GB2224885A

GB2224885A - Electric arc interrupter

Info

Publication number: GB2224885A
Application number: GB8826523A
Authority: GB
Inventors: George Francis Chrisp
Original assignee: Individual
Current assignee: Individual
Priority date: 1988-11-12
Filing date: 1988-11-12
Publication date: 1990-05-16
Anticipated expiration: 2008-11-12
Also published as: GB2224885B; GB8826523D0

Abstract

An arc interrupter 5 mounted in a housing between two conductors 2, 4 comprises a fixed contact 7, a movable contact 15 mounted for guided movement between a make position and a break position, a fixed arcing electrode 17, 18 connected to each of the fixed and movable contacts 7, 15, one or more further fixed electrodes 30 positioned between the other two electrodes 17, 18 and one or more arc-driving permanent magnets 23, 24, 32 which are coaxial with arcing surfaces 19, 20, 33 of the electrodes 17, 18, 30. The contacts 7, 15 are located outside their respective electrodes 17, 18. During opening of the interrupter 5 an arc is struck between contacts 7 and 15 after which it moves between surfaces 19, 33 then progressively also between the other opposite arcing surfaces 33 until it terminates on surface 20. The permanent magnets 23, 24, 32 produce magnetic flux which interacts with the arc between the arcing surfaces so that the arc is driven around the axis 6. 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 particularly those for use above 36 kilovolts.

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 a compact interrupter in which multiple arcing electrodes are used to obtain a relatively uniform voltage gradient across the total arc gap during the break operation. A compact multiple arcing electrode form is made practicable by the use of arc-driving permanent magnets. 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 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 strip form or in a block.

An arc interrupter, according to the invention, comprises a fixed contact, a movable contact, a fixed electrode connected to said fixed contact, a fixed electrode connected to said movable contact, one or more fixed electrodes positioned intermediate said fixed-contact electrode and said movable - contact electrode, said electrodes provide coaxial arcing surfaces separated by axial gaps, one or more arc-driving permanent magnets coaxial with said arcing surfaces, said movable contract which is mounted for movement between a make position in which said movable contract extends from and outside said movable contract electrode and is in engagement with said fixed contact connected to and outside said fixed-contact 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 drawing in which: Figure 1 is a vertical 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.

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 and 4 carry one phase of the current supplied through the switch.

An 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 four 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 of contact fingers is loaded by a steel compression spring 12 whereby contact pressure is 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 fingers 9 after it has disengaged from contact fingers 8, Fand 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 fingers 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. Electrode 17 has an axis 6.

A similar fixed annular arcing electrode 18 shares common axis 6 and is located alongside the movable contact guide sleeve 25 to which it is electrically connected and supported by a pair of brass lugs 22. Adjacent and outside the electrode 18 is the movable contact 15. The guide sleeve 25 is clamped to the conductor 4.

Two fixed annular arcing electrodes 30 are positioned intermediate the annular arcing electrodes 17 and 18 and share common axis 6. The intermediate electrodes 30 have lugs 31 attached by which they are supported on post insulators (not shown). The post insulators are angularly mounted to have maximum electrical clearance.

The annular arcing electrodes 17, 18 and 30 enclose within their cross-section, annular shaped arc-driving permanent magnets 23, 24 and 32.

The arc-driving permanent magnets 23, 24, and 32 may either be formed from a flexible strip of rubber. or plastic embedding ferrite or rare earth cobalt alloy, or form a complete ring of permanent magnetic material. The magnetic polarity of the permanent magnets 23, 24 and 32 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, 18 and 30 consists of a copper strip of rectangular cross-section, with an arcing surface insert 16 of arc resistant metal.

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.

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 ghost outline) in the closed (make) position 29.

With the movable contact 15 in the make position, 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 causes the movable contact 15 to move and be guided parallel to the common axis 6 of the arcing electrodes 17, 18 and 30 to the position 28 (shown in full outline).

During movement of the movable contact 15, it first disengages from contact fingers 8 of the fixed contact 7 and then from the contact fingers 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 moves between surfaces 19 and 33 then progressively also between the other opposite arcing surfaces 33 until it terminates on surface 20.

The arc-driving permanent magnets 23, 24 and 32 produce magnetic flux with which the arc interacts and is driven around the arcing surfaces 19, 20 and 33 like staves in rolling or oscillating barrels.

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 mechanism causing the movable contact 15 to return to the position 29 (shown in ghost outline).

The switch described with reference to Figure 1 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 contact fingers 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.

Claims

1. An arc interrupter comprising a fixed contact, a movable contact, a fixed electrode connected to said fixed contact, a fixed electrode connected to said movable contact, one or more fixed electrodes positioned intermediate said fixed-contact electrode and said movable-contact electrode, said electrodes provide coaxial arcing surfaces separated by axial gaps, 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 outsidesmovable-contact electrode and is in engagement with said fixed contact connected to and outside said fixed-contact electrode and in which said movable contact is 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 drawing

7. 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.

8. An electric switch according to Claim 7, 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.

9. An electric switch according to Claim 7, substantially as hereinbefore described with reference to Figure 1 of the accompanying drawing.