GB2531349A

GB2531349A - Circuit breaker with coil for arc displacement

Info

Publication number: GB2531349A
Application number: GB1418466.7A
Authority: GB
Inventors: Stephen Ernest Lane; Stefan Keith Buckland; Christopher Aaron Nazeri
Original assignee: Hawker Siddeley Switchgear Ltd
Current assignee: Hawker Siddeley Switchgear Ltd
Priority date: 2014-10-17
Filing date: 2014-10-17
Publication date: 2016-04-20
Also published as: WO2016059430A1; GB201418466D0

Abstract

A circuit breaker has primary contacts 3,5 that move between a closed and an open configuration where there is a primary contact gap 12 between them and are in series in a current path with secondary contacts 9,7 and current terminals 30,32. Secondary contacts 30,32 also open and close and have a coil 50a connected in parallel with them and disposed adjacent the primary contacts to generate a magnetic field transverse to the primary contact gap 12. Upon opening the secondary contacts current diverts through the coil generating a magnetic field that drives an arc traversing the primary contact gap away from it. There may be a second coil (fig 2,50) in parallel with coil 50a on the opposite side of the primary contacts to generate a second magnetic field transverse to the primary gap and an arc chamber (fig 1, 40) adjacent the primary contacts towards which the magnetic field drives an arc. The primary and secondary contacts can be driven by a common actuator. Coil 50a can have a high permeability core 54a whose ends are on opposite sides of the primary contact gap. Air can be ejected across the primary gap on opening the primary contacts.

Description

CIRCUIT BREAKER WITH COIL FOR ARC DISPLACEMENT

The present invention relates to circuit breakers, and in particular to circuit breakers incorporating an arc displacement mechanism to drive an arc drawn between two relatively moveable contacts away from the vicinity of the contacts.

In circuit breakers capable of interrupting large overload currents, an important feature is the minimisation of arcing between the contacts of the circuit breaker as the contacts open during overcurrent fault situations. Various arc extinguishing techniques are known in the art, including those which aim to displace the arc from the opening contacts, thereby stretching the arc over a greater distance than that which prevails between the opening contacts and moving the arc towards an arc extinguishing structure.

It is an object of the present invention to provide a transverse magnetic field between two contacts that are moving apart in a circuit breaker so as to displace an arc forming therebetween from its position between the contacts.

It is another object of the invention to minimise the duration of arcing between the contacts by enabling rapid extinguishing of an arc drawn between two separating contacts.

According to one aspect, the present invention provides a circuit breaker comprising: first and second relatively moveable primary contacts, each including a respective contact surface, adapted to move between a closed configuration in which the contact surfaces are in physical contact with one another and an open configuration in which the contact surfaces are separated by a primary contact gap, the first primary contact being connected to a first current terminal via first current path and the second primary contact being connected to a second current terminal via a second current path; the second current path including a pair of relatively moveable secondary contacts, each including a respective contact surface, adapted to move between a closed configuration in which the contact surfaces are in physical contact with one another and an open configuration in which the contact surfaces are separated by a secondary contact gap, wherein the second current path includes a coil electrically parallel to the pair of secondary contacts and disposed adjacent to the primary contacts so as to generate a magnetic field transverse to the primary contact gap.

The second current path may include a second coil disposed adjacent to the primary contacts so as to generate a second magnetic field transverse to the primary contact gap, the second coil being on an opposite side of the primary contact gap to the first coil. The second coil may be electrically parallel to the pair of secondary contacts. The circuit breaker may include an arc interrupting chamber disposed adjacent to the primary contacts, the coil being configured to use current in the second current path to drive an arc away from the primary contact gap towards the arc interrupting chamber. The circuit breaker may include an actuator configured to drive at least one of the relatively moveable primary contacts between said open and closed configurations. The circuit breaker may include at least one actuator configured to drive at least one of the relatively moveable primary contacts between said open and closed configurations and at least one of the relatively moveable secondary contacts between said open and closed configurations.

The circuit breaker may be configured such that the same actuator is configured to drive at least one of the primary contacts and at least one of the secondary contacts in a single opening stroke. One of the primary contacts and one of the secondary contacts may share a common contact plate displaceable by the actuator. The coil may include a high permeability core, one end of which is disposed adjacent to the primary contact gap. Each of the coils may include a high permeability core having an end disposed adjacent to the primary contact gap, the ends of the cores being on opposing sides of the primary contact gap. The circuit breaker may include an air displacement device configured to eject air across the primary contact gap. The actuator may be configured to operate the air displacement device on opening the primary contacts.

