GB1562384A - Electric switches - Google Patents

Description

(54) ELECTRIC SWITCHES (71) We, NORTHERN ENGINEERING INDUSTRIES LIMITED, a British Company of NEI House, Regent Centre, Newcastle-upon Tyne, NE3 3SB, I do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following state ment This invention relates to electric switches for outdoor use in conditions exposed to atmospheric pollution and is particularly, although not exclusively, applicable to high- voltage outdoor switches such as disconnectors, isolators, earthing switches, loadbreaking switches, making switches and sequential isolators and isomakers associated with circuit-breakers. It is, however, broadly applicable to any electrical contact arrangement or assembly of mating parts which are required to engage and disengage under conditions in which the parts may be exposed to atmospheric pollution and specifically where there is the possibility of icing.

Atmospheric pollution in outdoor switchgear installations, especially in coastal sites, leads to contamination and degradation of the contacts involved in high-voltage switches; moreover in conditions of low temperature, ice formation on the contacts can prevent operation of the switching device and reduce electrical conductivity. It is, therefore, necessary either to provide protective means from weather conditions or else to arrange for the contact mechanisms to have the facility to overcome the conditions created by the environment in which they operate.

Specifically to overcome conditions of icing it is known to provide a mechanism which will open or close contacts by the sheer force of operation and this is known to be an uneconomical solution. Further more a "free-entry" contact arrangement is known in which the contact pressure of the switch is released before the co-operating contact begins to move; this is used to help crack any ice formed. This solution is relatively complex and costly to apply and there is the danger that under extreme conditions the contact operating mechanism itself may fail to operate.

An object of the present invention is to overcome the disadvantages of previous solutions and provide one which is simple and economically less expensive to apply.

Since icing conditions occur in only certain regions of the world, it is an advantage if any features required to prevent the formation of ice or to aid its removal can be so designed to be added to a standard manufacturing range of switches. This invention provides features which may be used to convert one of a standard range of switches into one suitable for operation in climatic conditions where icing may occur.

According to the present invention there is provided an electric switch for outdoor use in conditions exposed to atmospheric pollution having parts on which ice is liable to build up and obstruct relative movement between a fixed contact and a contact arm which is movable into electrical contact with the fixed contact, in which the movable contact arm includes an ice-shedding member formed of a flexible material which inhibits the formation and/or adhesion of ice, and so mounted as to shield part of the leading edge of the movable contact arm and to project forward from it so as to be free to flex to crack off ice adhering to it.

In one form of the invention the iceshedding member is corrugated or formed to include air spaces to increase its deformability.

The surface of the ice-shedding member may be of P.T.F.E., polypropylene, silicone rubber or other such material. Alternatively, the ice-shedding members may be made conductive by loading with carbon or other conducting material.

The ice inhibiting nature of the material employed reduces the adhesion of ice which has formed and the deformability promotes the formation of cracks in the ice layer thus facilitating its removal by the edges of the fixed contact housing durihg a closing operation. Similarly, when the switch is being opened the same factors help to break any ice which may have been formed between the fixed contact housing and the movable contact during the period that the switch is in the closed-circuit position.

The preceding features are applicable to a disconnector Qsolator, isolating switch, etc.) and to earthing switches.

Further features and details of the invention will be apparent from the following description of certain specific embodiments which will be given by way of example with reference to the accompanying drawings in which: Figure 1 is a diagrammatic perspective view of a typical 3-phase disconnector or isolator with an attached earthing switch.

Figure 2 is an enlarged perspective view of one fixed-contact housing and the cooperating end of a movable contact arm.

Figure 3 is a diagrammatic plan view of the end portion of the movable contact arm of a disconnector with a shroud fitted.

Figure 4 is a section on the line A-A of Figure 3, and Figure 5 is a view similar to Figure 2 of a modified construction.

Figure 1 shows a typical 3-phase disconnector of the rotating centre post type in the open circuit position. Each phase consists essentially of a movable contact arm 10 mounted on a rotatable post insulator 11 and two fixed contact assemblies 12 mounted on fixed post insulators 13. Each fixed contact assembly 12 comprises a spherical housing having a slot-like opening 15 through which the outer end of the movable contact arm 10 can enter to engage with fixed contact fingers 14 within (Seen in Figure 2).

