GB1593994A

GB1593994A - Electric circuit breakers

Info

Publication number: GB1593994A
Application number: GB2435777A
Authority: GB
Original assignee: AEI
Current assignee: AEI
Priority date: 1978-05-18
Filing date: 1978-05-18
Publication date: 1981-07-22

Description

(54) IMPROVEMENTS IN OR RELATING TO ELECTRIC CIRCUIT BREAKERS (71) We, ASSOCIATED ELEC TRICAL INDUSTRIES LIMITED, of 1, Stanhope Gate, London W1A IEH, a British Company, 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 statement:- This invention relates to electric circuit breakers of the kind incorporating a tubular contact which is movable axially between an open position in which it is spaced from a co-operating contact, and a closed position in which it makes contact therewith, and in which the contacts are mounted within a gas-filled enclosure.

Circuit breakers of the above kind are frequently connected to high voltage lines, and for this reason it is common to mount the sealed enclosure of such a circuit breaker on an insulating support column extending upwards from a base assembly which accommodates control equipment for effecting the opening and closure of the circuit breaker contacts, the required movement being transmitted from the control equipment to the movable contact or contacts of the circuit breaker by means of an insulating drive rod which extends upwards through the support column to an operating mechanism coupled to the contact or contacts at the top of the support column.

When the contacts of such a circuit breaker are required to open it is desirable for this to take place as rapidly as possible, but because the drive rod is necessarily of appreciable length and possesses a significant degree of inertia it tends to restrict the initial acceleration of the movable contact or contacts, which is clearly undesirable.

An object of the invention is to provide a way of increasing the initial acceleration of the movable contact or contacts in such a circuit breaker.

According to the invention an electric circuit breaker of the kind referred to incorporates within said enclosure, an arcing chamber accommodating at least the contact making portion of said co-operating contact, the chamber being mainly closed apart from an opening through which the movable contact is arranged to extend, such that arcing between the contacts as they are opened results in an increase in the pressure of the gas within the chamber, at least during the initial opening movement, the pressurised gas acting on the movable contact and assisting in the acceleration of the latter towards the open position, and wherein the movable contact is provided in its wall with one or more ports for connecting the interior of the movable contact, after it has been withdrawn from said cooperating contact through a predetermined distance, to a lower pressure region outside of said chamber so as to cause gas to flow rapidly from the chamber through the tubular contact for the suppression of arcing.

The port or ports may be arranged to lie within the chamber when the contacts are closed, but to emerge from the chamber to connect the interior of the contact to the main enclosure space outside the chamber, after the movable contact has been withdrawn from the co-operating contact through a pre-determined distance.

If desired the co-operating contact may be so arranged that the pressure rise within the chamber produces a flow of arc suppressing gas through that contact as well as through the movable contact when the contacts separate.

An advantage of the invention is that the greater the degree of arcing, the greater will be the pressure rise within the chamber, thereby producing a greater accelerating force on the movable contact and a more rapid flow of arc extinguishing gas through the movable contact.

The chamber may incorporate a pressure relief valve to limit the pressure rise within the chamber when the contacts open to interrupt a very high fault current.

The contact making part of the movable contact may remain within the chamber throughout its whole range of movement, although in some cases it may be arranged to be withdrawn completely from the chamber when in the fully open position.

The chamber conveniently incorporates a transverse partition which divides the chamber into a first compartment in which the movable contact engages the cooperating contact, and a second compartment into or through which the contact making portion of the movable contact is withdrawn as the contact moves from the closed to the open position, the partition being, of course, apertured for the passage of the movable contact.

The partition may carry at least one nonreturn valve allowing the passage of gas from the first to the second compartment, but not in the reverse direction.

A rise in the gas pressure within the first compartment as the contacts first separate will then produce some rise in pressure in the second compartment, but when arcing takes place within the second compartment giving rise to an increase in pressure therein greater than that in the first compartment the non-return valves will close, thereby restricting the transfer of gas back into the first compartment. Accordingly the pressure within the first compartment will fall as the pressure in the second compartment continues to rise.

