US3705144A

US3705144A - Vacuum interrupter or switch for electric power networks

Info

Publication number: US3705144A
Application number: US208209A
Authority: US
Inventors: Pierre Genequand
Original assignee: Battelle Memorial Institute Inc
Current assignee: Battelle Memorial Institute Inc
Priority date: 1970-12-24
Filing date: 1971-12-15
Publication date: 1972-12-05
Anticipated expiration: 1989-12-05
Also published as: GB1382817A; FR2120815A5; DE2163900A1

Abstract

A single-pole interupter, for a ower network, having a plurality of contact elements arranged to form in the open position a series of spaced interrupting gaps, each contact element being provided with screenin means for shielding these interrupting gaps from each other. Means are provided for preventing the sidcharge that occurs upon opening the interrupter from restarting once the current has passed through zero during the first change in alternation after the interrupter is opened.

Description

VACUUM INTERRUPTER OR SWITCH FOR ELECTRICPOWER NETWORKS 7 Sheets-Sheet Filed Dee. 15 1971 2 L?. A inv h il.

V fs..

Dec. 5, 1972 P, GEM-:QUAND 3,705,144

VACUUM INTERRUPTER 0R SWITCH Fon Emzcfrmc POWER NETWORKS Filed Dec. l15, 1971 7 Sheets-Sheet 3 Dec. 5, 1972 P. GENEQUAND 3,705,144

VACUUM INTERRUPTER OR SWITCH FOR ELECTRIC POWER NETWORKS Filed Deo. l5, 1971 '7 Sheets-Sheet L1 FIG. l2

De 5 1972 P. GENEQUAND l 3,705,144

VACUUM INTERRUPTER- OR SWITCH FOR ELECTRIC POWER NETWORKS Filed Dec. 15, 1971 I 7 sheets-sheet V5 w22 'l H3 F/Gf /4 i Y. 97A FIG /5 ZL/f De@ 5, 1972 P. GENEQUAND VACUUM INTERRUPTER OR SWITCH FOR ELECTRIC POWER NETWORKS Filed Dec. l5, 1971 7 Sheets-Sheet` 6 Dec' 5 1972 P. GENEQUAND 3,705,144

VACUUM INTERRUPTER OR SWITCH FOR ELECTRIC POWER NETWORKS Filed Deo. l5, 1971 '7 Sheets-Sheet 7 FIG. v I9 United States Patent() 3,705,144 VACUUM 'INTERRUPIER OR SWITCH FOR ELECTRIC POWER NETWORKS Pierre Genequand, Geneva, Switzerland, assignor to Battelle Memorial Institute, Carouge/ Geneva, Switzerland Filed Dec. 15, 1971, Ser. No. 208,209 Claims priority, application Switzerland, Dec. 24, 1970, 19,029/70; Nov. 22, 1971, 16,945/71 Int. Cl. H01h 33/ 66 U.S. Cl. 200-144 B 22 Claims ABSTRACT F THE DISCLOSURE The invention relates to a vacuum single-pole interrupter or switch for alternating electric current, having a plurality of contact elements operating in series, said contact elements belonging to first and second contact armatures capable of moving in relation to each other along an axis of displacement, the contact elements of one armature cooperating with those of the other armature so as together to form a chain of contact elements constituting, when the interrupter is closed, a conduction path alternately passing through the contact elements of said two armatures and forming, when the interrupter is open, a series of interrupting gaps alternately deined by said contact elements, the two end elements of this chain being electrically connected to the one and the other, respectively of two terminals for connection of this interrupter to an electrical network.

The problem of breaking a high voltage alternating current circuit has long existed, particularly in grid systems. The problem consists in imparting to the medium in which the contact elements operate and in which ilashes the discharge resulting from a break, the ability to recover very quickly, after the current has dropped to zero, suflicient dielectric strength to enable a potential difference of some 100 kv. to be set up across the contact elements without causing the discharge to be restarted. In other words, it is the phenomenon of the dielectric restoration of the medium in which the discharge flashes that constitutes one of the key elements of the problem.

Besides the solutions which consist in using a fluid under pressure (compressed air, oil, sulphur hexaiiuoride) for the medium and in which dielectric restoration is dependent on the deionization mechanism, several solutions have been put forward in which the contact elements are required to operate in a vacuum. The devices embodying these solutions are known as vacuum interrupters or switches. In interrupters of this type, dielectric restoration is dependent on the charge carriers and on the vapour issuing from the hot points of the cathode known as cathodic spots condensing on the walls adjacent the location where the discharge took place and in particular on the contact elements per se. Since such condensation is all the faster when the surfaces on which it takes place are more closely set together, vacuum interrupters are characterized by a small gap between the contact elements, of the order of 1 cm. This provides substantial advantages as regards the control mechanism since the 'ice latter is only required to move the contact elements over short distances. The forces of inertia to be overcome are thus small so that the vacuum interrupter can be made to operate with little noise.

With arcs in a vacuum, there exist two llow conditions for the current discharge, i.e. the diffuse arc flow conditions and the single column flow conditions.

Under diluse arc ilow conditions, which obtain with small currents (intensities of less than 2 ka.), the current is conveyed by several parallel conical columns, termed Reece cones, Whose apexes are located on the cathode and form the cathodic spots mentioned earlier. These cathodic spots move by sweeping across the cathode, somewhat like gas molecules, at speeds of some 10 to m./s., and the corresponding Reece cones, which have a very short life, something of the order of 1 microsecond to 1 millisecond, keep going through subdivision. They each convey a current of not more than 30 to 100 a. Under these diffuse arc flow conditions, the cathode is subjected to little erosion, not exceeding 50 to 100 rtg/as.

Under single column ow conditions, the current is conveyed by a single column resulting from a regrouping of the Reece cones. This single column, which carries all of the current, has little mobility and as a result causes destructive fusion of the contact elements. The molten regions give rise to much evaporation of the metal, so that the discharge comes to behave like a high pressure arc. Dielectric restoration is then adversely affected and the discharge starts up again after the current has dropped to zero. To increase cooling to prevent fusion and hence to limit evaporation does not solve the problem. The reason for this is that the heat conductivity of the metal from which the contact elements are made is such as not to enable the heat generated at the point of impact of the discharge to be removed sufficiently quickly. Since this point has very little mobility a considerable amount of power comes to be concentrated there. Attempts have been made to compel the point of impact to move, as by subjecting the discharge to a magnetic iield. There are for instance solutions in which the contact elements are divided up into curvilinear petals" by helicoidal slots. The current is then compelled to follow within the contact elements a spiral path and to generate as a result a magnetic field capable of moving the arc by electromagnetic interaction. Solutions of this kind are for instance described in U.S. Pats. Nos. 3,210,505, 3,185,799, 3,185,- 798, 3,185,797, 3,089,936 and 2,949,520 and in French Pat. No. 1,410,884. However, because of the resulting complex shape of the electrodes, these solutions are not sufficient to prevent the appearance of single column ow conditions when the current increases.