In freezing climatic conditions ice can build up on the movable contact arm 10 and the fixed contact housings 12 and this buildup of ice can prevent the satisfactory closing operation of the disconnector. Similarly, when the disconnector is in the closedcircuit position and the movable contact arm 10 is in engagement with the fixed contact housings 12, as shown in dotted lines in Figure 1, ice can build up between the arm 10 and the fixed housing 12 and can prevent the satisfactory opening operation of the disconnector.

Also shown in Figure 1 is a typical earthing switch, each phase of which has a movable contact arm 10a and a fixed contact assembly 12a generally similar to the fixed contact 12 of the disconnector. The earthing switch can suffer from the same icing-up problem in the circuit-open or circuit-closed position as can the disconnector.

The present invention is concerned with providing ice-shedding shrouds which will prevent or reduce the build-up of ice and will make it easier to crack and dislodge any ice that does form. The essence of the invention resides in discouraging the adhesion of ice to metal parts by covering such parts with water-repellent and ice-inhibiting materials, in lengthening the ice bridges which build up between adjacent and mating parts, so as to weaken them, and in exploiting flexing and the creation of wave-like ripple motion in the shrouding materials to crack the ice and facilitate its dislodgment and removal.

In Figure 2, which shows one fixed contact housing 12 and the end portion of a movable contact arm 10 in engagement with fixed contact fingers 14, the arez surrounding the opening 15, including the frame 16, is superposed by a flexible facing of polytetrafluorethylene (P.T.F.E.). This facing is carried down in the form of an apron 17. A hood or cowl 18, made of polypropylene, is also attached to the housing above the slotted opening. This hood or cowl tends to act as a water-shed to divert rain and ice from the opening as well as to facilitate the shedding of ice by virtue of its deformability.

In the modified arrangement of Figure 5 the hood incorporate projecting tongues or strips 25 of silicone rubber or similar material having suitable elastic deformation properties to provide a curtain which would be brushed aside by the contact arm as it approaches the slot in the housing and would subsequently re-form behind the arm.

A shroud 19 made of polypropylene, described in greater detail with reference to Figures 3 & 4, is attached to the end of the movable contact arm 10.

When a disconnector (isolator, isolating switch etc.) is in the open-circuit position, with its contact arms 10 disengaged from its fixed contact housings 12, as shown in fill line in Figure 1, ice can form on the contact arms 10 and their shrouds 19, and on the housings 12, and icicles can form and hang down from each hood 18 in front of each slot 15 (Figure 2).

When closing operation is intiated, causing the insulators 11 (Figure 1) to revolve, the arms 10 move towards engagement with the fixed contact housings. When the ice-coated leading edge of a moving contact arm meets the ice-coated housing and hood 18, the impact causes the hood 18, P.T.F.E. facings and apron 17, and shroud 19 to deform and wave-like ripple motions to travel through them which crack and dislodge the ice. This is finally removed by the edges of the frame 16 or opening 15, allowing the contact arm 10 to pass through the slotted opening 15 into engagement with the fixed contact fingers 14.

When a disconnector is in the closedcircuit position with its contact arms 10 entered into the contact housings and engaged with the fixed contacts, as shown in Figure 2, ice can form on the housings and arms and can build up to form a bridge or couple between them. When an opening operation is initiated, the flexibility of the P.T.F.E. and polypropylene facings and shrouds allows some movement of the contact arms to occur, under the influence of the operating mechanism, and wave-like ripple motions are created in the facings and shrouds which crack and dislodge the ice, allowing the contact arms to disengage and move to the open position.

Figures 3 and 4 show a preferred shape of polypropylene shroud 19 attached to the end of the contact arm (other shapes may be more suitable for other types of contact arm associated with other disconnectors, isolators, etc.). The shroud may be attached to the arm by local screws or clamping plates in the non-contact areas. suitablv Dositioned so as not to impair the flexibility and deformability of the shroud. In an alternative moulded form of construction (not shown) the shroud may incorporate sleeves which slip over and around the arm and which may be attached by screwing or clamping on the underside of the arm or attached, for example, by an adhesive.

Facings and shrouds similar to those shown in Figure 2 may be fitted to the contact housing 1 2a of the earthing switch (Figure 1); the shrouds will be of different shape since the contact housings are mounted with their slotted openings vertical instead of horizontal to suit the plane of operation of the movable contact arms.

Advantage is taken of the fact that the earthing switch contact arms are at earth potential, when in the open position, to provide fixed covers which enclose their ends to protect them from ice formation.

