US3555223A

US3555223A - Vacuum circuit interrupters with co-axial movable main and movable auxillary contacts

Info

Publication number: US3555223A
Application number: US780621A
Authority: US
Inventors: Alfred Alexander Robinson; James William Calvesbert
Original assignee: English Electric Co Ltd
Current assignee: English Electric Co Ltd
Priority date: 1968-01-03
Filing date: 1968-12-03
Publication date: 1971-01-12
Anticipated expiration: 1988-01-12

Abstract

The load current carrying contacts of a vacuum circuit interrupter are surrounded by a normally open pair of annular contacts which are closed before, and opened after, the load current carrying contacts are opened, so that arcing between the load current carrying contacts is negligible; substantially all the arcing occurring between the annular contacts. Each annular contact may incorporate a helical conductor, the two helical conductors being wound magnetically in opposition, with the advantage that a magnetic field, which causes spreading and rotation of the arc, is established before the arc is struck.

Description

United States Patent AXIAL MOVABLE MAIN AND MOVABLE AUXILIARY CONTACTS 7 Claims, 2 Drawing Figs.

US. Cl 200/144, 200/146 Int. Cl HOlh 33/66 Field of Search 200/ 1 44.2;

ZOO/146, 153.20, 148(Cursory) [56] References Cited UNITED STATES PATENTS 3,017,480 1/1962 Klaassen 200/146 3,218,421 11/1965 Latour 200/148 3,261,954 7/1966 Yonkers ZOO/144(2) FORElGN PATENTS 1,506,165 11/1967 France ZOO/144(2) Primary ExaminerRobert K. Schaefer Assistant Examiner- Robert A. Vanderhye AttorneyStevens, Davis, Miller & Mosher ABSTRACT: The load current carrying contacts of a vacuum circuit interrupter are surrounded by a normally open pair of annular contacts which are closed before, and opened after, the load current carrying contacts are opened, so that arcing between the load current carrying contacts is negligible; sub stantially all the arcing occurring between the annular contacts. Each annular contact may incorporate a helical conductor, the two helical conductors being wound magnetically in opposition, with the advantage that a magnetic field, which causes spreading and rotation of the arc, is established before the arc is struck.

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25 22 i i u 24 /771 k fii l\ W PATENT-EU Mf l9?! SHEET 2 OF 2 ,R E W 88 TWW M L V A W w we R W. M A Am ATTORNEYS VACUUM CIRCUIT INT ERRUPTERS WITH (IO-AXIAL MOVABLE MAIN AND MOVABLE AUXILIARY CONTACTS This invention relates to vacuum circuit interrupters.

A vacuum circuit interrupter which is arranged so that an arc struck between a pair of relatively movable cooperating contacts is transferred to between a spaced-apart pair of fixed annular arcing electrodes, has the disadvantage that the arc causes a considerable amount of erosion of the contact surfaces of the pair of contacts before it is transferred to the arcing electrodes. Erosion of the contact surfaces of the pair of contacts limits the life of the vacuum circuit interrupter and is detrimental to the current carrying capacity of the vacuum circuit interrupter.

According to this invention a vacuum circuit interrupter comprises an evacuated envelope containing one pair of cooperating contacts in parallel with another pair of cooperating contacts, at least one contact of each pair being capable of movement relative to its cooperating contact, and a contact actuating arrangement which, for normal operation, is operative to close said one pair of contacts and to maintain those contacts engaged and the other pair of contacts open so that the normal load current is carried by said one pair, and, for a circuit interrupting operation, is operative to close and subsequently reopen said other pair of contacts and to open said one pair of contacts whilst said other pair is closed so-that substantially all the arcing occurs between said other pair of contacts.

Said one pair of contacts may, for example, be similar to the central contact members described in copending Ser. No. (617,199 of Alfred Alexander Robinson and James William Calvesbert, filed Jan. 4, 1967, now U.S. Pat. No. 3,412,688

, and said other pair of contacts may be similar to the tubular fixed arcing electrodes described in Ser. No. 617,199 of Alfrcd Alexander Robinson and James William Calvesbert, filed Ian. 4, 1967, with the exception that the contacts of said second pair of contacts of this invention are relatively movable into or out of engagement with each other whereas the tubnlnr fixed arcing electrodes of Ser. No. 617,199 of Alfred Alexander Robinson and James William Calvesbert, filed Jan. 4, 1967, are fixed and spaced apart.