It has been shown by C. W. Kimblin (I. Appl. Phys. 40 (1969), p. 1744) that the appearance of single column ow conditions is linked with a substantial increase in the anodic voltage drop, which can reach 100 v. or more, and that this effect becomes all the more marked when the columns of the diffuse arc are longer, such lengthening being equally well due to the spacing between the contact elements and to the edge eiect of the latter, i.e. the propensity of the discharge impact points to escape towards the edges of the contact elements.

Further, any interrupter, when open, must be able to withstand disruption, i.e. to bear a high potential difference without any discharge flashing across its contact elements. This is particular means that the medium between the contact elements must have high dielectric strength and that the state of the surface of these elements must be excellent. However, the best possible surface conditions are very rapidly affected by the erosive action of the discharges occurring when interrupter is being opened. As for the dielectric strength of the medium, it is dependent on the pressure prevailing therein. This pressure must remain such that the mean free path of a charged particle be suiciently long to prevent this particle from being accelerated to the point of generating an avalanche process (Paschen discharge). This means that it is not enough simply to create once and for all a high vacuum in the space lying between the contact elements. It is also necessary to prevent the latter later from giving rise to too much degassing. Use is therefore made in making the contact elements of ultra pure metals, in particular of metals which have been purified by zonal fusion. The last resort for increasing voltage resistance consists in increasing the distance between the electrodes. Now, breakdown voltage increases linearly with distance only over distances of less than about 10 mm. Over greater distances, the disruption voltage increases proportionately with the square root of the distance, i.e. more slowly. When the voltage to be withstood exceeds several tens of kilovolts, the interelectrode distance becomes large and this, lirstly, runs counter to maintaining diffuse arc flow conditions when the contact elements are being opened and, secondly, makes it necessary to provide a powerful and noisy actuating mechanism (to move the contact elements over a large distance in a very short time). As a result, it has been proposed to divide the space between the contact elements into several partial spaces by arranging a chain of pairs of contact elements wherein the pairs are mounted in series relationship one after the other, each pair having at least one movable contact elements. Such arrangements are in particular described in U.S. Patents Nos. 3,185,797, 3,185,798 and 2,976,382, and-in an article by H. C. Ross entitled Vacuum Switch Properties of Power Switching Applications published in Trans. AIEE 77 (1958) p. 104-117.

Vacuum switch or interrupter designers thus have to contend with two contradictory requirements, i.e. a short distance between the electrodes to prevent the discharge from being restarted after the current has dropped to zero, and a large distance between the contact elements to ensure resistance at high voltage. A suitable and economical compromise must therefore be found between these two requirements and the interrupter according to the present invention provides a novel compromise of this nature.

This interrupter is characterized in that each of the said contact elements is provided with screening means that are electrically connected therewith and that are placed in such a manner as to separate from one another those of the interrupting gaps of said series which are delimited by said contact elements and as to prevent any electrical ield line to extend through more than one of these interrupting gaps.

The following description relates to two forms of embodiment, given by way of example, of the interrupter provided by the invention. It is illustrated by the accompanying drawing, in which:

FIG. 1 is a side view, partly in section, of the iirst form of embodiment;

FIG. 2 is a section through part of the interrupter illustrated in FIG. l, with the interrupter shown in a rst particular position;

FIG. 3 is a similar section, with the interrupter shown in a second particular position;

FIG. 4 is an enlarged view of part of FIG. 3, illustrating the operation of the first form of embodiment;

FIGS. 5 to 9 are diagrams relating to various arrangements that some parts of this first form of embodiment can have;

FIGS. and 1l illustrate, partly in section, two variants ofthe first form of embodiment;

FIG. 12 is a side view, partly in section, of the second form of embodiment;

FIGS. 13 to 15 are partial sections of some elements visible in FIG. 12;

FIG. 16 shows on an enlarged scale a variant of a par of FIG. l2;

FIG. 17 shows, partly in section, like FIGS. 1 and 3, another variant of the rst embodiment;

FIG. 18 is a horizontal section along line XVIII-XVIII of FIG. 17;

FIG. 19 is a section like that of FIG. 16, of a variant similar to that shown in FIG. 17 applied to the second embodiment.

In the example illustrated in FIG. l, the interrupter comprises a fluidtight exhausted enclosure 1 which rests on a base 2 forming the bottom of the lower half 1b of the enclosure and into which enters via a iluidtight bellows sealing member 3 a conductive actuating rod 4 serving to operate the movable armature of the interrupter. This movable armature is made up of a series of three

circular metal shells

5, 6 and 7, which are coaxially suspended on the actuating rod 4 one inside the other. These shells are isolated from each other by insulating

spacers

8 and 9 and, except for the outer shell 5, they are isolated from the actuating rod 4 by shoulders 10 and 11 formed in the spacers and by an insulating washer 12 placed between the head 13 of the rod 4 and the inner shell 7. The

shells

5, 6 and 7 and the

insulating elements

8, 9 and 12 are pressed against the head 13 by a nut 14 which at the same time applies the outer shell 5 against the shoulder 15 of the rod 4 to ensure electrical contact between the rod and the outer shell. The rod 4 is uidtightly secured by a welding 16 to the top of the bellows 3 and the latter is fastened to the upper half 1a of the enclosure 1 by a welding 17. The stationary armature of the interrupter is formed in similar manner by a series of three

metal shells

18, 19 and 20 which are coaxially mounted inside each other and which are fixed to the base 2 by a threaded conductive rod 21. These shells are isolated from each other and from the base 2 by insulating

spacers

22, 23 and 24 and, except for the inner shell 20, they are isolated from the threaded rod 21 by

shoulders

25 and 26 formed in the

spacers

22 and 23 respectively. The threaded rod 21 is moreover isolated from the base 2 by an insulating washer 27 having a shoulder 28. The inner shell 20 iS clamped beneath the head 29 of the threaded rod 21 so as to be in electrical contact with the latter. A nut 30 simultaneously to assemble together the

shells

18, 19 and 20 and the insulating

elements

22, 23, 24 and 27, to ix these components to the base 2 and to ensure electrical contact between the inner shell 20 and the threaded rod 21. The base 2 carries a threaded stud 31 which is electrically connected thereto by a welding 32. The two halves 1a and 1b of the enclosure 1 are secured to each other by a welding 33. The air contained in the enclosure 1 is removed through a withdrawal pipe 44 which, when the pressure reaches the lowest possible value (of the order of 10*s torr and below), is sealed by nipping and is made fluidtight by a welding 45. The threaded rod 21 acts as one of the terminals of the interrupter, which terminal has secured thereto by a nut 34 a conductor 35, the latter thus being electrically connected to the inner shell 20 of the stationary armature. The stud 31 acts as the other ternnnal of the interrupter and this terminal has secured thereto by a nut 36 a conductor 37, the latter thus being electrically connected to the outer shell 5 of the movable armature.

