Patent Description:
A vacuum circuit breaker (VCB) normally comprises a vacuum circuit interrupter and an actuator for operating the interrupter between open and closed states.

Conventionally, the actuator comprises an electromagnetic device coupled to the contacts of the interrupter by bellows, the electromagnetic actuator and the bellows being located outside of the vacuum enclosure that contains the interrupter. Such VCBs are large, relatively slow to operate and relatively difficult to control precisely. Also, the bellows are prone to failure. The slow speed and low precision control is caused at least in part by the use of electromagnetic actuators. The relatively large size is due in part to the external bellows. International patent application <CIT> discloses an electromechanical disconnect switch for use in a VCB, the switch having a piezoelectric actuator and a switching chamber comprising a self-contained environment that may consist of a high pressure gas or a vacuum.

It would be desirable to address the problems outlined above.

The invention provides a vacuum circuit breaker as claimed in claim <NUM>. The vacuum circuit breaker may include a switching device comprising: first and second body parts, at least one of said body parts being movable with respect to the other part; a first operating device coupled to said at least one body part and being operable to move said at least one body part towards said other body part into a closed state; and at least one piezoelectric actuator coupled to either one or both of said body parts and being operable to move said at least one body part away from said other body part out of said closed state.

In preferred embodiments said first and second body parts each has a contact face, the respective contact faces being engaged with one another in said closed state, said at least one piezoelectric actuator being operable to move said at least one body part to cause said contact faces to disengage.

Said first and second body parts may be magnetised or magnetisable to create a magnetic latching effect to hold said body parts in said closed state, and wherein said at least one piezoelectric actuator is operable to move said at least one body part away from the other body part to break said magnetic latching effect. Said first and second body parts may be magnetised or magnetisable to create a magnetic latching effect to hold said contact faces in engagement, and wherein said at least one piezoelectric actuator is operable to move said at least one body part to cause said contact faces to disengage such that said magnetic latching effect is broken.

In preferred embodiments said first operating device is an electromagnetic operating device that magnetises, in use, at least one of, and preferably both of, said first and second body parts.

Optionally at least one of, and preferably both of, said first and second body parts comprises one or more permanent magnet or is otherwise permanently magnetised.

In preferred embodiments the piezoelectric actuator of either one of said body parts is operable to engage with the other of said body parts to cause said body parts to move away from one another, typically causing the respective contact faces to disengage.

Typically the piezoelectric actuator of any one of said body parts is operable to engage with the contact face of other of said body parts to cause body parts to move away from one another, typically causing the respective contact faces to disengage.

Typically the piezoelectric actuator of any one of said body parts is operable to engage with the other of said body parts when in said closed state, and particularly when the respective contact faces are engaged.

Conveniently said at least one piezoelectric actuator is incorporated into, for example embedded in, the respective body part.

Typically said at least one piezoelectric actuator is expandable to move said at least one body part away from said other body part out of said closed state. Preferably, said at least one piezoelectric actuator has an expansion axis and is positioned with respect to the respective body part so that, upon expansion along said expansion axis, said at least one piezoelectric actuator expands outwardly from the respective body part. Said at least one piezoelectric actuator may be positioned so that an end of said at least one piezoelectric actuator is substantially level or level with the contact face of the respective body part, and is movable outwardly from said contact face upon expansion of said at least one piezoelectric actuator. Said end may be substantially level or level with said contact face when said at least one piezoelectric actuator is in an equilibrium or a contracted state.

In preferred embodiments a first piezoelectric actuator is coupled to said first body part and a second piezoelectric actuator is coupled to said second body part. Preferably the respective piezoelectric actuators are aligned for engagement with one another. Preferably the respective piezoelectric actuators are engagable with one another upon expansion of the or each piezoelectric actuator.

In preferred embodiments said first operating device comprises an electromagnetic operating device comprising at least one electromagnetic coil, the electromagnetic operating device being operable to move the or each body part by controlling the energisation of said at least one electromagnetic coil. Preferably, said electromagnetic operating device is configured to move the, or each, body part towards, and typically into engagement with, the other body part upon energisation of said at least one electromagnetic coil.

Said electromagnetic operating device may be configured to move the, or each, body part away from the other body part upon de-energisation of said at least one electromagnetic coil. Said at least one electromagnetic coil may be located around the, or each, of said body parts.

The or each of said body parts may be formed at least partly from ferromagnetic or magnetisable material.

In preferred embodiments both of said body parts are movable with respect to the other part, typically to allow said contact faces to move into or out of engagement with one another.

In preferred embodiments said body parts are coupled to a mechanical coupling mechanism for imparting movement of the, or each, body part to an object to be actuated. Said mechanical coupling mechanism may comprise at least one flexible structure connected to each of the body parts and spanning the interface of the contact surfaces. The or each flexible structure may be integrally formed with the body parts, preferably by a respective flexure bearing. A gap may be provided between the or each flexible structure and an outer face of the body parts through which at least one electromagnetic coil of said electromagnetic operating device is wound. Typically, the or each flexible structure curves outwardly with respect to the body parts. A respective flexible structure may be provided at opposite outer faces of the body parts.

Typically said first and second body parts are incorporated into a support structure that supports the body parts and controls said movement into and out of contact with one another.

Also disclosed is an actuator comprising the switching device, wherein said body parts are coupled to a mechanical coupling mechanism for imparting movement of the, or each, body part to an object to be actuated.

Also disclosed is a method of operating the switching device or the actuator of the third aspect, the method comprising:.

The vacuum circuit breaker comprises: a housing providing a vacuum chamber; a vacuum interrupter having a movable first contact and a second contact, and an actuator coupled to the vacuum interrupter to move said first contact into and/or out of engagement with said second contact, wherein said vacuum interrupter and said actuator are located in said vacuum chamber, and wherein said vacuum chamber is partitioned into first and second sub-chambers by a partition, each of said first and second sub-chambers being in vacuum in use, and wherein said first and second contacts are located in said first sub-chamber and said actuator is located in said second sub-chamber. Said actuator is preferably a piezoelectrically operated actuator. Said actuator is preferably a hybrid actuator comprising a first non-piezoelectric operating device and a second piezoelectric operating device.

Said partition may comprise a diaphragm. Said partition is preferably flexible, preferably in the direction of movement of said first contact and/or in the direction of movement of said actuator. Said partition is preferably non-resilient. Said partition may be comprised of multiple parts.

Said partition provides a non-hermetic seal between the first and second sub-chambers.