Valve means operable to open the first compartment to a region of lower pressure, when the pressure in the second compartment exceeds a predetermined value, may be provided to ensure a more rapid reduction in the pressure within the first compartment after the contact making portion of the movable contact has been withdrawn therefrom.

The chamber is preferably of cylindrical shape coaxial with the contacts and in such a case the partition may be constituted by a piston movable within the chamber independently of the movable contact, the latter extending through an opening in the piston to engage the co-operating contact in a first compartment formed on one side of the piston. Then as the contacts initially separate and produce an arc between them, the pressure rise within said first compartment will cause the piston to move away from said co-operating contact, thereby tending to compress the gas within the second compartment on the opposite side of the piston, thereby enhancing the rise in pressure produced in that compartment due to arcing therein when the contact making portion of the movable contact is withdrawn into it through the piston. The piston may carry one or more non-return valves as in the case of the fixed partition so that the gas pressure in the second compartment is raised partly by movement of the piston and partly from actual gas flow from the first compartment.

The gas employed within the circuit breaker enclosure is conveniently SF6 although other insulating gases could alternatively be used, the gas within the enclosure preferably being at atmospheric pressure or above.

Several different embodiments of the invention will now be described with reference to Figures 1 to 11 of the accompanying schematic drawings, in which Figures 1 and 2 represent in diagrammatic form a section through part of one circuit breaker in accordance with the invention showing the contacts in the closed and partly open position respectively.

Figures 3 and 4 represent similar views of a second circuit breaker, Figures 5 to 11 represent modified forms of the circuit breaker illustrated in Figures 3 and 4.

Referring first to Figures 1 and 2 the circuit breaker comprises an outer enclosure 1 which can be of any suitable known construction, and which is shown only in part, and within which are supported a fixed contact 2 and a tubular movable contact 3 projecting coaxially towards each other from opposite ends of the enclosure.

The movable contact 3 is movable axially between a closed position in which it engages the fixed contact 2 as shown in Figure 1 and an open position in which it is spaced therefrom, the movable contact being coupled to any suitable form of actuating mechanism (not shown) for producing the opening and closing movement thereof.

The circuit breaker also includes, within the outer enclosure, a cylindrical arcing chamber 4 which is arranged to surround the contact making portions 5, 6 of the two contacts 2, 3 when the contacts are closed.

The arcing chamber 4 comprises a cylindrical wall 7 of insulating material closed at one end by a flanged metal disc 8 which carries the fixed contact 2, the disc 8 being itself fixed to a metal plate 9 which is sealed to the adjacent end of the outer enclosure 1, the plate 9 serving to support the chamber 4 within the enclosure 1 as well as providing a terminal for the fixed contact 2.

The wall 11 at the opposite end of the chamber 4 has a central hole 12 through which the tubular movable contact 3 extends, the hole closely surrounding the wall of the contact as shown.

The enclosure contains an insulating gas such as SF3 at a pressure at or above atmospheric pressure and in the static condition, for example with the contacts closed as shown in Figure 1, the pressure of the gas within the chamber 4 is the same as that in the remainder of the enclosure I.

When the circuit breaker is opened by rapid movement of the contact 3 from the closed position shown in Figure 1 towards the open position an arc will be produced between the contacts as represented at 13 in Figure 2. This results in a sudden increase in the pressure of the gas within the chamber 4, which acts on the contact 3 and assists in accelerating it towards the open position.

The side of the movable contact 2 is provided with ports 14 which lie within the chamber 4 when the contact is in the closed position and also during the initial part of its opening movement, but so that when the contact has moved a predetermined distance, as shown in Figure 2, the ports 14 emerge from the chamber and connect the interior of the contact with the main part of the enclosure space, which is at a lower pressure. Accordingly gas is caused to flow rapidly from the chamber 4 to the main enclosure space through the interior of the movable contact 3, which assists in the suppression of arcs formed between the contacts 2 and 3 when these are opened.

