EP2715761A1

EP2715761A1 - Vacuum interrupter

Info

Publication number: EP2715761A1
Application number: EP11723910.3A
Authority: EP
Inventors: Rama Shanker Parashar
Original assignee: Alstom Technology AG
Current assignee: General Electric Technology GmbH
Priority date: 2011-05-24
Filing date: 2011-05-24
Publication date: 2014-04-09
Anticipated expiration: 2031-05-24
Also published as: WO2012159669A1; EP2715761B1; ES2538594T3

Abstract

A vacuum interrupter assembly comprises at least one vacuum interrupter (10). The or each vacuum interrupter (10) includes a vacuum-tight enclosure; first and second electrically conductive rods (26,28), each rod (26, 28) being connected in use to an electrical network (42, 44) at a first end; a first electrode (30) being mounted near or at a second end of the first rod (26); a slotted coil (38) being operably mounted at a second end of the second rod (28); and a second electrode (32) being mounted on an inner surface of the slotted coil (38). The first electrode (30) and the slotted coil (38) are located inside the vacuum- tight enclosure, and the rods (26,28) are positioned to locate at least a portion of the first electrode (30) inside the slotted coil (38).

Description

VACUUM INTERRUPTER

This invention relates to a vacuum interrupter assembly and an apparatus incorporating the vacuum interrupter assembly.

The operation of multi-terminal high voltage direct current (HVDC) transmission and distribution networks involves load and fault/short- circuit current switching in DC power networks. The availability of switching components to perform such switching permits flexibility in the planning and design of HVDC applications such as parallel HVDC lines with a tap-off line or a closed loop circuit.

A known solution for load and fault/short- circuit current switching is the use of semiconductor- based switches, which are typically used in point-to- point high power HVDC transmission. The use of semiconductor-based switches results in faster switching and smaller values of let-through fault current. The disadvantages of using such switches however include high forward losses, sensitivity to transients and the lack of tangible isolation when the devices are in their off-state.

Another known solution for load and fault /short-circuit current switching is a vacuum interrupter. The operation of the vacuum interrupter relies on the mechanical separation of electrically conductive contacts to open the associated electrical circuit. Such a vacuum interrupter is capable of allowing high magnitude of continuous AC current with a high short-circuit current interrupting capability. The conventional vacuum interrupter however exhibits poor performance in interrupting DC current because of the absence of current zero. Although it is feasible to use the conventional vacuum interrupter to interrupt low DC currents up to a few hundred amperes due to the instability of an arc at low currents, such a method is not only unreliable but is also incompatible with the levels of current typically found in HVDC applications.

It is possible to carry out DC current interruption using conventional vacuum interrupters by applying a forced current zero or artificially creating a current zero. This method of DC current interruption involves connecting an auxiliary circuit in parallel across the conventional vacuum interrupter, the auxiliary circuit comprising a capacitor or a combination of a capacitor and an inductor. The auxiliary circuit remains isolated by a spark gap during normal operation of the vacuum interrupter.

When the contacts of the vacuum interrupter begin to separate, the spark ignition gap is switched on to introduce an oscillatory current of sufficient magnitude across the vacuum interrupter and thereby force the current across the interrupter to pass through a current zero. This allows the vacuum interrupter to successfully interrupt the DC current. Such an arrangement however becomes complex, costly and space consuming due to the need to integrate the additional components of the auxiliary circuit.

According to a first aspect of the invention, there is provided a vacuum interrupter assembly comprising at least one vacuum interrupter, the or each vacuum interrupter including a vacuum-tight enclosure; first and second electrically conductive rods, a first end of each rod being adapted to be connected, in use, to an electrical network; a first electrode being mounted near or at a second end of the first rod; a slotted coil being operably mounted at a second end of the second rod; and a second electrode being mounted on an inner surface of the slotted coil, wherein the first electrode and the slotted coil are located inside the vacuum-tight enclosure, and the rods are positioned to locate at least a portion of the first electrode inside the slotted coil.

The above arrangement of the first electrode and the slotted coil in the vacuum interrupter enables the generation of a self-induced axial magnetic field that is perpendicular to the arc current drawn between the first and second electrodes during the current interruption process. In the presence of the axial magnetic field, the arc voltage begins to rise while the arc current begins to drop rapidly until it reaches a value lower than the chopping current value of the electrode material. At this point the current drops instantly to zero, which results in full dielectric recovery and successful current interruption. The ability to create a current zero in this manner therefore renders the vacuum interrupter assembly compatible for use as a load break switch or a circuit breaker in both AC and DC networks.