According to another aspect, the present invention provides a method of operating a circuit breaker comprising: providing first and second relatively moveable primary contacts, each including a respective contact surface, adapted to move between a closed configuration in which the contact surfaces are in physical contact with one another and an open configuration in which the contact surfaces are separated by a primary contact gap, passing operating current from a first current terminal to the first primary contact via first current path; passing the operating current from the second primary contact to a second current terminal via a second current path, the second current path comprising (i) a pair of relatively moveable secondary contacts, each including a respective contact surface, adapted to move between a closed configuration in which the contact surfaces are in physical contact with one another and an open configuration in which the contact surfaces are separated by a secondary contact gap, and (U) a coil disposed adjacent to the primary contacts so as to be capable of generating a magnetic field transverse to the primary contact gap, the coil being electrically parallel to the pair of secondary contacts; upon opening the secondary contacts by an actuator, diverting substantially all the current in the second current path through the coil to thereby generate said magnetic field transverse to the contact gap, and upon opening of the primary contacts by an actuator, using the magnetic field traversing the primary contact gap to thereby drive an arc traversing the primary contact gap away from the primary contact gap.

The method may include opening the primary and secondary contacts using the same actuator in a single opening stroke.

Embodiments of the present invention will now be described by way of example and with reference to the accompanying drawings in which: Figure 1 shows a schematic perspective sectioned view of parts of a circuit breaker with electromagnetic actuator and arc chute; Figure 2 shows a schematic perspective view of components of the circuit breaker of figure 1; Figure 3 shows a schematic perspective view of coil arrangements in the circuit breaker of figure 1; Figure 4 shows a schematic perspective view of components of the circuit breaker of figure 1; Figure 5 shows a side view of a coil arrangement of figure 3; Figures shows a schematic perspective view of components of the circuit breaker of figure 4.

Throughout the present specification, descriptors relating to relative orientation and position, such as "top", "bottom", "horizontal", "vertical", "left", "right", "up", down", "front", "back", side, as well as any adjective and adverb derivatives thereof, are used in the sense of the orientation of components as presented in the drawings. However, such descriptors are not intended to be in any way limiting to actual use of the described or claimed invention, With reference to figure 1, there is shown a DC circuit breaker 1 including a fixed contact arm 2 having a contact surface 3 formed thereon and a moving contact arm 4 also having a contact surface 5 formed thereon, For convenience, the contact arrangements comprising arms 2, 4 and contact surfaces 3, 5 may be designated as the primary contacts.

The circuit breaker 1 also includes a further fixed contact arm 6 having a contact surface 7 formed thereon and a moving contact arm S also having a contact surface 9 formed thereon. For convenience, the contact arrangements comprising arms 6, 8 and contact surfaces 7, 9 may be designated as the secondary contacts.

In the example shown, the primary moving contact arm 4 and the secondary moving contact arm 8 are constructed from a single piece with one arm 4 extending upward from an actuator shaft 10 and the other arm 8 extending downward from the actuator shaft 10.

The moving contact arms 4, 8 are displaceable in a horizontal direction as shown in figure 1 along an axis 11 of an actuator 20 between (i) an open configuration (as shown in the drawing) in which the contact surfaces 3 and 5 are separated from one another and in which the contact surfaces 7 and 9 are separated from one another and (ii) a closed configuration in which the contact surfaces 3 and 5 are brought together and in which the contact surfaces 7 and 9 are brought together, by axial motion of the actuator shaft 10 to the right. In the open configuration, a primary contact gap 12 is formed between the contact surfaces 3, 5 and a secondary contact gap 13 is formed between the contact surfaces 7, 9.

Movement of the contact arms 4, 8 is facilitated by way of the actuator 20 which may be any suitable actuator mechanism such as an electromagnetic coil 21. Such actuator mechanisms 20 may include a dual mechanism to separately provide opening and closing forces, in accordance with known practice. The actuator mechanism 20 may also include a latching mechanism according to known practice, e.g. for bistable operation.

