GB2167605A

GB2167605A - Support for a current transformer on a switch terminal

Info

Publication number: GB2167605A
Application number: GB08528241A
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: 1986-05-29
Also published as: AU5021285A; GB8528241D0; AU584652B2; GB8429433D0; NZ214147A; MX159509A

Abstract

A switch in which input and output conductors 8, 38 extend through insulating bushings supported by an outer casing 4, in which at least one bushing comprises an insulating tube 9 having one end projecting outwards from the casing, a removable weathershield 21-25 surrounds the outer end of the tube, and a current transformer 15 is fitted around the tube between the casing wall and the weathershield, so that it can be withdrawn from the circuit breaker over the tube following removal of the weathershield. The switch is constituted by a vacuum switch unit 1 having a fixed and movable contacts 2,3, the latter being actuated by a rotatable shaft 27 projecting from the casing 4. A flexible coupling 34 joins the movable contact 3 to a lead 38. <IMAGE>

Description

SPECIFICATION Circuit breakers This invention relates to circuit breakers of the kind in which input and output conductors, connected electrically to the respective contacts extend through openings in a surrounding casing, and are supported therein by means of insulating bushings. The invention is more especially, though not exclusively, concerned with circuit breakers of this kind designed for outdoor use, the external part of the bushings, in such a case, carrying or being in the form of weathershields having a corrugated outer surface to increase the flashover path in order to reduce the risk of current tracking.

The input and output conductors of such circuit breakers are commonly surrounded by current transformers, and the replacement of such transformers, if this becomes necessary, has usually involved substantial dismantling of the equipment.

In accordance with the present invention, in a circuit breaker of the kind referred to, at least one said bushing comprises an insulating tube through which the respective input or output conductor extends, the bushing being fixed to the wall of the casing so that it extends through an opening therein with a part projecting outwards from the casing, a weathershield surrounds and is removably secured to the outwardly projecting part of the tube, and a current transformer is fitted around the tube between the casing wall and the weathershield, so that it can be withdrawn from the circuit breaker over the tube following removal of the weathershield.

The weathershield conveniently comprises a plurality of separate axially-overlapping, dish-shaped collars, which are held in position by an insulating cap fixed to the free end of the tube, the cap being apertured for the passage of the respective conductor.

The inner end of the insulating tube preferably extends into the casing and is of enlarged external diameter compared with the remainder of the tube; the adjacent end of the latter is conveniently surrounded by a tubular support member having a flanged end held in abutment with the enlarged end of the insulating tube, the flange being attached in gas- and liquid-tight manner to the part of the casing around the opening, for example by means of studs, so as to secure the bushing assembly casing. The current transformer conveniently surrounds the tubular part of the support member, and is accommodated within a cover the edge of which is sealed in a gas- and liquid-tight manner to the flange of the support tube.

The inner end of the weathershield conveniently comprises a flanged moulding which bears against the outer end of the current transformer cover and forms a gas- and liquid-tight seal therewith. The engagement of the moulding with the cover preferably serves to hold the latter in position although alternative or additional retaining means for the cover may be employed if desired.

One circuit breaker embodying the invention will now be described by way of example, with reference to Figures 1 to 3 of the accompanying schematic drawing, in which Figures 1 and 2 represent an axial section and or transverse section respectively through the circuit breaker, and Figure 3 represents an enlarged section through a part of the circuit breaker.

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 cylindrical 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 conductor 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 gasand 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 overmovement 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 cylidner 34 having lognitudinal 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.

Claims

1. A circuit breaker of the kind referred to wherein at least one said bushing comprises an insulating tube through which the respective input or output conductor extends, the bushing being fixed to the wall of the casing so that it extends through an opening therein with a part projecting outwards from the casing, a weathershield surrounds and is removably secured to the outwardly projecting part of the tube, and a current transformer is fitted around the tube between the casing wall and the weathershield, so that it can be withdrawn from the circuit breaker over the tube following removal of the weathershield.

2. A circuit breaker according to Claim 1 wherein the weathershield comprises a plurality of separate axially- overlapping, dish-shaped collars, which are held in position by an insulating cap fixed to the free end of the tube, the cap being apertured for the passage of the respective conductor.

3. A circuit breaker according to Claim .1 or 2 wherein the inner end of the insulating tube extends into the casing and is of enlarged external diameter compared with the remainder of the tube and the adjacent end of the latter is surrounded by a tubular support member having a flanged end held in abutment with the enlarged end of the insulating tube, the flange being attached in a gasand liquid-tight manner to the part of the casing around the opening.

4. A circuit breaker according to Claim 3 wherein the current transformer surrounds the tubular part of the support member, and is accommodated within a cover the edge of which is sealed in a gas- and liquid-tight manner to the flange of the support tube wherein the inner end of the weathershield comprises a flanged moulding which bears against the outer end of the current transformer cover and forms a gas- and liquid-tight seal therewith.

5. A circuit breaker of the kind referred to incorporating a bushing substantially as shown in and as hereinbefore described with reference to Figure 1 of the accompanying drawings.