Patent Description:
Electrical switches for use in high current applications are known. Such switches are typically designed to carry currents of up to <NUM>,<NUM> Amps. However, if the switch is closed onto a faulty load the switch could be required to carry a current in the range <NUM>,<NUM> to <NUM>,<NUM> Amps even if only briefly. An example of such an application is in the field of electric railways.

<CIT> discloses a coaxial two-way switch with a rotatable contact device which can be moved into at least two switching positions, in particular via a magnetic drive, and which is designed as an insulating disc with strip conductors applied on both sides, with which fork contacts which are connected to the inner conductor of the relevant coaxial conductor section interact.

<CIT> discloses a disconnection module for electrical apparatus e.g. circuit-breaker, which has two pairs of mobile contacts coupled by a rotation driving mechanism that is arranged for inversing rotation of one pair with respect to other pair.

Document <CIT> discloses a high voltage circuit breaker having fixed contacts on a carrier and movable contacts that move on shaft. The fixed contacts have a have permanent magnets that operate to extinguish any arcing between the contacts.

A particular problem associated with switches used in high current applications is the Lorentz force.

As the arm of the switch approaches an electrical contact to close a circuit pre contact arcing occurs and current starts to flow. The Lorentz force pinches the contact and the switch arm together and considerable force has to be employed to fully insert the switch arm into the contact. Because of this such switches tend to be large as they must include a driving mechanism to provide the necessary force to drive the arm home into the contact. Typically large springs or mechanical or hydraulic rams are employed. Use of such driving mechanisms tends to cause the arm or contact to deform or wear away so reducing the life of the switch. Typically such switches can only be used less than ten times before they need to be replaced at considerable cost.

A further problem with such known switches is that when pre contact arcing occurs, it always occurs between the same two points on the switch arm and contact. This erodes the switch arm and contact, further reducing the lifetime of the switch.

Both of these problems are particularly severe in the case of high current DC switches. This is due to the high rate of increase of the DC current, typically at a rate of around 40kA/ms.

The current invention seeks to overcome the problems of the prior art.

Accordingly,the present invention provides a electrical switch according to claim <NUM>.

Only a relatively small force needs to be used to open and close the switch of the current invention.

Further, pre contact arcing does not always occur between the same points on the wheel and arcing portion. The switch according to the invention therefore has a considerably longer lifespan than known switches.

Preferably the main portion comprises at least one pair of spaced apart main portion fingers, the body portion being adapted to be received between the main portion fingers.

Preferably the electrical switch further comprises at least one electrically conductive contact washer having a central aperture, the contact washer being arranged on a face of the wheel.

Preferably the wheel is sandwiched between contact washers.

Preferably the contact washer comprises a plurality of spaced apart first slots extending from the central aperture part way to the outer edge of the washer.

Preferably the contact washer comprises a plurality of spaced apart second slots extending from the outer edge of the washer part way to the central aperture.

Preferably the first slots are interdigitated with the second slots.

In a further aspect of the invention there is provided an electrical switch system comprising.

Preferably the electrical switch system further comprises a load connected to the other arm.

Preferably the load is an electric vehicle.

The present invention will now be described by way of example only and not in any limitative sense with reference to the accompanying drawings in which.

Shown in <FIG> in schematic form is a known switch <NUM> for use in a high current application. The switch <NUM> comprises a first electrically conductive arm <NUM> connected to a voltage source <NUM>. It further comprises a second electrically conductive arm <NUM> connected to a load <NUM>, which in this application is an electric train. The second arm <NUM> ends in a connector <NUM> which comprises first and second spaced apart fingers <NUM>,<NUM>. In <FIG> the two arms <NUM>,<NUM> are spaced apart and the switch <NUM> is in the open configuration.

In order to switch the switch <NUM> to the closed configuration the first arm <NUM> is moved towards the second arm <NUM> as shown in <FIG>. As the first arm <NUM> approaches the second arm <NUM> pre contact arcing occurs as shown and current starts to flow from the first arm <NUM> to the second arm <NUM>.

As the first arm <NUM> is moved further it is received between the spaced apart fingers <NUM>,<NUM>. At this point the current flowing from the first arm <NUM> and then through the fingers <NUM>,<NUM> causes the fingers <NUM>,<NUM> to be urged towards the first arm <NUM>, so gripping the first arm <NUM>, due to the Lorentz force. This is shown in <FIG>.

This gripping of the first arm <NUM> by the fingers <NUM>,<NUM> produces significant friction between the first arm <NUM> and fingers <NUM>,<NUM>. In order to push the first arm <NUM> fully home between the fingers <NUM>,<NUM> considerable force must be used, A spring <NUM> or other hydraulic or mechanical means is typically used to achieve this, as shown in <FIG>.