Although a circuit breaker 1 using a fixed and a moving contact arm for each of the primary and secondary contacts has been described, the circuit breaker 1 could be adapted to provide moving contact arms for both contacts of the primary and I or secondary contacts, More than one contact surface on each respective contact arm could also be provided and the relative movement of contacts could generally also be provided by way of pivoting contact arms rather than those deploying linear axial movement as depicted in the drawings.

The first primary contact surface 3 is electrically coupled to a first current terminal 30 by way of a first current path 31, which includes the arm 2. The second primary contact surfaceS is electrically coupled to a second current terminal 32 by way of a second current path 33, described further below.

Positioned adjacent to the primary contact surfaces 3, 5 is an arc interrupting chamber 40 which preferably includes some form of arc extinguishing mechanism, such as an arc chute 41. The arc chute 41 comprises a plurality of parallel, electrically conductive plates 42 (only some of which are shown to their full extent in the schematic drawing, the others being partially sectioned away), each separated by a suitable dielectric medium (e.g. air or other gas), which split the arc. In one configuration, the arc chute 41 may comprise 60 plates sustaining a 30V arc voltage between each adjacent pair of plates to give a total of 1BOOV. Arc chutes are well known in the art and other examples will not be further described here.

With reference to figure 2, further details of the circuit breaker I are shown. Coupled across the secondary contacts 7, 9 (i.e. electrically parallel therewith) is an electrically conductive coil 50. In the example of figure 2, the coil 50 is coupled to the arm 6 by way of a fixed coil connector 51, and to the arm 8 by way of a moveable coil connector 52. As readily seen in figure 3, the coil 50 comprises a number of turns 53 about a core 54 separated from the turns 53 by a spacer 55. An inner turn 56 terminates in an extension portion which serves as the fixed coil connector 51. An outer turn 57 terminates in an extension portion 58 which serves as part of the moveable coil connector 52 (figure 2).

The moveable coil connector 52 further includes a pivoting portion 59 which is pivotable relative to the extension portion 58 by bolt 60 and axle 61.

In the example of figure 2, the arm 4, arm 8, contact surfaces 9, 7, connector 59, coil 50, connector 51 and arm 6 exemplify the second current path 33. When the contact surfaces 9, 7 are closed, the second current path 33 comprises parallel current paths through the contacts 9, 7 and through the coil 50. When the contact surfaces 9, 7 are open, the second current path is provided through the coil 50.

As best seen in figure 4, the coil arrangements may be duplicated on the far side of the arm and contact assembly in a mirror image' arrangement comprising coil 50a, fixed coil connector 51a, moveable coil connector 52a, turns 53a, core 54a, spacer 55a, inner turn 56a, outer turn 57a, extension portion 58a, pivot portion 59a and bolt Boa coupled to axle 61. The coil turns 53, 53a are such that current flowing through the coils will generate magnetic fields through the cores 54, 54a in the same direction as one another and transverse to the primary contact gap 12. Thus, in a general aspect, this exemplifies an arrangement in which the coils are disposed on opposite sides of the primary contact gap 12.

Although the coils 50, 50a are preferably constructed from a generally rigid or semi-rigid electrically conductive metal, the turns 53, 53a may generally be constrained from movement along the axis of the coil by a helical groove 62 in the spacer 55, 55a, as best seen in figure 5. This groove 62 may be large enough to allow limited movement of the turns 53, 53a along the axis of the coil and or expansion, but prevent coil turns from electrical shorting by touching an adjacent turn, In use, the circuit breaker operates as follows. In a closed configuration, in which the first and second primary contact surfaces 3, 5 are in physical contact with one another, and in which the first and second secondary contact surfaces 9, 7 are in physical contact with one another, current flows between the first terminal 30 and the second terminal 32 (in either direction, depending on use). Current passes along the arm 2, across primary contact surfaces 3, 5, through arms 4, 8, across secondary contact surfaces 9, 7 and through arm 6. An additional current path in parallel to the secondary contact surfaces 7, 9 is provided by current flow through the coils 50a, 50b.

Upon the actuator receiving an opening signal, the actuator 20 begins an opening movement by driving the actuator shaft 10 to the left as viewed from the perspective of figure 1. Such an opening signal may be triggered, for example, by detection of an overcurrent condition or fault condition in a circuit to which the circuit breaker is connected by terminals 30, 32.