The generation of the self-induced axial magnetic field removes the need to incorporate additional equipment into the vacuum interrupter assembly in order to generate the required axial magnetic field and thereby reduces the complexity of the layout of the vacuum interrupter assembly. As such, the comparatively simpler layout of the vacuum interrupter assembly has the effect of reducing the amount of space required for the assembly and the associated installation costs, while the reduced number of components in the vacuum interrupter assembly improves the reliability of the current interruption process .

The shape of the slotted coil may vary, depending on the design requirements of the vacuum interrupter. The slotted coil may, for example, include either only a single slot, which preferably extends around the full perimeter of the coil, or a plurality of slots.

In embodiments of the invention, the first electrode may include a first electrode portion mounted at the second end of the first rod. In such embodiments, the first electrode may further include a second electrode portion mounted around the circumference of the first rod and adjacent to the first electrode portion.

The shape of the first electrode varies depending on the layout of the vacuum interrupter, which may be designed so that the position of the rods are fixed relative to each other, or that at least one rod is moveable relative to the other rod. In other embodiments, the slotted coil may include a support base being mounted at the second end of the second rod.

The use of a support base forming part of the slotted coil not only provides structural support for the slotted coil, but also provides a surface for mounting an additional electrode, if desired.

Preferably each electrode is made from a refractory material, which may be selected from a group of chromium-chromium, copper-tungsten, copper tungsten carbide, tungsten, chromium or molybdenum.

Such refractory materials are compatible for use as electrode material in a vacuum interrupter not only because of their low electrical contact resistance and high chopping current value properties, but also due to their ability to withstand the effects of the arc and assist in dielectric withstand subsequent to current interruption.

In embodiments of the invention, at least one rod may be moveable relative to the other rod to open or close a gap between the second ends of the rods .

In such embodiments employing a support base mounted on the second end of the second rod, the or each vacuum interrupter may further include a third electrode mounted on the support base, the first and third electrodes defining opposed contact surfaces, and at least one rod is moveable relative to the other rod to open or close a gap between the opposed contact surfaces . The capability to move at least one rod relative to the other rod allows the opposed contact surfaces to be brought into contact, which results in a low contact resistance between the rods and thereby allows the vacuum interrupter to carry a load current via the electrically conductive rods during normal operation of the associated external electrical network .

The same capability also allows the separation of the opposed contact surfaces to interrupt the current flowing through the vacuum interrupter.

In embodiments employing at least one moveable rod, the or each vacuum-tight enclosure further includes a tubular bellows with a hollow bore, the or each tubular bellows being operably connected to at least one rod and being controllable to expand or contract to move one rod relative to the other rod to open or close a gap between the second ends of the rods .

Corrugated walls of the tubular bellows allow the tubular bellows to undergo expansion or contraction so as to increase or decrease the tubular length of the tubular bellows and thereby initiate movement of one rod relative to the other rod while maintaining degree of vacuum inside the vacuum interrupter .

In other embodiments employing at least one moveable rod, the or each vacuum interrupter may further include an auxiliary coil located outside the vacuum-tight enclosure, the auxiliary coil being controllable to provide a pulsed magnetic field inside the vacuum-tight enclosure.

Once the arc current drops to a sufficiently low value, the auxiliary coil may be controlled to generate the pulsed magnetic field to boost the axial magnetic field and thereby help speed up the extinguishing of any residual arc. In addition, the ability to manipulate the timing of the generation of the pulsed magnetic field and the magnitude of the pulsed magnetic field provides precise control over the current interruption process.

In other embodiments employing the use of an auxiliary coil, the refractory material forming the electrode may be copper-chromium or silver tungsten carbide .

The provision of the auxiliary coil also allows each electrode to be made from material that has low chopping current value but are conducive to the high dielectric withstand requirements in a vacuum interrupter when the first and third electrodes are separated .

In embodiments of the invention, the positions of the second ends of the rods may be fixed relative to each other.

