GB2174546A - Circuit interrupters - Google Patents

Abstract

An electrical circuit interrupter employing axial rotation of arcs includes a fixed contact 1, an electromagnetic assembly 2 and a moveable contact assembly 3 co-axially aligned with each other. The contact assembly 3 includes first electrical contact means 20 to enable a main current path to be established and second electrical contact means 15 for slidably engaging the electromagnet assembly 2 to enable an auxiliary current path to be established. In operation movement of the contact assembly 3 into the open position causes the auxiliary current path to be established so that an arc is drawn between the contact assembly 3 and the fixed contact 1 to facilitate axial rotation of the arc and ultimately extinguishing of the arc. Movement into the closed position causes the contact assembly 3 to initially establish the auxiliary current path and to effect engagement of the first electrical contact means 20 with the fixed contact 1 thereby establishing the main current path in supremacy to the auxiliary current path. <IMAGE>

Description

SPECIFICATION Electrical circuit interrupters employing axial rotation of arcs This invention relates to electrical circuit interrupters employing axial rotation of arcs for use with alternating current.

According to the invention there is provided an electrical circuit interrupter employing axial rotation of arcs including an electrode connectable to a first electrical terminal, a contact assembly connectable to a second electrical terminal and co-axially aligned with the electrode, and an electromagnet assembly co-axially aligned with the electrode and the contact assembly, the electrode being provided with electrical contact means, the contact assembly including a first member provided with first electrical contact means to enable a main current to be established which first member is mechanically connected to a second member provided with second electrical contact means to enable an auxiliary current path to be established which second member is co-axially aligned with the electromagnet assembly and the electrode, the first and second members being connectable to a drive mechanism which is operable to move the contact assembly with respect to the electrode between an open and closed position, the electromagnet assembly being slidably engaged with the second electrical contact means and the second member to enable the auxiliary current path to be established whereby in operation movement of the contact assembly into the open position remote from the electrode causes the auxiliary current path to be established so that an arc is drawn across a space between the contact assembly and the electrode to facilitate axial rotation of the arc and ultimately extinguishing of the arc to interrupt the current flow between the first and second terminals and movement into the closed position causes the contact assembly to move as one unit to initially establish the auxiliary current path and to effect engagement of the first electrical contact means of the first member with the electrical contact means of the electrode thereby establishing the main current path in supremacy to the auxiliary current path to provide current flow between the first and second terminals.

Embodiments of the invention will now be described by way of example and with reference to accompanying diagrammatic drawings in which: Figure 1 is a cross sectional view of first embodiment of an electrical circuit interrupter, shown in a closed position with a main current path indicated by chain dotted lines, Figure 2 is a cross-sectional view of the electrical circuit interrupter of Figure 1 shown in a first stage of opening with a first arc extending between portions of the interrupter and with the main and an auxiliary current path indicated by chain dotted lines, Figure 3 is a cross-sectional view of the interrupter of Figure 1 and 2 shown in a second stage of opening with a second arc extending between portions of the interrupter and with the main and auxiliary current path indicated by chain dotted lines, Figure 4 is a cross-sectional view of the interrupter of the previous figures shown in a third stage of opening with the second arc extending between portions of the interrupter and with the main and auxiliary current paths indicated by chain dotted lines, Figure 5 is a cross-sectional view of a second embodiment of an electrical interrupter according to the invention shown in a closed position with a main current path indicated by chain dotted lines, Figure 6 is a cross-sectional view of the electrical circuit interrupter of Figure 5 shown in a first stage of opening with a first arc extending between portions of the interrupter and with the main and an auxiliary current carrying path indicated by chain dotted lines, Figure 7 is a cross sectional view of the interrupter of Figure 5 shown in a second stage of opening with a second arc extending between portions of the interrupter and the main and auxiliary current path indicated by chain dotted lines, and Figure 8 is a cross-sectional view of the interrupter of Figure 5 shown in a third stage of opening with the second arc extending between portions of the interrupter and with the main and auxiliary current paths indicated by chain dotted lines.

With reference to Figures 1 to 4 a first embodiment of the electrical circuit interrupter includes a fixed electrode 1, an electromagnet assembly 2 and a moveable contact assembly 3. The fixed electrode 1, the electromagnet assembly 2 and the moveable contact assembly 3 are positioned within an enclosure (not shown) and the enclosure is filled with a quantity of a dielectric fluid, for example, sulphur hexafluoride.

The electrode 1 is formed from a hollow cylinder 5 of electrically conducting metal, for example, copper. The cylinder 5 has an inturned flange 6 at one end thereof and an internal support member (not shown) at the other end thereof. The outer peripheral surface of the cylinder 5 provides a main contact surface 7 and auxiliary contacts 8 are attached to the internal support member. The auxiliary contacts 8, for example, resilient cluster contacts, are located within the hollow cylinder and are co-axially aligned with a central axis of the cylinder 5 so as to project towards a central aperture formed by the inturned flange 6.

