GB2223880A

GB2223880A - Electric arc interrupter

Info

Publication number: GB2223880A
Application number: GB8824197A
Authority: GB
Inventors: George Francis Crisp
Original assignee: Individual
Current assignee: Individual
Priority date: 1988-10-15
Filing date: 1988-10-15
Publication date: 1990-04-18
Anticipated expiration: 2008-10-15
Also published as: GB8824197D0; GB2223880B

Abstract

An arc interrupter 5 mounted in a housing between two conductors 2, 4 comprises a fixed contact 7, two arcing electrodes 17, 18, one or more arc-driving permanent magnets 23, 24 which are coaxial with arcing surfaces 19, 20 of the electrodes 17, 18 and a movable contact 15 mounted for guided movement between a make position and a break position. The fixed contact 7 is electrically connected to and located outside one of the electrodes 17 and the movable contact 15 is electrically connected to and located outside the other electrode 18. During opening of the interrupter 5 an arc is struck between the contacts 7 and 15 after which it moves between surfaces 19, 20. The permanent magnets 23, 24 produce magnetic flux which interacts with the arc so that the arc between the surfaces 19, 20 is driven around the axis 6. The movement of the arc assists in extinguishing the arc at an appropriate current zero. One of the electrodes 18 may be movable. <IMAGE>

Description

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

The proposed arc interrupter is arranged to have a relatively short arc extinguishing time and to facilitate relatively small phase centre dimensions in a multi-phase switch in which at least one proposed arc interrupter is contained in each phase.

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 gas ionised 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 preceding 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 magnetic 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 plastic material, produced in a block or strip shape.

The object of minimising arc erosion of the contacts and maximising efficiency of arc interruption can be furthered by the introduction of a movable function to one of the two arcing electrodes so that arcing is confined to the electrodes during the major portion of the contact breaking operation.

An arc interrupter, according to the invention, comprises a fixed electrode and an electrode which is either fixed or movable depending upon the variation of the invention, the said electrodes provide coaxial arcing surfaces separated by an axial gap, a fixed contact, a movable contact, one or more arc driving permanent magnets coaxial with said arcing surfaces, said movable contact which is mounted for movement between a make position in which said movable contact extends from and outside one said electrode and is in engagement with said fixed contact connected to and outside the opposite said electrode and in which said movable contact is in an openable 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 vertidal section through part of an electric switch including an arc interrupter whose arcing electrodes are fixed and whose fixed and movable contacts are both outside the arcing electrodes.

Figure 2 is a vertical section through part of an electric switch including an arc interrupter which has one fixed arcing electrode and one arcing electrode which moves simultaneously with the movable contact which with the fixed contact is outside the arcing electrodes.

Figure 3 shows the relative movement of the movable electrode and the movable contact together with their combined operating linkage, referring to Figure 2.

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 1 insulates a main copper conductor 2 from, and enables it to pass in sealed relationship through the housing. A second main conductor 4 insulated by a bushing 3 is similarly mounted relative to the housing at a location remote from the conductor 2. The conductors 2, 4 carrying one phase of the current supplied through the switch.

A arc interrupter 5 forms part of an openable main current path between the two main conductors 2 and 4.

The arc interrupter 5 has a fixed contact 7 which is mounted on the conductor 2. The contact 7 has two contact fingers 8 and two contact fingers 9, which are housed in an enclosure 10 which is clamped to the conductor 2.

The contact fingers 8 and 9 are shaped to pivot in their retaining recess 11 in enclosure 10, and each pair is loaded by a steel compression spring 12 whereby contact pressure in exerted on the portion of the movable contact 15 that is located between the contact fingers 8 and 9 when in engagement (as shown in ghost outline 29).

Contact finger 9 is longer than contact finger 8 so that the movable contact 15 upon operation of the interrupter 5 disengages from contact finger 9 after it has disengaged from contact finger 8, and an arc is struck preferentially between the arcing surface 14 of the contact finger 9 and contact 15 instead of between contact finger 8 and contact 15.

The contact finger 8 and 9 and spring 12 are retained sideways within the enclosure 10 by plate 13.