This configuration removes the need to mechanically move either rod during the current interruption process. This speeds up the current interruption process because the time required to interrupt the current is no longer limited by the time required to mechanically separate the rods. In embodiments where the positions of the first and second rods are fixed relative to each other, the vacuum interrupter assembly may further include a bypass switching circuit and an ignition circuit, the or each vacuum interrupter further including an auxiliary electrode coaxially located in a central bore of the first rod, an end of the auxiliary electrode protruding from the second end of the first rod, the bypass switching circuit being operably connected to the or each vacuum interrupter and being controllable to divert current to bypass the or each vacuum interrupter, the ignition circuit being operably connected to the or each auxiliary electrode and being controllable to establish a discharge current between the first and second electrodes. In such embodiments, the ignition circuit may include a spark ignition switch .

The inclusion of the bypass switching circuit in the vacuum interrupter assembly allows the bypass switching circuit to carry the load current during normal operation of the associated electrical network. In order to switch the current, the ignition current is controlled to establish a spark between the auxiliary electrode and the surrounding electrodes to establish a current passing through the vacuum interrupter. Once the peak value of the current is established, the bypass switching circuit is switched to an open state to allow the vacuum interrupter to carry out the current interruption process. Preferably the bypass switching circuit includes at least one semiconductor switch or at least one mechanical switch.

The choice of switching device for the bypass switching circuit may vary depending on various factors such as cost, size and weight of the switching device and performance requirements of the current interruption process.

In other embodiments, the vacuum interrupter assembly may include a plurality of series- connected and/or parallel-connected vacuum interrupters .

Multiple vacuum interrupters may be connected to define different configurations of the vacuum interrupter assembly in order to vary its operating voltage and current characteristics to match the requirements of the associated power application.

According to a second aspect of the invention, there is provided an apparatus comprising primary and secondary circuits, the primary circuit including a vacuum interrupter assembly according to any preceding claim, the secondary circuit including a series connection of at least one capacitor, at least one inductor and a spark ignition switch, wherein the primary and secondary circuits are connected in parallel .

In use, the secondary circuit is controllable to inject an oscillatory current into the primary circuit to force the arc current to zero. This not only provides precise control over the amount of time required to interrupt the current, but also reduces the time required for extinguishing the arc current, since the secondary circuit can be configured to achieve the current zero earlier than the primary circuit .

Preferably the primary circuit further includes at least one plasma switch connected in series with the vacuum interrupter assembly.

The capability of the plasma switch to generate a high arc voltage increases the total arc voltage across the series connection of the vacuum interrupter assembly and the plasma switch. This in turn speeds up the reduction of the arc current and reduces the overall time required for the current interruption process.

Moreover, the inclusion of the or each plasma switch results in the reduction in total power dissipation across the primary circuit. This in turn permits the ratings of the circuit elements to be reduced and thereby decreases the costs and space required for installation of the apparatus.

Examples of applications that are compatible with the vacuum interrupter assembly according to the invention include, for example, AC power networks, AC high voltage circuit breakers, AC generator circuit breakers, railway traction, ships, superconducting magnetic storage devices, high energy fusion reactor experiments, stationary power applications, and high voltage direct current (HVDC) multi-terminal networks. Preferred embodiments of the invention will now be described, by way of non-limiting examples, with reference to the accompanying drawings in which:

Figure 1 shows a vacuum interrupter assembly according to a first embodiment of the invention;

Figure 2 shows a vacuum interrupter assembly according to a second embodiment of the invention;

Figure 3 shows a vacuum interrupter assembly according to a third embodiment of the invention;

Figure 4 shows, in schematic form, a bypass switching circuit and an ignition circuit connected to the vacuum interrupter assembly of Figure 3;

Figure 5 shows, in schematic form, parallel-connected primary and secondary circuits according to a fourth embodiment of the invention.

A vacuum interrupter assembly according to a first embodiment of the invention is shown in Figure 1.

The vacuum interrupter assembly comprises a single vacuum interrupter 10.

The vacuum interrupter 10 includes a pair of cylindrical housings 12, first and second end flanges 14,16 and an annular structure 18 assembled to define a vacuum-tight enclosure. Each end flange 14,16 is brazed to a first end of a respective cylindrical housing 12 to form a hermetic joint. The two cylindrical housings 12 are joined together at their second ends via the annular structure 18. The annular structure 18 includes a central shield 20 that overlaps inner walls of the cylindrical housings 12 to protect the inner walls of the cylindrical housings 12 from metal deposition arising from arc discharge, while each end flange 14,16 includes an end shield 22 to improve the electrostatic field line distribution along the length of the vacuum interrupter 10.