Each of the armature carries a series of contact elements of circular shape around the axis 52 of the interrupter. The contact element of the outer shell 5 of the movable armature is shaped in the form of a crown 38 laid ilat and projecting inwardly of the shell. lSimilarly, the contact element of the inner shell 20 of the stationary armature is shaped in the form of a crown 39 laid ilat, but projecting outwardly of the shell. The contact elements of the other shells are formed by circular components of T-shaped cross-section, alternately in upstanding and upside down positions. Thus, the

shells

18 and 19 of the stationary armature have

contact elements

40 and 41,

respectively, which are of inverted T cross-section, whereas the

shells

6 and 7 of the movable armature have

contact elements

42 and 43, respectively, which are of upstanding T cross-section. 'Ihese circular components are secured at the middle of their horizontal portions to the edges of their associated shells so that these horizontal portions should extend outwardly and inwardly of their associated shell. The contact elements are so sized that their horizontal portions 46 should overlap each other so as to come into contact when the movable armature is pressed against the stationary armature (closed position of the interrupter, FIG. 2), while their vertical portions 47 form screens which prohibit any direct sighting between contiguous contact elements, even when the movable armature is moved away from the stationary armature (open position of the interrupter, FIG. 3). The displacements of the movable armature are controlled by a mechanism not shown, which operates the actuating rod 4, the latter being axially movable in relation to the enclosure 1 by virtue of the bellows sealing members 3.

When the various elements making up the interrupter are mounted in the enclosure 1 and once the latter is Huidtightly sealed along the ridge 33, a high vacuum is created in the interrupter by connecting the withdrawal pipe 44 to a high vacuum pumping unit with which a pressure of less than 10-8 torr can be obtained. While pumping is in progress, intensive degassing is performed, through heating, to reduce as far as possible any subsequent degassing, either while the interrupter is in storage or while it is in use. As will be explained later the pressure in the enclosure 1 must not rise above a limit p1 defined by torr. cm., the length d being that of the longest field line likely to appear in the interrupter. That is why the pumping operation is carried on for as long as the pressure does not reach a value of l-8 torr. Then the pressure becomes stabilized at this value, pumping is stopped, the pipe 44 is nipped and sealed with welding. The pressure then slowly rises again, as a result of a subsequent slow degassing action, but remains below a value of the order of -4 torr.

The described interrupter operates as follows. Be it supposed that the interrupter is closed 'with its contact elements occupying the positions shown in FIG. 2. Then the movable armature moves away from the stationary armature and disengages the contact elements (FIG. 3), the voltage across two contiguous contact elements is equal to the potential difference between the

conductors

35 and 37 divided by the number of interrupting gaps appearing between the contact elements, i.e. by the total number of shells minus one (in the described example), there are three shells (5, 6, 7) for the movable armature and three shells (18, 19, 20) for the stationary armature, i.e. six in all, hence five interruptions along the chain (38, 40, 42, 41, 43, 39). Because of the low pressure in the enclosure this reduced voltage only produces a discharge of the diffuse are type, formed by several parallel conical columns (termed Reece cones) Whose apexes are located on that one of the contact elements which happens to be at negative potential in relation to its neighbour. Thus, supposing that the interruption takes place when the terminal 21 is possible in relation to the terminal 31, the polarities are those indicated in FIG. 3. The diffuse arc discharges that come into being are as shown on an enlarged scale in FIG. 4 where the apexes 49 of the Reece cones 48 occurring in the interrupting gap between the horizontal portions of the

contiguous contact elements

41 and 43 are located on the contact element 41 whereas the Reece cones occurring in the interrupting gap between the

contiguous contact elements

42 and 41 are oppositely oriented, their apexes 51 being located on the contact element 42. These apexes, which constitute heat concentration points (cathodic spots), are highly mobile across the surface of the corresponding contact elements and as a result do no cause much erosion of this surface. There is thus little vaporization of the cathode metal and the Reece cones contain only little vapour. Since the vacuum in the enclosure 1 is very high, there is besides the cathodic drop no other voltage between contiguous contact elements. In particular, there is no additional arc voltage due to collisions between charged particles (electrons or ions from the vapour of the cathode metal) and residual gas molecules. Since, moreover, the residual pressure is such that the main free path of the electrons is greater than half of the largest distance lying between the interrupter components that are at different potentials, that any collisions with dual gas atomisor molecules could in no way cause an avalanche process to be initiated during the voltage rise which follows a current interruption. Consequently, dielectric restoration of the medium in the gaps where the discharges occur (i.e. between adjacent contact elements) takes place without difficulty as soon as the discharge current drops to zero. Because of this there is no restarting phenomenon.

Further, the vertical portions 47 of the intermediate contact elements prevent any direct sighting from one interrupting space to another. By this is meant that the vertical portions firstly prevent a particle from passing from one interrupting space to the next, this corresponding to prohibition of a direct sighting in the optical meaning of the expression direct sighting, and secondly prevent field lines from passing through more than one interrupting gap or join two non adjacent contact elements, this corresponding to the electrical meaning of the expression direct viewing. In this connection, besides the field lines which are located in the interrupting gap between two contiguous contact elements, like the field line 274 (FIG. 3), there may be field lines which join a contact element to the vertical portion of the adjacent contact element, like the field line 275, or to the shell carrying the next contact element of the same armature, like the field line 276. There could never be a field line such as the line 277 (drawn as a chain line) joining two non contiguous contact elements. Because of this, the interrupting gaps can be regarded as independent as regards their dielectric restoration.

As a result of this arrangement, firstly the dielectric restoration speed of the interrupting gaps as a Iwhole is increased, since the independence of these gaps makes it possible for the separate restoration speeds therefor to be added together, and secondly the static value of the disruption voltage is increased since no field line can pass through several potential jumps, this tending to reduce the final level of the restoration.

In other words, the described interrupter prevents the restarting phenomenon from occurring, improves resistance to disruption and reduces the time taken to read this resistance to disruption.

The characteristic features of the described interrupter lie: in the fact that the interruption of the circuit is not localized, but is spread over several interruptions that give rise to a cascade of series mounted discharge paths; in the presence of bafiles which prevent direct sighting from any one discharge path of a neighbouring discharge path; and in the presence of shells so arranged as to provide screens prohibiting the existence of long field lines or field lines causing a large potential drop.

`In the form of embodiment that has just been described and which is diagrammatically represented in FIG. 5, the baffles are simple insofar as each contact element, except for the

terminal contact elements

55 and 56, carries only one bafiie, this bale being symmetrically disposed in relation to this element, as shown by the element 57 and its baffle 58 which have been drawn in thicker lines. Other arrangements can be conceived, like that of FIG. 6 where the non terminal contact elements are all identical and are provided, like the element '59, with a single baffle i60, this baffle being placed asymmetrically. FIGS. 7 and 8 illustrate diagrammatically the case where some of the contact elements like the

elements

61 and 64, respectively, are provided with two

baiiles

62, 63 and 65, 66, respectively, whereas others, like the

elements

67 and 68, respectively, have none; in the case of FIG. 7, the

baffles

62 and 63 are symmetrically disposed on the element 61; in the case of FIG. 8, the baffles l65 and 66 are asymmetrically disposed on the element 64. Finally, FIG. 9 shows the case where some elements, such as the element `69, are provided with three symmetrically disposed bailies, like the

bailies

70, 71 and 72, whereas others, like the elements 73, have none. As will be appreciated, there are numerous possible variants as regards the number of baies, their location and their arrangement.

