a lever connecting the shaft with the contact stem extension can be viewed, indicating means being provided for enabling changes in the position of the lever when the contacts are closed to be monitored visually, so that the degree of contact wear can be readily observed.

Preferably the circuit breaker is mounted on a support with both conducting leads extending upwards in substantially the same plane at substantially the same angle to the vertical so that the ends of both are equally accessible, the rotatable actuating shaft extending generally downwards to a switch actuating mechanism, of any suitable known kind, located beneath the support.

One circuit breaker in accordance with the invention will now be described by way of example with reference to Figures 1 to 5 of the accompanying schematic drawings, in which Figures 1 and 2 represent an axial section and a transverse section respectively through the circuit breaker, Figure 3 represents an enlarged section through part of the circuit breaker, and Figures 4 and 5 show the circuit breaker mounted on two different support structures.

The circuit breaker comprises a vacuum switch 1 containing fixed and movable contacts 2, 3 respectively mounted within an outer casing 4, which is of a generally cyiindrical shape, having an opening 5 at one end. A short tubular stub 6 projects from the side of the casing 4, as shown.

The outer end of the stem 2.2 of the fixed contact 2 is connected electrically, by means of a coupling 7, to a conducting rod 8 which projects through the opening 5. The rod 8 is surrounded by a tube 9 of insulating material such as an epoxy or polyurethane resin, the inner end 11 of tube being of enlarged external diameter. Adjacent this enlarged portion, the tube 9 carries a support member 12 of generally tubular form having an outwardly projecting flange 14 at one end, the flange abutting the enlarged part 11 of the tube. The flange 14 is fixed to the end of the casing, as by studs (not shown) so that the tube 9 and conducting rod 8 are supported coaxially with respect to the casing 4. An O-ring 18 forms a gas- and liquid-tight seal between the surface of the casing 4 around the opening and the adjacent face of the flange 14.

A current transformer 15 surrounds the tubular part 16 of the support member 12, and is protected by a cylindrical cover 17 the rim 19 of which fits over the outside edge of the flange 14, and a gas- and liquid-tight seal is formed between them by a further O-ring 20.

The cover 17 is secured in position by a weathershield 21 fitted on to the outer end of the tube 9. The weathershield 21 comprises a plurality of separate collars, the innermost collar 22 comprising a stress cone and having a flange 23 which seals against the outer surface of the current transformer cover 17. The stress cone and the remainder 24 of the collars are formed of insulating material such as EPDM rubber and consist of a series of identical axially-overlapping dishes giving a corrugated outer surface to the weathershield so as to increase the creepage and flashover lengths. The weathershield is terminated by a insulating cap 25 of the same material which is secured to the tube 9 and holds the assembly of collars in place. The overlapping portions of the dished collars 24 and stress cone collar 22 are sealed with a silicone grease.The cap 25 and collars 22, 24 are removable from the tube 9, and this permits the current transformer to be readily removed and replaced if this proves to be necessary.

The outer end of the stem 3.3 of the other contact 3 of the vacuum switch 1 is connected, via an electrically insulating coupling 30 and a lever 26, to a shaft 27 which is pivotally supported from the casing 4 by a bush 28 and is connected at its opposite end to a suitable switch-actuating mechanism (not shown). The coupling 30 incorporates a telescopic section held in the extended position by compression springs 29 which allow a degree of over-movement of the shaft 27, following closure of the contacts 2, 3, and permits a known pressure to be applied to the contacts in the closed condition.

A metal collar 31 is fixed to the stem 3.3 of the movable contact 3, and carries a radial projection 32 terminating in a bulbous end portion 33. This fits into one end of a metal spring cylinder 34 having longitudinal slots 35 extending in an alternate fashion along it from opposite ends.

The inner surface of the cylinder is formed with an annular groove 40 into which the bulbous end portion 33 seats, and following the insertion of the end portion into the cylinder 34 a metal ring 36 is fitted around the cylinder over the groove to prevent withdrawal of the bulbous end portion therefrom whilst allowing a limited tilting movement of the cylinder 34 relative to the projection 32.

The bulbous end 37 of a further conducting rod 38 fits into the opposite end of the cylinder, which rod extends transversely outwards through the stub 6, and is held in position by a bushing 39 of similar construction to that supporting the rod 8, the cylinder also being capable of a degree of tilting movement relative to the rod.

The form of coupling between the collar 31, which is attached to the stem 3.3 of the movable contact 3, and the fixed conducting rod 38, permits opening and closing movement of the contact 3 to take place whilst, at the same time ensuring an adequate current transfer between the contact and the rod 38.

In use the casing is preferably filled with an insulating fluid, either in gaseous or liquid form.

A window 49 is provided above the lever 26 through which the latter can be viewed.

The lever 26 and a part of the coupling 25 are provided with holes (not shown) which initially are arranged to align with each other when the contacts are closed, the alignment or misalignment of the holes being observable through the window. As the contacts wear, the holes, viewed when the contacts are closed, will be gradually displaced with respect to each other, thus giving an indication of the amount of contact wear produced.

The circuit breaker is conveniently mounted on a support structure as shown in Figure 4.

This comprises a sheet metal cabinet 41, rectangular in plan view and having a roof 42 inclined slightly to the horizontal, the circuit breaker being mounted on the roof of the cabinet with its axis generally horizontal and the actuating shaft 27 extending downwards to switch-actuating control gear within the cabinet as shown diagrammatically at 43. A hinged flap or door 44 provides access to the control gear.