Typically said partition includes at least one aperture, preferably at least one differential aperture.

Advantageously said partition is configured to support molecular flow between said first and second sub-chambers. Said at least one aperture may be dimensioned to support said molecular flow between said first and second sub-chambers.

Said partition is configured to support Knudsen flow between said first and second sub chambers. Said partition provides a Knudsen number of greater than <NUM>. Preferably said at least one aperture is dimensioned to support Knudsen flow between said first and second sub-chambers.

In preferred embodiments said partition provides a barrier to the passage of molecules, in particular molecules emanating from said actuator during use, from said second chamber to said first chamber.

Further advantageous aspects of the invention will be apparent to those ordinarily skilled in the art upon review of the following description of a specific embodiment and with reference to the accompanying drawings.

An embodiment of the invention is now described by way of example and with reference to the accompanying drawings in which like numerals are used to denote like parts and in which:.

Referring now to <FIG>, there is shown, generally indicated as <NUM> and <NUM> an electrical circuit breaker device. The circuit breaker device <NUM>, <NUM> is intended for use in breaking an AC electrical power supply (in particular at low voltages (LV)) and so may be referred to as an AC circuit breaker. The circuit breaker <NUM>, <NUM> comprises a vacuum interrupter <NUM>, <NUM> and as such may be referred to as a vacuum circuit breaker (VCB). The vacuum interrupter <NUM>, <NUM> which may also be referred to as a vacuum switching device, comprises a movable electrical contact <NUM>, <NUM> and a fixed electrical contact <NUM>, <NUM> located in a vacuum chamber <NUM>, <NUM>, i.e. a chamber that is hermetically sealed and in vacuum, at least during use. The movable contact <NUM>, <NUM> is movable between an open state, in which it is electrically and physically separate from the fixed contact <NUM>, <NUM>, and a closed state in which it makes electrical (and typically physical) contact with the second contact <NUM>, <NUM>. The open state of the movable contact <NUM>, <NUM> corresponds to the open, or breaking, state of the vacuum interrupter <NUM>, <NUM>, and correspondingly of the circuit breaker <NUM>, <NUM>, in which it interrupts current flow in whatever circuit (not shown) it is part of. The closed state of the contact <NUM>, <NUM> corresponds to the closed, or making, state of the vacuum interrupter <NUM>, <NUM> and correspondingly of the circuit breaker <NUM>, <NUM>, in which current is able to flow between the contacts <NUM>, <NUM> and <NUM>, <NUM>.

Movement of the contact <NUM>, <NUM> between its open and closed states is effected by an actuator <NUM>, <NUM>. The VCB <NUM> of <FIG> is of a type in which the actuator <NUM> is located externally of the vacuum chamber <NUM> and is coupled to the movable contact <NUM> by a mechanical coupling mechanism <NUM>, for example a circuit breaker bellows device. The VCB <NUM> of <FIG> is of a type in which the actuator <NUM> is located in the same housing <NUM> as the vacuum interrupter <NUM>. In some embodiments, the actuator <NUM> is located within the vacuum chamber <NUM>. The actuator <NUM> may be separated from the vacuum interrupter <NUM> by a partition <NUM>. In any case, a coupling mechanism is typically provided between the actuator <NUM> and the movable contact <NUM> to allow the actuator <NUM> to move the contact <NUM>. The mechanical coupling between the actuator <NUM> and the vacuum interrupter <NUM> may take any convenient form, for example comprising a flexible coupling member that extends across the inside of the housing <NUM> between the actuator <NUM> and the vacuum interrupter <NUM>. For example the flexible member may be planar in form, e.g. comprising a sheet, plate or membrane, but it may alternatively take other forms, e.g. comprising a bar, strip or rod. Optionally, the flexible member is electrically conductive and electrically connects the movable contact <NUM> to an external circuit during use. In embodiments where the actuator <NUM> is located in a chamber separate from the vacuum chamber <NUM>, the flexible member may separate the inside of the housing <NUM> into first and second chambers <NUM>, <NUM>', the vacuum interrupter <NUM> being in the first chamber <NUM>, <NUM>' and the actuator <NUM> being in the other, i.e. the flexible member may serve as the partition <NUM> or be otherwise combined with the partition <NUM>. Both chambers <NUM>, <NUM>' may be in vacuum but there is typically a pressure differential between them. The ends of the flexible member <NUM> may be fixed to opposite sides of the housing <NUM> in any convenient manner.

The vacuum interrupter <NUM>, <NUM>, and therefore the VCB <NUM>, <NUM>, may operate in a normally closed state, i.e. with the contact <NUM>, <NUM> in its closed state to allow current to flow between the contacts <NUM>, <NUM> and <NUM>, <NUM> and so to flow in any given circuit (not shown) in which the circuit breaker <NUM>, <NUM> is installed during use. In such cases the VCB <NUM>, <NUM> is configured to open automatically in response to detection of a fault condition, e.g. in response to detection of a current overload or short circuit, to protect the circuit into which it is incorporated during use. It achieves this by causing the actuator <NUM>, <NUM> to move the first contact <NUM>, <NUM> to its open state in response to detection of the fault. To this end the VCB <NUM>, <NUM> includes, or is co-operable with, a controller (not shown) for effecting the open state upon detection of a fault. The controller typically comprises electrical and/or electronic circuitry that includes, or is connected to, one or more current sensors (not shown). The current sensor(s) are coupled in use to any convenient current conductor of the VCB <NUM>, <NUM> or circuit to which the VCB is connected. Upon detection of current, more particularly prospective current, above a threshold level by the sensor(s), the controller causes the VCB to open. In preferred embodiments this is achieved by adjusting the voltage applied to the piezoelectric actuator <NUM>. The controller does not typically open the contacts immediately upon detection of overcurrent, advantageously it monitors voltage and/or phase angle to determine a suitable opening instant, e.g. at the zero crossing point of the sinusoidal voltage signal (which typically has a frequency of <NUM> - <NUM>).

In some embodiments, the VCB <NUM>, <NUM> can be reset, i.e. closed, manually or semi-manually (e.g. by manual activation of a user control (not shown)) and/or automatically in response to the VCB <NUM>, <NUM> detecting that the fault has gone, and/or after a threshold period of time has expired since activation. Circuit breakers that reset automatically are commonly known as reclosers.