In an initial stage of the opening movement, the secondary contacts 7, 9 may generally commence an opening movement first: there may be little or no tendency for an arc to be generated between the secondary contact surfaces 7, 9 in view of the alternative current path still available through the coils 50, 50a. In addition, there may be less adhesion of the contact surfaces 7, 9 in view of the reduced level of normal current through the contact surfaces 7, 9 in view of the parallel current path available through the coils 50, 50a.

However, once the contact surfaces 7, 9 have separated, without arcing orwith little arcing, the full current passing through the circuit breaker passes through the coils 50, 50a generating a large magnetic field transverse to the primary contacts. The moment that the primary contact surfaces 3, 5 commence separation, which may be contemporaneous with, or slightly later than, the opening of the secondary contact surfaces 7, 9, the full current of any arc traversing the contact gap 12 between the primary contact surfaces 3, 5 is being used to generate a transverse magnetic field which serves to stretch the arc upwards into the arc interrupting chamber 40 and arc chute 41. Upon extinguishing of the arc between the primary contact surfaces 3, 5, the current ceases and the magnetic field in the coils 50, 50a collapses.

In this manner, normal circuit breaker current does not pass substantially through the arc extinguishing coils 50, 50a because the coils are effectively shorted by the secondary contacts. Therefore, the coils do not need to be rated for long term high current use. Only during commencement of opening of the circuit breaker do the coils 50, 50a receive full switching current which lasts only for the approximate duration of the switching event.

Thus, the coils may be of substantially reduced capacity compared to coils which must carry the normal circuit breaker current.

Preferably, the coils 50, 50a have a core 54, 54a which is of high saturation magnetization and magnetic permeability, such as a nickel-iron alloy, though mild steel may also work in some applications. Preferably, the coil materials exhibit low remanence such that remanent flux density after saturation is very low and preferably less than 20 mT, or more preferably less than 10 mT. Use of a low remanence material makes the circuit breaker performance relatively insensitive to changes in the direction of current in normal use.

Various modifications may be made to the apparatus described in connection with figures 1 to 5. The circuit breaker may be configured with only a single coil 50 or 50a on one side of the primary contact gap 12. Such a coil may carry twice as much current as a dual, parallel coil arrangement as shown in the figures. Although the coils 50, 50a are shown electrically parallel to one another and to the secondary contact surfaces 7, 9, they could alternatively be configured to be electrically in series with one another, and in parallel with the secondary contact surfaces 7, 9.

It may not be essential to provide a core material 54 of high magnetic permeability in one or both cores if sufficient magnetic field can be directed across the contact gap by the coil or coils alone.

The coils 50, 50a may be positioned in any suitable location relative to the primary contact gap 12 which enables sufficient magnetic field to be generated transverse to the contact gap. The turns of the coil or coils can be positioned somewhat more remotely from the contact gap by using a flux-carrying core that extends to a position adjacent to the contact gap such that sufficient magnetic field is generated transverse to the contact gap. Thus, the coil or coils 50, 50a may include one or more flux circuit elements conveying magnetic flux to a position adjacent to the primary contact gap 12 to influence the path of any arc across the primary contact gap during a circuit breaking operation, to stretch the arc up into the arc-interrupting chamber 40. The coil or coils 50, 50a could be positioned on a flux-carrying core that extends to both sides of the contact gap 12 forming a complete magnetic circuit with a gap only adjacent to the contact gap 12.

It can be seen that upon opening of the primary contacts by the actuator, current traversing the first and second primary contacts (e.g. by arcing) is passing through the coil or coils to generate a magnetic field traversing the contact gap to thereby drive an arc traversing the contact gap away from the contact gap. When the arc is extinguished, the current ceases and the magnetic field in the coil or coils collapses.

In the arrangement shown in the drawings, one actuator 20 may be used to drive both the primary and secondary contacts between their open and closed positions. More generally, however, more than one actuator may be provided to provide opening or closing actions, such as separate actuators for opening and closing operations, or separate actuators for the primary and secondary contacts. In the arrangement shown, the actuator 20 is configured to drive one of the primary contacts 5 and one of the secondary contacts 9 in a single opening stroke, or in a single closing stroke.

In the example shown, one of the primary contact surfaces 5 and arm 4 and one of the secondary contact surfaces 9 and arm 8 share a common contact plate displaceable by a the actuator, but other arrangements comprising two separate moving contact arms 4, 8 linked to a common actuator, or to separate actuators, can be used.

The dual coil arrangement as shown in figure 1, with secondary contact coil by-pass, has been found to be ideally suited to circuit breakers carrying a nominal 4000 A current.