The electromagnet assembly 2 includes a coil 9 formed from a strip of an electrically conducting metal, for example copper, which strip is spirally wound into an annular cross-section shape having a cylindrical space surrounding a central axis of the coil 9. An inner and outer turn of the strip is provided with portions which are formed into terminals 10, 11, respectively. The coil 9 is encapsulated in silicone resin to provide insulation and resistance to electrical and mechanical stresses.

The coil 9 is enclosed in a tubular shaped housing (not shown) made of a ferromagnetic metal, for example, steel, formed from a pair of co-operating cylinders having a cylindrical space surrounding a central axis of the housing. The housing has inturned flanges at one end thereof which abut against an arcing ring 12 positioned perpendicularly to the central axis of the housing. The other end of the housing is closed by an annular plate made of ferromagnetic metal. The arcing ring 12 made of electrically conducting metal, for example copper, is interposed between the flanges and connected to the inner turn of the coil 9 and ultimately to the terminal 10.An outer peripheral face of the housing is partially covered with an insulating material and an insulating sleeve (not shown) is positioned to abut against an inner peripheral face of the housing adjacent the central axis of the housing. The annular plate closing one end of the housing is provided with two sets of concentric rings made of an electrically conducting metal for example, copper. Each set comprises two rings, one on each side of the plate, each inboard and outboard ring being connected together by screws or studs.

The set having the smaller diameter is electrically connected to the plate with the inboard ring thereof making electrical contact with the terminal 10 of the coil 9, and with the outboard ring thereof being provided with a contact means, for example, contact rings. The set having the larger diameter is insulated from the plate with the inboard ring thereof making electrical contact with the terminal 11 of the coil 9, and with the outboard ring thereof being provided with a contact means, for example, contact rings.

The contact assembly 3 includes a hollow cylindrical member 13 open at one end 14 made of an electrically conducting metal, for example, copper, and a hollow cylindrical stem 15. The stem 15 is co-axially aligned with the cylindrical member 13 and mechanically connected to the cylindrical member 13 by webs 16 such that a free end 17 of the stem 15 projects beyond the open end 14 of the cylindrical member 13. The stem 15 is constructed from an inner hollow open ended core (not shown) of a ferromagnetic metal, for example, steel, and an outer hollow open ended casing (not shown) of an electrically conducting metal, for example, copper. The casing is superimposed onto the core and the free end 17 is capped with a plug 18 made of insulating material.The inner core and the outer casing of the stem 15 are electrically insulated from the cylindrical member 13-by insulating members 19 provided in the webs 16. The open end 14 of the cylindrical member 13 is provided with a main contact array 20 of resilient cluster finger contacts.

On assembly the free end 17 of the stem 15 is inserted through the cylindrical space surrounding the central axis of the housing and co-axially aligned therewith so that the electromagnet assembly 2 is positioned between the stem 15 and the cylindrical member 13. The electromagnet assembly 2 is then attached to pillars (not shown) made of an electrically conducting metal for example, aluminium, with one end of the pillars being connected to the set of rings of larger diameter which make contact with the terminal 11 of the coil 9, and with the other end of the pillars being connected to and supported from a mounting (not shown) attached to a wall of the enclosure thus locating the electromagnetic assembly 2 in co-axial alignment with contact assembly 3.An end 21 of the cylindrical member 13 and the stem 15 remote from the open end 14 and the free end 17 is then coupled through an insulated link to a driving mechanism (not shown). The driving mechanism being constructed from, for example, a spring loaded shaft actuated by a switch, and serves to move the contact assembly 3 as one unit with the stem 15 being slidable through the cylindrical space surrounding the central axis of the housing and the main contact array 20 being traversable over the insulated covering on the on the outer exterior face of the housing. The cylindrical member 13 is then connected for example, through the pillars to a terminal 22 extending into the wall of the enclosure.

The electrode 1 is then coaxially aligned with the electromagnet assembly 2 and the contact assembly 3 along a central axis of the interrupter, and the end of the electrode remote from the flange 6 is attached to a terminal 4 extending into a wall of the enclosure opposite to that containing the terminal 22. The electrode 1 is thereby fixed in relation ta the contact assembly 3 and located at a predetermined distance from the coil 9 and the arcing ring 12. The enclosure is then fitted together, filled with a quantity of the dielectric fluid and sealed.

In a closed position with reference to Figure 1 the main contact array 20 of the contact assembly 3 engages with the outer peripheral surface 7 of the electrode 1, and the free end 17 of the stem 15 slidably engages with auxiliary contacts 8 and extends into a space surrounding a central axis of the cylinder 5 by a predetermined amount. Also a portion of the stem 15 remote from the plug 18 slidably engages with the contact ring which is ultimately connected to the terminal 10 of the coil 9.