The interrupted illustrated in FIG. 1 comprises three contact elements per armature, to wit the

elements

38, 42 and 43 on the movable armature and the

elements

39, 40 and 41 on the stationary armature, thus producing ve circuit interruptions. It will be clear that this number of three elements per armature is not imperative and that, according to circumstances, for instance the power to be conveyed by the circuit and the voltage, use can be made of a larger number of contact element, thereby splitting up to a greater extent the circuit interrupting action.

It may be of advantage to increase the resiliency of the shells to enable the contact pressure to be more evenly distributed over the entire periphery of the contact elements. In such an event, it is preferred to increase the diameter of the flat bottoms by giving the shells a cylindrical shape, as is shown in FIG. 10 in the case of the

shells

74 and 75 of the movable armature and in the case of the

shells

76 and 77 of the stationary armature, instead of the frusto-

conical shells

5, 6, 7 and 18, 19, 20, respectively, visible in FIG. 1.

It may also be of advantage, still with a view to achieving a more uniform distribution of the contact pressure, to split, at least in one of the two armatures, one contact element into two parts with each part being supported by its own shell. This what is shown in FIG. 11 where it will be seen now the contact part 7'8 of the stationary armature is split into two

parts

78a and 78b with each part being supported by its own shell 78'a 78b, these two shells being connected to a common central portion 78" so as to form a composite support for the split contact element 78. Similarly, the contact element 79 of the stationary armature is split into two parts 79a and 7912 which are supported by the shells 79a and 79'b that are connected to a common central portion 79". This arrangement enables the two

parts

78a and 78b to move in relation to each other so that they can cooperate independently of one another with the contiguous contact elements S3 and 255 of the movable armature. The same applies to the two parts 79a and 79b of the contact element 79 which can thus cooperate independently of each other with the

contiguous contact elements

255 and 54 of the movable armature.

Of course, the T-shaped cross-section, Whether upstanding or inverted, of the contact elements in the interrupter illustrated in FIG. 1 is only one possibility among others and other cross-sections can be conceived, e.g. U-shaped, whether upstanding or inverted, with the limbs of one set being inserted between the limbs of the others. Some of the arrangements discussed earlier in particular that which is diagrammatically illustrated in FIG. 1, are derived from shapes of this kind.

FIG. 12 illustrates a second form of embodiment in which the contact elements, instead of being distributed in a common plane, over increasing diameters, as is the case with the first form of embodiment visible in FIG. l, are axially distributed and have identical diameters. This interrupter comprises an enclosure 80 mounted on a base 81 and capped by a cover 182, these elements being fluid tightly assembled together, as by welding.

The stationary armature comprises a stack of identical dishes 83 to 88 which are separated from each other by insulating spacers `89 to 91 of tubular shape. These dishes have a radial cross-section as shown, on an enlarged scale, in FIG. 13. They are formed with a central limb 92 having a rounded outline with the concave side thereof facing the axis of revolution 97, a at crown-shaped portion 93, a median groove 94, a conical portion 95 and a plane disc-shaped portion 96 which is placed at a level beneath that of the flat portion 93, to the same side thereof as the groove 94. The distance between the limb 92 and the groove 94 is such that the intervening space acts as a centering recess for receiving the associated tubular spacer. Except for the

outermost dishes

83 and 88, the dishes within the stack are arranged in pairs, like the pair 84, and the pair 86, 87, and the two dishes of a pair are in inverted relationship so that their central limbs 92 together constitute an anti-euvium screen of concave form, with the concave side facing the inside of the tube formed by the stack of

spacers

89, and 91, and so that the median groves 94 together constitute tield suppressing screens on the outside of this tube. The groove of the lowermost dish 183 caps an axial rim 98 provided at the centre of the base 81, inside the enclosure 80, whereas the groove of the uppermost dish 88 accommodates a clamping piece 99 which is welded to the top end of a clamping tube 100. This clamping tube is subjected to a pulling stress by means of a nut 101 which is screwed onto a threaded member 102 fastened to the lower part of this tube. The nut 101 beats on a flat support 103 on which the base 81 rests through the intermediary of a splined insulating sleeve 104.

The movable armature comprises a series of three

shells

105, 106 and 107 which are formed by the outer portions of bell-shaped members having as their axis of revolution the axis 97 of the interrupter. As shown by FIG. 14, which illustrates on an enlarged scale the prole of these bells, each bell includes a flat central boss 108, a conical bottom 109 which is connected to the central boss 108 by a conical flank 110, an inner peripheral boss 111, a flat crown-shaped portion 112, an outer peripheral boss 113, a connecting edge 114 and a conically ilared skirt-shaped outer portion 115 which constitutes the shell mentioned earlier. The

bells

116, 117 and 118 to which belong the

shells

107, 106 and 105 are fitted inside one another and are kept separate from each other by insulating

sleeves

119, 120 and 121, each sleeve bearing on the hat crownshaped portion of the associated bell (as shown by the chain line outline 122 in FIG. 14 from which may also be observed that the distance between the peripheral bosses 111 and 113 is such that the intervening space acts as a centering recess for the associated sleeve). Between the bottoms of the

bells

117 and 118 and the tops of the

sleeves

119 and 120, and on the top of the upper sleeve 121, are arranged supporting

members

123, 124 and 125 having a profile as shown on an enlarged scale in FIG. l5. Each of these members is circularly shaped around the axis 97 of the interrupter and comprises a flat central boss 126, a conical flange 127 which is connected to the central boss 126 by a conical flank 128, an inner peripheral groove 129, a flat crown-shaped plate 130, and an outer peripheral groove 131, the distance between these peripheral grooves being such that the intervening space acts as a centering recess for a sleeve, as shown by the chain line outline 132. The dimensions of these various parts and their conicities are such that the supporting members t exactly against the bottoms of the associated bells, so that the fitting of the

peripheral grooves

129 and 131 in the supporting members with the peripheral bosses 111 and 113 in the bells forms two field suppressing screens located on opposite sides of the junction between two consecutive insulating sleeves, as will be observed from FIG. 12 as regards the supporting members 124 and the bell 118. The lower supporting member 116 rests, through the intermediary of a central spacer 133, on an auxiliary shell 134 having a conical ange 135 which is parallel to the ange of this supporting member, and a conical skirt 136 which is parallel to the skirt of the inner bell '7. The hub of this auxiliary shell 134 comprises a central portion 137 surrounded by a crown 138. The central portion 137 is secured to the top end of an actuating rod 139, made of metal or other material, which is housed inside the clamping tube 100, its diameter being such as not to touch this tube. The crown 138 is connected, through the intermediary of a fluidtight bellows 140, to the clamping piece 99, this connection being effected in iluidtight manner, by welding at each end of the bellows 140. The upper supporting member 125 bears on a dished member 141 having a rim 142 and a central stud 143. The rim 142 is connected, through the intermediary of a fluidtight bellows 144, to the cover 82, this connection being effected in fluidtight manner, by welding at each end of the bellows 144. The central stud 1143 slides in a recess 145 formed in a threaded stopper 146 which is in turn accommodated in a threaded hole 147 in the cover 82. A spring 148 is prestressed between the stopper 146 and the bottom of the dished member 141.

