GB2218262A - Electric arc interrupter - Google Patents

Abstract

An electric switch has an arc interrupter 16 mounted in a housing between two main conductors 12, 14. The interrupter 16 comprises a fixed contact 20, a fixed electrode 40 which forms part of contact 20 defining a first arcing surface 46, a second fixed or pivotable electrode 34 defining a second arcing surface 48, a permanent magnet 38 and a movable contact 34 which may also comprise the second electrode 34, the arcing surfaces 46, 48 and the permanent magnet 38 being coaxial with one another when the contacts 20, 34 are open, and the contact 34 being mounted for angular movement, about a pivot axis 66 between a make position and a break position. During opening of the interrupter 16, an arc is struck between the contacts 20, 34 after which it moves between arcing surfaces 46, 48. The permanent magnet 38 produces magnetic flux which interacts with the arc so that the arc is driven around an axis 18 in the annular gap between the surfaces 46, 48. The movement of the arc assists in extinguishing the arc at an appropriate current zero. <IMAGE>

Description

"ELECTRIC ARC INTERRUPTER" The invention relates to electric arc interrupters.

An arc interrupter has been proposed for example in the United Kingdom patent application No. 8308651 (Publication 2119573A) in which an arc drawn between separating contacts is transferred from a movable contact to an annular arcing electrode during the later part of movement of the movable contact, this arcing electrode is coaxial with and connected to an arc-driving coil through which arc current flows. Consequently only when the movable contact has reached the later part of its movement is the arc-driving coil brought into the arc current path to produce a magnetic field, to drive the arc around the electrode and ultimately to-be extinguished.

For efficient extinguishment, the arc should be between conductive surfaces which are concentric, and be driven by the interaction of magnetic flux especially when approaching a current zero. Although this is achieved in the preceding example once the arc is transferred to the annular arcing electrode and time has elapsed for necessary magnetic flux to be established by the arc-driving coil, there is an initial but lengthy period when the arc and its roots are stationary on both the fixed and movable contacts, time during which erosion of contact material is more severe than that resulting from a mobile arc. Also of disadvantage, the duration of arcing to the instant of extinction is extended because of the late transfer of the arc from the movable contact to the annular arcing electrode.

A theoretical discussion relating to the rotation of arcs to assist in. extinguishment thereof is given in a paper by Fujiwara, K., Ono, S.I., entitled "Rotating Arc Driven by Magnetic Flux in SF6 Gas", 2nd International Symposium on Switching Arc Materials, Part II (Post conference materials), Lodz, Poland, 25 - 27th September, 1973 (published Lodz, Poland : Techn. Univ. Lodz 1975), pages 62 - 67.

An object of the invention is to provide an arc interrupter which is compact and suitable for voltages up to at least 36 kilovolts in which magnetic flux is immediately available to interact with the arc when the arc is struck and afterwards, to speed movement of the arc and its roots to reduce both arc erosion of the materials contacted and the time of arc duration. A further object of the invention to improve the efficiency of the arc interruption is to provide magnetic flux in the arc interrupter at a level independent of the level of arc current so that the speed of the arc driven around the arcing surfaces as it approaches a current zero is not reduced by a related reduction in the interacting magnetic flux. Thereby making the arc position at current zero the greatest distance from ionised gas previously produced by higher arc current.One other object is to eliminate the constraint placed upon the circuit-breaking capacity of the arc interrupter by a limited thermal rating of the arc-driving coil fitted in arc interrupters of existing design. A yet further object is to reduce the time delay in arc transfer from a fixed contact to its arcing electrode, by reducing the inductance of the loop circuit constituted by the path of the re-routed current and its original route. The above objects are achieved by the use of an arc-driving permanent magnet in the arc interrupter instead of an arc-driving coil.Although anisotropic metal permanent magnets of high coercive force may be used in this invention, the preferred type is the anisotropic ferrite permanent magnet of exceptionally high coercive force and which is impervious to self demagnetisation or demagnetisation by external alternating magnet fields and will only demagnetise when above the Curie point which at 450 degrees C. is far above the operating temperature of this application. The permanent magnet may be in the form of particles of ferrite materials or rare earth cobalt alloys embedded in an orientated manner in resilient rubber or plastics material, produced either in a block or strip shape.

An arc interrupter, according to the invention, comprises, a fixed electrode and an electrode which is either fixed or pivoted depending upon the variation of the invention, the said electrodes provide, respectively, first and second coaxial arcing surfaces separated by an annular gap, said first arcing surface being closer to the common axis of said arcing surfaces than said second arcing surface, a fixed contact, a movable contact which in variations of the invention is itself the said concentric arcing electrode providing said second arcing surface when in the break position in which said movable contact is disengaged from said fixed contacts, an arc-driving permanent magnet coaxial with said arcing surfaces, said movable contact which is mounted for angular movement about a pivot axis between a make position in which said movable contact extends from said pivot axis towards said common axis and is in engagement with said fixed contact and in which said movable contact is included in an openable main current path and a break position in which said movable contact is disengaged from said fixed contact.