In the closed position a main current carrying path is established through the interrupter between the terminal 4; the outer peripheral surface 7 of the cylinder 5; the main contact array 20 and the terminal 22 as shown by chain dotted lines, An auxiliary current carrying path is also capable of being formed in parallel to the main current carrying path.

In operation when the interrupter is used to interrupt a current flow established through the interrupter the drive mechanism connected to the contact assembly 3 is actuated by operation of the switch to move the contact assembly 3 as one unit away from the electrode 1.

In a first stage of opening, as shown in Figure 2 the main contact array 20 disengages from the outer peripheral surface 7 of the cylindrical member 5 thereby opening the main current carrying path. However, the auxiliary current carrying path is then established by the slidable engagement of the free end 17 with the auxiliary contact 8; and the slidable engagement of the stem 15 with the contact ring ultimately connected to the terminal 10; and the slidable engagement of the cylindrical member 13 and the contact ring ultimately connected to the terminal 11 as shown by chain dotted lines. During opening to the first stage a first arc or commutating arc 24 is drawn between the outer peripheral surface 7 of the cylindrical member 5 and the main contact array 20 across the space separating the electrode 1 and the contact assembly 3.As the first arc 24 is lengthened by the continued movement of the contact assembly 3, increasing voltage, generated by the first arc 24 is impressed across the auxiliary current carrying path until the current flowing through the first arc 24 is commutated that is directed into the auxiliary current carrying path. The current commutated into the auxiliary current carrying path flows through the coil 9 and thereby causes the coil 9 to generate magnetic flux, through the ferromagnetic metal of the housing, across the arcing ring 12 and across the space separating the arcing ring 12 from the electrode 1. The ferromagnetic core of the stem 15 increases the density of this flux radially along the stem 15 and particularly in the vicinity of the auxiliary contacts 8.When all the current flowing through the interrupter has been commutated into the auxiliary current carrying path the first arc 24 becomes extinguished.

In a second stage of opening as shown in Figure 3 the continued movement of the contact assembly 3 causes the stem 15 to disengage from the auxiliary contacts 8 thereby drawing a second or main arc 26 in series with the auxiliary current carrying path to maintain the auxiliary current carrying path as shown by chain dotted lines. The second arc 26 is drawn between an outer radial surface of the flange 6 and the free end 17 of the stem 15 across a space generated by retraction of the stem 15 into the insulating sleeve provided in the cylindrical space surrounding the central axis of the housing.

The covering of insulating material on the outer exterior face of the housing provides a mechanical support for the main contact array 20. During the second stage of opening the radial component of the magnetic field generated by the coil 9 and the ferromagnetic core of the stem 15 forces the second arc 26 which extends axially to rotate axially about the central axis of the interrupter, with the arc roots executing a circular motion. One arc root moves around the central axis of the cylinder 5 in the vicinity of the auxiliary contacts 8 and the other root moves around the outer peripheral surface of the stem 15. The second arc 26 rotates under the influence of a force at right angles to the magetic field, and as a consequence of centrifugal forces produced by local electromagnetic effects the second arc 26 is moved away from the central axis of the interrupter.

In a third stage of opening as shown in Figure 4 the stem 15 is fully retracted into cylindrical space surrounding the central axis of the coil 9 and the housing and the moving contact assembly 3 is brought to rest. In this position due to the presence of the insulating plug 18 provided on the stem 15 one of the roots of the second arc 26 is transferred from the outer peripheral surface of the stem 15 to the arcing ring 12 to maintain the auxiliary current path as shown by chain dotted lines.

Also during movement of the contact assembly 3 the second arc 26 is lengthened and as the second arc 26 axially rotates around the central axis of the interrupter the second arc 26 is cooled and deionized by the action of the dielectric fluid thereby causing the second arc 26 to be extinguished and hence the current flow to be interrupted between the terminals 4,22.

Conversely, when the interrupter is used to establish a current flow between terminals 4, 22 the drive mechanism is actuated to move the contact assembly 3 as one unit towards the electrode 1.

During closure when the free end 17 of the stem 15 has approached the auxiliary contacts 8 of the electrode 1 to within a distance at which the dielectric strength of gap is lower than the applied voltage a relatively short lived arc (not shown) is struck between the free end 17 of the stem 15 and the auxiliary contacts 8 of the electrode 1. The relatively short lived arc establishes the auxiliary current carrying path between the contact assembly 3 and the electrode 1.The current flowing through the auxiliary current carrying path and thereby through the coil 9 causes the coil 9 to generate a magnetic field such that the roots of the relatively short lived arc are forced to commence circular motion about the central axis of the stem 15 and the central axis of the interrupter, one of the roots of the relatively short lived arc moving around the surface of the auxiliary contacts 8 and the other root moving around the outer peripheral surface of the stem 15.