Shown in <FIG> in perspective view is a first embodiment of an electrical switch <NUM> according to the invention. The switch comprises a first electrically conductive arm <NUM> which comprises an electrically conductive arcing portion <NUM> and an electrically conductive main portion <NUM>. The arcing portion <NUM> comprises first and second spaced apart arcing fingers <NUM> pivotally connected to a base portion <NUM> by an arcing finger pivot <NUM>. The main portion <NUM> comprises a plurality of pairs of main portion fingers <NUM>, each pair of main portion fingers <NUM> being pivotally connected to the base portion <NUM> by a base portion pivot <NUM>. The base portion <NUM> is shown connected to a load <NUM> which is in turn connected to earth <NUM>.

The electrical switch <NUM> further comprises a second electrically conductive arm <NUM>. The second electrically conductive arm <NUM> comprises an electrically conductive body portion <NUM>. The second arm <NUM> further comprises an electrically conductive wheel <NUM> which is connected to the body portion <NUM> by a wheel axle <NUM> which extends along a wheel axis. The wheel <NUM> is free to rotate about the wheel axis.

The end of the second arm <NUM> proximate to the first arm <NUM> is shown in greater detail in <FIG>. As can be seen from this figure the body portion <NUM> comprises a plurality of electrically conductive receiving fingers <NUM>. Each receiving finger <NUM> terminates in an electrically taper <NUM>. The taper <NUM> may be electrically insulating. The electrically conductive wheel <NUM> is sandwiched between contact washers <NUM>. The contact washers <NUM> abut the body portion <NUM> ensuring a good electrical contact between the wheel <NUM> and the body portion <NUM>. In an alternative embodiment (not shown) the contact washer <NUM> is cylindrical and arranged around the wheel axle <NUM>. The wheel <NUM> is arranged around the contact washer <NUM>.

An example of a contact washer <NUM> is shown in plan view and side view in <FIG>. The contact washer <NUM> comprises an electrically conductive, preferably copper, disk defined by an outer edge <NUM>. Extending through the center of the disk is a central aperture <NUM>. A plurality of spaced apart first slots <NUM> extend from the central aperture <NUM> part way to the outer edge <NUM>. A plurality of spaced apart second slots <NUM> extend from the outer edge <NUM> part way to the central aperture <NUM>. The first slots <NUM> and second slots <NUM> are interdigitated. As can be seen in side view, the center of the washer <NUM> is slightly raised with respect to the outer edge <NUM> so that the washer <NUM> is slightly bowl shaped and matches the profile of the wheel <NUM>.

Returning to <FIG>, each contact washer <NUM> is centered on a face of the wheel <NUM> with the center of the central aperture <NUM> coaxial with the wheel axle <NUM>.

Returning to <FIG>, the switch <NUM> is shown in the open configuration with the first and second arms <NUM>,<NUM> spaced apart. The switch <NUM> further comprises a pivot mechanism <NUM> connected to each of the pairs of arcing fingers <NUM> and main potion fingers <NUM>. In order to switch the switch <NUM> from the open configuration to a closed configuration the pivot mechanism <NUM> simultaneously pivots the pair of arcing fingers <NUM> and multiple pairs of main portion fingers <NUM> towards the second electrically conductive arm <NUM>. As the arcing fingers <NUM> approach the wheel <NUM> pre-contact arcing occurs between the arcing fingers <NUM> and wheel <NUM>. As pivoting continues the edge of the wheel <NUM> is received between the arcing fingers <NUM>. Current flows from the arcing fingers <NUM> through the wheel <NUM> and contact washers <NUM> to the body portion <NUM> of the second arm <NUM>. This current flow causes the arcing fingers <NUM> to grip the wheel <NUM> firmly. As pivoting continues further the wheel <NUM> rotates around the wheel axis, so allowing pivoting to continue with little resistance.

As pivoting continues further each pair of main portion fingers <NUM> slides onto a taper <NUM> and then onto a receiving finger <NUM>. A significant portion of the current is flowing through the arcing fingers <NUM> and wheel <NUM>. The remainder of the current is divided between each of the pairs of main portion fingers <NUM>. The current flowing through a single pair of main portion fingers <NUM> to its associated receiving finger <NUM> is therefore relatively small and so the Lorentz force between the main portion fingers <NUM> and the receiving finger <NUM> is also small. The pivot mechanism <NUM> can therefore pull the main portion fingers <NUM> onto the receiving fingers <NUM> with relatively little force, so closing the switch <NUM>.

The switch <NUM> is designed such that the main portion fingers <NUM> slide onto the receiving fingers <NUM> shortly after the arcing fingers <NUM> engage the wheel <NUM>. Typically the time difference is of the order a few milliseconds so as to avoid overheating the arcing fingers <NUM> and contact washers <NUM>.

The switch <NUM> according to the invention can therefore be switched from the open configuration to the closed configuration (and vice versa) with relatively little force. The switch <NUM> is shown in the closed configuration in <FIG>. A further advantage of the switch <NUM> according to the invention is that the wheel <NUM> is not necessarily in the same orientation with respect to the remainder of the second arm <NUM> each time the switch <NUM> is opened or closed. The erosion of the wheel <NUM> caused by pre contact arcing is therefore spread around the periphery of the wheel <NUM> rather than concentrated at one spot.