A fixed annular arcing electrode 17 is located alongside the fixed contact 7, with the fixed contact 7 outside and adjacent the periphery of the electrode 17. The electrode 17 is electrically connected to the fixed contact 7 through the pair of brass lugs 21 attached to and supporting the electrode 17 and bolted to the fixed contact enclosure 10.

A second fixed annular arcing electrode 18 is opposite the other electrode 17 separated by a gap and shares a common axis 6. The electrode 18 is electrically connected to the movable contact guide sleeve 25 through a pair of brass lugs 22 attached to and supporting the electrode 18. The electrode 18 is adjacent the movable contact 15 which is also outside the electrode 18. The guide sleeve 25 is clamped to the conductor 4.

The annular arcing electrodes 17 and 18 enclose within their U-shaped cross-section annular shaped arc-driving permanent magnets 23 and 24 respectively which are retained in position by the spun-over inside edge of the electrodes.

The arc-driving permanent magnets 23 and 24 may either be, formed from a flexible strip of rubber or plastic embedding ferrite or rare earth cobalt alloy, or from a complete ring of permanent magnet material. The magnet polarity of the permanent magnets 23 and 24 may either be as illustrated in Figure 1 or reversed.

The movable contact 15 whose movement is parallel to the common axis 6 of the arcing electrodes 17 and 18 consists of a copper strip of rectangular cross-section.

The movable contact 15 is guided in its movement between its make position 29 (shown in ghost outline) and its break position 28 (shown in full) by the guide sleeve 25. The guide sleeve 25 also houses two sets of multi-finger bent-over contacts 26 which have two multi-finger leaf-springs 27 to press them onto the flat surface of the movable contact 15.

The contacts 26 and the springs 27 are also bolted to the guide sleeve 25 by the bolts which also secure the arcing electrode lugs 22.

The movable contact 15 has a hole at one end in which a link pin 31 is located. The link pin 31 also passes through a hole in the end of a pair of links 30 of insulating material, positioned on each side of the contact 15. The other end of the links 30 are similarly pivotally secured to a mild steel lever 32 which is fixed to a rotatable operating shaft 33 for rotation therewith.

Operation, with reference to Figure 1 The interrupter 5 is shown in the open (break) position, and the movable contact 15 is shown in a second position (in a ghost outline) in the closed (make) position 29.

With the movable contact 15 in the closed position 29, the current path is through the conductor 2, the fixed contact 7 (the contact fingers 8 and 9 of which are forced slightly apart by the movable contact 15), the movable contact 15, the movable contact guide sleeve 25 clamped to the conductor 4, and the conductor 4.

Actuation of the operating mechanism turns shaft 33 and the lever 32. The lever 32 pulls the links 30 to the position shown in full outline at 34, which causes the movable contact 15 to be guided parallel to the common axis 6 of the arcing electrodes 17 and 18 to the position 28 shown in full outline.

During movement of the movable contact 15, it disengages from contact finger 8 of the fixed contact 7 and then from the contact finger 9, an arc is struck between the contact 15 and the contact finger 9. Electromagnetic forces act on the arc and cause the arc root on the contact finger 9 to move to the arcing surface 14 of the contact finger 9 at its tip adjacent arcing electrode 17, and hence to the electrode 17, this at the earliest practicable time during the opening operation of the interrupter 5.

During further movement of the movable contact 15 the arc on its arcing surface 16 transfers to the arcing surface 20 of arcing electrode 18 and extends between surfaces 19 and 20 of arcing electrodes 17 and 18.

The arc-driving permanent magnets 23 and 24 produce magnetic flux with which the arc interacts and is driven around the arcing surfaces 19 and 20 like a stave in a rolling or oscillating barrel.

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 5 is closed by reverse operation of the links 30 causing the movable contact 15 to return to the position 29 (shown in ghost outline).

The switch described with reference to Figure 1 has a normal rating of 15.5 kilovolts, 630 amperes, and a fault rating of 12.5 kiloamperes. The switch can have a housing made either from metal or from insulating material for example cast epoxy resin, and an interrupter 5 provided for each phase of current supplied.

Depending upon its application, 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 conductors of a current phase.