With continued movement of the contact assembly 3 the stem 15 slidably engages with the auxiliary contacts 8 thereby extinguishing the relatively short lived arc. Further movement of the contact assembly 3 causes the main contact array 20 to engage with the outer peripheral surface 7 of the cylinder 5 thereby short circuiting the auxiliary current carrying path to establish the main current carrying path through the interrupter, hence permitting current flow between the two terminals 4 and 22 of the interrupter.

In a modification of the first embodiment of the interrupter the hollow stem 15 is provided at the free end 17 thereof with apertures (not shown) which extend through the hollow casing and inner core of the stem 15. In addition a piston and cylinder unit (not shown) is provided at the end 21 of the cylindrical member 13 and the stem 15 which are driven by movement of the contact assembly 3 when the drive mechanism thereof is operated.

The hollow stem 15 is filled with a quantity of the dielectric fluid and on actuation of the drive mechanism of the contact assembly 3 dielectric fluid is pumped through the apertures by the action of piston and cylinder unit into a region surrounding the area occupied by second arc 26 thereby increasing the cooling and de-ionizing effects of the dielectric fluid on the second arc 26.

In another modification of the first embodiment particularly for use at relatively high normal cur rent ratings, an insulating sleeve 28 (shown in dotted lines in Figure 1) may be fitted around the stem 15, to break the auxiliary current path in the closed position of the interrupter so that excessive heat energy generated by current flow is prevented.

Also when the interrupter is being used for relatively high normal current ratings additional contact means (not shown) may be provided to establish an additional current carrying path from the cylindrical member 13 to the terminal 22.

Further portions of the interrupter made of metal and located adjacent to areas in which the arcs are struck may be reinforced with regions of arc resisting materials for example tungsten copper to minimise erosion caused by the roots of the arcs.

Also an annular shaped disc (not shown) made of insulating material may be positioned on an interior face of the inner inturned flange of the housing adjacent the central axis of the housing and perpendicular thereto and partially overlapping the arcing ring 12. The disc serves to break the connection between the arcing ring 12 and the inner inturned flange of the housing so that one of the roots of the second arc 26 is directed onto the arcing ring 12 more rapidly in the third stage of opening as shown in Figure 4 due to increased centrifugal bias produced by the local electromanetic effects on the second arc 26.

In addition the connections of the terminals 10 and 11 of the coil 9 may be reversed such that terminal 11 is connected to the inner turn of the coil 9 and the arcing ring 12, and terminal 10 is connected to the outer turn of the coil 9. The reversal of the connections enables centripetal forces produced by local electromagnetic effects to exert an influence on the second arc 26 so that the second arc is moved towards the central axis.

Also the stem 15 may be constructed from an inner solid core of a ferromagnetic metal, for example, steel and an outer casing of an electrically conducting metal, for example, copper.

In addition the ferromagnetic metal core may be omitted from the stem 15, the stem in such a case being constructed from a solid or hollow cylinder of an electrically conducting metal, for example, copper.

With reference to Figures 5 to 8 a second embodiment of the electrical circuit interrupter includes a first electrode 40, an electromagnet assembly 41, a moveable contact assembly 42, and a second electrode 43. The first electrode 40, the electromagnet assembly 41, the second electrode 43 and the moveable contact assembly 42 are positioned within an enclosure (not shown) and the enclosure is filled with a quantity of dielectric fluid, for example, sulphur hexafluoride.

The first electrode 40 is formed from a hollow cylinder 44 of electrically conducting metal, for example, copper. The cylinder 44 is open ended and an outer peripheral surface 45 thereof provides a main contact surface. The cylinder 44 encloses and supports a set of auxiliary contacts 46 for example, a cluster of resilient fingers. The auxiliary contacts 46 are co-axially aligned with a central axis of the cylinder 44, and accommodate in a bore thereof surrounding the central axis a resilient member 47, made of an insulating material, which is moveable to reveal or occlude the bore.

The electromagnet assembly 41 includes a coil 48 formed from a strip of an electrically conducting metal, for example, copper, which strip is spirally wound in an annular cross-section shape-having a cylindrical space surrounding a central axis of the coil 48. An inner and outer turn of the strip is provided with portions which are formed into terminals 49, 50 respectively. The coil 48 is encapsulated in silicone resin to provide insulation and resistance to electrical and mechanical stresses. The coil 48 is enclosed in a tubular shaped housing (not shown) made of a ferromagnetic metal, for example, steel, formed from a pair of co-operating cylinders having a cylindrical space surrounding a central axis of the housing. The housing has inturned flanges at one end thereof which abut against an arcing ring 51 positioned perpendicularly to the central axis of the housing.The other end of the housing is closed by an annular plate made of ferromagnetic metal. The arcing ring is made of electrically conducting metal for example copper and is interposed between the flanges and connected to the inner turn of the coil 48 and ultimately to the terminal 49. An outer peripheral face of the housing is partially covered with an insulating material. The annular plate closing one end of the housing is provided with two sets of concentric rings made of an electrically conducting metal, for example, copper. Each set comprises two rings, one on each side of the plate, each inboard and outboard ring being connected together by screws or studs.The set having the smaller diameter is electrically connected to the plate with the inboard ring thereof making electrical contact with the terminal 49 connected to the inner turn of the coil 48, and with the outboard ring thereof being connectable to the auxiliary contacts 46. The set having the larger diameter is insulated from the plate, with the inboard ring thereof making electrical contact with the terminal 50 connected to the outer turn of the coil 48, and with the outboard ring thereof being connectable to the first electrode 40.