Each cylindrical housing 12 is metallised and nickel-plated. The length and diameter of the respective cylindrical housing 12 varies depending on the operating voltage rating of the vacuum interrupter 10, while the dimensions and shape of the first and second end flanges 14,16 and the annular structure 18 may vary to correspond to the size and shape of the cylindrical housings 12.

The vacuum interrupter 10 also includes a tubular bellows 24 and first and second electrically conductive rods 26,28.

The first end flange 14 includes a hollow bore dimensioned to accommodate the tubular bellows 24, while the second end flange 16 includes a hollow bore dimensioned to accommodate the second rod 28 within its hollow bore. The tubular bellows 24 also includes a hollow bore for retention of the first rod 26.

The first and second rods 26, 28 are respectively retained within the hollow bores of the tubular bellows 24 and the second end flange 16 so that the second ends of the rods 26, 28 are located inside the enclosure and the first ends of the rods 26,28 are located outside the enclosure. The first and second rods 26,28 may be fabricated from, for example, oxygen- free high conductivity (OFHC) copper.

The vacuum interrupter 10 further includes first, second and third electrodes 30,32,34, and a multiple slotted coil 38. The multiple slotted coil 38 includes a plurality of slots (not shown) .

It is envisaged that, in other embodiments, the multiple slotted coil may be replaced by a slotted coil that includes only a single slot. Preferably such a single slot would extend completely around the full perimeter, e.g. the circumference, of the coil.

The first electrode 30 consists of first and second electrode portions 30a, 30b. The first electrode portion 30a is in the form of a rounded electrode portion that is mounted at the second end of the first rod 26. The second electrode portion 30b is in the form of a annular electrode portion that is mounted around the circumference of the first rod 26 and is adjacent to the first electrode portion 30a.

The second electrode 32 is mounted on an inner surface of the multiple slotted coil 38.

The multiple slotted coil 38 includes a support base 36. The support base 36 is mounted at the second end of the second rod 28.

The third electrode 34 is mounted at the centre of the support base 36. The rods 26, 28 are coaxially aligned so that the first and third electrodes 30,34 define opposed contact surfaces. The third electrode 34 includes a recess 40 for receipt of the first electrode portion 30a and the shape of the recess 40 corresponds to the shape of the rounded first electrode portion 30a so as to maximise contact between the first and third electrodes 30,34.

Each electrode 30,32,34 is made from a refractory material, which may be selected from a group of, for example, chromium-chromium, copper-tungsten, copper tungsten carbide, tungsten, chromium or molybdenum. These refractory materials not only exhibit excellent electrical conductivity, but also display high dielectric strength in the presence of the arc during the current interruption process. Moreover, these refractory materials have relatively high chopping current values, which helps to rapidly extinguish the arc once the current has dropped below the chopping current value.

Corrugated walls of the tubular bellows 24 allow the tubular bellows 24 to undergo expansion or contraction so as to increase or decrease the tubular length of the tubular bellows 24. This allows the first rod 26 to move relative to the second rod 28 between a first position where the first and third electrodes 30,34 are kept in contact, and a second position where only a portion of the first electrode portion 30a remains located inside the multiple slotted coil 38. The second rod 28 is kept at a fixed position .

In use, the first end of the first rod 26 is connected to a positive terminal 42 of a DC network, while the first end of the second rod 28 is connected to a negative terminal 44 of the DC network.

During normal operation of the connected DC network, the tubular bellows 24 is controlled to move the first rod 26 to the first position to bring the first and third electrodes 30,34 into contact. This allows current to flow between the positive and negative terminals 42,44 of the connected DC network via the electrically conductive rods 26,28. The low contact resistance resulting from the contact between the first and third electrodes 30,34 means that there is no flow of current through the multiple slotted coil 38.

In the event of a fault resulting in a high fault current flowing in the connected DC network, the current must be interrupted in order to prevent the high fault current from damaging components of the DC network. Interruption of the fault current permits isolation and subsequent repair of the fault in order to restore the DC network to normal operating conditions .

The current interruption process is initiated by controlling the tubular bellows 24 to move the first rod 26 toward its second position so as to separate the opposed contact surfaces of the first and third electrodes 30,34. The separation of the opposed contact surfaces results in the formation of a gap between the first electrode 30 and the second and third electrodes 32,34, which leads to the formation of an arc in this gap. The arc consists of metal vapour plasma, which continues to conduct the current flowing between the first and third electrodes 30,34.