The particular application used as an example is to a disconnector of the rotating centre post type. The principles are equally applicable to disconnectors, isolators, switches etc., of other types such as rotating-end post, rocking-post, vertical-arm, vertical-break and swinging-bushing, having single or double breaks.

WHAT WE CLAIM IS:- 1. An electric switch for outdoor use in conditions exposed to atmospheric pollution having parts on which ice is liable to build up and obstruct relative movement between a fixed contact and a contact arm which is movable into electrical contact with the fixed contact, in which the movable contact arm includes an ice-shedding member formed of a flexible material which inhibits the formation and/or adhesion of ice, and so mounted as to shield part of the leading edge of the movable contact arm and to project forward from it so as to be free to flex to crack off ice adhering to it.

2. A switch as claimed in Claim 1 in which the ice-shedding member is corrugated or formed to include air spaces to increase its deformability.

3. A switch as claimed in Claim 1 or Claim 2 in which the surfaces of the iceshedding member are of P.T.F.E.

4. A switch as claimed in Claim 1 or Claim 2 in which the surfaces of the iceshedding members are of polypropylene.

5. A switch as claimed in Claim 1 or Claim 2 in which the surfaces of the iceshedding members are of silicone rubber.

6. A switch as claimed in any one of Claims 1 to 5 in which the ice-shedding members are made conductive by loading with carbon or other conducting material.

7. A switch as claimed in any one of the preceding claims which is a disconnector or isolator.

8. A switch as claimed in any one of claims 1 to 6 which is an earthing switch.

9. A switch as specifically described herein herein with reference to Figures 1 to 5 of the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (9)

**WARNING** start of CLMS field may overlap end of DESC **. polypropylene facings and shrouds allows some movement of the contact arms to occur, under the influence of the operating mechanism, and wave-like ripple motions are created in the facings and shrouds which crack and dislodge the ice, allowing the contact arms to disengage and move to the open position. Figures 3 and 4 show a preferred shape of polypropylene shroud 19 attached to the end of the contact arm (other shapes may be more suitable for other types of contact arm associated with other disconnectors, isolators, etc.). The shroud may be attached to the arm by local screws or clamping plates in the non-contact areas. suitablv Dositioned so as not to impair the flexibility and deformability of the shroud. In an alternative moulded form of construction (not shown) the shroud may incorporate sleeves which slip over and around the arm and which may be attached by screwing or clamping on the underside of the arm or attached, for example, by an adhesive. Facings and shrouds similar to those shown in Figure 2 may be fitted to the contact housing 1 2a of the earthing switch (Figure 1); the shrouds will be of different shape since the contact housings are mounted with their slotted openings vertical instead of horizontal to suit the plane of operation of the movable contact arms. Advantage is taken of the fact that the earthing switch contact arms are at earth potential, when in the open position, to provide fixed covers which enclose their ends to protect them from ice formation. The particular application used as an example is to a disconnector of the rotating centre post type. The principles are equally applicable to disconnectors, isolators, switches etc., of other types such as rotating-end post, rocking-post, vertical-arm, vertical-break and swinging-bushing, having single or double breaks. WHAT WE CLAIM IS:-

1. An electric switch for outdoor use in conditions exposed to atmospheric pollution having parts on which ice is liable to build up and obstruct relative movement between a fixed contact and a contact arm which is movable into electrical contact with the fixed contact, in which the movable contact arm includes an ice-shedding member formed of a flexible material which inhibits the formation and/or adhesion of ice, and so mounted as to shield part of the leading edge of the movable contact arm and to project forward from it so as to be free to flex to crack off ice adhering to it.

2. A switch as claimed in Claim 1 in which the ice-shedding member is corrugated or formed to include air spaces to increase its deformability.

3. A switch as claimed in Claim 1 or Claim 2 in which the surfaces of the iceshedding member are of P.T.F.E.

4. A switch as claimed in Claim 1 or Claim 2 in which the surfaces of the iceshedding members are of polypropylene.

5. A switch as claimed in Claim 1 or Claim 2 in which the surfaces of the iceshedding members are of silicone rubber.

6. A switch as claimed in any one of Claims 1 to 5 in which the ice-shedding members are made conductive by loading with carbon or other conducting material.

7. A switch as claimed in any one of the preceding claims which is a disconnector or isolator.

8. A switch as claimed in any one of claims 1 to 6 which is an earthing switch.

9. A switch as specifically described herein herein with reference to Figures 1 to 5 of the accompanying drawings.