The contact assembly 42 includes a hollow cylindrical member 52 open at one end 53 made of an electrically conducting metal, for example, copper and a hollow cylindrical stem 54. The stem 54 is co-axially aligned with the cylindrical member 52 and mechanically and electrically connected to the cylindrical member by webs 55 such that a free end 56 of the stem 54 projects beyond the open end 53 of the cylindrical member 52. The stem 54 is constructed from an inner hollow open ended core (not shown) of a ferromagnetic metal, for example steel and an outer hollow open ended casing (not shown) of an electrically conducting metal, for example, copper. The casing is superimposed onto the core and the free end 56 is capped with a plug 57 made of insulating material. The open end 53 of the cylindrical member 52 is provided with a main contact array 58 of resilient cluster finger contacts.

The second electrode 43 is annular in shape and is formed from electrically conducting metal, for example copper. An inner peripheral face 59 of the electrode surrounding a central axis thereof is covered with a layer of insulating material.

On assembly the electromagnet assembly 41 is co-axially aligned with and supported within the first electrode 40 such that the arcing ring 51 projects away from the first electrode 40. The auxiliary contacts 46 and associated resilient member 47 thereby being co-axially aligned with the central axis of the housing so as to extend into the space surrounding the central axis of the housing. An end 60 of the first electrode 40 remote from the arcing ring 11 is then connected to a terminal 61 extending into a wall of the enclosure.

The free end 56 of the stem 54 is then inserted through the space surrounding the central axis of the second electrode 43 and the second electrode 43 is attached to to a wall of the enclosure remote from the first electrode 40 so that the second electrode 43 occludes the open end 53 of the cylindrical member 52. A set of slidable contacts (not shown) connects the second electrode 43 to the contact assembly. The second electrode 43 is also supported on the pillars at a predetermined distance from the arcing ring 51 of the electromagnet assembly 41 in the first electrode 40.

The contact assembly 42 is then co-axially aligned with the central axis of the housing and the first electrode 40 along a central axis of the interrupter and an end 62 of the contact assembly 42 remote from the free end 56 of the stem 54 is coupled through an insulating link to a driving mechanism (not shown). The driving mechanism is constructed from, for example, a spring loaded shaft actuated by a switch, and serves to move the contact assembly as one unit with the stem being slidable through the cylindrical space surrounding the central axis of the second electrode 43 and through the cylindrical space surrounding the central axis of the housing to abut against and move the resilient member 47 located in the first electrode 40.The cylindrical member 52 is then connected for example, through a mounting to a terminal 63 extending through the wall of the enclosure remote from the first electrode 40.

The first and second electrodes 40, 43 and the electromagnet assembly 41 are thereby fixed in relation to the contact assembly 42. The enclosure is then fitted together, filled with a quantity of dielectric fluid, and sealed.

In a closed position with reference to Figure 5 the main contact array 58 of the contact assembly 42 engages with the outer peripheral surface 45 of the first electrode. Also the free end 56 of the stem 54 slidably engages with the auxiliary contacts 46 and extends beyond the housing along the central axis of the interrupter into the first electrode 40 by a predetermined distance by abutting against the resilient member 47 thereby compressing the resilient member 47 into the first electrode 40.

In the closed position a main current carrying path is established through the interrupter between the terminal 61, the outer peripheral surface 45 of the cylinder 44, the main contact array 58 and the terminal 63 as shown by chain dotted lines. Also an auxiliary current carrying path is capable of being established in parallel to the main current carrying path.

In operation when the interrupter is used to interrupt a current flow established through the interrupter the drive mechanism connected to the contact assembly 42 is actuated by operation of the switch to move the contact assembly 42 as one unit away from the first electrode 40 and the electromagnet assembly 41.