With the use of an arc-driving permanent magnet the movement of the arc differs from that resulting from the interaction of magnetic flux from an arc-driving coil. The coil when excited by arc current produces magnetic flux so phased in relationship to the arc as to cause effective arc movement; with optimum phasing, the movement of the arc is in one direction for a period of 45 electrical degrees then reversed for a period of 135 electrical degrees this sequence is repeated until arc extinguishment. With an arc-driving permanent magnet the comparative arc movement is in one direction for a period of 180 electrical degrees then reversed for a period of 180 electrical degrees with this sequence repeated until arc extinguishment.

The invention includes an electric switch comprising at least one arc interrupter according to the invention.

Electric switches will now be described by way of example only to illustrate the invention with reference to the accompanying drawings in which: Figure 1 is a vertical section through part of an electric switch including an arc interrupter whose movable contact is ultimately a concentric arcing electrode and whose contact pivot is parallel to the common axis of the arcing surfaces.

Figure 2 is a vertical section through part of an electric switch including an arc interrupter whose arcing electrodes are fixed and whose contact pivot is parallel to the common axis of the arcing surfaces.

Figure 3 is a vertical section on the line I - I in Figure 4 through part of an electric switch including an arc interrupter whose arcing electrodes are fixed and whose contact pivot is parallel to the common axis of the arcing surfaces.

Figure 4 is a horizontal section on the line II - II in Figure 3.

Figure 5 is a vertical section through part of an electric switch including an arc interrupter whose movable contact is ultimately a concentric arcing electrode and whose contact pivot is normal to the common axis of the arcing surfaces.

Figure 6 is a vertical section through part of an electric switch including an arc interrupter whose movable contact is ultimately a concentric arcing electrode and houses a permanent magnet and whose contact pivot is normal to the common axis of the arcing surfaces.

Description, with reference to Figure 1: An electric switch (see Figure 1) has a metal housing (not shown) which is filled with an insulating medium for example sulphur hexafluoride (SF6) gas under pressure. A bushing 10 insulates a main copper conductor 12 from, and enables it to pass in sealed relationship through the housing. A second main conductor 14 insulated by a bushing 26 is similarly mounted relative to the housing at a location remote from the conductor 12. The conductors 12, 14 carry one phase of the current supplied through the switch.

An arc interrupter 16 forms part of an openable main current path between the two main conductors- 12 and 14. The conductor 12 and the interrupter 16 are coaxial on the common axis 18.

The arc interrupter 16 has a fixed contact 20 which is mounted on the inner end of conductor 12. The contact 20 has a steel stud 22 which is screwed into a threaded bore 24 in the conductor 12. A first annular copper contact consists of the base of arcing electrode 40 to which a semi-circular fixed contact pivot block 30 is attached, is mounted on and held in engagement with the conductor 12 by the stud 22. A peg 42, fixed in a bore in the end of the conductor 12, extends into the bore 44 to substantially prevent the rotation of the members 30 and 40 relative to the conductor 12. A second annular copper contact member 32 is located on the stud 22. A segment has been removed from one side of the fixed contact pivot block 30 to allow a movable contact 34 (described more fully below) to sit between the members 32 and 40.The lower surface 52 of the fixed contact pivot block 30 is slightly inclined to a line which is normal to the axis 18.

The contact member 32 is cup-shaped and is retained relative to the stud 22 by a steel compression spring-36, which is located within the contact member 32 and is trapped between the base of the contact member 32 and a spring cup 54. The spring cup 54 is retained on the stud 22 by a pin 56 located in a transverse passage in the free end of the stud 22.

The spring 36 acts on the contact 32 so that it tends to pivot about the stud 22 in a direction transversely of the axis 18 (as it is permitted to do because of the inclined surface 52 of the fixed contact pivot block 30) whereby contact pressure is exerted on the portion of the movable contact 34 that is located between the contact members 32 and 40.

A fixed assembly 50 is secured to the free end of the conductor 12.

The assembly 50 comprises a cup-shaped cylindrical arcing electrode 40, an arc-driving permanent magnet 38 whose magnetic polarity may either be as illustrated in Figure 1 or reversed, and ferromagnetic material described next below.

The ferromagnetic material is mild steel and consists of a saucer-shaped pole piece 68 with a narrow radial split, is located below bushing 10 around conductor 12 and sits on the top of the permanent magnet 38.

The movable contact 34 is pivoted on a block (not shown) attached to the free end of conductor 14. The contact.34 is movable in a plane about a pivot axis between the make position in which it is in engagement with the fixed contact 20 (shown in ghost outline 64) and a break position in which it is disengaged from the contact 20 (shown in full 34). The axis 66 of the movable contact 34 is parallel to the axis 18 and the contact 34 is normal to the axis 18. Thus the length of the arc interrupter 16 is kept to a minimum.

The movable contact 34 is a copper annulus of flat section of varying width normal to its axis. The portion of the contact 34 which is in engagement with the fixed contact 20 in the make position is the portion closest to the links 60 operating the contact 34, and is of increased section extending to its pivot block (not shown). The increased section of contact 34 carries continuous current when the contact 34 is in the make position.