Referring now to <FIG> and <FIG>, there is shown, generally indicated as <NUM> a hybrid actuatorsuitable for use in a circuit breaker, especially a vacuum circuit breaker of any of the types described above. The preferred actuator <NUM> may be described as hybrid in that it comprises a combination of electromagnetic and piezoelectric operating devices, i.e. a magneto-piezo hybrid actuator. The hybrid magneto-piezo actuator may be said to comprise a hybrid magneto-piezo switching device, as is described in more detail hereinafter.

The actuator <NUM> comprises a body <NUM> having first and second parts 322A, 322B each having a contact face 324A, 324B. The first and second parts 322A, 322B are arranged so that contact faces 324A, 324B oppose one another. The first and second parts 322A, 322B are movable with respect to each other between a closed or contacting state (not illustrated), in which the contact faces 324A, 324B are in contact with one another, and a non-contacting state (as shown in <FIG> and <FIG>) in which the body parts 322A, 322B are spaced apart to define a gap <NUM> between the contact faces 324A, 324B (in the contacting state the gap <NUM> is closed). In preferred embodiments, including the illustrated embodiment, both of the parts 322A, 322B are moveable, i.e. they both move towards each other when adopting the contacting state and away from each other when adopting the non-contacting state. In alternative embodiments (not illustrated) either one of the body parts may be fixed, the other of the body parts being movable towards and away from the fixed body part to adopt the contacting and non-contacting states. Typically, the, or each (as applicable) body part 322A, 322B moves substantially linearly. In alternative embodiments, a relatively small air gap may be present between the contact faces in the contacting state. In such cases the gap is sufficiently small that it allows the body parts 322A, 322B to be magnetically latched together.

The body parts 322A, 322B are formed from a ferromagnetic material, for example comprising iron, nickel or cobalt, or a suitable alloy of iron, nickel or cobalt.

The preferred actuator <NUM> includes an electromagnetic operating device <NUM> comprising one or more electromagnetic coil <NUM> (which may comprising one or more windings), and optionally a coil holder (not shown). The coil <NUM> is typically annular and is shown in <FIG> in cross section. The coil <NUM> is typically configured to form a solenoid. In the illustrated embodiment, the coil <NUM> is wrapped around the body <NUM>. As such the body <NUM> passes through the coil <NUM>, preferably being disposed substantially along the longitudinal axis of the coil <NUM>. Preferably, the coil <NUM> is substantially centrally located around the body <NUM>, typically overlapping with the contact faces 324A, 324B.

In alternative embodiments (not illustrated), the coil <NUM> may be embedded in either one or both of the body parts 322A, 322B. For example, an annular recess (not shown) may be formed in one or both of the contact faces 324A, 324B for receiving the coil <NUM>. In such cases, the coil <NUM> may be carried by, typically fixed to, one of the body parts in the recess. Optionally, the relative dimensions of the recess and the coil are such that the coil projects from its recess, the other body part being provided with a recess for receiving the projecting portion of the coil when the body parts are in the contacting state.

In use, the coil <NUM> is energised by applying a voltage to it causing current to flow through the coil, the current creating an electromagnetic field around the coil. To this end the coil <NUM> is connected to any convenient electrical power supply (not shown). The coil <NUM> may be de-energised by reducing the current flowing through the coil <NUM> and/or by reversing the polarity of the voltage applied to the coil <NUM>. When energised, the coil <NUM> acts as an electromagnet that causes the body parts 322A, 322B to move into the contacting state, i.e. creates a magnetic field and magnetic force that moves the body part(s). In preferred embodiments, when energised the coil <NUM> magnetises the body parts 322A, 322B to create latching residual magnetism between them, i.e. the body parts 322A, 322B are held in the contacting state by residual magnetism to create a magnetic latching effect. To this end the body parts 322A, 322B are formed at least partly from magnetisable, or ferromagnetic, material that is non-permanently magnetised but is susceptible of being magnetised by the electromagnetic field generated in use by the coil <NUM>. In alternative embodiments, one or both of the body parts may be formed at least partly from permanently magnetised material.

In preferred embodiments, the body parts 322A, 322B serve as an electromagnetic core for the coil <NUM>. In alternative embodiments where one of the body parts moves and the other is stationary, the movable part 322A may be regarded as an electromagnetic core for the coil <NUM>, while non-movable part 322B may be regarded as a yoke.

The body parts 322A, 322B may be held in the contacting state by one or more of a variety of ways depending on the embodiment. For example, where one or both of the first or second body parts 322A, 322B comprises a permanent magnet, or is otherwise formed at least partly from magnetisable material, they may be held together by residual magnetism in the first and/or second body parts 322A, 322B. Alternatively, or in addition, the coil <NUM> may remain energised to maintain the contacting state by the electromagnetic force created by the electromagnetic field around the coil. In the illustrated embodiment, the coil <NUM> creates residual magnetism in the first and second parts 322A, 322B such that, when the coil <NUM> is subsequently de-energised, the first and second parts 322A, 322B are held together to maintain the contacting state by the latching effect of the residual magnetism.

The coil <NUM> may be operated to release the body parts 322A, 322B from the contacting state by controlling the voltage applied to the coil <NUM>, and in particular by controlling the current flowing in the coil. For example, in embodiments where the coil <NUM> is energised to maintain the contacting state by electromagnetism, the body parts 322A, 322B may be released by de-energising the coil <NUM> (e.g. reducing the current flowing in the coil). In preferred embodiments, a suitable voltage may be applied to the coil <NUM> resulting in an electromagnetic field that has the effect of overcoming or cancelling any residual magnetism (or permanent magnetism as applicable) that is maintaining the latched contacting state. Conveniently, this is achieved by applying a voltage to the coil with opposite polarity to the voltage used to close the actuator <NUM>.

Preferably, one or more slots <NUM> are formed in each body part 322A, 322B in order to suppress eddy currents during use. The slots may be filled with a suitably non-conductive material, e.g. an epoxy resin, or left unfilled.

The actuator <NUM> includes a piezoelectric operating device <NUM>. In preferred embodiments, the piezoelectric operating device <NUM> is operable to move the body parts 322A, 322B from the contacting state to the non-contacting state. Typically this involves a pushing action, i.e. the piezoelectric operating device <NUM> acts to push the body parts 322A, 322B away from one another.

The piezoelectric operating device <NUM> comprises at least one piezoelectric actuator <NUM> (also known as a piezoelectric driver) coupled to the, or each, body part 322A, 322B and arranged to move the, or each, body part 322A, 322B relative to the other body part. In preferred embodiments, each body part 322A, 322B is provided with a respective piezoelectric actuator <NUM>. In alternative embodiments (not illustrated), only one of the body parts 322A, 322B is provided with a piezoelectric actuator.