In a first stage of opening, as shown in Figure 6, the main contact array 58 disengages from the outer peripheral surface 45 of the cylinder 44 thereby opening the main current path. However, the auxiliary current carrying path is then be established by the sliding engagement of the free end 56 of the stem 54 with the auxiliary contacts 46, to permit electrical current flow through the coil 48 connected between the terminals 49 and 50 in engagement with the first electrode and the auxiliary contacts 46; and by the effecting of electrical current flow through the stem 54 and the webs 55 to the cylindrical member 52 of the contact assembly 42 as shown by chain dotted lines.During opening to the first stage a first or commutating arc 64 is drawn between the outer peripheral surface 45 of the cylinder 44 and the main contact array 58 across the distance separating the first electrode 40 and the contact assembly 42. As the first arc 64 is lengthened by continued movement of the contact assembly 42 an increasing voltage, generated by the first arc 64, is impressed across the auxiliary current carrying path until the current flowing through the first arc 64 is commutated, that is, directed into the auxiliary current carrying path. The current commutated into the auxiliary current carrying path flows through the coil 48 and thereby causes the coil 48 to generate magnetic flux, effective through the ferromagnetic metal of the housing, across the arcing ring 51 and across the space separating the arcing ring 51 from the first electrode 40.The ferromagnetic core of the stem 54 increases the density of this flux radially along the stem 54, particularly in the vicinity of the auxiliary contacts 46. When all the current flowing through the interrupter has been commutated into the auxiliary current path the first arc 64 becomes extinguished.

In a second stage of opening as shown in Figure 7 the continued movement of the contact assembly 42 causes the stem 54 to disengage from the auxiliary contacts 46 thereby causing the resilient member 47 to occlude the bore surrounding the central axis of the first electrode 40, and thereby drawing a second or main arc 66 in series with the coil 48 to maintain the auxiliary current carrying path as shown by chain dotted lines. The second arc 66 is drawn between the arcing ring 51 and the free end 56 of the stem 54 across a space formed by retraction of the stem 54 into the cylindrical space surrounding the central axis of the second electrode 43. The insulating material on the peripheral face 59 serves as an axial bearing for the stem 54.An outer peripheral surface (not shown) of the second electrode 43 provides a contact surface to effect mechanical support of the moveable main contact array 58. During the second stage of opening the radial component of the magnetic field generated by the coil 48 and the ferromagnetic core of the stem 54 forces the second arc 66 which extends axially to rotate about the central axis of the interrupter, with the arc roots executing a circular motion. One arc root moves around the arcing ring 51 and the other moves around the outer peripheral surface of the stem 54. The second arc 66 rotates under the influence of a force at right angles to the magnetic field, and as a consequence of centrifugal forces produced by local electromagnetic effects the second arc 66 is moved away from the central axis of the interrupter.

In a third stage of opening as shown in Figure 8 the stem 54 is fully retracted into the cylindrical space surrounding the central axis of the second electrode 43, and the moving contact assembly 42 is brought to rest. In this position due to the presence of the insulating plug 57 provided on the stem 54 one of the roots of the second arc 66 is transferred from the outer peripheral surface of the stem 54 to the second electrode 43 to maintain the auxiliary current carrying path as shown by the chain dotted lines. During movement of the contact assembly 42 the second arc 66 is lengthened and as the second arc 66 axially rotates around the central axis of the interrupter the second arc 66 is cooled and deionized by the action of the dielectric fluid thereby causing the second arc 66 to be extinguished and hence the current flow to be interrupted between the terminals 61 and 63.

Conversely, when the interrupter is used to establish a current flow between terminals 61 and 63 the drive mechanism is actuated to move the contact assembly 42 as one unit towards the first electrode 40. During closure at the stage at which the free end 56 of the stem 54 has approached the auxiliary contacts 46 of the first electrode 40 to a distance at which the dielectric strength of the gap is lower than the applied voltage a relative short lived arc (not shown) is struck between the free end 56 of the stem 54 and the auxiliary contacts 46. The relatively short lived arc establishes the auxiliary current carrying path between the contact assembly 42 and the first electrode 40.The current flowing through the auxiliary current carrying path and thereby through the coil 48 causes the coil 48 to generate a magnetic field such that the roots of the relatively short lived arc are forced to commence circular motion about the central axis of the stem 54 and the central axis of the interrupter, one of the roots of the relatively short lived arc moving around the surface of the auxiliary contacts 46 and the other root moving around the outer peripheral surface of the stem 54.Further movement of the contact assembly 42 causes the stem 54 to compress the resilient member 47 into the first electrode and effects engagement of the main contact array 58 with the outer peripheral surface 45 of the cylinder 44 thereby short circuiting the auxiliary current carrying path to establish the main current carrying path through the interrupter, hence permitting current flow between the terminals 61 and 63 of the interrupter.

In a modification of the second embodiment of the interrupter the hollow stem 54 is provided at the free end 56 thereof with apertures (not shown) which extend through the hollow casing and inner core of the stem 54. In addition a piston and cylinder unit (not shown) is provided at the end 62 of the cylindrical member 52 and the stem 54 which are driven by movement of the contact assembly 42 when the drive mechanism thereby is operated.