The contact 34 has a hole in which a link pin 62 is located, the pin 62 also passes through a hole in the end of each of a pair of links 60 of insulating material positioned on each side of the contact 34. The other end of the links 60 are similarly pivotally secured to a mild steel lever which is fixed to a rotatable operating shaft (lever and shaft not shown).

Operation, with reference to Figure 1: The arc interrupter 16 is shown in the open position in full line, and in the closed position after movement of the movable contact 34 in arrowed direction in which part of the movable contact 34 is shown as 64 in ghost outline. When the interrupter 16 is in the closed position the main current path is through the main conductor 12, the fixed contact 20 (the contact member 32 of which is forced slightly apart by the movable contact 34), the movable contact 34, the movable contact pivot block and the main conductor 14.

Actuation of the operating mechanism pulls the links 60 to the position shown which causes the movable contact 34 to rotate in a plane about its pivot axis which is parallel to axis 18 to the position shown in full outline at 70.

During movement of the movable contact 34, it first disengages from contact member 32 of the fixed contact 20 and then from the member 40, an arc is struck between the contact 34 and the edge 28 of member 40.

The arc-driving permanent magnet 38 produces magnetic flux with which the arc interacts and is driven around the arcing surfaces 46 and 48 like the spoke in a rotating or oscillating wheel. The magnetic field of the magnet 38 is intensified around the arc by the pole piece 68.

The movement of the arc through the SF6 gas aids in dissipating energy from the arc and ionised gas in the vicinity of the arc so that conditions are optimised for the arc to extinguish at a current zero.

At an appropriate current zero the arc is extinguished.

The interrupter 16 is closed by reverse operation of the links 60 causing the movable contact 34 to return to the position 64 shown in ghost outline.

The switch described with reference to Figure 1 has a normal rating of 15.5 kilovolts, 560 amperes, and a fault condition rating of 12.5 kiloamperes. The particular switch described is an automatic recloser type of switch. In recloser switches, an interrupter-16 is provided for each phase of current supplied.

However, other applications for switches having interrupters constructed in accordance with the invention are envisaged. The axis of the interrupter 16 can be other than vertical. The switch can have a housing made from either metal or from insulating material for example cast epoxy resin.

For other applications the rating of the switch can be varied. A higher or lower rating for the switch can be achieved in a number of ways either alone or in combination. For example the contact pressure can be altered, and the pressure of the insulating gas can be altered.

Alternatively, the rating of switches can be increased by using two or more interrupters which are operable simultaneously with one another and which are connected in series between the main conductors of a current phase.

Description, with reference to Figure 2: Another embodiment of an electric switch (see Figure 2) has a metal housing (not shown) which is filled with an insulating medium e.g.

SF6 gas. Bushing 110 insulates the main conductor 112, from, and enables it to pass in sealed relationship through the housing. A second main conductor insulated by a bushing (not shown) is similarly mounted relative to the housing at a location remote from the conductor 112. The second main conductor mechanically supports the outer cylindrical arcing electrode 114 and the movable contact 134 and is electrically connected to them. The relationship with the arc interrupter 116, the location, and the arrangement of the outer cylindrical arcing electrode and the movable contact 134 on the second main conductor and its bushing is similar to that shown in Figure 4.

An arc interrupter 116 forms part of an openable main current path between the two main conductors 112 and another not shown. The conductor 112 and the interrupter 116 are coaxial on the common axis 118.

The arc interrupter 116 has a fixed contact 120 which is mounted on the inner end of conductor 112. The contact 120 has a steel stud 122 which is screwed into a threaded bore 124 in the conductor 112.

A first annular copper contact consists of the base of arcing electrode 140 to which a semi-circular fixed contact pivot block 130 is attached, is mounted on and held in engagement with conductor 112 by the stud 122. A peg 142, fixed in a bore in the end of the conductor 112, extends into the bore 144 to substantially prevent the rotation of the members 130 and 140 relative to the conductor 112.

A second annular copper contact member 132 is located on the stud 122. A segment has been removed from one side of the fixed contact pivot block 130 to allow a movable contact 134 to sit between the members 132 and 140. The lower surface 152 of the fixed contact pivot block 130 is slightly inclined to a line which is normal to the axis 118.

The contact member 132 is cup-shaped and is retained relative to the stud 122 by a steel compression spring 136, which is located within the contact member 132 and a spring cup 154. The spring cup 154 is retained on the stud 122 by a pin 156 located in transverse passage in the free end of the stud 122.

The spring 136 acts on the contact 132 so that it tends to pivot about the stud 122 in a direction transversely of the axis 118 whereby contact pressure is exerted on the portion of the movable contact 134 that is located between the contact members 132 and 140.

A fixed assembly 150 is secured to the free end of the conductor 112. The assembly 150 comprises a cup-shaped cylindrical arcing electrode 140, an arc-driving permanent magnet 138 whose magnetic polarity may either be as illustrated in Figure 2 or reversed.