Finally, the clamping piece 99 is welded to a glass tube 1149 which surrounds the clamping tube 100 and which is terminated at its lower end by a pleated folded-back sleeve 150. This sleeve, in which the pleats are only made to provide for heat expansion, is welded to the lower end of a uidtight metal bellows 151 whose top end is tluidtightly connected to the base 81 of the interrupter. The glassmetal welding 152 is surrounded by a peripheral screening hood 153 having an inner part 154 and an outer part 155.

The contact elements carried by the stationary and movable armatures are distributed in three identical

superposed stages

156, 157 and 158, each of which is constructed as shown on an enlarged scale in FIG. 16. Each stage, e.g. stage 156, comprises a part 159 which is attached to the movable armature, and two parts, 160 and 161, which are attached to the stationary part. Each of these parts is of circularly symmetrical cross-section about the axis 97 of the interrupter. In cross-section the member 159 which is `attached to the movable armature is shaped like an asymmetrical inverted U with

unequal limbs

162 and 163, the longer limb 162 being remote from the axis 97 and the shorter limb being closer to this axis. The longer limb 1-62 of this member 159 extends into the peripheral channel formed by the first, 160, of the two members which are attached to the stationary armature, the cross-section of this first member being shaped like an asymmetrical U having a longer limb 164 remote from the axis and a shorter limb 165 nearer the axis. The shorter limb 163 of the member 159 extends into the peripheral channel formed by the second, 161, of the two members which are attached to the stationary armature, the cross-section of this second member being shaped like an asymmetrical U having a shorter limb 166 remote from the axis and a longer limb 167 nearer the axis, this longer limb being extended downwards by an appendage 168. The

members

159, 160 and 161 each comprise a

fastening rim

169, 170 and 171, respectively, by means of which it is fastened to the associated armature. Thus, the member 159 of stage 156 is fastened by the fastening rim 169 to the tip of the shell 105, the member 160 of this selfsame stage is attached by the fastening rim 170 to the plane portion 9683 of the dish 83 and the member 161 is attached by the fastening rim 171 to the plane portion 9684 of the dish 84. When the interrupter is closed, the electrical connection between the contact elements of the stage 1516 is established via the bottom 172 of the peripheral channel formed by the member 160, the tip 173 of the outer edge 162 of the inverted peripheral channel formed by the member 159, the tip 174 of the inner edge 163 of this selfsame channel and the bottom 175 of the peripheral channel formed by the member 161. This is what is shown by the chain line outlines visible in FIG. 16. There is thus set up, at the level of the stage 1516, an electrical connection between the

dishes

83 and 84 of the stationary armature; at the level of the stage 157, an electrical connection between the dishes and 86 of this selfsame stationary armature; and, at the level of the stage 158, an electrical connection between the dishes 87 and 88 again of this selfsame stationary armature. Since the dishes 84 and 85, on the one hand, and 86 and 87, on the other hand, are in electrical contact with each other, and since the lowermost dish 83 is in electrical contact with the base 81, and the uppermost dish 88 is in electrical contact with the clamping tube 100 through the intermediary of the clamping piece 99, and the clamping tube is in electrical contact with the support 103 through the intermediary of the member 102 and of the nut 101, it will be apparent that, in the closed position of the interrupter, the latter sets up an electrical connection between the base 81 and the support 103. It is therefore to these latter parts that are connected the

terminals

176 and 177 by vmeans of which the interrupter is connected to the

current supply cables

178 and 179, respectively. To afvoid having current flowing through the threads of the nut 101 and of the member 10.2, there is provided an arm 180 which establishes a direct electrical connection between the support 103 and the clamping tube 100.

It will be apparent that there is a similarity between this interrupter and the one described with reference to FIG. 1l: the members 159 belonging to the

stages

156, 157 and 158 (FIG. l2) constitute the contact elements of the movable armature, whereas the lower U-shaped members belonging to one stage (e.g. the U-shaped member 16011 of the stage 157) and the upper U-shaped members belonging to the sub-jacent stage (e.g. the U-shaped member 161 of the stage 156) constitute the two parts of split contact elements of the stationary armature, the dishes to which are secured these members (c g. the dishes 87 and 86 and the dishes 85 and 84, respectively) constituting the associated composite supports.

The operation of this second form of embodiment is in respects similar to that of the first form of embodiment illustrated in FIG. l. The edges 164 and 165 (FIG. 16) of the peripheral channel formed by the part 160 and the

edges

166 and 167 of the peripheral channel formed by the part 161 constitute within any one stage the baffles that prevent direct sighting of one interrupting gap from another, e.g. of the interrupting gap 182 from the interrupting gap 181 in the stage 156 illustrated in this ligure. The same applies to the other stages 157 and 158 (FIG. 12). However, the cylindrical screen which has as its cross-section the appendage 168 (FIG. 16) of the longer limb 167 of the part 1161 of stage 156, as also the analogous screens in the other stages do not exist in FIG. 1: these are so-called anti-vapour screens for preventing the vapour generated by the discharge in the

interruption gaps

181 and 182 from diusing within the enclosure 80. As for the auxiliary shell 134, it simultaneously constitutes, firstly, another, additional, anti-vapour screen and, secondly, an additional baflie for preventing direct sighting between the clamping piece 99 and the inner shell 107.

As explained earlier the nut 101 serves to clamp the members making up the stationary armature and to iix them to the support 103 and to the base 81. As for the threaded stopper 146 it serves to adjust the prestressing of the spring 148, this spring urging the movable armature against the stationary armature. It is therefore this spring which exerts the contacting pressure between the contact elements of the stages 156 to 158 and it is against the action of this spring that the actuating rod 139 has to be moved when it is required to separate the contact elements upon opening the interrupter.

It will be apparent that this second form of embodiment has the advantage, in relation to the first, of being produced from a limited number of standard parts, thereby reducing the number of machining operations. The dishes 83 to 88 are identical and are easily made by stamping. The contact elements of the various stages only comprise three types of diiferent parts, i.e. the

parts

159, 160 and 161, which parts only differ from one stage to the next as regards the diameter of their

fastening rims

169, 170 and 171, respectively. Simple lathe operations will easily impart to these diameters the values they are required to have in the stages for which they are intended. The bells :5, 106 and 107 are all identical as regards their profile, which profile is very well suited to production by stamping. Only the length of their skirts 115 (FIG. 414) changes from one bell to the next so that they can all be derived from the longest such bell, i.e. the outer bell 118, by simple removal of the excess length. The supporting

members

123i, 124 and 125 are all identical and are designed to be produced by stamping. Further, the arrangement that has been adopted makes it possible to modify to a large extent the number of interrupting gaps without having to resort to new parts: it suiiices to increase the number of stacked stages; this adds to the length of the interrupter without substantially modifying its diameter.

It should be pointed out that the arrangement that has been adopted for this second form of embodiment avoids having to expose to the vacuum for no good purpose purely mechanical components. Thus the clamping spring 148 and the

device

146, 147 for modifying its prestressing are located outside the exhausted enclosure 80. The same applies to the clamping device of the stationary armature, i.e. the nut 101, the member 102 and the tube 1100. Moreover, the actuating rod 139 is not subjected to any pull: it only operates on a thrust basis against the action of the force exerted by the spring 148 so that even when the switch is closed it remains subjected to a compressive force and never to a pulling force.