Typically, the, or each, piezoelectric actuator <NUM> comprises a stack of layers of piezoelectric material (the layers running along the d<NUM> axis). Any suitable conventional piezoelectric material may be used, for example lead zirconate titanate, e.g. PZT-<NUM> Navy type VI or PIC <NUM> (PI). In preferred embodiments, the stack comprises one or more co-fired multilayer ceramics. The piezoelectric actuator <NUM> may for example be of a type that is operable in a bipolar or semi-bipolar manner. The piezoelectric actuator <NUM> expands along an expansion axis EA in response to the application of voltage of one polarity (e.g. a positive voltage in this example). Optionally, the piezoelectric actuator <NUM> may be of a type that contracts along the expansion axis EA in response to the application of voltage of the opposite polarity (e.g. a negative voltage in this example). Typically, the piezoelectric actuator <NUM> has an equilibrium length (in the direction of the axis EA) that it adopts in the absence of an applied voltage, increases this length in response to the application of voltage of the relevant polarity and returns to the equilibrium length in the absence of such voltage. The preferred piezoelectric actuator <NUM> contracts from the equilibrium length upon application of voltage of the opposite polarity and returns to the equilibrium length in the absence of such voltage.

Advantageously, the speed at which the piezoelectric actuator <NUM> returns to the equilibrium length can be increased by applying a voltage of the opposite polarity to that which caused it to expand or contract as applicable. For example, in the present example, application of a positive voltage causes the piezoelectric actuator <NUM> to expand along axis EA and, when in an expanded state, application of a negative polarity voltage causes the piezoelectric actuator <NUM> to contract more quickly than just the absence of a voltage. In any event, it will be understood that by adjusting the voltage applied to the piezoelectric actuator <NUM> it may be caused to expand and contract along the expansion axis EA, wherein the voltage adjustment may involve adjusting the magnitude and/or polarity of the applied voltage.

Electrodes (not shown) are provided for applying an electrical input signal to the, or each, piezoelectric actuator <NUM>. Typically at least two electrodes are provided (at least one positive and one negative). The electrodes are connected to an electrical power supply (not shown), which may or may not be the same as the power supply for the coil <NUM>. In any event the application of voltages to the piezoelectric actuator(s) <NUM> and the coil <NUM> is controlled separately, for example by a controller (not shown), programmed or otherwise configured to control the operation of the actuator <NUM> as described herein. For example the controller may comprise a microprocessor, microcontroller or other logic device incorporated into electrical circuitry for applying voltages to the coil <NUM> and the piezoelectric actuator(s) <NUM>.

By way of example, in a typical embodiment, the, or each, piezoelectric actuator <NUM> may have a length (in the direction EA) of approximately <NUM>, a height of approximately <NUM> and a width of approximately <NUM>. Depending on the applied voltage, the piezoelectric actuator <NUM> may expand or contract along the EA axis by up to approximately <NUM>% of its length. The applied voltage range may be for example -<NUM> V to +<NUM> V. Typically piezoelectric layer thickness may be approximately <NUM>. The piezoelectric actuator is typically substantially cuboid in shape but may take other shapes as suits the embodiment.

In preferred embodiments, the, or each, piezoelectric actuator <NUM> is coupled to the respective body part 332A, 332B such that expansion of the piezoelectric actuator <NUM> pushes the body parts 322A, 332B away from each other. Typically the arrangement is such that, upon expansion (e.g. from a contracted state to the equilibrium state, or from a contracted state to an expanded state, or from the equilibrium state depending on the embodiment), the piezoelectric actuator <NUM> engages with the contact face 324A, 324B of the other body part 322A, 322B to repel the body parts 322A, 332B away from each other. To this end it is preferred that the expansion axis EA is substantially parallel with the direction of movement of the respective body part 322A, 322B. Preferably, the piezoelectric actuator <NUM> is positioned such that one of its ends (in the direction of the expansion axis) is substantially flush or level, preferably exactly flush or level, with the respective contact face 324A, 324B of its respective body part 322A, 322B when the piezoelectric actuator <NUM> is in a contracted or equilibrium state (preferably in a contracted state in order to increase the stroke of the actuator <NUM>). Preferably, the piezoelectric actuator <NUM> is embedded in the respective body part 322A, 322B, e.g. located in a recess formed in the respective body part 322A, 322B, preferably such that one end is located at the respective contact face 324A, 324B. Optionally, said one end of each piezoelectric actuator <NUM> is provided with a tip <NUM> formed from relatively hard material, e.g. high-hardness steel, in comparison with the piezoelectric material, to protect the piezoelectric material from the effects of impacts during use. Alternatively, the piezoelectric actuator <NUM> may be incorporated into, for example embedded in, or otherwise mounted on or carried by the respective body part in any convenient manner.

In preferred embodiments, a respective piezoelectric actuator <NUM> is provided in each body part 322A, 322B, the actuators <NUM> being aligned with each other so that, upon expansion, they engage with each other to repel the body parts 322A, 322B away from each other. Hence the combined stroke of the piezoelectric actuators <NUM> amplifies the repelling effect of the piezoelectric actuators <NUM>.

In use, with the body parts 322A, 322B in the non-contacting state and with the piezoelectric actuators <NUM> in a relatively contracted state (e.g. in the equilibrium state or contracted with respective to the equilibrium state depending on the configuration of the embodiment), the body parts 322A, 322B may be brought together into the contacting state by energising the coil <NUM>. Preferably, the arrangement of the piezoelectric actuators <NUM> is such that their ends do not prevent the contact faces 324A, 324B from engaging with each other in the contacting state. The body parts 322A, 322B may be maintained in the contacting state by maintaining energisation of the coil <NUM> or by residual magnetism after de-energisation of the coil <NUM>. When it is desired to move the body parts 322A, 322B apart, the coil <NUM> is preferably de-energised, most preferably by reversing the polarity of the voltage applied to the coil <NUM>. However, de-energisation of the coil <NUM> is not essential since, advantageously, separation of the body parts 322A, 322B is effected by the piezoelectric actuators <NUM>. In particular, upon expansion of the piezoelectric actuators <NUM> in response to application of a suitable voltage signal, the piezoelectric actuators <NUM> push the body parts 322A, 322B apart, towards and, in some embodiments, into the non-contacting state. This separation of the body parts 322A, 322B causes any residual magnetism that was holding the parts 322A, 322B together to disappear and, as such, the body parts 322A, 322B do not move back to the contacting state until the next time the coil <NUM> is energised. In a preferred mode of use, upon establishing the contacting state, the coil <NUM> is de-energised by reducing the voltage applied to it. It is also preferred that, when separating the body parts 322A, 322B, in addition to expansion of the piezoelectric actuators <NUM>, a reverse-polarity voltage is applied to the coil <NUM> to facilitate separation of the body parts 322A, 322B.