The movable contact 134 is a copper plate which is L-shaped similar to contact 232 (see Figure 4). The end potion of the contact 134 which engages with the fixed contact 120 in the make position is the portion of the contact 134 closest to the outer cylindrical arcing electrode 114 in the break position. The least distance between the contacts 120 and 134 is greater than the gap between the surfaces 126 and 146.

The movable contact 134 is driven by a pair of links of insulating material, positioned on each side of it and linked to it with a pin which passes through it and the pair of links. The other ends of the links are similarly pivotally secured to a mild steel lever which is fixed to a rotatable driving shaft for rotation therewith (except for the section through contact 134 these components are not shown).

The movable contact 134 is pivoted on the free end of the second main conductor from which it is electrically insulated at the pivot by a bush and two thrust washers of insulating material, and is positioned by a contact pivot block which is clamped and located around the main conductor. The movable contact 134 is electrically connected to the main conductor by means of two pairs of bridging contacts loaded by a steel compression spring (the un-numbered components referred to are similar to items 214, 254, 270 and 272 shown in Figure 4).

The outer arcing electrode 114 comprises a copper U-section ring which is attached to a brass lug which in turn is attached to the contact pivot block. The electrode 114 is supported to maintain a uniform annular gap between its arcing surface 126 and the opposite arcing surface 146 and suitable mechanical clearance to the movable contact 134. (The arrangement is similar to that shown in the portion of Figure 4 which features lug 250 and contact pivot block 254).

Operation, with reference to Figure 2: The arc interrupter 116 is shown in the open (break) position 162 and the movable contact 134 is shown again in ghost outline in the closed (make) position 128.

With the movable contact 134 in the closed (make) position, the main current path is through the main conductor 112, the fixed contact 120 (the contact member 132 of which is forced slightly apart by the movable contact 134), the movable contact 134, the bridging contacts and the second main conductor. (The latter two components are arranged similarly to those shown as 270 and 214 in Figure 4).

Actuation of the operating mechanism causes the movable contact 134 to rotate in a plane about its pivot axis which is parallel to axis 118 to the position shown in full outline at 162.

During movement of the movable contact 134, it first disengages from contact member 132 of the fixed contact 120 and'then from the member 140, an arc is struck between the contact 134 and the edge 128 of member 140.

The arc-driving permanent magnet 138 produces magnetic flux with which the arc interacts and is moved causing its roots also to move along the movable contact 134 and about the arcing surface 146 opposite until the arc root on the movable contact 134 transfers to the arcing suface 126 of the electrode 114. With the arc root transferred from the movable contact 134 to the arcing surface 126, the arcing electrode 114 is now in the arc current path in place of the movable contact 134. With the arc roots established on the arcing surfaces 126 and 146 the arc is driven around these arcing surfaces like a spoke in a rotating or oscillating wheel.

The movement of the arc through the SF6 gas aids in dissipating energy from the arc and ionised gas in the vicinity of the arc so that conditions are optimised for the arc to extinguish at a current zero.

At an appropriate current zero the arc is extinguished.

The switch described with reference to Figure 2 has a normal rating of 15.5 kilovolts, 560 amperes, and a fault condition rating of 12.5 kiloamperes. The particular switch described is an automatic recloser type of switch. In recloser switches, an interrupter 116 is provided for each phase of current supplied.

For other applications the rating of the switch can be varied in a number of ways either alone or in combination. For example the contact pressure can be altered, and the pressure of the insulating gas can be altered.

Alternatively, the rating of switches can be increased by using two or more interrupters which are operable simultaneously with one another and which are connected in series between the main conductors of a current phase.

Description, with reference to Figures 3 and 4: Another embodiment of an electric switch (see Figures 3 and 4) has a metal housing (not shown) which is filled with an insulating medium e.g. SF6 gas. Bushing 210 insulates the main conductor 212 from, and enables it to pass in sealed relationship through the housing.

A second main conductor 214 is similarly mounted relative to the housing at a location remote from the conductor 212. The two main conductors carry one phase of the current supplied through the switch An arc interrupter 216 forms part of an openable main current path between the two main conductors 212 and 214. The conductor 212 and the interrupter 216 are coaxial on the common axis 218.

The interrupter 216 has a fixed contact 220 which is mounted on the conductor 212, positioned below and adjacent the bushing 210. The contact 220 has two contact fingers 222 and two contact fingers 224, which are housed in an enclosure 226 which is clamped to the conductor 212.

The contact fingers 222 and 224 are shaped to pivot in their retaining recess 228 in enclosure 226, and each pair is loaded by a steel compression spring 230 whereby contact pressure is exerted on the portion of the movable contact 232 that is located between the contact fingers 222 and 224 when in engagement (as shown in ghost outline at 258 in Figure 3).

Contact finger 224 is longer than contact finger 222 so that the movable contact 232 upon operation of the interrupter 216 disengages from contact finger 224 after it has disengaged from contact finger 222, and an arc is struck preferentially between the arcing surface 234 of the contact finger 224 and contact 232 instead of between contact finger 222 and contact 232.