Description, with reference to Figure 2 and Figure 3 Another embodiment of an electric switch (See Figure 2) has a metal housing (not shown) which is filled with an insulating medium for example sulphur hexaflUQride (SF6) gas under pressure. A bushing 41 insulates a main copper conductor 42 from,and enables it to pass in sealed relationship through the housing. A second main conductor 44 insulated by a bushing 43 is similarly mounted relative to the housing at a location remote from the conductor 42. The conductors 42 and 44 carry one phase of the current supplied through the switch.

An arc interrupter 45 forms part of an openable main current path between the two main conductors 42 and 44.

The arc interrupter 45 has a fixed contact 47 which is mounted on the conductor 42. The contact 47 has two contact fingers 48 and two contact fingers 49, which are housed in an enclosure 50 which is clamped to the conductor 42.

The contact fingers 48 and 49 are shaped to pivot in their retaining recess 51 in enclosure 50, and each pair is loaded by a steel compression spring 52 whereby contact pressure is exerted on the portion of the movable contact 55 that is located between the contact fingers 48 and 49 when in engagement (as shown in ghost outline 69).

Contact finger 49 is longer than contact finger 48 so that the movable contact 55 upon operation of the interrupter 45 disengages from contact finger 49 after it has disengaged from contact finger 48, and an arc is struck preferentially between the arcing surface 54 of the contact finger 49 and contact 55 instead of between contact finger 48 and contact 55.

The contact fingers 48 and 49 and spring 52 are retained sideways within the enclosure 50 by plate 53.

A fixed annular arcing electrode 57 is located alongside the fixed contact 47, with the fixed contact 47 outside and adjacent the periphery of the electrode 57. The electrode 57 is electrically connected to the fixed contact 47 through the pair of brass lugs 61 attached to and supporting the electrode 57 and bolted to the fixed contact enclosure 50.

A second annular arcing electrode 58 which is movable is opposite the other electrode 57, is separated by a variable gap and shares a common axis 46. The electrode 58 is electrically connected to the movable contact guide block 65 by a flexible conductor 85 via a disc 86 and a cylindrical conductor 87. The electrode 58 is attached to and supported by the disc 86 which is pierced by a number of holes spaced to give a rim-hub-spokes form.

The annular arcing electrodes 57 and 58 enclose within their Ushaped cross-section annular shaped arc-driving permanent magnets 63 and 64 respectively which are retained in position by the spun-over inside edge of the electrodes.

The arc-driving permanent magnets 63 and 64 may either be 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 permanents 63 and 64 may either be as illustrated in Figure 2 or reversed.

The disc 86 of the movable arcing electrode 58 is bolted to the cylindrical conductor 87. The movement of the conductor 87 is guided by a bush 89 of electrically insulating material which lines the bore of a hole in the contact guide block 65, through which it passes.

The conductor 87 has located at one end a link pin 74. The link pin 74 also passes through a hole in the end of a pair of links 73 of insulating material, positioned on each side of the conductor 87. The other end of the links 73 are similarly pivotally secured to a mild steel lever 75 which is fixed to a rotatable operating shaft 76 for rotation therewith.

The movable contact 55 whose movement is parallel to the common axis of the arcing electrodes 57 and 58 consist of a copper strip of rectangular cross-section.

The movable contact 55 is guided in its movement between its make position 69 (shown in ghost outline) and its break position 68 (shown in full) by the guide sleeve 65. The guide sleeve 65 also houses two sets of multi-finger bent-over contacts 66 which have two multi-finger leaf-springs 67 to press them onto the flat surface of the movable contact 55.

The contacts 66 and the springs 67 are bolted to the guide sleeve 65.

The movable contact 55 has a hole at one end in which a link pin 71 is located. The link pin 71 also passes through a hole in the end of a pair of links 70 of insulating material, positioned on each side of the contact 55. The other end of the links 70 are similarly pivotally secured to a mild steel lever 72 which is fixed to a rotatable operating shaft 76 for rotation therewith.

The links 70 and 73 driving the movable contact 55 and the movable electrode 58 respectively act simultaneously and are spaced apart from each other.

Operation, with reference to Figure 2 and Figure 3 The interrupter 45 is shown in the open (break) position, and the movable contact 55 is shown (in ghost outline) in the closed (make) position 69.