In some embodiments, one or more resilient biasing mechanism (for example one or more springs - not shown) may be provided to urge the body parts 322A, 322B apart and preferably into the non-contacting state. The resilient bias is overcome when the coil <NUM> is energised to bring the body parts 322A, 322B together, and (when applicable) by the subsequent residual magnetism that latches the body parts 322A, 322B together. Hence, when the piezoelectric actuators <NUM> are operated to separate the body parts 322A, 322B, the body parts are movable by the resilient bias.

An advantage of using the piezoelectric actuators <NUM> is the speed and precision at which their expansion and contraction can be controlled (in particular when moving the body parts 322A, 322B out of the contacting state in preferred embodiments) in comparison with the electromagnetic operating device <NUM>. However, the amount by which each piezoelectric actuator <NUM> expands and contracts is relatively small for its size. In contrast, the electromagnetic operating device <NUM> supports a relatively large travel for the body parts 322A, 322B (in particular when moving from the non-contacting state to the contacting state in preferred embodiments) in comparison to that which could be effected by piezoelectric actuators alone. In addition, the electromagnetic operating device <NUM> is able to create a higher actuating force than the piezoelectric actuators <NUM>. Hence, the hybrid actuator <NUM> is provided with a relatively large stroke with relatively high force, while being operable in a relatively fast and precise manner.

The body parts 322A, 322B are incorporated into a support structure that supports the body parts 322A, 322B and allows the relative movement between the contacting and non-contacting states. The relative position of the body parts 322A, 322B when they are at their furthest apart in the non-contacting state (which may correspond to a rest state of the body parts 322A, 322B) is typically determined by the configuration of the support structure into which the body parts 322A, 322B are incorporated and may differ from embodiment to embodiment. The support structure may take any suitable form, but in the illustrated example, the body parts 322A, 322B are incorporated into a support structure that includes a first flexible structure <NUM> connected to each of the body parts 322A, 322B and spanning the interface of the contact surfaces 324A, 324B. Conveniently, the flexible structure <NUM> is integrally formed with the body parts 322A, 322B, e.g. at a respective flexure bearing <NUM>. Preferably, the flexible structure <NUM> extends across substantially the entire length of the actuator <NUM> in the direction of movement of the body parts 322A, 322B. The flexible structure <NUM> may be sheet-like in form, or may comprise one or more strips. The flexible structure <NUM> extends across an outer face <NUM> of the body parts 322A, 322B. Preferably a gap is provided between the flexible structure <NUM> and the outer face <NUM> through which the coil <NUM> is wound. The flexible structure <NUM> is conveniently formed from the same material as the body parts 322A, 322B. The flexible structure <NUM> is advantageously resiliently flexible. The flexible structure <NUM> preferably curves outwardly with respect to the body parts 322A, 322B. Preferably, a similar flexible structure <NUM>' is provided at the opposite outer face <NUM> of the body parts 322A, 322B, the coil <NUM> being wound between the flexible structure <NUM> and the outer face <NUM>.

In preferred embodiments, the flexible structures <NUM>, <NUM>' determine the positions of the body parts 322A, 322B in the non-contacting state, i.e. the rest position of each body part 322A, 322B. The flexible structures <NUM>, <NUM>' determine the extent of the travel of the body parts 322A, 322B between the contacting state and the non-contacting state. The resilience of the structures <NUM>, <NUM>' causes them to urge the body parts 322A, 322B apart and into the non-contacting state, i.e. the structures <NUM>, <NUM>' may serve as the resilient biasing devices described above.

The flexible structures <NUM>, <NUM>' serve as a mechanical coupling device between the body parts 322A, 322B and whatever item or structure (not shown in <FIG>) the actuator <NUM> actuates in use. In this example, the flexible structures <NUM>, <NUM>' translate movement of the body parts 322A, 322B in the direction of the expansion axis EA into movement along a perpendicular actuation axis AA. The flexible structure <NUM> includes a coupling element <NUM> (for example an abutment or a connector) for coupling with the structure/item to be actuated. In the illustrated embodiment, the coupling element <NUM> moves upwards (as viewed in <FIG>) along axis AA in response to movement of the body parts 322A, 322B towards each other, and moves downwards (as viewed in <FIG>) along axis AA in response to movement of the body parts 322A, 322B away from each other. In alternative embodiments (not illustrated) the or each flexible structure <NUM>, <NUM>' may be configured so that the coupling element <NUM> moves downwards (as viewed in <FIG>) along axis AA in response to movement of the body parts 322A, 322B towards each other, and moves upwards (as viewed in <FIG>) along axis AA in response to movement of the body parts 322A, 322B away from each other. For example this may be achieved by configuring the or each flexible structure <NUM>, <NUM>' to bow inwardly towards the body 322A, 322B rather than outwardly as illustrated.

Advantageously, the flexible structures <NUM>, <NUM>' act as an amplifier by causing the actuation stroke of the hybrid actuator <NUM> (which in this example is the extent of travel of the coupling element <NUM>) to be greater that the travel of the body parts 322A, 322B.

In preferred embodiments, the coil <NUM> generates a magnetic field that latches the contact faces 324A, 324B together as described by the Biot-Savart law. As the contact faces 324A, 324B close together, the flexible structures <NUM>, <NUM>' - which are themselves part of the magnetic circuit of the actuator - convert the relatively short horizontal (as viewed in <FIG>) motion of the closing body parts 322A, 322B, into a relatively large vertical (as viewed in <FIG>) motion. The preferred arc-shape of the flexible structures <NUM>, <NUM>' causes them to act as springs to damp the collision of the two contact faces during closing, and to provide an opening force to break the body parts apart; either when receiving a command to open the circuit, or during a power-loss condition.

The piezoelectric actuators <NUM> provide a substantial impulse triggered at a precise time to overcome the magnetic latching force and move the body parts 322A, 322B apart. This de-latching action preferably occurs simultaneously while a reverse bias is applied to the coil <NUM> to collapse the magnetic field. The deviation in time for the piezoelectric actuator(s) is much greater than the deviation for a reverse bias pulse in the coils alone. The improvement in accuracy obtained by using the piezoelectric actuators allows for better point-on-wave precision and lower latency, while the magnetic coil(s) <NUM> allow for a larger range of motion and therefore a bigger contact gap (improved dielectric strength).