The contact fingers 222 and 224 and spring 230 are retained sideways within the enclosure 226 by plate 240, one plate 240 on each side of the enclosure 226.

A fixed assembly 260 is immediately below the fixed contact 220.

The assembly 260 is coaxial with the axis 218 and is bolted to the main conductor 212. The assembly 260 comprises a cup-shaped cylindrical arcing electrode 236 and an arc-driving permanent magnet 238 whose magnetic polarity may either be as illustrated in Figure 3 or reversed.

The movable contact 232 is a copper plate which is L-shaped when seen along the axis 252 (see Figure 4). The end portion 248 of the contact 232 which engages with the fixed contact 220 in the make position is the portion of the contact 232 closest to the outer cylindrical arcing electrode 242 in the break position. The least distance between the contacts 220 and 232 is greater than the gap between the surfaces 244 and 246. The end portion 248 of the contact 232 has a slightly tapered leading edge to assist the contact 232 to engage the fixed contact 220.

The movable contact 232 has a hole in which a link pin 256 is located, the pin 256 also passes through a hole in the end of each of a pair of links 262 of insulating material, position on each side of the contact 232. The pin 256 is retained in position by spring clips. The other end of the links 262 is similarly pivotally secured to a mild steel lever which is fixed to a rotatable shaft for rotation therewith (the latter components are not shown).

The movable contact 232 is pivoted on the free end of main conductor 214 from which it is electrically insulated at the pivot by a bush and two thrust washers of insulating material, and is positioned by contact pivot block 254 which is clamped and located around the main conductor 214. The movable contact 232 is electrically connected to the main conductor 214 by means of two pairs of bridging contacts 270 loaded by a steel compression spring 272.

The outer arcing electrode 242 comprises a copper U-section ring which is attached to a brass lug 250 which in tdrn is attached by two bolts to the contact pivot block 254. The electrode 242 is supported to maintain a uniform annular gap between its arcing surface 246 and the opposite arcing surface 244 and suitable mechanical clearance to the movable contact 232.

Operation, with reference to Figures 3 and 4: The arc interrupter 216 is shown in the open (break) position 266 and the movable contact 232 is shown again'in ghost outline in the closed (make) position 258.

With the movable contact 232 in the closed (make) position 258, the main current path is through the main conductor 212, the fixed contact 220 (the contact fingers 222 and 224 of which are forced slightly apart by the movable contact 232), the movable contact 232, the bridging contacts 270, the cylindrical contact 268 attached to contact 232, and the main conductor 214.

Actuation of the operating mechanism pulls the links 262 to the position shown in full outline at 264, which causes the movable contact 232 to rotate in a plane about the axis 252 to the position shown in full outline at 266.

During movement of the movable contact 232, it first disengages from contact fingers 222 of the fixed contact 220 and then from the contact fingers 224, an arc is struck between the contact 232 and the contact finger 224.

The arc-driving permanent magnet 238 produces magnetic flux with which the arc interacts and is moved causing its roots also to move along the movable contact 232 and about the arcing surface 244 opposite until the arc root on the movable contact 232 transfers to the arcing surface 246 of the electrode 242. With the arc root transferred from the movable contact 232 to the arcing surface 246, the arcing electrode 242 is now in the arc current path in place of the movable contact 232. With the arc roots established on the arcing surfaces 244 and 246 the arc is driven around these arcing surfaces like a spoke in a rotating or oscillating wheel.

The movement of the arc through the SF6 gas aids in dissipating energy from the arc and ionised gas in the vicinity of the arc-so that conditions are optimised for the arc to extinguish at a current zero.

At an appropriate current zero the arc is extinguished.

The arc interrupter 216 is closed (to make) by reverse operation of the links 262 causing the movable contact 232 to move from the position 266 shown in full line to position 258 shown in ghost outline.

The switch described with reference to Figures 3 and 4 has a normal rating of 36 kilovolts, 630 amperes, and a fault rating of 12.5 kiloamperes. The particular switch described is suitable for automatic reclosers, and for circuit breakers. ' In these an arc interrupter 216 is provided for each phase of current supplied.

Bowever, other applications for switches having arc interrupters constructed in accordance with the invention are envisaged. The axis of the arc interrupter 216 can be other than vertical. The switch can have a housing made either from metal or from insulating material for example cast epoxy resin.

For other applications, the rating of the switch can be varied. A higher or lower rating for the switch can be achieved in a number of ways either alone or in combination depending on the variation required. For example, the arc interrupter contact pressure can be altered, the pressure of the insulating gas can be altered, and the number of contacts increased to raise the current rating.

Alternatively, the voltage rating of switches can be increased by using two or more arc interrupters which are operable simultaneously with one another and which are connected in series between the main conductors of a current phase.

Description, with reference to Figure 5: Another embodiment of an electric switch (see Figure 5) has a metal housing (not shown) which is filled with an insulating medium e.g.

SF6 gas. Bushing 310 insulates the main conductor 312 from, and enables it to pass in sealed relationship through the housing. A second main conductor 314 is similarly mounted relative to the housing at a location remote from the conductor 312. The two main conductors carry one phase of the current supplied through the switch.

