WO2014048483A1

WO2014048483A1 - Electrical switch with thomson coil drive

Info

Publication number: WO2014048483A1
Application number: PCT/EP2012/069170
Authority: WO
Inventors: Joerg Ostrowski; Markus Abplanalp; Bernhard Petermeier
Original assignee: Abb Technology Ag
Priority date: 2012-09-28
Filing date: 2012-09-28
Publication date: 2014-04-03

Abstract

An electrical switch, in particular a medium or high voltage switch, comprises two movable coils {8a, 8b) as well as two movable metal parts (10a, 10b), with the coils (8a, 8b) being arranged, e.g., between the metal parts (10a, 10b). Each coil (8a, 8b) is mechanically connected to the metal part (10a, 10b) on the opposite side and able to push the same away from the center of the assembly. The two coils (8a, 8b) can be arranged electrically in parallel to each other. Upon application of a current pulse to the coils (8a, 8b), the coils (8a, 8b) are attracted to each other due to their parallel magnetic fields, while the metal plates (10a, 10b) are accelerated outwards due to eddy currents. These two effects combine to separate the metal (10a, 10b) parts quickly.

Description

Electrical switch with Thomson coil drive

Technical Field

The invention resides in the field of electrical switching. It relates to an electrical switch with a Thomson coil drive that has a static frame, a first and a second switch member movable in respect to each other, a coil arrangement comprising at least one electrical coil and a pulse generator for generating a pulse in the coil arrangement and thereby to move the first switch member in respect to the second switch member.

Background Art

The installation of distributed energy generation (i.e. in windmills, solar power, etc.) results in increased short circuit currents in today's electric networks. Whenever this short circuit current cannot be safely handled by the installed protection devices, additional measures are required. Either the protection devices, especially breakers, have to be replaced with more powerful ones, or the grid has to be split. Alternatively, a fault current limiter (FCL) can be used to limit the fault current below the limit of the existing network.

Other motivations for FCL are, e.g., the increased coupling of grids to increase power quality and the reduced costs for other components.

At present, fault current limitation at medium voltage level is mainly implemented by fuses, pyrotechnic limiters, and current limiting reactors. Fuses and pyrotechnic limiters are one-shot devices, i.e. at least one part or the whole limiting device has to be replaced after a fault. Current limiting reactors are huge and cause a significant voltage drop and losses even during nominal operation. New solutions are currently under demonstration, such as superconducting FCLs or saturated iron core FCLs.

Another potential solution is the combination of a fast mechanical switch with a limiting device in parallel. This allows to have small nominal losses when the current is flowing through the closed switch. In case of a fault, the switch has to be opened as quickly as possible (e.g. within less than 2 ms) . The current will commutate into the parallel limiting device. Many implementations are possible, e.g. a direct commutation into a power dissipating element (resistor, positive-temperature coefficient resistor (PTC), varistor) or a first commutation into a power electronic switch followed by a further commutation to the power dissipating element. In all implementations the key missing element is the fast commutation switch, especially a very fast actuator for opening this switch. (Since the closing of the switch is usually not time critical here, any standard drive can be used for closing of the switch.)

Fast actuators are, e.g., also required for hybrid breakers, in particular for DC switching applications .

One known fast actuator for such switches is the Thomson coil drive. It comprises at least one coil and at least one switch member. These two parts are positioned such that a current pulse in the coil generates eddy currents in the switch member, which lead to a repulsive force between the two parts.

A switch of this type is disclosed in US 7 235 751. It has a first and a second switch member and a Thomson drive adapted to accelerate one of these members, while the other remains stationary with the frame of the switch. The Thomson drive comprises a coil arrangement having two coils and a pulse generator. The pulse generator generates a pulse in one of the coils, which in turn generates eddy currents in the movable mem- ber, thereby accelerating the movable member away from the coil.

This type of drive is well suited for operating electrical switches, in particular medium- and high- voltage switches, because it allows to quickly interrupt a switch, even though it is of very simple mechanical design.

One disadvantage of Thomson coil drives arises from the fact that the force exerted by the coil on the movable member quickly decreases with increasing distance between the two components.

Disclosure of the Invention

The problem to be solved by the present invention is to provide a switch with a Thomson coil drive that provides faster switching action.

This problem is solved by the switch of claim 1. Accordingly, the switch comprises a static frame as well as a first and a second switch member. Further, it comprises a coil arrangement with at least one electrical coil and a pulse generator ^' for generating a current pulse in the coil arrangement and thereby to move the first switch member relative to the second switch member. According to the invention, both the first and the second switch member are movable relative to the frame and the switch is adapted to accelerate both the first and the second switch member in opposite directions by means of the current pulse.

