GB2080626A

GB2080626A - Circuit interrupters

Info

Publication number: GB2080626A
Application number: GB8121552A
Authority: GB
Original assignee: AEI
Current assignee: AEI
Priority date: 1980-07-16
Filing date: 1981-07-13
Publication date: 1982-02-03
Also published as: GB2080626B

Abstract

An electrical circuit interrupter including a pair of separable contacts (1a, 11) which during contact separation are totally enclosed within a gas-filled chamber (7) incorporates means for injecting an arc-extinguishing liquid between the separating contacts through radial holes (9) in an insulating inner cylinder (8) and also through an arc-ring (10). The arc-extinguishing liquid is suitably a perfluoro-alkane having 3 to 8 carbon atoms per molecule, and the gas within the chamber (7) is suitably sulphur hexafluoride. <IMAGE>

Description

SPECIFICATION Electrical circuit interrupters This invention relates to electrical circuit interrupters, in particular for high voltage systems, and an object of the invention is to provide a particularly advantageous means for quenching electrical arcs which tend to be produced in such devices when they are activated, by injecting an arc-extinguishing liquid into the vicinity of the arcs.

It is known from U.K. Patent Specification No.

1492037 for an electrical circuit interrupting device to include separable contacts which, during contact separation, are totally enclosed within a chamber containing an arc-extinguishing fluid under pressure from 2 to 100 pounds per square inch above that ambient pressure, wherein the said fluid consists of one or more perfluoro-alkanes having from, 3 to 8 carbon atoms in the molecule.

According to this invention an electrical circuit interrupter including a pair of separable contacts which during contact separation are totally enclosed within a gas filled chamber, incorporates means for injecting an arc-extinguishing liquid between the pair of contacts when the latter are separated.

Suitable arc-extinguishing liquids comprise one or more perfluoro-alkanes having 3 to 8 carbon atoms in the molecule. Preferably the arc-extinguishing liquid includes a perfluoro-alkane having five carbon atoms in the molecule.

The said chamber preferably contains gaseous sulphur hexafluoride.

The liquid injected between the contacts when the latter are separated serves to cool an arc extending between the contacts by dissociation and also increases the pressure around the arc. Both of these effects facilitate extinction of the arc. A circuit interrupter according to the invention conveniently incorporates a reservoir to which the liquid returns after it has recombined and condensed subsequent to arc extinction.

In a preferred embodiment of the invention in which one of the contacts moves to break the circuit, the liquid is injected between the contacts from apertures in an assembly attached to the moving contact.

In another preferred embodiment the liquid is injected from a jet orjets which break the liquid into small droplets into a cavity surrounding the contacts. The droplets are preferably guided between the contacts by the shape of the cavity.

Preferably the liquid is stored in an accumulator, being pumped under pressure into the accumulator through a non-return valve from a suitable supply.

Liquid for extinction of arcs is then arranged to be released under pressure from the accumulator through a valve which is opened by a mechanical linkage actuated by the interrupter operating mechanism. After use for extinguishing an arc, liquid is allowed to accumulate in a reservoir in the base of the interrupter, from which it can be pumped back into the accumulator for subsequent use, by a separately operable pump.

Alternatively the liquid may be positively pumped from a reservoir by a piston operated by the interrupter actuating mechanism.

The foregoing may be better understood from the following description with reference to Figures 1 to 5 of sectional views of examples of a number of different embodiments of the invention.

Figure 1 is a split view showing two positions of the nozzles and contact assembly of an interrupter, Figure 2 shows a similar view of a second interrupter, Figure 3 shows a similar view of a third interru pter, Figure 4 shows a suitable form of liquid storage accumulator of an interrupter, and Figure 5shows a liquid pumping system and reservoir.

In Figure 1 the fixed nozzle contacts 1 a and 2a are carried respectively on contact tubes 3 and 4 which are in turn mounted on end plates (not shown) which form the end closures of the porcelain housing of the interrupter. The fixed contacts are bridged to complete the electrical circuit by a moving contact assembly 5 which is driven by a linkage 6 from a suitable mechanism (not shown).

The moving contact assembly also carries a cylindrical injection unit formed from insulating material and comprising an outer case 7 and inner cylinder 8. Arc extinguishing liquid is injected during actuation of the device between the nozzles 1a and 2a through radial holes 9 in the inner cylinder 8.

Liquid is also injected through holes in the arc ring 10 to accelerate transference of the arc from the contact fingers 11 to the nozzles 1a and 2a.

Arc extinguishing liquid is fed into the injection unit via tubes 12 which slide in fixed tubes 13 which are in turn fed from a pressurised reservoir pump system (not shown).

The embodiment of the invention shown in Figure 2 is similar to that shown in Figure 1, but differs in that it has a fixed contact nozzle 1b and a moving contact nozzle 2b which is carried by the moving contact assembly. In the closed position the nozzles 1b and 2b are in close proximity and are arranged to disengage after the contact fingers have disengaged from the nozzle 1 so that the current is rapidly transferred from the contact fingers to the nozzles 1b and 2b. A cylinder 14 in conjunction with the moving contact assembly and injector unit encloses an annular cavity 15.Apertures 16 communicate between this cavity and the nozzle region so that gases generated by arcing during separation of the contacts are retained in the cavity 15 for reinjection into the nozzle region as the current between the nozzles falls to zero and the gas pressure between the nozzles decreases. By this means the pressure and flow of arc extinguishing gas is prolonged, thereby improving the arc extinguishing capability of the interrupter.