Finally, it will be observed that in this interrupter the

terminals

176 and 177 are both electrically connected to the stationary armature only, i.e. to the extreme contact elements thereof, the movable armature not being connected to any terminal.

Of course, either of the two described forms of embodiment can be equipped with the discharge confinement device called cathodic barrier and described in Swiss patent application No. 17,52'6/70. This is what is diagrammatically illustrated in FIG. 16 in which are to be seen, for the purpose of confining the discharge within the interrupting gap 181, the annular

cathodic barriers

184 and 185 provided on the part 160 and the

cathodic barriers

186 and 187 provided on the contact element 159, and, for the purpose of confining the discharge in the interrupting gap i182, the annular cathodic barriers 188 and 1-89 provided on the contact element 159 and the

cathodic barriers

190 and 191 provided on the part 161.

Furthermore, it may be of advantage to provide the screened contact elements, like the element 159 (FIG. 16) of the stage 156 (the latter being screened by virtue of the fact that its

flanges

162 and 163` are trapped in the peripheral channels i116() and 161, respectively), with helicoidal slots like the slots 195 formed on the outer flange 162, and like the slots 196 formed on the inner flange 163 of this contact element 159. As is known in conventional interrupters, such an arrangement brings about rapid displacement of the discharge impact points along the helicoidal petals dened by these slots in the contact element, like the petal 197 or the peta 198i. This displacement helps to spread the heating action due to the discharges and limits erosion of the contact surfaces and hence vaporization of the metal from which are are made. These helicoidal slots, however, must not reach the cathodic barriers 186, 1-87 and 1818, 189, respectively, otherwise the effectiveness of the latter would be adversely affected.

Since the purpose of cutting up the -llanges into petals is to channel the current owing in the contact elements along helicoidal paths, a similar, although less marked, eifect can be obtained by forming on these contact elements grooves instead of slots, the presence of these grooves having the effect of locally increasing by a nite amount the electrical resistance of these contact elements whereas that of the slots renders such an increase infinite. These resistance increasing grooves, which, in pairs, define petals along which the current is channeled, can be formed on the

flanges

166 and 167 and on the bottom 175 of the part 161, as well as on the flanges 164 and 1165 and on the bottom 172 of the part 160. They are preferably formed on the surfaces of these parts lying opposite the surfaces between which the discharges take place. Along these surfaces they have helicoidal or spiral outlines such that the current being channelled by these grooves sets up a magnetic field having a component capable of causing the discharge to travel along the contact elements in a circular translationary movement centered on the axis 97 of these elements.

A similar arrangement can be provided in the interrupter of FIG. l. For this, the grooves are formed in the surfaces of the contact elements lying opposite the bafes (or screening flanges) 47. Thus referring to FIG. 4, the grooves are formed on the underneath surface of the element 41 and on the top surfaces of the

elements

42 and 43.

In connection 'with the arrangements illustrated in FIGS. l0 and 1l, it should be noted that the added flexibility that they impart to the armatures can in some cases be bothersome for the movable armature since it increases its vibrational tendencies. in such cases, it is preferred to stick to shells of conical shape for the movable armature, like the

shells

5, 6 and 7 in FIG. 1, and to use ilexible shells like the shells 76 and 77 (FIG. l0) or 78'a, 78b, 78" and 79'a, 79'b, 79" (FIG. 11) only for the stationary armature.

In either of the above described embodiments of the vacuum interrupter the discharge that occurs when it is opened does not restart once the current has passed through zero during the alternation change that follows this opening action. This result is achieved by providing the contact elements, besides the small spacing made possible by resorting to several of such elements to dene a plurality of interrupting gaps arranged in series, with an extensive contact area and by arranging between adjacent interrupting gaps screens which render the latter electrically independent from one another. These steps create conditions which prevent discharges generated in the interrupting gaps from passing from diffuse arc flow conditions to single column flow conditions and which as a result stop these discharges from restarting once the current, as it alternates, crosses the iirst zero crossing point after opening the interrupter.

This however is only true in so far as the discharges occur without fail under diffuse arc conditions when the interrupter is opened. The variant that will now be described, and that applies to either of the preceding embodiments, to reduce the risk of having discharges occurring under column flow conditions.

It will be recalled that, according to the Mitchell theory, transition from diluse arc ow conditions (characterized by the existence in parallel of several highly mobile elementary discharges, called Reece cones) to column flow conditions (characterized by a single concentrated arc having little mobility) results from instabilities of the diffuse ow conditions that occur when the inter-electrode voltage exceeds 40 'v. Since this voltage is the sum of a cathodic voltage of 20 v. (in the immediate vicinity of the cathode) and of an ohmic drop RI within the plasma existing in the space lying between contact elements, this ohmic drop RI must be kept below 20 V. to prevent transition. If the contact elements are provided with an extensive area S and if their spacing d is kept small, the resistance R can be lowered according to the known law R=k d/S which applies whenever the cones are sufficiently numerous to overlap one another partly. In other words, to prevent transition between diffuse flow conditions and column flow conditions, the value S/d must be made as high as possible for each of the interrupting gaps. This is what the above described forms of interrupter achieve.

But when the discharge is started, i.e. as the contact elements begin to move apart, there is formed a bridge of liquefied metal; this bridge is progressively drawn out and finally bursts. Thus, for a brief period of time after the burst, there is a transitory stage during which the contact elements continue to move apart until they reach maximum spacing corresponding to the open state of the interrupter. During this transitory state, the instantaneous value S/d varies greatly and to an extend in no way related to the final value corresponding to the open state, and it may happen that, before even the Reece cones have been able to disperse, the current exceeds the critical value (of the order of ka. in the case of contact elements made of copper) that enables a single column to be formed. The contact elements should therefore be adapted so as to prevent without fail the current from reaching during the transitory state the critical value that leads to the formation of a single column, in other words be adapted to start, between the pairs of contact elements being moved apart, a plurality of discharges under diffuse fiow conditions with the current having to flow in the interrupting gaps set up between these Contact elements being divided up between them. Technically this amounts to increasing the simultaneity of the breaking action between all points of the two contact elements being moved apart, whilst maintaining a high pressure at all of these points when the contact elements are in contact in the closed position of the interrupter. This is what is achieved by the variants depicted in FIGS. 17 and 18 in relation to the first embodiment, and in FIG. 19, in relation to the second embodiment, it being assumed that one of the two armatures is movable and the other is stationary.

In the variant illustrated in FIGS. 17 and 18, the contact elements of the stationary armature are splitting by cutting therein radial slots, such as the slots 239 in the case of the contact element 39, the slots 240 in the case of the contact element 40 and the slots 241 in the case of the contact element 41. In this way, each Contact element fraction forms the tip of a contact fingen Thus, the fractions 339 of the contact element 39 form the tips of contact fingers 220. The same applies to the fractions 340 of contact element 40, `which form the tips of fingers 218, and to the fractions 341 of contact ele ment 41 which form the tips of lingers 219. This arrangement imparts to the adjacent fractions of any one contact element an individual -fiexiblity which endows them with some mobility in relation to each other, such mobility multiplying, -when the interrupter is in the closed position, the points at which a stationary contact element touches the two movable contact elements that are adjacent thereto and with which it cooperates: it is then each fraction which touches, individually, these two contact elements. As a result, the machining tolerances may be less tight and the heating action due to current throughfiow is better distributed and less large.