The position of the ports 14 can readily be chosen to determine the instant at which the gas flow commences, and the dimensions of the chamber 4 selected to give a required pressure rise and gas flow during the opening of the contacts.

A spring loaded valve, as at 15, can be provided to limit the pressure rise which could occur, for example, when the circuit breaker opens to interrupt a very high fault current. Some pressure control may also be achieved by the provision of one or more small bleed holes in a wall of the chamber as at 16.

The circuit breaker of Figures 3 and 4 is similar to that shown in Figures 1 and 2, except that the interior of the chamber 4 is divided into two compartments X, Y by a transverse insulating partition 17 also formed with a hole 18 through which the movable contact 3 projects when engaging the fixed contact 2, the compartment X which accommodates the fixed contact usually, but not necessarily, being smaller than compartment Y, as shown. When the contacts are opened and an arc is formed between them the pressure initially rises in the compartment X, and this assists in accelerating the movalbe contact 3 towards the open position. Gas under pressure also passes from the compartment X to the compartment Y through one or more nonreturn valves in the partition 17 as at 19.

When the contact making portion of the movable contact 3 leaves the compartment X, and the arc between the contacts extends into the compartment Y, the pressure in the latter will build up at a greater rate, causing the non-return valve or vales 19 to close restricting the transfer of pressure from the compartment Y to the compartment X which helps to maintain a higher pressure in the compartment Y which continues to assist in the acceleration of the contact 3 towards the open position. Finally the ports 14 emerge from the compartment Y which connects the interior of the movable contact 3 to a lower pressure region within the main enclosure space, whereupon gas from the compartment Y is forced rapidly through the movable contact and assists in the suppression of the arc formed between the contacts as they are opened.

In some cases the ports 14 may be arranged to emerge from the compartment Y before the contact making portion of the movable contact 3 leaves the compartment X as shown in Figure 5, thus initiating the arc suppressing flow of gas into the movable contact at an earlier instant. This will also cause the gas pressure in the compartment X to start falling, and when it is below that in the compartment Y the non-return valves 19 will close; then when the contact making portion of the contact 3 enters the compartment Y and the pressure within the latter is further increased gas will flow not only into the movable contact but towards the fixed contact through the opening 18 in the partition 17, which assists in suppressing any arc that is formed.

Figure 6 illustrates a modified form of the circuit breaker illustrated in Figure 5 in which the closure of a non-return valve 19.1 in the partition 17 when the pressure in the compartment Y exceeds that in the compartment X opens a valve 19.2 in the disc 8, thereby leading into a more rapid reduction in the pressure in the compartment X. A spring as at 20 may be arranged to control the instants at which the valves 19.1 and 19.2 operate.

A projecting sleeve 21 may surround the opening 18 on the side of the partition 17 facing the disc 8 as shown in Figure 7. The sleeve 21 not only reduces the volume of gas immediately surrounding the contacts at the instant of opening, thereby ensuring a rapid raise in the pressure of the gas acting on the movable contact, but ensures that gas at the lowest temperature initially passes from the compartment X to the compartment Y through the non-return valve 19.

The valve 19 can, as shown in Figure 8, be located at an end of a duct 19a connecting the compartments X, Y, the duct containing gas permeable material 22 of high specific heat, for further reducing the temperature of gas passing from compartment X to compartment Y during the opening of the contacts.

The circuit breaker illustrated in Figure 8 also has a plurality of metal fingers 23 projecting from the disc 8, around the fixed contact 2, the length of these being selected to control the length of the arc formed in the compartment X during the opening of the contacts. The fingers may be in some cases replaced by a solid metal sleeve, if desired.