An arc interrupter 316 forms part of an openable main current path between the two main conductors 312 and 314. The conductor 312 and the interrupter 316 are coaxial on the common axis 318.

The interrupter 316 has a fixed contact 320 which is mounted on the conductor 312, positioned below and adjacent the bushing 310. The contact 320 has two contact fingers 322 and two contact fingers 324, which are housed in an enclosure 326 which is clamped to the conductor 312.

The contact fingers 322 and 324 are shaped to pivot in their retaining recess 328 in enclosure 326, and each pair is loaded by a steel compression spring 330 whereby contact pressure is exerted on the portion of the movable contact 332 that is located between the contact fingers 322 and 324 when in engagement (as shown in ghost outline at 348).

Contact finger 324 is longer than contact finger 322 so that the movable contact 332 upon operation of the interrupter 316 disengages from contact finger 324 after it has disengaged from contact finger 322, and an arc is struck preferentially between the arcing surface 334 of the contact finger 324 and contact 332 instead of between contact finger 322 and contact 332.

The contact fingers 322 and 324 and spring 330 are retained sideways within the enclosure 326 by plate 340, one plate 340 on each side of the enclosure 326.

A fixed assembly 350 is immediately below the fixed contact 320.

The assembly 350 is coaxial with the axis 318 and is bolted to the base of the fixed contact enclosure 326. The assembly 350 comprises an inverted cup-shaped cylindrical electrode 336 and an arc-driving permanent magnet 338 whose magnetic polarity may either be as illustrated in Figure 5 or reversed. The magnet is secured within the electrode by the spun-over rim of the electrode.

The movable contact 332 is a copper annulus whose pivot axis 360 is normal to the common axis 318 of the arcing surfaces 324 and 344.

The pivot on one side is constituted by a cylindrical conductor which is part of the electrical circuit of the movable contact 332 and is connected to the main conductor 314 by means of spring-loaded bridging contacts within the pivot block which clamps on to main conductor 314. The main conductor 314 is insulated by the bushing 346 to pass through the switch housing (not shown). The pivot block also contains a bearing which supports the cylindrical conductor and permits the smooth rotation of the movable contact 332 about its pivot axis 360. The pivot on the other side of the movable contact 332 comprises a metal cylinder attached to the movable contact 332.

This second metal cylinder is supported by a bearing within a metal block which is bolted to a post-type insulator which is attached at its other end to the inner surface of the switch housing (not shown).

The movable contact 332 has an attached lug 354 which has a hole in which a link pin 356 is located. The link pin 356 also passes through a hole in the end of a pair of links 358 of insulating material, positioned on each side of the lug 354. The other end of the links 358 are similarly pivotally secured to a mild steel lever 352 which is fixed to a rotatable operating shaft 362 for rotation therewith.

Operation, with reference to Figure 5: The interrupter 316 is shown in the open (break) position, and the movable contact 332 is shown in a second position (in ghost outline) in the closed (make) position 348.

With the movable contact 332 in the closed position 348, the main current path is through the main conductor 312, the fixed contact 320 (the contact fingers 322 and 324 of which are forced slightly apart by the movable contact 332), the movable contact 332, the pivot block attached to the main conductor 314, and the main conductor 314.

Actuation of the operating mechanism turns shaft 362 and the lever 352. The lever pulls the link 358 to the position shown in full outline at 364, which causes the movable contact 332 to rotate in a plane about the axis 360 to the position shown in full outline at 366.

During movement of the movable contact 332, it first disengages from contact finger 322 of the fixed contact 320 and then from the contact finger 324, an arc is struck between the contact 332 and the contact finger 324. Electromagnetic forces act on the arc and cause the arc root on the contact finger 324 to move to the arcing surface 334 of the contact finger 324 at its tip adjacent arcing electrode 336, and hence to the electrode 336, this at the earliest practicable time during the opening operation of the interrupter 316. The arc extends between surfaces 342 and 344.

The arc-driving permanent magnet 338 produces magnetic flux with which the arc interacts and is driven around the arcing surfaces 342 and 344 like the spoke in a rotating or oscillating wheel.

The movement of the arc through the SF6 gas aids in dissipating energy from the arc and ionised gas in the vicinity of the arc so that conditions are optimised for the arc to extinguish at a current zero.

At an appropriate current zero the arc is extinguished.

The interrupter 316 is closed by reverse operation of the links 358 causing the movable contact 332 to return to the position 348 shown in ghost outline.

The switch described with reference to Figure 5 has a normal rating of 15.5 kilovolts, 560 amperes, and a fault rating of 12.5 kiloamperes. The particular switch described is an automatic recloser type of switch. In recloser switches, an interrupter 316 is provided for each phase of current supplied. However, other applications for switches having interrupters constructed in accordance with the invention are envisaged. The axis of the interrupter 316 can be other than vertical. The switch can have a housing made either from metal or from insulating material for example cast epoxy resin.

For other applications, the rating of the switch can be varied. A higher or lower rating for the switch can be achieved in a number of ways either alone or in combination depending on the variation required. For example, the interrupter contact pressure can be altered; the pressure of the insulating gas can be altered, and the number of finger contacts increased to increase the current rating.