The mobility of each finger in relation to its neighbours is all the greater when the radial slots are deep. But a greater mobility is accompanied by a reduction of the force with which each fraction touches the or each contiguous movable contact elements. This is a drawback because the force with which each fraction is applied against the movable contact element with which it cooperates must be sufiicient to avoid, firstly, any resistive welding tending to attach this fraction to this contact element and, secondly, any separation of the contacts by a magnetic bouncing effect. A suitable compromise must therefore be found between the fiexibility of the fingers and the force they exert when the interrupter is closed. This compromise, which rests on static considerations, determines the depth to which the radial slots must extend into the corresponding

shells

18, 19 and 20, and defines the radii R1, R2 and R3 reached by their bottoms. These parameters can be calculated in an approximate way but their definite values are determined by empiric tests.

The splitting up of the stationary contact elements has another advantage which is most important when the armature is being opened: it is that the extra breaking current that springs between the contact elements when the latter are being separated is distributed between several parallel partial discharges, with at least one per finger, so that each only conveys a limited amount of current. If the current at each discharge starting point does not exceed a limiting value (of the order of 5 ka. in the case of contact elements made of copper), the corresponding discharges are bound to start up in diffuse arc form. This however supposes that each of the fractions into which the stationary contact elements are divided separate simultaneously. In this connection, if one fraction separates from its movable contact element before the others, the current it was conveying before this separation occurred produces, by a self-inductance effect, a discharge which, because it is short-circuited by the fractions that have not yet separated, only lasts for as long as this self-inductance effect is capable of maintaining, between this fraction and the corresponding mobile contact element, the minimum voltage of 20 v. representing the cathodic drop within this discharge. This length of time, which is very short since it does not exceed a few microseconds, represents the maximum time lag that may be tolerated for the separation between the first and last fractions to open of one stationary contact element: it thus defines the simultaneity with which these fractions must be separated from the corresponding movable contact element. In practice, during this time lag, the fingers must not be allowed time to follow the movable contact element in its breaking movement. This amounts to giving to the mass of the various fractions and to the elasticity of the corresponding fingers values such that the vibration period of these fingers is much greater than the time taken by the movable contact element to move away therefrom.

These dynamic considerations, which are of the greatest importance, must be taken into account when reaching the compromise that determines the depth of the slots. They involve, 'besides the elasticity of the material used for the

shells

39, 40, 41 of the movable armaturesuch elasticity governing the fiexibility of each finger-the suspended mass constituted by the mass of the contact element fraction forming the tip of this finger. Here again, the depth of the slots and the mass of the contact element fractions carried by the fingers are adjusted by empirical tests.

As is apparent from FIG. 18, the fingers of one shell can be angularly offset in relation to the fingers of another shell: thus the fingers 218 formed in the outer shell 18 are angularly offset by half a width in relation to the fingers 219 formed in the shell 19. Also, the angular width of the fingers of one shell is not necessarily equal to the angular width of the fingers of another shell: if the fingers 218 have the same angular width as the ngers 2119, the fingers 220 of the inner shell 20 have a double angular width.

If the interrupter has contact elements in the form of annuli stacked on top of each other into a substantially cylindrical tubular structure, like that shown in FIG. 12,. the splitting up of the stationary contact elements leads to the arrangement shown in FIG. 19. It will be observed from the latter, which must be compared with FIG. 16, how the radial slots formed on the contact elements are arranged. Thus the annulus is provided with radial slots of which may be seen the portions 251 located on its outer flank 1164, the portions 252 on its inner flange 1165 and the portions 253 located on its mounting annulus '170. The annulus 161 is also provided with radial slots of which may be seen the portions 261 located on its outer lflange 166, the portions 262 located on its inner liange '167 and the portions 263 located on its mounting annulus 171. In this way, each of the

stationary annuli

160, 161 belonging to one stage (here stage 156) is split up into sections which form the tips of contact fingers, such as the lingers 270 in the case of the annulus 1-60 and the lingers 271 in the case of the annulus 161.

Obviously the splitting up of the stationary contact elements into fingers 270, `271 in no way prevents the movable contact elements from being divided into petals by helical slots, as described above and as is apparent from FIG. 19 in the case of the movable contact element 159 which is divided into

petals

197, 198 by

helical slots

195, 196.

Since the elasticity of the contact fingers might be the cause of bouncing when the interrupter is being closed, it may be of advantage to provide means capable of preventing this phenomenon from occurring. This is what is shown in FIG. 19, where the bottoms of the

grooves

172, 175 of the

contact elements

160, 161, respectively, are each defined by

oblique surfaces

280, 281, respectively, which form bevels into which extend the

tips

173, 174 of the

flanks

162 and 163, respectively, of the movable contact element 159. The presence of these bevels has the elect of preventing any bouncing of the lingers 270, 271 when the interrupter is being closed, the friction of the tips '173, 174 against the

surfaces

280, 281 absorbing the energy that would cause such bouncing.

If for reasons of simplicity the cathodic barriers appearing in FIG. 116 have not been shown in FIG. 19, clearly there is nothing to stop the stationary contact members that are split up into ngers from being so provided.

We claim:

r1. A vacuum single-pole interrupter for alternating electric current, having a plurality of contact elements operating in series, said contact elements belonging to irst and second contact armatures capable of moving in relation to each other along an axis of displacement, the contact elements of one armature cooperating with those of the other armature so as together to form a chain of contact elements constituting, when the interrupter is closed, a conduction path alternately passing through the contact elements of said two armatures and forming, when the interrupter is open, a series of interrupting gaps alternately defined 'by said contact, the outermost two elements of this chain being electrically connected to the rst and second, respectively, of a pair of terminals serving to connect the interrupter to an electric network, characterized in that each of said contact elements is provided with screening means which are electrically connected therewith and which are arranged so as to separate from each other those interrupting gaps which, within said series, are defined by this contact element and so as to prevent any one electric field line from extending through more than one of these interrupting gaps.

2. An intrrupter according to claim f1, characterized in that each of the said contact elements consists of a circular conductive crown which has at least one annular contacting surface and which is located at the periphery of a round conductive support, at least one of the crowns of at least one of the two armatures being provided with at least one dange substantially at right angles to the contacting surface of said crown, and the supports bearing the crowns of at least one of said armatures having a concave shape enabling them to fit into one another, in that within each of said armatures the supports are arranged in coaxial positions, that are aligned along said axis of displacement, and are attached to each other by fastening means which isolate them electrically from one another, the flanges being in all of the crowns of this armature oriented in a common direction, and in that, within any one armature, the concave supports are tted into each other, the arrangement being such that, when the interrupter is closed, the contact surfaces borne by the crowns of one armature are pressed against the homologous contact surfaces borne by the crowns of the other armature thus foming said conduction path, and that, when the interrupter is open, the contact surfaces bome by the crowns of one armature are separated from the homologous contact surfaces 'borne by the crowns of the other armature thus forming said series of interrupting gaps, the flanges and the supports of these crowns together forming said screening means.