As the gap between the opposed contact surfaces increases and the magnitude of current increases, the multiple slotted coil 38 begins to draw current via the second electrode 32. The shape of the multiple slotted coil 38 causes the drawn current to flow in a preferential direction within the multiple slotted coil 38, which results in generation of an axial magnetic field in the gap between the first electrode 30 and the second electrode 32. The direction of the generated axial magnetic field is perpendicular to the direction of current being drawn between the first electrode 30 and the second electrode 32.

In the presence of the axial magnetic field, the metal vapour plasma is forced away from the gap between the first electrode 30 and the second and third electrodes 32,34. Subsequently the arc voltage begins to rise while the magnitude of the drawn current begins to drop rapidly. When the magnitude of the drawn current reaches a value lower than the chopping current value of the electrode material, the arc energy becomes insufficient to sustain the current, which leads to the arc becoming highly unstable and the current dropping instantly to zero. This allows full dielectric recovery and successful current interruption to take place.

The duration of current interruption is limited by the time required to mechanically move the first rod 26 from the first position to the second position, which is typically a few milliseconds. Once the first rod 26 reaches the second position, the current will typically drop to zero in about 10 to 20 ps . The arrangement of the first rod 26 and the multiple slotted coil 38 therefore allows the separation of the first and third electrodes 30,34 to result in the generation of a self-induced axial magnetic field to assist in the extinguishing of the arc formed between the first electrode 30 and the second and third electrodes 32,34. This removes the need to incorporate additional equipment into the vacuum interrupter assembly in order to generate the required axial magnetic field, and thereby reduces the complexity of the layout of the vacuum interrupter assembly .

The comparatively simpler layout of the vacuum interrupter assembly has the effect of reducing the amount of space required for the assembly and the associated installation costs, while the reduced number of components in the vacuum interrupter assembly improves the reliability of the current interruption process .

A vacuum interrupter assembly according to a second embodiment of the invention is shown in Figure 2. The structure and operation of the vacuum interrupter assembly of Figure 2 is the same as that of the vacuum interrupter assembly of Figure 2, except that the second embodiment includes an auxiliary coil 46 being located outside the vacuum-tight enclosure of the vacuum interrupter 110 and above the end flange 14.

The auxiliary coil 46 is associated with a DC current source 48. In use, the DC current source 48 is controlled to supply a pulsed DC current to the auxiliary coil 46 so that the auxiliary coil 46 generates a pulsed magnetic field inside the vacuum- tight enclosure.

During the fall in current following the generation of the axial magnetic field, the auxiliary coil 46 is controlled to generate the pulsed magnetic field once the current reaches a low value. This results in the pulsed magnetic field being superimposed on the axial magnetic field, and thereby boosts the strength of the axial magnetic field. This helps to reduce the time required to extinguish the residual arc .

The provision of the auxiliary coil 46 in the vacuum interrupter assembly allows each electrode 30,32,34 to be made from material that has low chopping current value but are conducive to the high dielectric withstand requirements in the vacuum interrupter 110 during open condition. Examples of such electrode material includes copper-chromium and silver tungsten carbide .

The provision of the auxiliary coil 46 in the vacuum interrupter assembly also permits precise control over the timing of injection of the pulsed DC current into the auxiliary coil 46 and the magnitude and duration of the injected pulsed DC current and thereby improves the performance of the current interruption process.

A vacuum interrupter assembly according to a third embodiment of the invention is shown in Figure 3. The structure and operation of the vacuum interrupter assembly of Figure 3 is the same as that of the vacuum interrupter assembly of Figure 1, except that, in the third embodiment of the invention, the tubular bellows is omitted from the vacuum interrupter 210 and the hollow bore of the first end flange 14 is dimensioned to accommodate the first rod 26. The omission of the tubular bellows means that the positions of the first and second rods 26,28 are fixed relative to each other. Since the position of the first rod 26 is fixed, the third electrode may be omitted from the vacuum interrupter assembly of Figure 3.

The first and second rods 26, 28 are positioned so that only a portion of the first rod 26 is located just inside the multiple slotted coil 38.

The vacuum interrupter assembly further includes an auxiliary electrode 50, a bypass switching circuit 52 and an ignition circuit 54.

The auxiliary electrode 50 is coaxially located in a central bore of the second rod 28, so that an end of the auxiliary electrode 50 protrudes from the second end of the first rod 26. The auxiliary electrode 50 is hermetically sealed by vacuum brazing against the first rod 26 using metallised ceramic spacers .