It will be understood that the hybrid actuator is not limited to use with the flexible structures <NUM>, <NUM>'. For example, the hybrid actuator may be used with, or may include, other types of mechanical or electromechanical coupling device, e.g. a rod, lever and/ or bellows device, or other arrangement for coupling the actuator to an item to be actuated. Moreover, such couplings need not be configured to impart actuation in a direction perpendicular to the direction of movement of the body parts 322A, 322B. For example, the coupling arrangement may be configured to impart actuation in a direction parallel with the direction of movement of the body parts. Furthermore, the hybrid actuator may be incorporated into a support structure other than the one provided in this example by the flexible structures <NUM>, <NUM>', which support structure may determine the relative positions of the body parts and/or the permissible movement of the, or each, body parts as applicable. For example, the body parts may be coupled together by a stem that passes through each body part, at least one of the body parts being movable along the stem towards and away from the other body part. The support structure may for example hold one of the body parts in a fixed position and allow the other body part to move. In typical embodiments, the support structure allows one or both of the body parts to move by an amount that exceeds the displacement that can be effected by the piezoelectric actuator(s). Resilient biasing means may be provided to return the, or each, body part (as applicable) to a rest position.

In alternative embodiments, the or each piezoelectric actuator may be located behind the respective body part with respect to the other body part and be contractable to pull the respective body part away from the other body part. In such cases the piezoelectric actuator may be coupled between the respective body part and a support structure. In further alternative embodiments (not illustrated) one or more piezoelectric actuators may be provided to push, upon expansion, one or more of the body parts towards the other. To this end the piezoelectric actuator may be located behind the respective body part (with respect to the other body part) and configured to push against a support structure to move the respective body part towards the other body part.

In preferred embodiments, the or each piezoelectric actuator acts to push one body part with respect to another body part. This action may be by means of a direct coupling between the piezoelectric actuator and the other body part (or whatever object the piezoelectric actuator is intended to push away). For example in the illustrated example the piezoelectric actuator <NUM> of one body part 322A acts directly on the piezoelectric actuator <NUM> of the other body part 322B. Alternatively, there may be an indirect coupling between the piezoelectric actuator and the other body part (or whatever object the piezoelectric actuator is intended to push away). For example the or each piezoelectric actuator may act on a coupling member (e.g. a rod) that is provided between it and the other body part (or whatever object the piezoelectric actuator is intended to push away).

In preferred embodiments, the action of the piezoelectric actuator(s) <NUM> does not perform any mechanical unclamping or unlocking of the body parts 322A, 322B. Rather, the piezoelectric actuator(s) serve to break the magnetic latching effect that holds the body parts together. This is achieved by pushing the body parts far enough apart to break the magnetic latching effect between them. Once the magnetic latching effect is broken, the body parts 322A, 322B may be moved further apart into the non-contacting state, which movement is, in the present embodiment, effected by the flexible structures <NUM>, <NUM>', but could alternatively be caused by whatever other structure the body parts may be incorporated into in alternative embodiments.

In alternative embodiments, the piezoelectric actuator(s) <NUM> may be operated to hold the body parts 322A, 322B apart (i.e. the piezoelectric actuator(s) adopt a relatively expanded state to maintain an air gap between the body parts) and then operated, when required, to contract to allow the body parts to move together under whatever magnetic forces may be present depending on the embodiment (e.g. from a permanent magnetic field, an electromagnetic and/or a residual magnetic field as applicable).

In preferred embodiments, the magnetic latching effect is created by the electromagnetic operating device <NUM> as described above. In alternative embodiments, the electromagnetic operating device <NUM> may be omitted, in particular in embodiments where either or both the body parts 332A, 332B comprise (permanent) magnets with respective magnetic poles arranged to magnetically latch the body parts 322A, 322B together when the body parts are close enough together. As such, the magnetic body parts 322A, 322B magnetically hold the body parts 322A, 322B in the contact state. When it is desired to move the body parts 322A, 322B to the non-contacting state, the magnetic latching effect can be broken by the piezoelectric actuators <NUM> in the same manner described above. In such embodiments, another operating device (not shown) may be provided for moving the body parts 322A, 322B towards one another in order to create the magnetic latching effect. The other operating device may take any suitable conventional form (typically a non-piezoelectric form), typically comprising one or more actuating devices e.g. an electric actuator(s), mechanical actuator(s) or electro-mechanical actuator(s) or any combination thereof. Such embodiments may still be referred to as hybrid actuators since they employ more than one type of actuator to operate, in particular a piezoelectric actuator to move the body parts apart and another type to move the body parts together.

The hybrid actuator <NUM> may be said to comprise a hybrid magneto-piezo switching device which, in the illustrated embodiment, comprises the movable body parts 322A, 322B, the piezoelectric operating device <NUM> and the electromagnetic operating device <NUM> (or alternative operating device in cases where the electromagnetic operating device is omitted). The hybrid magneto-piezo switching device need not necessarily be used as part of an actuator. For example it may alternatively be used in a magnetic circuit (not illustrated), e.g. as an adjustable reluctance device or for selectively creating an air gap in the circuit, or as a magnetic latch device. Alternatively still, the hybrid magneto-piezo switching device may be used in an electrical switch. The contacting state described herein may be said to correspond to the closed state of the hybrid magneto-piezo switching device. In typical embodiments, the respective contact faces of the body parts 322A, 322B engage with one another in the closed (or contact) state and are pushed apart by expansion of the piezoelectric actuator(s). However, in some embodiments there may be a gap between the contact faces in the closed state.

The hybrid actuator is suitable for use in vacuum circuit breakers. In particular the hybrid actuator may be coupled to a vacuum interrupter and be operable to open and close the contacts of the interrupter.

<FIG> shows an embodiment of a vacuum circuit breaker (VCB) <NUM> embodying the invention. The VCB <NUM> comprises a vacuum interrupter <NUM> and an actuator <NUM>. In this example, the actuator <NUM> is the same as the actuator <NUM> described above with reference to <FIG> and <FIG>. However, in alternative embodiments (not illustrated) the actuator <NUM> may take other forms, for example a conventional electromagnetic actuator or a conventional piezoelectric amplifier, especially an amplified piezoelectric amplifier.