Figure 3 illustrates an alternative method of liquid injection in which the arc extinguishing liquid is injected through nozzles 17 which break the liquid into small droplets. The droplets are contained and guided into the vicinity of fixed nozzles 1c and 2c by a dome-shaped cylindrical housing 18. This housing may be extended as was the casing 14 in Figure 2, to retain gas under pressure generated by the arc radiation.

Figure 4 shows an accumulator 31 for arc extinguishing liquid. A valve 32 serves to release liquid from the accumulator 31 into distribution pipes 33 which lead to the injectors. The valve 32 is actuated buy a rod 19 driven by a cam 20. The cam is, in turn, driven by one of the bell cranks 34 which couple the interrupter contact drive to the interrupter mechanism. The cam is engaged early in the interrupter opening stroke by a pin 21 and disengages towards the end of this stroke. On the closing stroke, the pin 21 ridges overth cam 20 which is depressed against a spring 22, leaving the valve 32 closed. Used liquid is allowed to return through a port 23 to the base of the interrupter, whence it is pumped back to the accumulator.

Figure 5 shows a positive arc extinguishing liquid displacement system for use with fluorocarbons which liquify at relatively low pressures such as would exist in circuit interrupters in accordance with the invention. The liquid is stored in a reservoir 24 at the base of the interrupter. A stepped piston 25 is used to force liquid through a pipe 26 to the injectors. The piston 25 is actuated by the operating rod to which it is connected between the upper end of the latter and the bell crank linkage to the interrupter contacts. The full piston displacement is delivered during the initial part of the fluid delivery stroke to rapidly fill the distribution system. The larger diameter piston 37 is then disengaged on further movement, by by-pass channels 27. Up to this point in the stroke, by-pass channels 28 have permitted liquid to flow from the upper cylinder 35 to the lower cylinder 36 and thence to the discharge pipe 26. As the channels 27 are brought into action the smaller piston 38 seals off the channels 28 and liquid is delivered to the injectors by the smaller piston 38 only. Towards the end of the stroke corresponding to the final, isolating part of the contact travel, a third set of by-pass channels 29 come into action allowing liquid to flow past the smaller piston 38. During the closing stroke the valve 30 opens allowing the cylinders 34 and 35 to refill from the reservoir 24.

This positive liquid displacement system is especially applicable for use with the injection and contact arrangement shown in Figure 2, because in this contact arrangement liquid discharge through the jets is unrestricted throughout the contact travel.

Claims

1. An electrical circuit interrupter including a pair of separable contacts enclosed within a gas-filled chamber and incorporating means for injecting an arc-extinguishing liquid between the contacts as the contacts separate.

2. An electrical circuit interrupter according to Claim 1 in which the arc extinguishing liquid is such that a significant proportion of the liquid injected between the contacts before the arc is extinguished is vapourised and dissociated.

3. An electrical circuit interrupter according to Claim 1 or Claim 2 in which during contact separation the arc-extinguishing liquid is injected into a housing surrounding the contacts in the form of small droplets and the shape of the housing is such as to guide the droplets between the separating contacts.

4. An electrical circuit interrupter according to Claim 1 or Claim 3 in which the arc-extinguishing liquid contains one or more perfluoro-alkanes having 3 to 8 carbon atoms per molecule.

5. An electrical circuit interrupter according to Claim 1 or Claim 3 or Claim 4 in which the arc-extinguishing liquid contains a periluoro-slkane having 5 carbon atoms per molecule,

6. An electrical circuit interrupter according to any preceding Claim in which the contents are in the form of coaxially slidable tubes,

7. An electrical circuit interrupter according to any preceding Claim incorporating a reservoir to which the arc-extinguishing liquid returns after having been injected between the contact

8.An electrical circuit interrupter according to any preceding Claim in which a cavity is is restricted communication with the arcing regionbetween the contacts, so that in use there is a net flow of gas from the arcing region into the cavity as the arc builds up and a net outflow of gas from the cavity into the arcing region as the arc decays.

9. An electrical circuit interrupter according to any preceding Claim including a pressurised containerfrom which the arc-extinguishing liquid is directed between the contacts.

10. An electrical circuit interrupter according to any of Claims 1 to 8 including a piston operated by the interrupter actuating mechanism for pumping the arc-extinguishing liquid between the contacts.

11. An electrical circuit interrupter according to Claim 10 in which the piston is stepped and slides in a similarly stepped cylinder provided with by-pass channels connecting sections of different crosssectional area such that the liquid is pumped at different rates as the piston travels over different regions of its stroke.

12. An electrical circuit interrupter according to any preceding Claim wherein the chamber enclosing the separable contacts contains gaseous sulphur hexafluoride.

13. An electrical circuit interrupter substantially as described hereinabove with reference to Figure 1 of the accompanying drawings.

14. An electrical circuit interrupter substantially as described hereinabove with reference to Figure 2 ofthe accompanying drawings.

15. An electrical circuit interrupter substantially as described hereinabove with reference to Figure 3 of the accompanying drawings.

16. An electrical circuit interrupter according to any preceding Claim incorporating a liquid storage accumulator substantially as described hereinabove with reference to Figure 4.

17. An electrical circuit interrupter according to any preceding claim incorporating a liquid pumping system and reservoir substantially as described hereinabove with reference to Figure 5.