As shown in Figure 4, the bypass switching circuit 52 is connected in parallel with the vacuum interrupter 210, while the ignition circuit 54 is connected in series with the auxiliary electrode 50. The ignition circuit 54 includes a spark ignition switch .

During normal operation of the connected DC network, the bypass switching circuit 52 is switched to a closed state to allow the load current to flow through the bypass switching circuit 52 and thereby bypass the vacuum interrupter 210.

In the event of a fault in the connected DC network, the bypass switching circuit 52 is switched to an open state to prevent current from flowing through the bypass switching circuit 52, and the ignition circuit 54 is controlled to establish a discharge current between the first and second electrodes 30,32. This is done by establishing a radio frequency discharge between the auxiliary electrode 50 and the surrounding conductors. The generated plasma rapidly spreads between the gap between the first and second electrodes 30,32, and begins to draw a current. This in turn causes current to flow through the multiple slotted coil 38 and thereby leads to the generation of an axial magnetic field. As in the first and second embodiments, the presence of the axial magnetic field increases the arc voltage and decreases the arc current until it extinguishes.

The switching of the bypass switching circuit 52 between open and closed states may be performed using a semiconductor switch or a mechanical breaker depending on availability, cost and performance requirements.

The time required for the vacuum interrupter assembly in Figure 4 to interrupt current is limited by the time needed for the bypass switching circuit 52 to achieve an open state. The switching time for a mechanical breaker is typically a few milliseconds while, the switching time for a semiconductor switch is typically less than 10 ps .

The time required to fully open the mechanical breaker therefore might require multiple ignitions through the vacuum interrupter 210 to sustain the arc until the mechanical breaker is fully opened.

It is envisaged that the vacuum interrupter assembly according to embodiments of the invention may be used to carry out the current interruption process for conditions other than high fault current conditions .

Other than current interruption in DC networks, the vacuum interrupter assembly in Figures 1 to 4 may also be used to interrupt current in AC power networks, AC high voltage circuit breakers and AC generator circuit breakers.

An apparatus according to a fourth embodiment of the invention is shown in Figure 5.

The apparatus comprises primary and secondary circuits 56,58, whereby the primary and secondary circuits 56,58 are connected in parallel.

The primary circuit 56 includes a series connection of a vacuum interrupter assembly according to the first or second embodiment, and a plasma switch 60 connected in series with the vacuum interrupter 10,110,210 according to any of the first, second and third embodiments. The plasma switch 60 may be, for example, a hydrogen plasma switch.

The secondary circuit 58 includes a series connection of a capacitor 62, an inductor 64 and a spark ignition switch 66. In use, the plasma switch 60 is controllable to generate a high arc voltage, which is combined with the arc voltage across the vacuum interrupter assembly to increase the total arc voltage across the series connection of the vacuum interrupter 10,110,210 and the plasma switch 60. The increase in total arc voltage in turn speeds up the reduction of the arc current and thereby reduces the overall time required for the current interruption process.

Moreover, the inclusion of the plasma switch 60 results in the reduction in total power dissipation across the primary circuit 56. This in turn permits the ratings of the circuit elements of the primary circuit 56 to be reduced and thereby decreases the costs and space required for installation of the apparatus .

In use, the secondary circuit 58 is controllable to inject an oscillatory current into the primary circuit 56 to force the arc current to zero. The ability to force the arc current to zero not only provides precise control over the amount of time required to interrupt the current, but also speeds up the time required for extinguishing the arc current, since the secondary circuit 58 can be configured to achieve the current zero earlier than the primary circuit 56.

It is envisaged that, in other embodiments, the plasma switch may be omitted from the apparatus so that the secondary circuit is connected in parallel with the vacuum interrupter 10,110,210. In other embodiments, it is envisaged that a vacuum interrupter assembly may include a plurality of series-connected and/or parallel-connected vacuum interrupters .

Multiple vacuum interrupters may be connected to define different configurations of the vacuum interrupter assembly in order to improve its operating voltage and current characteristics. For example, connecting multiple vacuum interrupters in series increases the dielectric strength of the vacuum interrupter assembly and thereby permits the use of the vacuum interrupter assembly at higher operating voltages, while connecting multiple vacuum interrupters in parallel permits the vacuum interrupter to interrupt higher levels of current.