The vacuum interrupter <NUM>, or vacuum switching device, comprises a movable electrical contact <NUM> a fixed electrical contact <NUM> located in a vacuum chamber <NUM>, i.e. a chamber that is hermetically sealed and in vacuum, at least during use. The movable contact <NUM> is movable between an open state (as illustrated), in which it is electrically and physically separate from the fixed contact <NUM>, and a closed state in which it makes electrical and physical contact with the fixed contact <NUM>. Each contact <NUM>, <NUM> has a contact surface <NUM>', <NUM>' which are disposed in opposition to each other (as illustrated) in the open state and which engage with each other in the closed state. The open state corresponds to the open, or breaking, state of the vacuum interrupter <NUM> and correspondingly of the circuit breaker <NUM>, in which it interrupts current flow in whatever circuit (not shown) it is part of. The closed state corresponds to the closed, or making, state of the vacuum interrupter <NUM>, and correspondingly of the circuit breaker <NUM>, in which current is able to flow between the contacts <NUM>, <NUM>.

Movement of the contact <NUM> between its open and closed states is effected by the actuator <NUM>. In typical embodiments, the actuator <NUM> moves the contact <NUM> into and out of engagement with the contact <NUM> as required. In alternative embodiments, the actuator may only move the contact into or out of engagement with the other contact. For example the actuator may be operable to separate the contacts, and the contacts may be closed together manually, or vice versa.

The VCB <NUM> is of a type in which the actuator <NUM> is located in the same housing <NUM> as the vacuum interrupter <NUM>. The housing <NUM> may be formed from any suitable material. The actuator <NUM> is located in the vacuum chamber <NUM> and is coupled to the movable contact <NUM>. The mechanical coupling between the actuator <NUM> and the vacuum interrupter <NUM> may take any convenient form. In the illustrated embodiment, the coupling comprises a flexible, electrically conductive structure <NUM> and an electrical, and preferably also thermal, isolator <NUM> that electrically, and preferably also thermally, isolates the actuator <NUM> from the flexible structure <NUM>. The isolator <NUM> couples the actuator <NUM> to the flexible structure <NUM>, and may for example comprise one or more blocks or layers of electrical and/or thermally isolating material(s). In this example the coupling element <NUM> of the actuator <NUM> is coupled to the isolator <NUM>, e.g. by abutment or by adhesive.

The flexible structure <NUM> (which is shown in end view in <FIG>) extends across the inside of the housing <NUM> between the actuator <NUM> and the vacuum interrupter <NUM>. The illustrated flexible structure <NUM> takes the form of a strip of electrically conductive material, but it may alternatively take other forms, e.g. comprising a bar, rod, sheet, plate or membrane. The ends of the flexible structure <NUM> may be fixed to opposite sides of the housing <NUM> in any convenient manner.

The actuator <NUM> is coupled to the flexible structure <NUM> such that operation of the actuator <NUM> causes the flexible structure <NUM> to flex upwards and downwards as viewed in <FIG>. Preferably the flexible structure <NUM> is non-resilient, e.g. has substantially no resilience or a low resilience, to provide little or no resistance to being flexed. This may be achieved by appropriate selection of the material from which the flexible structure <NUM> is made and/or its thickness and/or its shape. The contact <NUM> is coupled to the flexible structure <NUM> such that its flexing is transmitted into corresponding movement of the contact <NUM> towards and away from the fixed contact <NUM>.

The flexible structure <NUM> is electrically connected to the movable contact <NUM> and to a terminal (not shown) of the VCB <NUM> and serves as an electrical conductor for carrying electrical current between the contact <NUM> and the respective VCB terminal during use (and therefore to an external circuit in which the VCB is incorporated for protection). To this end, the flexible structure <NUM> is formed wholly or partly from an electrically conductive material, or may include an electrical conductor. For example, the flexible structure <NUM> may be a metal, e.g. copper, strip.

While there are advantages in including the actuator <NUM> in the same chamber <NUM> as the vacuum interrupter <NUM>, e.g. miniaturisation, in arriving at this aspect of the present invention a problem has been identified, namely outgassing from components of the actuator <NUM> (e.g. coils or piezoelectric coatings) or from the mechanical coupling can have a detrimental affect on the performance of the vacuum interrupter <NUM>. For example outgassing can cause a change, in particular an increase, in pressure in the vacuum chamber and/or results in the presence of molecules in the vacuum chamber both of which can lead to a degradation in performance of the interrupter <NUM>, e.g. by reducing dielectric strength.

To address this problem, a partition <NUM> is provided in the housing <NUM> to partition the vacuum chamber <NUM> into first and second sub-chambers 416A, 416B, the voltage interrupter <NUM> being in the first sub-chamber 416A and the actuator <NUM> being in the second sub-chamber 416B. The partition <NUM> serves as a barrier for preventing molecules from passing from the second sub-chamber 416B to the first sub-chamber 416A. In preferred embodiments, the partition <NUM> comprises a diaphragm or other sheet-like structure. However the partition <NUM> may comprise any other suitable structure and may comprise one or more parts. While the partition <NUM> separates the sub-chambers 416A, 416B from each other, it does not have to provide a hermetic seal between the sub-chambers 416A, 416B, i.e. does not have to hermetically seal the sub-chambers from each other. Moreover, the partition <NUM> does not hermetically seal the sub-chambers from each other. Therefore one or more apertures (not shown) or other formations or imperfections (not shown) may be present in the partition <NUM> and/or at the interfaces between the partition <NUM> and any component to which it is fixed, e.g. surfaces of the chamber <NUM> and/or the mechanical coupling between the actuator <NUM> and the contact <NUM> and/or the contact <NUM>, as applicable. Any aperture(s), including those provided by formation(s) such as channels or gaps, in or around the partition <NUM> are preferably of a type known as a "differential aperture", meaning that they are sufficiently small to at least restrict and ideally prevent molecules from passing from the second sub-chamber 416B to the first sub-chamber 416A. To this end, the configuration of the partition <NUM> and its interfaces is such that any apertures provide a high Knudsen number (Kn), where Kn > <NUM>.

In the illustrated embodiment, the partition <NUM> (in the preferred form of a diaphragm) extends across the inside of the chamber <NUM>, covering the whole cross sectional area of the chamber <NUM> (subject to any apertures/formations described above) and is fixed, e.g. sealed non-hermetically or otherwise fixed non-hermetically, to the wall(s) of the chamber <NUM> (and any other component(s) of the VCB that may pass through the partition <NUM>) in any convenient manner, for example by brazing e.g. vacuum brazing. In this example, the partition <NUM> is also fixed, non-hermetically, to the movable contact <NUM>. In particular the partition <NUM> surrounds the contact <NUM> and is fixed to the contact <NUM> around its periphery. The diaphragm is flexible to accommodate movement of the contact <NUM>.