Whilst in the embodiments so tar described the movable contact 3 co operates with a stationary contact 2, the latter may be arranged to move away from the movable contact under the pressure produced in the compartment X on the initial opening movement of the contacts, and a circuit breaker incorporating this feature is illustrated in Figure 9.

In this circuit breaker the "fixed" contact 2.1 is slidably supported within a cylindrical sleeve 24 projecting from the surface of the disc 8 towards the supporting plate 9. The contact is biased inwards by means of a spring 25, a stop such as a radially extending flange 26 at the outer end of the contact, defining the normal rest position of the contact. Then when the contacts are opened the increase in pressure within the compartment X forces the contact 2.1 away from the movable contact 3 compressing the spring 25 which returns the contact 2.1 to the rest position when the pressure within the compartment X subsequently falls.

The circuit breaker illustrated in Figure 10 is a modification of that shown in Figure 6. In this embodiment the compartment X opens into a further compartment Z through an opening 32 in the disc 8 within the fixed contact 2. At least one non-return valve 19.3 in the partition 17 is arranged to open a valve 19.4 in the outer wall of the compartment Z when the pressure in the compartment Y exceeds that in the compartment X, thereby connecting the compartment Z to a lower pressure region within the main enclosure. An arc suppressing flow of gas will then take place through the fixed contact 2 as well as the movable contact 3 as indicated by the arrows.

A further embodiment of the invention is illustrated in Figure 11. In this embodiment the partition 17 is replaced by a piston 27.

The piston has a central opening 28 through which the contact making end of the movable contact 3 projects, the contact and the piston being axially movable relative to each other. The piston 27 normally rests against shoulder 31 on the movable contact 3 when the latter is in the closed position.

Then when the contacts 2, 3 separate the arc between them initially produces a pressure rise within the compartment X on the fixed contact side of the piston 27, the pressurised gas acting on the piston 27 as well as directly on the movable contact 3, which accelerates the piston away from the fixed contact 2 as well as assisting in accelerating the movable contact 3 towards the open position.

The degree of acceleration will depend upon the rate at which the gas pressure rises, which in turn will depend upon the current being interrupted, but in view of its larger mass the piston 27 will be accelerated at a slower rate than the contact 3. At some stage therefore the contact making portion of the movable contact 3 will be withdrawn from the piston; the pressure within the compartment Y continuing to increase due to presence of the arc and the movement of the piston, so as to produce an arc suppressing flow of gas through the movable contact 3 when the ports 14 leave the chamber 4. A spring as at 30 can be provided to assist the movement of the piston 27. The piston 27 may also be provided with one or more non-return valves as at 29 similar to the valve 19 in the partition 17. On closing movement of the contacts the shoulders 31 on the movable contact will urge the piston 27 towards its initial position.

In the embodiments described sleeves or plates or other elements of a material capable of absorbing gas and of releasing it rapidly on heating may be located within one or both of the compartments X and Y so as to lie in the vicinity of any arc which is formed when the contacts are opened, the arc resulting in the release of gas which increases the pressure generated in one or both of the compartments.

Instead of the ports 14 connecting the interior of the movable contact 3 to the main enclosure space when the contacts are opened, they can alternatively be arranged to connect the interior of the contact to a region of reduced pressure, produced for example by a piston carried by the movable contact.

WHAT WE CLAIM IS: 1. An electric circuit breaker of the kind referred to incorporating within said enclosure, an arcing chamber accommodating at least the contact making portion of said co-operating contact, the chamber being mainly closed apart from an opening through which the movable contact is arranged to extend, such that arcing between the contacts as they are opened results in an increase in the pressure of the gas within the chamber, at least during the initial opening movement, the pressurised gas acting on the movable contact and assisting in the acceleration of the latter towards the open position, and wherein the movable contact is provided in its wall with