Alternatively, the rating of the switches can be increased by using two or more interrupters which are operable simultaneously with one another and which are connected in series between the main conductors of a current phase.

Description, with reference to Figure 6: Another embodiment of an electric switch (see Figure 6) has a metal housing (not shown) which is filled with an insulating medium e.g. SF6 gas. Bushing 410 insulates the main conductor 412 from, and enables it to pass in sealed relationship through the housing.

A second main conductor 414 is similarly mounted relative to the housing at a location remote from the conductor 412. The two main conductors carry one phase of the current supplied through the switch.

An arc interrupter 416 forms part of an openable main current path between the two main conductors 412 and 414. The conductor 412 and the interrupter 416 are coaxial on the common axis 418.

The interrupter 416 has a fixed contact 420 which is mounted on the conductor 412, positioned below and adjacent the bushing 410. The contact 420 has two contact fingers 422 and two contact fingers 424, which are housed in an enclosure 426 which is clamped to the conductor 412.

The contact fingers 422 and 424 are shaped to pivot in their retaining recess 428 in enclosure 426, and each pair is loaded by a steel compression spring 430 whereby contact pressure is exerted on the portion of the movable contact 432 that is located between the contact fingers 422 and 424 when in engagement (as shown in ghost outline 448).

Contact finger 424 is longer than contact finger 422 so that the movable contact 432 upon operation of the interrupter 416 disengages from contact finger 424 after it has disengaged from contact finger 422, and an arc is struck preferentially between the arcing surface 434 of the contact finger 424 and contact 432 instead of between contact finger 422 and contact 432.

The contact fingers 422 and 424 and spring 430 are retained sideways within the enclosure 426 by plate 440, one plate 440 on each side of the enclosure 426.

A fixed central arcing electrode 436 is immediately below the fixed contact 420. The central arcing electrode 436 is coaxial with the axis 418 and is bolted to the base of the fixed contact enclosure 426. The central arcing electrode 436 is shaped like an inverted truncated cone, and is centralised by its inner conducting surface on to the conical surface of the base of the fixed contact enclosure 426.

The movable contact 432 is a copper annulus whose pivot axis 460 is normal to the common axis 418 of the arcing surfaces 442 and 444.

The movable contact 432 partially encloses within its inverted U-shaped -cross-section an annular shaped arc-driving permanent magnet 438 which is retained in position by the spun-over inside edge of the contact.

The arc-driving permanent magnet 438 may either be that formed from a flexible strip of rubber or plastic embedding ferrite or rare earth cobalt alloy or a complete ring of permanent magnet material. The magnetic polarity of the permanent magnet 438 may either be as illustrated in Figure 6 or reversed.

The movable contact 432 has a pivot on one side constituted by a cylindrical conductor which is part of the electrical circuit of the movable contact 432 and is connected to the main conductor 414 by means of spring-loaded bridging contacts within the pivot block which clamps on to the main conductor 414. The main conductor 414 is insulated by the bushing 446 to pass through the switch housing (not shown). The pivot block also contains a bearing which supports the cylindrical conductor and permits smooth rotation of the movable contact 432 about its pivot axis 460. The pivot on the other side of the movable contact 432 comprises a metal cylinder attached to the movable contact 432. This second metal cylinder is supported by a bearing within a metal block which is bolted to a post-type insulator which is attached at its other end to the inner surface of the switch housing (not shown).

The movable contact 432 has an attached lug 454'which has a hole in which a link pin 456 is located. The link pin 456 also passes through a hole in the end of a pair of links 458 of insulating material, positioned on each side of the lug 454. The other end of the links 458 are similarly pivotally secured to a mild steel lever 452 which is fixed to a rotatable operating shaft 462 for rotation therewith.

Operation, with reference to Figure 6: The interrupter 416 is shown in the open (break) position, and the movable contact 432 is shown in a second position (in ghost outline) in the closed (make) position 448.

With the movable contact 432 in the closed position 448, the main current path is through the main conductor 412, the fixed contact 420 (the contact fingers 422 and 424 of which are forced slightly apart by the movable contact 432), the movable contact 432, the pivot block attached to the main conductor 414, and the main conductor 414.

Actuation of the operating mechanism turns shaft 462 and the lever 452. The lever pulls the link 458 to the position shown in full outline at 464, which causes the movable contact 432 to rotate in a plane about the axis 460 to the position shown in full outline at 466.

During movement of the movable contact 432, it first disengages from contact finger 422 of the fixed contact 420 and then from the contact finger 424, an arc is struck between the contact 432 and the contact finger 424. Electromagnetic forces act on the arc and cause the arc root on the contact finger 424 to move to the arcing surface 434 of the contact finger 424 at its tip adjacent arcing electrode 436, and hence to the electrode 436, this at the earliest practicable time during the opening operation of the interrupter 416. The arc extends between surfaces 442 and 444.