This invention enables the normal load current carrying contacts of a vacuum circuit interrupter to be separated during a circuit interrupting operation with a negligible amount of arcing occurring between them.

One embodiment of this invention will now be described by way of example with reference to the accompanying drawings, of which:

FIG. 1 is a sectional view of a circuit interrupter in ac cordance with this invention, taken on the line H of FIG. 2;

and

FIG. 2 is a view on the line "-11 of FIG. 1.

Referring to thedrawings, there is illustrated a vacuum circuit interrupter for use at currents of over lkA r.rn.s. The vacuum circuit interrupter has one pair of cooperating con tacts l0 and 11 and another pair of

cooperating contacts

12, 13. The

contacts

12, 13 areannular and coaxially surround the

contacts

10, 11. The contacts to 13 are contained within an envelope having a tubular casing 14 of insulating material joined to a pair of

end plates

15, 16. The envelope is constructed to withstand a high vacuum.

The

contacts

10 and 11 and their associated components are similar and for the sake of convenience only the first con tact I0 and its associated components will now be described in detail.

The contact 10 comprises a contact member 17 mounted on the end of a rod 18. The contact surface of the contact member 17 comprises a contact annulus 19 which surrounds a central depression 20. The contact annulus 19 is made of a material such that welds between the

contacts

10 and 11 are easily broken on separation of the contacts, and such that the eiectron emission at high temperatures is low.

The end plate 15 carries a bearing housing 21 which is aligned axially of the tubular casing 14. The bearing housing 21 has an annular flange member 22 which is secured to the end plate 15. The annular flange member 22 carries an outer bush 23 which extends towards the interior of the envelope. The outer bush 23 carries an outer sleeve bearing 24 on its radially inner surface. An inner bush 25 extends on both sides of the end plate 15, protrudes axially beyond both ends of the outer bush 23 and carries an inner sleeve bearing 26 on its radially inner wall. The inner bush 25 is slidably supported within the outer sleeve bearing 24. The

sleeve bearings

24 and 26 are constructed of polytetrafluorethylene (known as P.T.F.E.).

The rod 18 passes through and slides within the inner sleeve bearing 26.

Annular plate 27 is mounted on the end of the inner bush 25 adjacent the contact 11. The inner wall of the annular plate 27 is spaced from the rod 18. The annular plate 27 is connected to the annular flange member 22 by a flexible bellows 28, whereby the vacuum may be maintained whilst allowing movement of the annular plate 27 relative to the end plate 15. The rod 18 carries a flange 29 between the contact member 17 and the annular plate 27. A further flexible bellows 30 is connected between the flange 29 and the annular plate 27, whereby the vacuum may be maintained whilst allowing movement of the flange 29 relative to the annular plate 27 and/or the end plate 15.

The rod 18 carries a terminal plate 31 outside the evacuated enclosure and beyond the end of the inner bush 25 remote from the annular plate 27. The terminal plate 31 conveniently provides a terminal whereby the contact 10 may be connected in an electrical circuit. The end of the inner bush 25 adjacent the terminal plate 31 is spigotted into an annular conducting plate 32'which is electrically connected to the terminal plate 31 by three flexible conductors 33 (see FIG. 2).

The

contacts

12 and 13 are similar to each other and for the sake of convenience only the contact 12 which coaxially surrounds the contact 10, will be described in detail.

The contact 12 is mounted on the annular plate 27 so as to surround the flexible bellows 30. The contact 12 has an annular contact member 34 mounted on one end of a stainless steel structural tube 35. The other end of the tube 35 is secured to the annular plate 27. A cylindrical sleeve 36 surrounds and is spaced from the structural tube 35. One end of the sleeve 36 engages with the annular contact member 34, and the other end engages with the annular plate 27.