The circuit breaker may also include a puffer or arc blow-out arrangement. This arrangement may comprise an air displacement device which is configured to eject air across the contact gap 12 when the contact surfaces 3, 5 are being relatively displaced from the closed position to the open position. The actuator 20 may be configured operate the air displacement device on opening the primary contact, e.g. by means of a bellows or other device coupled to the actuator. Blowing air rapidly across the contact gap 12 during an opening operation may further assist in extinguishing an arc more quickly. The air displacement device may also be configured as a damper to operate during the opening stroke of the actuator to reduce the impact on the opening mechanism and limit stop at the end of the opening stroke.

Other embodiments are intentionally within the scope of the accompanying claims.

Claims

CLAIMS1. A circuit breaker comprising: first and second relatively moveable primary contacts, each including a respective contact surface, adapted to move between a closed configuration in which the contact surfaces are in physical contact with one another and an open configuration in which the contact surfaces are separated by a primary contact gap, the first primary contact being connected to a first current terminal via first current path and the second primary contact being connected to a second current terminal via a second current path; the second current path including a pair of relatively moveable secondary contacts, each including a respective contact surface, adapted to move between a closed configuration in which the contact surfaces are in physical contact with one another and an open configuration in which the contact surfaces are separated by a secondary contact gap, wherein the second current path includes a coil electrically parallel to the pair of secondary contacts and disposed adjacent to the primary contacts so as to generate a magnetic field transverse to the primary contact gap.
2. The circuit breaker of claim I in which the second current path includes a second coil disposed adjacent to the primary contacts so as to generate a second magnetic field transverse to the primary contact gap, the second coil being on an opposite side of the primary contact gap to the first coil.
3. The circuit breaker of claim I in which the second coil is also electrically parallel to the pair of secondary contacts.
4, The circuit breaker of claim 1 further including an arc interrupting chamber disposed adjacent to the primary contacts, the coil being configured to use current in the second current path to drive an arc away from the primary contact gap towards the arc interrupting chamber.
5. The circuit breaker of claim 1 further including an actuator configured to drive at least one of the relatively moveable primary contacts between said open and closed configurations.
6. The circuit breaker of claim I further including at least one actuator configured to drive at least one of the relatively moveable primary contacts between said open and closed configurations and at least one of the relatively moveable secondary contacts between said open and closed configurations.
7. The circuit breaker of claim 6 configured such that the same actuator is configured to drive at least one of the primary contacts and at least one of the secondary contacts in a single opening stroke.
8. The circuit breaker of claim 7 in which one of the primary contacts and one of the secondary contacts share a common contact plate displaceable by the actuator.
9. The circuit breaker of claim 1 in which the coil includes a high permeability core, one end of which is disposed adjacent to the primary contact gap.
10. The circuit breaker of claim 2 in which each of the coils includes a high permeability core having an end disposed adjacent to the primary contact gap, the ends of the cores being on opposing sides of the primary contact gap.
11. The circuit breaker of claim 5 further including an air displacement device configured to eject air across the primary contact gap, and in which the actuator is configured operate the air displacement device on opening the primary contacts.
12. A method of operating a circuit breaker comprising: providing first and second relatively moveable primary contacts, each including a respective contact surface, adapted to move between a closed configuration in which the contact surfaces are in physical contact with one another and an open configuration in which the contact surfaces are separated by a primary contact gap, passing operating current from a first current terminal to the first primary contact via first current path; passing the operating current from the second primary contact to a second current terminal via a second current path, the second current path comprising (i) a pair of relatively moveable secondary contacts, each including a respective contact surface, adapted to move between a closed configuration in which the contact surfaces are in physical contact with one another and an open configuration in which the contact surfaces are separated by a secondary contact gap, and (ii) a coil disposed adjacent to the primary contacts so as to be capable of generating a magnetic field transverse to the primary contact gap, the coil being electrically parallel to the pair of secondary contacts; upon opening the secondary contacts by an actuator, diverting substantially all the current in the second current path through the coil to thereby generate said magnetic field transverse to the contact gap, and upon opening of the primary contacts by an actuator, using the magnetic field traversing the primary contact gap to thereby drive an arc traversing the primary contact gap away from the primary contact gap.
13. The method of claim 12 further including opening the primary and secondary contacts using the same actuator in a single opening stroke.