The arc-driving permanent magnet 438 produces magnetic flux with which the arc interacts and is driven around the arcing surfaces 442 and 444 like the spoke in a rotating or oscillating wheel.

The movement of the arc through the SF6 gas aids in dissipating energy from the arc and ionised gas in the vicinity of the arc so that conditions are optimised for the arc to extinguish at a current zero..

At an appropriate current zero the arc is extinguished.

The interrupter 416 is closed by reverse operation of the links 458 causing the movable contact 432 to return to the position 448 shown in ghost outline.

The switch described with reference to Figure 6 has a normal rating of 15.5 kilovolts, 560 amperes, and a fault rating of 12.5 kiloamperes. The particular switch described is an automatic recloser type of switch. In recloser switches, an interrupter 416 is provided for each phase of current supplied. However, other applications for switches having interrupters constructed in accordance with the invention are envisaged. The axis of the interrupter 416 can be other than vertical. The switch can have a housing made either from metal or from insulating material for example cast epoxy resin.

For other applications, the rating of the switch can be varied. A higher or lower rating for the switch can be achieved in a number of ways either alone or in combination depending on the variation required. For example, the interrupter contact pressure can be altered, the pressure of the insulating gas can be altered, and the number of finger contacts increased to increase the current rating.

Alternatively, the rating of the switches can be increased by using two or more interrupters which are operable simultaneously with one another and which are connected in series between the main conductors of a current phase.

Claims (19)

CLAIMS.

1. An arc interrupter comprising a fixed electrode and an electrode which is either fixed or pivoted depending upon the variation of the invention, the said electrodes provide, respectively, first and second coaxial arcing surfaces separated by an annular gap, said first arcing surface being closer to the common axis of said arcing surfaces than said second arcing surface, a fixed contact, a movable contact which in variations of the invention is itself the said concentric arcing electrode providing said second arcing surface when in the break position in which said movable contact is disengaged from said fixed contacts, an arc-driving permanent magnet coaxial with said arcing surfaces, said movable contact which is mounted for angular movement about a pivot axis between a make position in which said movable contact extends from said pivot axis towards said common axis and is in engagement with said fixed contact and in which said movable contact is in an openable main current path and a break position in which said movable contact is disengaged from said fixed contact.

2. An arc interrupter according to Claim 1, in which said pivot axis is parallel to said common axis.

3. An arc interrupter according to Claim 1, in which said pivot axis is normal to said common axis.

4. An arc interrupter according to any preceding claim, in which said interrupter comprises two of said fixed contacts parallel with and remote from one another, two of said fixed electrodes which provide said first arcing surface coaxial with and spaced axially apart from one another, one said fixed electrode which provides said second arcing surface coaxial with and common to both said first arcing surfaces, two of said arc-driving permanent magnets with one pole face adjacent their respective said fixed contact and at one end of their respective said fixed electrode which provides said first arcing surface and the second pole face of said permanent magnets at the other end of their respective said fixed electrode which provides said first arcing surface, with the said permanent magnets pole faces which face each other being at the same magnetic polarity, and two of said movable contacts each mounted for angular movement relative to their common said second arcing surface said movable contacts being electrically connected to and movable simultaneously with one another.

5. An arc interrupter according to Claim 4, in which said pivot axis of said movable contacts are coaxial with one another.

6. An arc interrupter according to any preceding claim, in which said interrupter comprises ferromagnetic material which forms part of a magnetic circuit produced by said arc-driving permanent magnet.

7. An arc interrupter according to Claim 1, substantially as hereinbefore described with reference to Figure 1 of the accompanying drawings.

8. An arc interrupter according to Claim 1, substantially as hereinbefore described with reference to Figure 2 of the accompanying drawings.

9. An arc interrupter according to Claim 1, substantially as hereinbefore described with reference to Figures 3 and 4 of the accompanying drawings.

10. An arc interrupter according to Claim 1, substantially as hereinbefore described with reference to Figure 5 of the accompanying drawings.

11. An arc interrupter according to Claim 1, substantially as hereinbefore described with reference to Figure 6 of the accompanying drawings.

12. An electric switch comprising a housing containing insulating medium and conductor means which form an op'enable main current path within the housing and which includes at least one arc interrupter as claimed in Claim 1.

13. An electric switch according to Claim 12, in which said conductor means include two of said arc interrupter which are operable simultaneously with one another and which are electrically connected to one another in series.

14. An electric switch comprising a housing containing insulating medium and conductor means which form an openable main current path within the housing and which include at least one arc interrupter as claimed in Claim 4.

15. An electric switch according to Claim 12, substantially as hereinbefore described with reference to Figure 1 of the accompanying drawings.

16. An electric switch according to Claim 12, substantially as hereinbefore described with reference to Figure 2 of the accompanying drawings.

17. An electric switch according to Claim 12, substantially as hereinbefore described with reference to Figures 3 and 4 of the accompanying drawings.

18. An electric switch according to Claim 12, substantially as hereinbefore described with reference to Figure 5 of the accompanying drawings.

19. An electric switch according to Claim 12, substantially as hereinbefore described with reference to Figure 6 of the accompanying drawings.