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

Claims

**WARNING** start of CLMS field may overlap end of DESC **. compartment Y during the opening of the contacts. The circuit breaker illustrated in Figure 8 also has a plurality of metal fingers 23 projecting from the disc 8, around the fixed contact 2, the length of these being selected to control the length of the arc formed in the compartment X during the opening of the contacts. The fingers may be in some cases replaced by a solid metal sleeve, if desired. Whilst in the embodiments so tar described the movable contact 3 co operates with a stationary contact 2, the latter may be arranged to move away from the movable contact under the pressure produced in the compartment X on the initial opening movement of the contacts, and a circuit breaker incorporating this feature is illustrated in Figure 9. In this circuit breaker the "fixed" contact 2.1 is slidably supported within a cylindrical sleeve 24 projecting from the surface of the disc 8 towards the supporting plate 9. The contact is biased inwards by means of a spring 25, a stop such as a radially extending flange 26 at the outer end of the contact, defining the normal rest position of the contact. Then when the contacts are opened the increase in pressure within the compartment X forces the contact 2.1 away from the movable contact 3 compressing the spring 25 which returns the contact 2.1 to the rest position when the pressure within the compartment X subsequently falls. The circuit breaker illustrated in Figure 10 is a modification of that shown in Figure 6. In this embodiment the compartment X opens into a further compartment Z through an opening 32 in the disc 8 within the fixed contact 2. At least one non-return valve 19.3 in the partition 17 is arranged to open a valve 19.4 in the outer wall of the compartment Z when the pressure in the compartment Y exceeds that in the compartment X, thereby connecting the compartment Z to a lower pressure region within the main enclosure. An arc suppressing flow of gas will then take place through the fixed contact 2 as well as the movable contact 3 as indicated by the arrows. A further embodiment of the invention is illustrated in Figure 11. In this embodiment the partition 17 is replaced by a piston 27. The piston has a central opening 28 through which the contact making end of the movable contact 3 projects, the contact and the piston being axially movable relative to each other. The piston 27 normally rests against shoulder 31 on the movable contact 3 when the latter is in the closed position. Then when the contacts 2, 3 separate the arc between them initially produces a pressure rise within the compartment X on the fixed contact side of the piston 27, the pressurised gas acting on the piston 27 as well as directly on the movable contact 3, which accelerates the piston away from the fixed contact 2 as well as assisting in accelerating the movable contact 3 towards the open position. The degree of acceleration will depend upon the rate at which the gas pressure rises, which in turn will depend upon the current being interrupted, but in view of its larger mass the piston 27 will be accelerated at a slower rate than the contact 3. At some stage therefore the contact making portion of the movable contact 3 will be withdrawn from the piston; the pressure within the compartment Y continuing to increase due to presence of the arc and the movement of the piston, so as to produce an arc suppressing flow of gas through the movable contact 3 when the ports 14 leave the chamber 4. A spring as at 30 can be provided to assist the movement of the piston 27. The piston 27 may also be provided with one or more non-return valves as at 29 similar to the valve 19 in the partition 17. On closing movement of the contacts the shoulders 31 on the movable contact will urge the piston 27 towards its initial position. In the embodiments described sleeves or plates or other elements of a material capable of absorbing gas and of releasing it rapidly on heating may be located within one or both of the compartments X and Y so as to lie in the vicinity of any arc which is formed when the contacts are opened, the arc resulting in the release of gas which increases the pressure generated in one or both of the compartments. Instead of the ports 14 connecting the interior of the movable contact 3 to the main enclosure space when the contacts are opened, they can alternatively be arranged to connect the interior of the contact to a region of reduced pressure, produced for example by a piston carried by the movable contact. WHAT WE CLAIM IS:

1. An electric circuit breaker of the kind referred to incorporating within said enclosure, an arcing chamber accommodating at least the contact making portion of said co-operating contact, the chamber being mainly closed apart from an opening through which the movable contact is arranged to extend, such that arcing between the contacts as they are opened results in an increase in the pressure of the gas within the chamber, at least during the initial opening movement, the pressurised gas acting on the movable contact and assisting in the acceleration of the latter towards the open position, and wherein the movable contact is provided in its wall with

one or more ports for connecting the interior of the movable contact; after it has been withdrawn from said co-operating contact through a predetermined distance, to a lower pressure region outside of said chamber so as to cause gas to flow rapidly from the chamber through the tubular contact for the suppression of arcing.