An alternative form of support structure is shown in Figure 5. This similarly comprises a sheet metal cabinet 41, rectangular in plan and in this case the roof 42 is inclined at approximately 45" to the ground, the circuit breaker being mounted on the roof of the cabinet with its axis lying in a vertical plane and substantially parallel to the roof, with the conducting rods 8, 38 each extending in an upward direction so that their ends are both equally accessible.

The actuating shaft 27 similarly extends into the cabinet 41 and is coupled to control gear 43 housed within the cabinet which similarly has a door or flap 44 to provide access to the control gear, the door or flap in this case being shown hinged at the top.

In practice for a three phase supply, three circuit breakers as above described with reference to Figures 1 to 3 are conveniently mounted on the same cabinet roof of either of the two support structures illustrated, and are arranged to be operated simultaneously by the same control gear.

The three single phases are thus supported by a weatherproof cabinet which houses the operating mechanism, interphase drives and opening spring. Other components within the cabinet can be multicore cable terminations, control switches, protective relays and indicating instruments.

The shape of the cabinets described provides easy access to the operating mechanism and interphase drives for initial adjustment and subsequent maintenance. The use of a top hinged door or flap provides some weather protection for anyone working on or inspecting the internally mounted components.

A circuit breaker as above described has a number of further advantages over existing forms of equipment. Thus the enclosure of the main parts of the circuit breaker in a chamber filled with dry inert gas or insulating liquid reduces the overall size of the breaker and, in the case of a multiphase system, eliminates the possibility of internal interphase faults.

Moreover the switch 1 and internal insulation are protected against atmospheric pollution, and any metal parts within the casing 4 are thus protected against oxidation and chemical attack.

In addition all the internal components of a single phase (8, 7, 1, 31, 34, 30, 29 together with a metal spinning 50 surrounding the elements 31 and 34) may be pre-assembled to setting dimensions and then bolted into place as a unit. Assembly is completed simply by plugging in and bolting the side bushing 39 to make contact with the cylinder 34 and inserting a drive pin 46 to couple the drive lever 26 to the moving contact assembly of the interrupter.

Claims

1. A circuit breaker of the kind referred to incorporating a vacuum switch mounted within a sealed enclosure of a generally cylindrical form containing an insulating fluid, conducting leads to the vacuum switch contacts extend through insulating bushings supported by the enclosure wall, and the movable contact is connected to the respective conducting lead by a coupling which permits transfer of current to take place between the contact and the lead whilst allowing the opening and closing movement of the contact.

2. A circuit breaker according to Claim 1 wherein the enclosure is of a generally cylindrical shape with the envelope of the vacuum switch supported substantially coaxially within it, the conducting lead to the fixed contact extends in an axial direction through an end of the enclosure, and the lead to the movable contact extends transversely through the side of the enclosure.

3. A circuit breaker according to Claim 2 wherein the coupling between the movable contact and the respective conducting lead comprises a cylinder having longitudinal slots extending into it from each end so as to provide a plurality of spring fingers, a projection extending transversely from a conducting member carried by the external part of the stem of the contact or an extension thereof, extending into one end of the cylinder, and the conducting lead extending into the opposite end of the cylinder, the spring fingers bearing resiliently against the projection and lead respectively.

4. A circuit breaker according to Claim 3 incorporating, for actuating the movable contact,a rotatable shaft extending into the enclosure transverse to the direction of movement of the contact through a gas- and liquid-tight bearing, and coupling means between the shaft and an extension of the contact stem arranged to produce a linear movement of the contact stem on the rotation of the shaft.

5. A circuit breaker according to Claim 4 wherein the coupling means incorporates a telescopic section held in the extended position by compression springs, which allow a degree of over-movement of the rotatable shaft, following the closure of the contacts, thereby allowing a known pressure to be applied to the contacts.

6. A circuit breaker according to Claim 5 including a transparent window in a part of the casing through which a lever connecting the shaft with the contact stem extension can be viewed, indicating means being provided for enabling changes in the position of the lever when the contacts are closed to be monitored visually, so that the degree of contact wear can be readily observed.

7. A circuit breaker according to any one of Claims 2 to 6 wherein the circuit breaker is mounted on a support with both conducting leads extending upwards in substantially the same plane at substantially the same angle to the vertical with the rotatable actuating shaft extending generally downwards to a switch actuating mechanism located beneath the support.

8. A circuit breaker according to Claim 7 wherein the support comprises the roof of a cabinet housing the switch actuating mechanism, the roof being inclined to the horizontal.

9. A circuit breaker according to Claim 8 wherein the roof is substantially parallel to the axis of the circuit breaker.

10. A circuit breaker according to any one of Claims 2 to 6 wherein the circuit breaker is mounted with its axis approximately horizontal on the roof of a cabinet with the rotatable shaft extending generally downwards to a switch actuating mechanism housed within the cablinet, the roof of the cabinet being inclined to the horizontal.

11. A circuit breaker of the kind referred to substantially as shown in and as hereinbefore described with reference to Figures 1 to 3 of the accompanying drawings.

12. A circuit breaker according to Claim 11 mounted on a support structure substantially as shown in and as hereinbefore described with reference to Figure 4 or Figure 5 of the accompanying drawings.