Three transverse slots 37 are formed in the end of the cylindrical sleeve 36 adjacent the annular contact member 34. The slots 37 extend circumferentially of the cylindrical sleeve 36 at right angles to the axis of the rod 18 so as to extend around a major part of the circumference of the cylindrical sleeve 36 and leave a small amount of the material of the cylindrical sleeve 36 between their circumferentially spaced ends. Oblique intermediate slots (not shown), which all lie on one side of the cylindrical sleeve 36 and thus are not visible in FIG. 11, are formed in the small amount of material of the cylindrical sleeve 36 between the circumferentially spaced ends of the transverse slots 37. The oblique intermediate slots interconnect opposed ends of adjacent transverse slots 37 so as to form the end portion of the cylindrical sleeve 36 adjacent the annu- Ear contact member 34 as a substantially helical conducting coil with stepped turns, the steps being defined by the oblique slots which form oblique step portions. The oblique step portions interconnect adjacent nearly complete ring portions defined by the transverse slots 37. The end of the cylindrical sleeve 36 immediately adjacent the annular contact member 34 remains as a continuous annulus.

The construction of the contact 12 as described above is similar to the construction of the tubular fixed arcing electrodes shown in FIGS. 4 and 5 of copending Ser. No. 617,199 of Alfred Alexander Robinson and James William Calvesbert, tiled Jan. 4, 1967. The contact 12 is connected electrically with the terminal plate 31 by the first contact 10, through the annular plate 27, the inner bush 25, the annular conducting plate 32 and the flexible conductors 33, and, since in atypical example the bellows 30 is constructed of 0.006 inches thick stainless steel, it will be understood that the contacts and 12 are connected electrically in parallel through the terminal plate 31 rather than through the much higher electricalimpedance path afforded by the bellows 30.

It should be understood that there is one important difference between the construction of the contact 12 and that of the contact 13. The oblique intermediate slots of the two

contacts

12, 13 diverge from each other so that the stepped turns of the substantially helical conducting coils are oppositely wound.

Shields may also be provided within the envelope to protect the envelope against the efiect of arcs drawn during a circuit interrupting operation. Such shields are well known in the art.

The end of the rod 18 of the contact 10 bears against a fixed backplate 38 when the contact 10 is in the closed position. The end of the rod 18 of the contact 11 is connected to a suitable actuator of which only part of the outer casing 39 is shown. Three compression springs 40 bear between the terminal plate 31 of the contact 10 and the backplate 38. Three compression springs 41 bear between the annular conducting plate 32 adjacent the end plate and the backplate 38. Three compression springs 42 bear between the annular conducting plate 32 adjacent the end plate 16 and the actuator casing 39.

The terminal plate 31 are each provided with three recesses 43 so that the terminal plates 31 do not foul the

respective springs

41, 42. Only one of the compression springs 42 is shown in the drawings, but the position of the other two will be understood by reference to FIG. 2.

the

contacts

12 and 13"engage and movement of the contact I 12 is stopped (after dampedosc ation )-be.cause the pressure applied by the springs 4210 'th r tactl3is greater than the pressure applied by the springs 41 to the contact 12. At this point current begins toflow through the

contacts

12 and 13 as well as continuing toflow through thecontacts l0 and ill which continue moving together"; I't'will be appre ciated that the flow of current throughthe substantially helical conducting coils formed inthe. cylindrical 36 of the contacts l2 and l3 induces a radial magneticti'e ld -iri the region of the annular contact members 34. Theconta continues to move in engagement with the contact ll 'u r he headof the bolt 47 abuts the adjustable stop 45, whereby further movement of the contact lll is prevented and the

contacts

10 and 11 part. At this point all the current flowing through the circuit interrupter is compelled to flow through

thecontacts

12 and 13 which are stationary. It will be appreciated thatthe contacts influence of the springs 41 so thatthe

contacts

12, 13 remain engaged with a suitable contact pressure between them. The contact 12 moves with the, contact. 13 untilits annular conducting plate 32 abuts the heads of the bolts 47 carried by the terminal plate 31 of the contact 10. At this point further movement of the contact,12 is prevented, the contact 13 contiriues to move withthe contact 11 and the

contacts

12 and 13 part, an are being struck between the annular contact members 34. The arc is compelled to spread and rotate around the Three bolts 47 are bolted to each terminal plate 31. The I bolts 41 pass through holes 48 formed in the adjacent annular conducting plate 32 with their heads lying on the side of the adjacent annular conducting plate 32 remote from the respective terminal plate 31. The diameter of the holes 48 is less than the diameter of the heads of the bolts 47.

The head of one of the bolts 47 bolted to the terminal plate 31 of the contact 10 is adapted to contact the adjustable stop when the contact 10 reaches its contact open position.

The heads of the bolts 47 bolted to the terminal plate 31 of the contact 11 are adapted to abut the support plate 44 when the contact 11 is in its closed position.