In other words, in the switch according to the invention there are at least two switch members that are accelerated, namely into directions opposite to each other. As described below, this is based on the under- standing that, for a given amount of energy, a larger separating speed between two switch members can be achieved, if the energy is split to accelerate both switch members instead of accelerating one switch member only.

In one embodiment, the at least one coil of the coil arrangement is movable with respect to the frame and is adapted to be accelerated by the current pulse.

In a further embodiment, the coil arrangement comprises at least a first and a second coil, which can e.g. be spatially separated, i.e. can be arranged at a distance from each other.' For example, in this case, the coils are electrically arranged in parallel (and not in series) in order to reduce the inductance and thereby, for a given capacitance, to increase switching speeds.

The present switch is particularly suited for switching medium and high voltages, i.e. voltages of at least 1.5 kV, because for such voltages high contact speeds are required in order to reduce and/or shorten sparking between the contacts. The switch can, e.g., be used in a (fast) commutation switch, in particular in a fault current limiter, but it is also suited for other applications .

Brief Description of the Drawings

The invention will be better understood and objects other than those set forth above will become apparent when consideration is given to the following detailed description thereof. Such description makes refer^¬ ence to the annexed drawings, wherein:

Fig. 1 shows a simplified sectional view of a first embodiment of the invention,

Fig. 2 shows the embodiment of Fig. 1 after the current pulse,

Fig. 3 shows a view of a specific design of the embodiment of Figs. 1, and 2,

Fig. 4 shows a sectional view of the drive of a second embodiment, Fig. 5 shows a sectional view of the drive of a third embodiment, and

Fig. 6 shows a sectional view of the drive of a fourth embodiment .

Modes for Carrying Out the Invention Definitions :

In the present text, the term "movable" expresses the possibility of a non-destructive motion of a part in respect to the frame or another part by a non- vanishing distance, for example by approximately at least 2 mm, without prior disassembly of the switch.

Similarly, the term "non-movable" expresses the impossibility of a non-destructive motion of the part by a non-vanishing distance, for example by approximately at least 2 mm, without prior disassembly of the switch.

First embodiment:

The embodiment of an electrical switch shown in Fig. 1 comprises a static housing or frame schematically depicted as a rectangle with reference number 1. This frame, e.g., comprises a stand or mount for mounting the switch and, for a high voltage switch, e.g., a gas- tight housing. It is static in the sense that it is non- movable during a switching operation of the switch. It can, e.g., be conductive and enclose the movable components of the switch.

The switch further comprises nominal current terminals 2 carrying the current to be interrupted by the switch. The terminals 2 are connected to stationary contacts 3. In the conducting state of the switch, as depicted in Fig. 1, each stationary contact 3 is in electrical contact with a movable contact 4. The movable contacts are interconnected by means of a flexible conductor, schematically indicated as reference number 5. Each movable contact 4 is mechanically connected to an actua^¬ tor rod 6, and the two actuator rods are connected to a Thomson drive 7.

The flexible conductor 5 is only one of vari^¬ ous conceivable solutions for implementing this type of switch. Alternatively, a tulip or contact band with a sliding contact could be used, or the change in length could be used for separating the two contacts.

To interrupt the switch, i.e. to move it from its conducting state shown in Fig. 1 to its nonconducting state as shown in Fig. 2, the actuator rods 6 are moved such that the movable contacts 4 move away from the stationary contacts 3, thereby interrupting the electrical connection between the terminals 2.

It must be noted that the components described so far can vary widely within the scope of the present invention. For example, the number of contacts, their electrical interconnections, their location, as well as their geometry and nature of connection to the Thomson drive can vary.

Thomson drive 7 in the embodiment of Figs. 1 and 2 comprises a coil arrangement including at least a first coil 8a and a second coil 8b. Each of these coils 8a, 8b is wound around a common axis A.

Coils 8a and 8b are embedded in or mounted to a first and a second coil carrier 9a, 9b, respectively. These coil carriers 9a, 9b are, e.g., of a non-metallic material, provide mechanical stability to the coils 8a, 8b and serve to receive the forces exerted on the coils 8a, 8b.

In the embodiment of Figs. 1 and 2, both coils 8a, 8b are independently movable along axis A with respect to frame 1.

In addition, the embodiment of Figs. 1 and 2 further comprises a first and a second metal part 10a, 10b, respectively, each e.g. consisting of a metal disk with a central bore 11. The metal parts 10a, 10b are also independently movable along axis A in respect to frame 1. The metal parts 10a, 10b form at least part of a first and a second movable switch member, respectively.