With the movable contact 55 in the closed position 69, the current path is through the conductor 42, the fixed contact 47 (the contact fingers 48 and 49 of which are forced slightly apart by the movable contact 55), the movable contact 55, the movable contact guide sleeve 65 clamped to the conductor 44, and the conductor 44.

Actuation of the operating mechanism turns shaft 76 and the lever 72. The lever 72 pulls the links 70 to the position shown in full outline at 77, which causes the movable contact 55 to be guided parallel to the common axis 46 of the arcing electrodes 57 and 58 to the position 68 shown in full outline.

During movement of the movable contact 55 it first disengages from contact finger 48 of the fixed contact 47 and then from the contact finger 49, an arc is struck between the contact 55 and the contact finger 49. Electromagnetic forces act on the arc and cause the arc root on the contact finger 49 to move to the arcing surface 54 of the contact finger 49 at its tip adjacent arcing electrode 57, and hence to the electrode 57, this at the earliest practicable time during the opening operation of the interrupter 45.

During further movement of the movable contact through its intermediate position 62 (shown in ghost outline) the arc on its arcing surface 56 transfers to the arcing surface 60 of arcing electrode 58 which at this instant is in position 90 (shown in ghost outline). The arc now extends between surfaces 59 and 60 of electrodes 57 and 58, and is no longer between fixed contact 47 and movable contact 55.

The arc-driving permanent magnets 63 and 64 produce magnetic flux with which the arc interacts and is driven around the arcing surfaces 59 and 60 like a stave in a rolling or oscillating barrel.

the movable electrode 58 is in position 91 (shown in ghost outline) when the movable contact 55 is in the closed position 69, and moves to position 90 simultaneously with the movable contact 55 movement from position 69 to 62 but in the opposite direction. Referring also to Figure 3, movement hereinbefore described corresponds to the simultaneous movement of the lever positions 80 and 79, and related movable arcing electrode 58 and movable contact 55 link pin positions 84 and 81 to positions 83 and 82 respectively.

Continuing rotation of the common operating shaft 76 moves the movable arcing electrode lever 75 and the connected operating links 73 attached to the cylindrical conductor 87 of the movable arcing electrode 58 by link pin 74. Movement now in the same direction as simultaneous movement of movable contact 55 to the contact break position 68 (shown in full outline).

At the same time the movable contact lever 72 moves its links 70 to position 77 (shown in full outline), link pin 71 connecting the links 70 to the movable contact 55 moves the latter to its break position 68.

At an appropriate current zero the arc is extinguished.

The interrupter 45 is closed by reverse operation of the links 70 and 73 causing the movable contact 55 and the movable electrode 58 to return to positions 69 and 91 respectively (shown in ghost outline).

The switch described with reference to Figure 2 and Figure 3 has a normal rating of 15.5 kilovolts, 630 amperes and a fault rating of 12.5 kiloamperes. The switch can have a housing made either from metal or from insulating material, for example cast epoxy resin, and an interrupter 45 provided for each phase of current supplied.

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 conductors of a current phase.

Claims

1. An arc interrupter consisting a fixed electrode and an electrode which is either fixed or movable depending upon the variation of the invention, the said electrodes provide coaxial arcing surfaces separated by an axial gap, a fixed contact, a movable contact, one or more arc-driving permanent magnets coaxial with said arcing surfaces, said movable contact which is mounted for movement between a make position in which said movable contact extends from and outside one said electrode and is in engagement with said fixed contact connected to and outside the opposite said electrode and in which said movable contact is in an openable 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 movable contact is guided between said make position and said break position.

3. An arc interrupter according to Claim 1, in which the pivot axis of said movable contact is normal to the common axis of said electrodes.

4. An arc interrupter according to Claim 1, in which the pivot axis of said movable contact is parallel to the common axis of said electrodes.

5. 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.

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

7. An arc interrupter according to Claim 1, substantially s hereinbefore described with reference to Figure 2 and Figure 3 of the said accompanying drawings.

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

9. An electrode switch according to Claim 8, 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.

10. An electric switch according to Claim 8, substantially as hereinbefore described with reference to Figure 1 of the accompanying drawings.

11. An electric switch according to Claim 8, substantially as hereinbefore described with reference to Figure 2 and Figure 3 of the accompanying drawings.