The adjustable stop 46 is adapted to abut the adjacent annular conducting plate 32 and thus maintain the required separation between the

second contacts

12, 13 during normal operation when the

first contacts

10, 11 are closed. g

In operation of the vacuum circuit interrupter; considering first the position shown in FIG. 1 in which the contacts 10 and ated to move the contact 11 away from the end plate 15,

whereupon the following sequence of movement of the movable parts of the vacuum circuit interrupter occurs. The

contacts

10 and 12 move with the contactll under the influence of the

springs

40 and 41, the springs 4ll maintaining the

contacts

10 and 11 engaged with an adequate contact pressure between them so that they continue to carry the current. This movement continues until the annular contact members 34 of contact surface ofthe annular contact members 34 by the already established radial magnetic field in the region of the annular contact members 34 until the arc is extinguished at the occurrence of the next current zero. The contact 11 and the contact 13 finally come to rest when the actuator reaches the end of its travel in the contact opening direction.

in order to close the contacts of the vacuum circuit interrupter the actuator is actuated to move the contact 11 towards the endplate 15. Because of thepressure applied to its annular conducting plate 32 by. the springs 42, the contact 13 moves with the contact 111 until its annular contact member34 engages with the annular member 34 ofthe contact 12. At this stage current may. flow through the vacuum circuit interrupter via the

contacts

12 and 13. Because the pressure exerted by springs 42 is greater than the pressure exerted by the springs 41, the contact 13 continues to move towards the end plate 15 with the contact ill, and thus forces the contact 12 towards the end plate 15, until the annular conducting plate 32 of the contact l3 abuts the adjustable stop 46. At this stage the contacts l2 and 13 remain stationary and. engaged whilst the contact lll'continues moving towards the end plate 15. After a predetermined period of time thecontact 11 abuts the contact 10 whereupon current may flow through the vacuum circuit interrupter via the parallel paths provided by the contacts 10 and lland' the

contacts

12 and 13. The contacts 10 and ll then move together towards. the backplate '38. After a predetermined period of time the heads of the bolts 47 carried by the terminal plate 31 of the contactltl engage with the annular conducting plate 32 of the contact 12 soth'at the contact 12 moves with the contacts 10 and lland the contacts 12 and l? separated. The contacts 10 and ll and thecontacts 12 move together until the position illustrated in FIG. 1 is reached, where the heads of the bolts 47 carried by the terminal plate 31 of the contact ll abut the support plate 44, the end of-the rod R8 of the contact lil'abuts the backplate 3b, and the actuator has reached the end of its travel in the con- .tact closing direction. It'will beappreciated that the final movement of the contacts ill-and l2 compresses the springs 40 so that an adequate contact pressure is applied between the

contacts

10 and 11. Furthermore it will be appreciated that the

contacts

12 and 13 do not part until after contact between the

contacts

10 and 11 has been firmly established.

Various modifications and refinements of the vacuum circuit interrupter hereinbefore described are possible within the scope of this invention For example, the construction of the

contacts

12, 13 may be simplified, the arrangement of the substantially helical conducting coils and the structural tube being replaced by a simple annular contact member, if the vacuum circuit interrupter is only intended for use at currents below 10 kA r.m.s. Furthermore the number of transverse slots 37 may be varied, thus altering the number of turns of the substantially helical conducting coils to suit the designed current rating of the vacuum circuit interrupter. The two

flexible bellows

28 and 30 of the contact 10 and the contact 12 may be replaced by a single bellows assembly providing that the contact l and the contact 12 are connected together and the contact surface of the contact annulus 19 of the contact 10 is nearer the end plate 16 then the contact surface of the annular contact member 34 of the contact 12. This single flexible bellows arrangement may have the disadvantage that the bounce which might occur between the

contacts

12 and 13 may be transmitted to the

contacts

10 and 11 and result in premature arcing.

The construction of the

contacts

10 and 11 as described above is similar to the construction of the central contact members described in copending Ser. No. 617,199 of Alfred Alexander Robinson and James William Calvesbert, filed Jan. 4, 1967. However, the annular contact members 17 of the

first contacts

10 and 11 may be replaced by simple butt contact members.