The vacuum interrupter assembly in Figures 1 to 4 and the apparatus in Figure 5 are compatible for use, but are not limited to, applications such as railway traction, ships, superconducting magnetic storage devices, high energy fusion reactor experiments, stationary power applications, and high voltage direct current (HVDC) multi-terminal networks.

Claims

1. A vacuum interrupter assembly comprising at least one vacuum interrupter, the or each vacuum interrupter including a vacuum-tight enclosure; first and second electrically conductive rods, a first end of each rod being adapted to be connected, in use, to an electrical network; a first electrode being mounted near or at a second end of the first rod; a slotted coil being operably mounted at a second end of the second rod; and a second electrode being mounted on an inner surface of the slotted coil, wherein the first electrode and the slotted coil are located inside the vacuum-tight enclosure, and the rods are positioned to locate at least a portion of the first electrode inside the slotted coil.

2. A vacuum interrupter according to Claim 1 wherein the slotted coil includes only a single slot.

3. A vacuum interrupter according to Claim 1 wherein the slotted coil includes a plurality of slots .

4. A vacuum interrupter assembly according to any preceding claim, wherein the first electrode includes a first electrode portion mounted at the second end of the first rod.

5. A vacuum interrupter assembly according to Claim 4, wherein the first electrode further includes a second electrode portion mounted around the circumference of the first rod and adjacent to the first electrode portion.

6. A vacuum interrupter assembly according to any preceding claim, wherein the slotted coil includes a support base being mounted at the second end of the second rod.

7. A vacuum interrupter assembly according to any preceding claim, wherein each electrode is made from a refractory material.

8. A vacuum interrupter assembly according to Claim 7, wherein the refractory material is selected from a group of chromium-chromium, copper-tungsten, copper tungsten carbide, tungsten, chromium or molybdenum.

9. A vacuum interrupter assembly according to any preceding claim, wherein at least one rod is moveable relative to the other rod to open or close a gap between the second ends of the rods .

10. A vacuum interrupter assembly according to Claim 9 when dependent from Claim 6, wherein the or each vacuum interrupter further includes a third electrode mounted on the support base, the first and third electrodes defining opposed contact surfaces, and at least one rod is moveable relative to the other rod to open or close a gap between the opposed contact surfaces .

11. A vacuum interrupter assembly according to Claim 9 or Claim 10, wherein the or each vacuum- tight enclosure further includes a tubular bellows with a hollow bore, the or each tubular bellows being operably connected to at least one rod and being controllable to expand or contract to move one rod relative to the other rod to open or close a gap between the second ends of the rods .

12. A vacuum interrupter assembly according to any of Claims 9 to 11, wherein the or each vacuum interrupter further includes an auxiliary coil located outside the vacuum-tight enclosure, the auxiliary coil being controllable to provide a pulsed magnetic field inside the vacuum-tight enclosure.

13. A vacuum interrupter assembly according to Claim 12 when dependent from Claim 7, wherein the refractory material is copper-chromium, copper- tungsten, copper tungsten carbide, tungsten, chromium, molybdenum or silver tungsten carbide.

14. A vacuum interrupter assembly according to any of Claims 1 to 8, wherein the positions of the second ends of the rods are fixed relative to each other .

15. A vacuum interrupter assembly according to Claim 14 further including a bypass switching circuit and an ignition circuit, the or each vacuum interrupter further including an auxiliary electrode coaxially located in a central bore of the first rod, an end of the auxiliary electrode protruding from the second end of the first rod, the bypass switching circuit being operably connected to the or each vacuum interrupter and being controllable to divert current to bypass the or each vacuum interrupter, the ignition circuit being operably connected to the or each auxiliary electrode and being controllable to establish a discharge current between the first and second electrodes .

16. A vacuum interrupter assembly according to Claim 15, wherein the ignition circuit includes a spark ignition switch.

17. A vacuum interrupter assembly according to Claim 15 or Claim 16, wherein the bypass switching circuit includes at least one semiconductor switch or at least one mechanical switch.

18. A vacuum interrupter assembly according to any preceding claim including a plurality of series- connected and/or parallel-connected vacuum interrupters .

19. An apparatus comprising primary and secondary circuits, the primary circuit including a vacuum interrupter assembly according to any preceding claim, the secondary circuit including a series connection of at least one capacitor, at least one inductor and a spark ignition switch, wherein the primary and secondary circuits are connected in parallel .

20. An apparatus according to Claim 19, wherein the primary circuit further includes at least one plasma switch connected in series with the vacuum interrupter assembly.