The hollow stem 54 is filled with a quantity of the dielectric fluid and on actuation of the drive mechanism of the contact assembly 42 dielectric fluid is pumped through the apertures by the action of piston and cylinder unit into a region surrounding the area occupied by second arc 66 thereby increasing the cooling and de-ionizing effects of the dielectric fluid on the second arc 66.

In another modification of the second embodiment particularly for use at relatively high normal current ratings, an insulating sleeve 70 (shown in dotted lines in Figure 5) may be fitted around the stem 54, to break the auxiliary current path in the closed position of the interrupter so that excessive heat energy generated by current flow is prevented.

When the interrupter is being used for relatively high normal current ratings additional contact means (not shown) may be provided to establish an additional current carrying path from the cylindrical member 52 to the terminal 63.

Further portions of the interrupter made of metal and located adjacent to areas in which the arcs are struck may be reinforced with regions of arc resisting materials, for example tungsten copper, to minimise erosion caused by the roots of the arcs.

In addition the connection of the terminals 49 and 50 of the coil 48 may be reversed such that terminal 50 is connected to the inner turn of the coil 48 and the arcing ring 51 and terminal 49 are connected to the outer turn of the coil 9. The reversal of the connections enables centripetal forces produced by local electromagnetic effects to exert an influence on the second arc 66 so that the second arc is moved towards the central axis of the interrupter.

The stem 54 may be constructed from an inner solid core of a ferromagnetic metal, for example steel, and an outer casing of an electrically conducting metal, for example, copper.

In addition the ferromagnetic metal core may be omitted from the stem 54, the stem in such a case being constructed from a solid or hollow cylinder of an electrically conducting metal, for example, copper.

A third embodiment of the electrical circuit interrupter includes a combination of elements from the first and second embodiments described in preceding paragraphs, which enables a substantially similarly physically dimensioned interrupter to be used for relatively high current ratings. The elements include the moving contact assembly 3 and associated electromagnet assembly 2 of the first embodiment shown in Figures 1 to 4; and the first electrode 40 and associated electromagnetic assembly 41 of the second embodiment shown in Figures 5 to 8. The first electrode and the electromagnet assemblies are fixed relative to the contact assembly which is provided with a drive mechanism which is actuable to move the contact assembly as one unit toward or away from the first electrode.

In a closed position a main current carrying path is established through the interrupter between a first terminal, an outer peripheral surface of the first electrode, a main contact array of the contact assembly, and a second terminal. An auxiliary current carrying path may be formed in parallel to the main current carrying path.

In operation when the interrupter is used to interrupt a relatively high current flow established through the interrupter, the drive mechanism connected to the contact assembly is actuated to move the contact assembly away from the first electrode.

During movement of the contact assembly the main contact array disengages from the outer peripheral surface of the first electrode thereby opening the main current path and effecting formation of a first or commutating arc between the first electrode and the contact assembly. The current flowing through the first arc is commutated into the auxiliary current carrying path to cause the two coils of the electromagnet assemblies to generate magnetic flux through the two ferromagnetic housings, across the two arc rings and across the space separating the arc rings. When all the current flowing through the interrupter has been commutated into the auxiliary current carrying path the first arc becomes extinguished.With continued movement of the contact assembly a second or main arc is drawn in series with the auxiliary current carrying path between an arcing ring of the electromagnet assembly associated with the first electrode and a free end of a stem forming part of the contact assembly. Further movement of the contact assembly fully retracts the stem into a cylindrical space surrounding a central axis of the electromagnet assembly associated with the contact assembly and thereby transfers one of the arc roots from the stem to an arcing ring of the electromagnet assembly associated with the contact assembly such that the second arc is caused to rotate axially about a central axis of the interrupter. At this stage the roots of the second arc are each forced to rotate around respective arcing rings, each arcing ring exerting a driving force on the second arc to facilitate cooling and deionizing of the second arc by the dielectric fluid thereby causing the second arc to be extinguished and hence the current flow interrupted.

Claims (12)

1. An electrical circuit interrupter employing axial rotation of arcs including an electrode connectable to a first electrical terminal, a contact assembly connectable to a second electrical terminal and coaxially aligned with the electrode, and an electromagnet assembly co-axially aligned with the electrode and the contact assembly, the electrode being provided with electrical contact means, the contact assembly including a first member provided with first electrical contact means to enable a main current to be established which first member is mechanically connected to a second member provided with second electrical contact means to enable an auxiliary current path to be established which second member is co-axially aligned with the electromagnet assembly and the electrode, the first and second members being connectable to a drive mechanism which is operable to move the contact assembly with respect to the electrode between an open and closed position, the electromagnet assembly being slidably engaged with the second electrical contact means and the second member to enable the auxiliary current path to be established whereby in operation movement of the contact assembly into the open position remote from the electrode causes the auxiliary current path to be established so that an arc is drawn across a space between the contact assembly and the electrode to facilitate axial rotation of the arc and ultimately extinguishing of the arc to interrupt the current flow between the first and second terminals and movement into the closed position causes the contact assembly to move as one unit to initially establish the auxiliary current path and to effect engagement of the first electrical contact means of the first member with the electrical contact means of the first member with the electrical contact means of the electrode thereby establishing the main current path in supremacy to the auxiliary current path to provide current flow between the first and second terminals.