3. An interrupter according to claim 2, characterized in that said crowns are concentric crowns of increasing diameters arranged one within the other and alternately belonging to one then the other of said armatures, said crowns together forming a substantially plane annular structure at right angles to said axis of displacement.

4. An interrupter according to claim 2, characterized in that said crowns are coaxial crowns of substantially equal diameters which are stacked one above the other and which alternately belong to one then the other of said armatures, said crowns together forming a substantially cylindrical tubular structure coaxial with said axis of displacement.

5. An interrupter according to claim 2, characterized in that the said outermost two elements of said chain belong to different armatures, whereby the interrupter may be connected to the network through the intermediary of these two armatures.

6. An interrupter according to claim 2, characterized in that the said outermost two elements of said chain belong to one armature, whereby the interrupter may be connected to the network through the intermediary of this one armature.

7. An interrupter according to claim 2, characterized in that each of said armatures includes at least one crown having at least one of said flanges.

8. An interrupter according to claim 2, characterized in that the crowns of one of said armatures each have at least two flanges and in that the crowns of the other armature have no anges.

9. An interrupter according to claim 2, characterized in that, within each of said armatures, crowns having at least one flange alternate with crowns having no flanges.

10. An interrupter according to claim 2, characterized in that, within at least one of the armatures, at least one of said crowns is split into two concentric parts of which one includes one of the contact surfaces of this crown and is secured to the edge of a first circular member, and of which the other includes the other contact surface of this crown and is secured to the edge of a second circular member, said two circular members being connected to each other at the central portions thereof so as together to form a composite support enabling relative movement of one of the contact surfaces of said crown in relation to the other.

11. An interrupter according to claim 3, characterized in that the cross-section of each of said concentric crowns is shaped like a T lying the right way up in the case of the crowns of one of said armatures and upside down in the case of the crowns of the other armature, the limb of this T constituting the cross-section of the ange of said crown.

12. An interrupter according to claim 4, characterized in that the cross-section of each of the coaxial crowns of the lirst of said armatures is shaped like two superposed Us, the bottoms of these Us respectively constituting the cross-section of either of the two contact surfaces of this crown and the limbs of these Us forming the cross-section of each of two pairs of flanges, with one pair encircling one of said contact surfaces and with the other pair encircling the other contact surface, and in that the crosssection of each of the coaxial crowns of the second of said armatures is shaped like an inverted U having unequal limbs, the ends of these limbs respectively constituting the cross-sections of either of the two contact surfaces of this crown, said crowns being so arranged that the limbs of the inverted U of the cross-section of the crown of the second armature extend into the respective Us of the cross-sections of the crowns of the rst armature.

13. An interrupter according to claim 12, characterized in that the crowns of said first armature are split into two parts of which one has as its cross-section one of said Us and of which the other has as its cross-section the other of said Us, each of these parts being secured to the edge of a member shaped like a wide-brimmed dish, these dishes being assembled back to back so as to constitute a composite support.

14. An interrupter according to claim 12, characterized in that the supports of the crowns of said second armature are shaped like conical bells all having the same meridian profile, these conical bells being fitted into each other and being kept electrically isolated from each other by insulating spacers which maintain their bottoms equidistant from one another, and each of the crowns of this second armature having an outer peripheral limb by means of which this crown is secured to the edge of the associated bell.

15. An interrupter according to claim 2, characterized in that said contact elements are provided with cathodic barriers so arranged as to delimit the contact surfaces of each said element.

16. An interrupter according to claim 1, characterized in that some portions at least of said contact elements are provided with lines along which the resistance oiered to electric current flow is increased, pairs of said lines delimiting in said portions paths of lesser resistance which channel the electrical current flowing therein, the shape of these lines being so selected that the electromagnetic action exerted by this current on the discharges occurring in said interruption gaps will impart to these dischargers a circular translationary movement along these contact elements.

17. An interrupter according to claim 16, characterized in that said lines of increased resistance are formed by grooves.

18. An interrupter according to claim 16, characterized in that said lines of increased resistance are formed by slots.

19. An interrupter according to claim 1, characterized in that one of said armatures is a stationary armature of which each contact element consists of a plurality of sections which are attached to this armature by elastic elements that render these sections movable in relation to each other in planes passing through said axis of displacement, the mass of these sections and the elasticity of these elastic elements being chosen so that when the interrupter is closed each of the sectioned contact elements of the stationary armature touches each of the corresponding contact elements of the other armature at at least one point per section, and so that when the interrupter opens the inertia of these sections prevents them from accompanying the contact elements of the other armature while they are moving away.

20. An interrupter according to claim 19, characterized in that each of the sections belonging to one Contact element of said stationary armature has the shape of an annulus sector, each of these sectors being secured to the tip of a radial finger consisting of the portion of said round support lying between two adjacent slots belonging to a plurality of meridian slots formed in said support from its outer edge, the axis of said support corresponding to said displacement axis and said radial fingers constituting said elastic elements, the flexibility of said lingers being determined by the radial depth of the slots.

21. An interrupter according to claim 20, characterized in that the mass of said sections and the radial depth of said meridian slots are so selected that the natural period of the exing vibrations of each of said lingers in the axial direction is greater than the time taken by the contact elements of the movable armature to move away from the contact elements formed by said sections.

22. An interrupter according to claim 19, characterized in that at least one of the two surfaces along which two cooperating contact elements contact each other when the interrupter is closed is oblique in relation to said axis of displacement thereby to increase the friction of the surfaces against each other and to prevent said contact elements from bouncing.

References Cited UNITED STATES PATENTS 2,976,382 3/1961 Lee 200-144 B 3,211,866 10/1965 Crouch et al. 200`l44 B 3,244,843 4/ 1966 Ross 200-144 B FOREIGN PATENTS 1,389,836 1/1965 France 200-l44 B 1,145,151 3/1969 Great Britain 200--144 B 1,901,067 10/1969 Germany 200--144 B ROBERT S. MACON, Primary Examiner U.S. c1. xn.l 20o- 166 o Dedication 3,705,144.-Perre Genequand, Geneva, Switzerland. VACUUM INTERRUPT-v ER OR SWITCH FOR ELECTRIC POWER NETWORKS. Patent dated Dec. 5, 1972. Dedication filed Mar. 26, 1984, by the assignee, Battelle Memorial Institute. Hereby dedicates to the People of the United States the entire remaining term of said patent.

[Official Gazette May 29, 1984.]

Dedication 3,705,144.-Perre Genequand, Geneva, Switzerland. VACUUM INTERRUPT- ER OR SWITCH FOR ELECTRIC POWER NETWORKS. Patent dated Dec. 5, 1972. Dedication filed Mar. 26, 1984, by the assignee, Battelle Memorial Institute.

Hereby dedicates to the People of the United States the entire remaining term of said patent.

[Official Gazette May 29, 1984.]