Shown in <FIG> is the end of the second arm <NUM> of an alternative embodiment of the invention. In this embodiment the body portion <NUM> comprises a plurality of pairs of receiving fingers <NUM>. The main portion <NUM> of the first arm <NUM> comprises a plurality of single main portion fingers <NUM> each pivotally connected to the base portion <NUM>. The operation of this second embodiment is similar to that of the first embodiment only with the main portion fingers <NUM> being received between pairs of receiving fingers <NUM> rather than vice versa.

Shown in <FIG> is an example of an electrical switch <NUM> not falling within the scope of the invention. The electrical switch <NUM> comprises a first electrically conductive arm <NUM>. The first arm <NUM> comprises an electrically conductive arcing portion <NUM> and an electrically conductive main portion <NUM>. The arcing portion <NUM> comprises a resiliently deformable rail <NUM> having a slot <NUM> running along its length. The rail <NUM> is connected to a base portion <NUM>. The main portion <NUM> comprises a plurality of main portion fingers <NUM> fixedly extending from the base portion <NUM>.

The switch <NUM> further comprises a second electrically conductive arm <NUM>. The second arm <NUM> comprises a body portion <NUM>. Connected to the body portion <NUM> by a wheel axle <NUM> which extends along a wheel axis is an electrically conductive wheel <NUM>. The wheel <NUM> is free to rotate about the wheel axle <NUM>. The body portion <NUM> comprises a plurality of receiving fingers <NUM> extending towards the first electrically conductive arm <NUM>.

The switch <NUM> further comprises a displacement mechanism <NUM> connected to the first arm <NUM>. The displacement mechanism <NUM> is adapted to linearly displace the first arm <NUM> towards and away from the second arm <NUM>.

The switch <NUM> is shown in the open configuration with the first and second arms <NUM>,<NUM> spaced apart. In order to switch the switch <NUM> to the closed configuration the displacement mechanism <NUM> displaces the first arm <NUM> towards the second arm <NUM> until the wheel <NUM> engages the slot <NUM> running along the length of the rail <NUM>. As the first arm <NUM> is displaced further the wheel <NUM> rotates and the rail <NUM> is deformed until the receiving fingers <NUM> are received between the main portion fingers <NUM>, so closing the switch <NUM>. As before, the switch <NUM> can be switched between open and closed configurations with relatively little force so making the switch <NUM> reliable and inexpensive to manufacture.

Shown in <FIG> is an electrical switch system <NUM> according to the invention. The electrical switch system <NUM> comprises an electrical switch <NUM> as previously described. Connected to one arm <NUM>,<NUM> is a power supply <NUM>. The power supply <NUM> can provide a high current, typically in the range <NUM>,<NUM> to <NUM>,<NUM> Amps, more preferably in the range <NUM>,<NUM> - <NUM>,<NUM> Amps. More preferably the current is in the range <NUM>,<NUM> to <NUM>,<NUM> Amps. The other arm <NUM>,<NUM> of the switch <NUM> is connected to a load <NUM> which is in turn connected to earth <NUM>. The load <NUM> is typically an electrically powered vehicle such as a train but the invention is not so limited.

In the embodiment of <FIG> the switch <NUM> comprises a plurality of pairs of main portion fingers <NUM>. In an alternative embodiment the switch <NUM> comprises a single pair of main portion fingers <NUM>.

The switch <NUM> can be employed in both AC and DC systems.

Claim 1:
A electrical switch (<NUM>) comprising a first electrically conductive arm (<NUM>) comprising a first electrically conductive arcing portion (<NUM>) and an electrically conductive main portion (<NUM>); a second electrically conductive arm (<NUM>) comprising an electrically conductive body portion (<NUM>)
at least one of the first and second arms (<NUM>, <NUM>) being adapted to be displaced relative to the other to move the switch (<NUM>) between an open configuration in which the first and second arms (<NUM>, <NUM>) are spaced apart and a closed configuration in which the main portion (<NUM>) is in contact with the body portion (<NUM>);
the electrical switch (<NUM>) further comprising a pivot mechanism (<NUM>) to pivot the arcing portion (<NUM>) and the main portion (<NUM>) into contact with the body portion (<NUM>)
characterised in that
the second electrically conductive arm (<NUM>) further comprises an electrically conductive wheel (<NUM>) connected to the body portion (<NUM>) by a wheel axle (<NUM>) which extends along a wheel axis, the wheel (<NUM>) being free to rotate about the wheel axis, the wheel (<NUM>) being in electrical contact with the body portion (<NUM>), wherein in the closed configuration the arcing portion (<NUM>) is in contact with the wheel (<NUM>), the switch (<NUM>) being adapted such that as the switch (<NUM>) is switched from the open configuration to the closed configuration the arcing portion (<NUM>) contacts the wheel (<NUM>) before the main portion (<NUM>) contacts the body portion (<NUM>); wherein the arcing portion (<NUM>) comprises at least one pair of spaced apart arcing fingers (<NUM>), the wheel (<NUM>) being adapted to be received between the fingers (<NUM>), and in that the pivot mechanism (<NUM>) is adapted to pivot the arcing portion (<NUM>) into contact with the wheel (<NUM>).