In the illustrated embodiment, the actuator <NUM> and mechanical coupling between the actuator <NUM> and the movable contact <NUM> (i.e. the flexible structure <NUM> and the isolator <NUM> in this example) are located in the second sub-chamber 416B while the vacuum interrupter <NUM> is located in the first sub-chamber 416A. In this example, a rear part of the body of contact <NUM> is in the second sub-chamber 416B but the active parts of the vacuum interrupter, in particular the inter-engagable contact surfaces of the contacts, are in the first sub-chamber 416A.

In alternative embodiments the location of the partition <NUM> may be such that the segregation of components between the sub-chambers is different to that illustrated in <FIG>, for example the partition may intersect the mechanical coupling between the actuator <NUM> and the movable contact <NUM> so that a part of the mechanical coupling is located in the first sub-chamber 416A. It is preferred however that substantially all of the mechanical coupling is in the second sub-chamber 416B, i.e. isolated from the contacts of the vacuum interrupter <NUM>. In any event at least the contacts <NUM>, <NUM>, and more particularly the inter-engagable contact surfaces of the contacts <NUM>, <NUM>, are located in the first sub-chamber 416A to be isolated from the affects of outgassing caused by the other components. In practice it may be said that the vacuum interrupter <NUM> is located in first sub-chamber 416A (even if non-active parts of it may be exposed to the second sub-chamber). The partition <NUM> is sealed non-hermetically or otherwise fixed non-hermetically to any component that it intersects.

Instead of comprising a diaphragm, the partition <NUM> may comprise any other suitable structure(s), for example a linkage or assembly of plates (not illustrated). Any aperture(s), including formation(s) such as channels or gaps, in or around the structures(s) are preferably of the "differential aperture" type. In addition, the partition <NUM> is configured, i.e. is flexible and/or movable, to accommodate the movement caused by the actuator <NUM>. In preferred embodiments the partition <NUM> may be said to comprise circuit breaker bellows.

In preferred embodiments, the partition or diaphragm <NUM> comprises a metallic foil, preferably a low mechanical resistance metallic foil. In this context low mechanical resistance may for example meaning exhibiting a K-value of <NUM> n/mm or less. The partition <NUM> is preferably non-resilient. By way of example the partition <NUM> may be made from aluminium-silicon copper, copper-silver, silver or a nickel alloy. The diaphragm, or other structure used to provide the partition, may be separate from or combined with the flexible conductor structure <NUM>. The partition <NUM> may contain apertures, e.g. holes, channels, gaps and or defects providing a high Knudsen number, for example a Knudsen number of <NUM> or more, i.e. a hermetic seal is not required and is not desired. Without a hermetic seal the diaphragm, or other partitioning structure, has a low mass, low mechanical resistance and is simple to manufacture. Such factors dramatically improve yield.

During use, each of the sub-chambers 416A, 416B is in vacuum, i.e. held at a vacuum pressure, preferably at least Medium Vacuum pressure, more preferably at least high vacuum pressure (typically pressures in the order of <NUM>-<NUM> mBar or lower). Initially at least, each sub-chamber 416A, 416B may be at the same or substantially the same vacuum level. During use, as a result of outgassing from the components in the second sub-chamber 416B a pressure differential between the sub-chambers 416A, 416B may arise (the pressure in the second sub-chamber may increase). However, the pressure differential is relatively small. For example, the sub-chambers 416A, 416B may be initially at the same pressure (e.g. ~<NUM>-<NUM> mBar), but continuous outgassing from components in the second sub-chamber 416B such as coils or piezoelectric coatings causes a differential rate of rise in pressure between the two sub-chambers over time. Increased pressure caused by the outgassing would, if the vacuum interrupter were exposed to it, lead to degradation in performance in the interrupter by reducing dielectric strength. The segregation provided by the partition <NUM> prevents, or substantially prevents this.

A standard vacuum interrupter (VI) typically has bellows to maintain ultra-high vacuum (UHV) pressures, and such bellows must contend with substantial pressure gradients from atmosphere to UHV. In contrast, the partition <NUM> provided in preferred embodiments of the present invention supports a molecular flow regime (as opposed to a laminar or viscous flow regime). The molecular flow may be referred to as Knudsen flow. Knudsen flow occurs where a characteristic length (or other relevant dimension e.g. the width of an aperture or channel) of the flow space (which in this case would be provided by the aperture(s) in the partition <NUM>) is of the same or a smaller order of magnitude than the mean free path of the molecules (in this case any molecules present in the sub-chamber 416B as a result of outgassing from one or more components of the actuator <NUM>). In this case it may be said that the partition <NUM> provides a high Knudsen number. The Knudsen number (Kn) is the ratio of the mean free path (A) of the molecules to the characteristic dimension (d): Kn = λ/d. The partition <NUM> provides a Knudsen number greater than <NUM>. Alternatively Knudsen number may be greater than or equal to <NUM>. In any event, as a result there is almost no pressure differential between the two sub-chambers (e.g. ~<NUM>-<NUM> mBar in the first chamber 416A and ~<NUM>-<NUM> mBar in the second sub-chamber). Any aperture(s) in the partition <NUM> are very small (typically less than <NUM>).

The mean free path (A) is the average distance a gas molecule can travel before colliding with another gas molecule and is a function of the vacuum pressure inside the vessel. In the high-vacuum regime in which the circuit breaker operates the mean free path is typically on the order of <NUM>.

Claim 1:
A vacuum circuit breaker (<NUM>) comprising:
a housing (<NUM>) providing a vacuum chamber (<NUM>);
a vacuum interrupter (<NUM>) having a movable first contact (<NUM>) and a second contact (<NUM>), and
an actuator (<NUM>) coupled to the vacuum interrupter to move said first contact into and/or out of engagement with said second contact,
said vacuum interrupter and said actuator being located in said vacuum chamber,
wherein said vacuum chamber is partitioned into first and second sub-chambers (416A, 416B) by a partition (<NUM>), each of said first and second sub-chambers being in vacuum in use,
and wherein said first and second contacts are located in said first sub-chamber and said actuator is located in said second sub-chamber,
characterized in that said partition provides a non-hermetic seal between the first and second sub-chambers, and is configured to provide a Knudsen number of greater than <NUM> and to support Knudsen flow between said first and second sub chambers.