We claim:

1. In a vacuum circuit interrupter comprising an evacuated envelope containing one pair of cooperating contacts and another pair of cooperating contacts electrically in parallel with said one pair, at least one contact of each pair being capable of movement relative to its cooperating contact; and contact actuating means for moving the movable contact of each pair into and out of engagement with its cooperating contact, said contact actuating means being operative to separate the contacts of said one pair before separating the contacts of the other pair; the improvement comprises said contact actuating means including:

i. stop means which, when said one pair of contacts are engaged for normal operation, cooperates with one of the contacts of the other pair to hold said other pair of contacts apart so that the normal load current is carried sole ly by said one pair of contacts;

ii. biasing means acting on said one of said other pair of contacts so as to bias it towards the other of said other pair of contacts; and

iii. means operative during the early stages of a circuit interrupting operation for moving said stop means so as to permit engagement of said other pair of contacts under the influence of said biasing means before said one pair of contacts are separated.

2. In a vacuum circuit interrupter according to claim 1, wherein the improvement further comprises the contacts of said other pair being annular and coaxially surrounding said one pair of contacts.

3. In a vacuum circuit interrupter according to claim 2, wherein the improvement further comprises each of the annular contacts of said other pair including a substantially helical conductor, the helical conductor of one of the annular contacts being wound in the opposite direction to the helical conductor of the other annular contact so that a radial magnetic field is established in the region of the contact surfaces of the annular contacts when current is carried by said other pair of contacts.

4. In a vacuum circuit interrupter according to claim 1 wherein the improvement further comprises both the contacts of each pair being movable.

5. In a vacuum circuit interrupter according to claim 4,

wherein the improvement further comprises the contacts of said one pair being each capable of movement relative to each of the contacts of said other pair and vice versa.

6. In a vacuum circuit interrupter according to claim 4,

wherein the improvement further comprises:

i. a terminal plate carried by one of said one pair of contacts outside said evac'uatedenvelope;

ii. a conducting plate which is mechanically and electrically coupled to the adjacent contact of said other pair and is located outside said evacuated envelope;

iii. a flexible conductor connected between said terminal plate and said conducting plate; and

iv. further biasing means and stop means which, in combination with said first mentioned biasing means and stop means control movement of said terminal plate and said conducting plate relative to one another and to said evacuated envelope in the direction of movement of the contacts so as to similarly control movement of the respective contacts.

7. In a vacuum circuit interrupter according to claim 1,

wherein the improvement further comprises the contacts of said one pair being butt contacts.

Claims

1. In a vacuum circuit interrupter comprising an evacuated envelope containing one pair of cooperating contacts and another pair of cooperating contacts electrically in parallel with said one pair, at least one contact of each pair being capable of movement relative to its cooperating contact; and contact actuating means for moving the movable contact of each pair into and out of engagement with its cooperating contact, said contact actuating means being operative to separate the contacts of said one pair before separating the contacts of the other pair; the improvement comprises said contact actuating means including: i. stop means which, when said one pair of contacts are engaged for normal operation, cooperates with one of the contacts of the other pair to hold said other pair of contacts apart so that the normal load current is carried solely by said one pair of contacts; ii. biasing means acting on said one of said other pair of contacts so as to bias it towards the other of said other pair of contacts; and iii. means operative during the early stages of a circuit interrupting operation for moving said stop means so as to permit engagement of said other pair of contacts under the influence of said biasing means before said one pair of contacts are separated.

4. In a vacuum circuit interrupter according to claim 1, wherein the improvement further comprises both the contacts of each pair being movable.

5. In a vacuum circuit interrupter according to claim 4, wherein the improvement further comprises the contacts of said one pair being each capable of movement relative to each of the contacts of said other pair and vice versa.

6. In a vacuum circuit interrupter according to claim 4, wherein the improvement further comprises: i. a terminal plate carried by one of said one pair of contacts outside said evacuated envelope; ii. a conducting plate which is mechanically and electrically coupled to the adjacent contact of said other pair and is located outside said evacuated envelope; iii. a flexible conductor connected between said terminal plate and said conducting plate; and iv. further biasing means and stop means which, in combination with said first mentioned biasing means and stop means control movement of said terminal plate and said conducting plate relative to one another and to said evacuated envelope in the direction of movement of the contacts so as to similarly control movement of the respective contacts.

7. In a vacuum circuit interrupter according to claim 1, wherein the improvement further comprises the contacts of said one pair being butt contacts.