Amendments to the claims have been filed, and have the following effect: (b) New or textually amended claims have been filed as follows:

2. An electrical circuit interrupter employing axial rotation of arcs as claimed in Claim 1, in which the electrode is formed from a hollow cylinder of electrically conducting metal, and the electrical contact means of the electrode are formed by an outer peripheral surface of the cylinder for enabling the main current path to be established and by an auxiliary set of contacts located co-axially within the hollow cylinder for enabling the auxiliary path to be established.

3. An electrical circuit interrupter employing axial rotation of arcs as claimed in Claim 2, in which the contact assembly includes a hollow cylindrical member of electrically conducting metal as the first member, the cylindrical member having the first electrical contact means at one end thereof, the first electrical contact means co-acting with the outer peripheral surface of the cylinder of the electrode when in the closed position to establish the main current path, and a stem having a ferromagnetic core as the second member, the stem being co-axially aligned within the cylindrical member such that a free end of the stem projects from the first member, an outer peripheral surface of the stem forming the second electrical contact means which co-act with the auxiliary set of contacts of the electrode to enable the auxiliary current path to be established.

4.- An electrical circuit interrupter employing axial rotation of arcs as claimed in Claim 3, in which the electromagnetic assembly includes a coil formed from a strip of electrically conducting metal spirally wound into an annular cross-section shape, an inner and an outer turn of the coil being provided with terminals and an arcing ring electrically connected to one of the terminals of the coil, the coil and the arcing ring being accommodated in an annular shaped housing formed from a pair of cooperating cylinders having inturned flanges at one end to locate the arcing ring, the terminals being slidably connectable to the stem to establish the auxiliary current path.

5. An electrical circuit interrupter employing axial rotation of arcs as claimed in any one of Claims 2 to 4, in which the electromagnetic assembly is co-axially positioned between the cylindrical member and the stem of the contact assembly so that the stem of the contact assembly slidably engages with an inner peripheral surface of the housing, the stem being electrically insulated from the cylindrical member and the cylindrical member being connectable to a terminal of the coil to establish the auxiliary current path.

6. An electrical circuit interrupter employing axial rotation of arcs as claimed in any one of Claims 2 to 4 in which the electromagnetic assembly is coaxially positioned in the hollow cylinder of the electrode so that the stem of the contact assembly which is electrically connected to the cylindrical member slidably engages with an inner peripheral surface of the housing, and the cylinder is electrically connectable to a terminal of the coil to establish the auxiliary current path.

7. An electrical circuit interrupter employing axial rotation of arcs as claimed in Claim 6, in which a co-axially positioned resilient member is provided within the cylinder of the electrode, the resilient member being moveable by the stem to expose or occlude the auxiliary set of contacts.

8. An electrical circuit interrupter employing axial rotation of arcs as claimed in Claim 7, in which a second electrode annular in shape is co-axially positioned between the electrode, the electromagnetic assembly and the stem and the cylindrical member, the stem being moveable in the bore of the second electrode.

9. An electrical circuit interrupter employing axial rotation of arcs as claimed in any one of the preceding claims, in which the stem is provided with apertures at the free end, and the stem is capable of containing a quantity of dielectric fluid such that on operation of the drive mechanism to move the contact assembly, dielectric fluid is pumped through the apertures to facilitate extinguishing of the arc.

10. An electrical circuit interrupter employing axial rotation of arcs as claimed in any one of the preceding claims, in which an insulating sleeve is positioned on the stem to break the auxiliary current path in the closed position so that excessive heat energy generated by current flow is substantially reduced.

11. An electrical circuit interrupter employing axial rotation of arcs as claimed in Claim 7, in which a second electromagnetic assembly is co-axially positioned between the cylindrical member and the stem of the contact assembly so that the stem of the contact assembly slidably engages with an inner peripheral surface of each of the housings during operation of the drive mechanism and is thereby electrically connectable to each of the coils and arcing rings to establish the auxiliary current path, each of the two arcing rings exerting a driving force on the arc thereby facilitating extinguishing of the arc.

12. An electrical circuit interrupter employing axial rotation of arcs arranged and adapted substantially to operate as herein described with reference to Figures 1 to 4 to Figures 5 to 8 or the electromagnetic assembly and the contact assembly of Figures 1 to 4 as modified by and amalgamated with the first electrode and electromagnetic assembly of Figures 5 to 8 of the accompanying drawings.