2. An electric circuit breaker according to Claim 1 wherein the said port or ports lie within the chamber when the contacts are closed, but emerge from the chamber to connect the interior of the contact to the main enclosure space outside the chamber, after the movable contact has been withdrawn from the co-operating contact through a predetermined distance.

3. An electric circuit breaker according to any one of Claims I or 2 wherein the cooperating contact is so arranged that the pressure rise within the chamber produces a flow of arc suppressing gas through that contact as well as through the movable contact when the contacts separate.

4. An electric circuit breaker according to any one of Claims 1 to 3 wherein the cooperating contact is supported so as to be moved away from the movable contact under the pressure developed within the said chamber, due to arcing between the contacts, as the contacts separate.

5. An electric circuit breaker according to Claim 4 wherein the said co-operating contact is supported within a sleeve, within which it can move axially and is biassed towards the movable contact by a spring, and the pressure developed within the said chamber as the contacts separate forces the co-operating contact away from the movable contact against the biassing action of the spring.

6. An electric circuit breaker according to any preceding Claim wherein the chamber incorporates a pressure relief valve to limit the pressure rise within the chamber when the contacts open to interrupt a very high fault current.

7. An electric circuit breaker according to any preceding Claim wherein the chamber incorporates a transverse partition which divides the chamber into a first compartment in which the movable contact engages the co-operating contact, and a second compartment into or through which the contact making portion of the movable contact is withdrawn as the contact moves from the closed to the open position.

8. An electric circuit breaker according to Claim 7 wherein the partition carries at least one non-return valve allowing the passage of gas from the first to the second compartment, but not in the reverse direction.

9. An electric circuit breaker according to Claim 7 or 8 wherein the chamber is of cylindrical shape coaxial with the contacts and the partition comprises a piston which is movable within the chamber independently of the movable contact, the latter being arranged to extend through an opening in the piston to engage the co-operating contact in the said first compartment formed on one side of the piston, the arrangement being such that as the contacts initially separate and produce an arc between them the pressure rise within the first compartment will act on the piston, and cause it to move away from the co-operating contact thereby tending to compress the gas in the second compartment on the opposite side of the piston.

10. An electric circuit breaker according to Claims 6 to 9 wherein the co-operating contact is hollow, the end remote from the movable contact opens into a further compartment, and the pressure rise produced within the said second compartment when the contacts separate acts on a valve which opens the further compartment to a region of relatively lower pressure, thereby causing gas to flow from the first compartment to said further compartment through the co-operating contact.

11. An electric circuit breaker according to any preceding claim wherein the chamber incoporates a material capable of absorbing gas and of releasing it rapidly on heating, which material is located so as to lie in the vicinity of any arc which is formed when the contacts are separated.

12. An electric circuit breaker according to Claim 1 incoporating means for generating a region having a lower pressure than the main enclosure space after the movable contact has been withdrawn from said cooperating contact through a predetermined distance.

13. An electric circuit breaker according to Claim 12 wherein the movable contact carries a piston slidable within a cooperating cylinder, and the movement of the piston within the cylinder as the contacts separate produces said region of lower pressure.

14. An electric circuit breaker according to any preceding Claim wherein the gas within the circuit breaker enclosure is SF.

15. An electric circuit breaker according to any preceding claim wherein the gas within the circuit breaker enclosure is at or above atmosphere pressure.

16. An electric circuit breaker substantially as shown in and as hereinbefore described with reference to Figures 1 and 2 or Figures 3 and 4, or any one of Figures 5 to 11 of the accompanying drawings.