Each of the actuator rods 6 is connected to one of the metal parts 10a, 10b (i.e. to one of the movable switch members) , respectively. Thus, a motion of the metal parts 10a, 10b along axis A induces a relative movement of the movable contacts 4 in respect to the stationary contacts 3.

In the following, the design of the components of the Thomson drive is described in more detail in reference to Figs. 1, 2 and 3, with Fig. 3 showing a possible design of the metal parts, the coils and the coil carriers, with first metal part 10a being omitted for better visibility of the other components. (It must be noted that the dimensions of the components of Fig. 3 differ somewhat from those of the components of Figs. 1 and 2. }

As can be seen, there are several support members, generally denoted by reference numbers 12a, 12b, 13a, 13b, which are provided to transmit axial pushing (but not necessarily pulling) forces between each coil carrier at its attributed metal part. Specifically, at least one first support member 12a, 13a is arranged to transmit a pushing force between first coil carrier 9a and first metal part 10a, while at least one second support member 12b, 13b is arranged to transmit a pushing force between second coil carrier 9b and second metal part 10b. The support members 12a, 13a mechanically couple first coil 8a to first metal part 10a in order to exert a force on the metal part when the coils 8a, 8b are accelerated towards each other, as described below. Similarly, the support members 12b, 13b mechanically couple second coil 8b to second metal part 10b in order to exert a force on the metal part when the coils 8a, 8b are accelerated towards each other, again as described below. For improved force distribution, there is at least one central first and second support member 12a, 12b, as well as at least one peripheral first and second support member 13a, 13b, respectively, with the central support members 12a, 12b being closer to axis A than the peripheral support members 13a, 13b. Further, there can for example be several central first and second support members 12a, 12b, such as three, alternatingly arranged at regular angular intervals, and there are several peripheral first and second support members 13a, 13b, such as three, again alternatingly arranged at regular angular intervals .

As can be seen, the switch further comprises a pulse generator 14 for generating current pulses in the coils 8a, 8b, as it is generally known for Thomson drives. Typically, pulse generator 14 comprises a capacitor and a switch for discharging the capacitor through the coils 8a, 8b.

In an embodiment, the coils 8a, 8b are electrically arranged in parallel, thereby reducing the inductance as described above.

Each coil 8a, 8b has two current terminals 15 for being connected to pulse generator 14. The connections are such that the fields generated by the coils 8a, 8b in response to a pulse from pulse generator 14 are parallel to each other, i.e. the coils are attracted to each other when a current pulse is generated.

Hence, when current generator 14 generates a current pulse, the following two processes generate a movement in the switch:

- On the one hand, first coil 8a generates eddy currents in adjacent second metal part 10b, which gives rise to a repulse force between the two parts, as it is known from Thomson drives. Similarly and in addition, a repulsive force is generated between second coil 8b and first metal part 10a. - On the other hand, since the fields generated by the coils 8a, 8b are parallel to each other, the coils 8a, 8b are attracted to each other.

Since the metal parts 10a, 10b as well as the coils 8a, 8b and the coil carriers 9a, 9b are movable along axis A, these forces will drive the metal parts 10a, 10b away from each other and the coils 8a, 8b towards each other, as indicated by the arrows in Fig. 1.

It must be noted that the forces between the coils 8a, 8b and their adjacent metal parts 10b, 10a, respectively, are based on eddy currents, and they are therefore dynamic and short-ranged. They are strongest during the initial phase of the current pulse.

In contrast to this, the attractive force be^¬ tween the coils 8a, 8b is present during the whole dura^¬ tion of the pulse and increases in strength when the coils are moving closer to each other. Hence, this attractive force increases over the duration of the pulse. The support members 12a, 12b, 13a, 13b are able to transmit this attractive force to the metal parts 10a, 10b, respectively, until the coils 8a and 8b meet at the cen^¬ ter of the switch.

To close the switch of Fig. 1, i.e. to re^¬ establish current through its nominal terminals, currents in opposite directions can be induced in coils 8a and 8b, such that a repulsive force is generated between them. This works only, however, if the support members 12a, 12b, 13a, 13b are able to transmit not only pushing forc^¬ es, but also pulling forces.

The embodiment of Fig. 1 has, in summary, various benefits:

- It uses a "double motion" design wherein the two switch members (with the first switch member comprising e.g. metal part 10a and the second switch member comprising metal part 10b) are both accelerated in opposite directions. As described below, such a scheme allows to achieve faster contact separation for a given amount of energy as compared to conventional single motion designs .

- Further, due to the parallel arrangement of the two coils, inductance is only half as compared to a single coil, which leads to a faster discharge of the charge in the pulse generator.

- Finally, the distance between the plates and the coils is small at the beginning of the process. Thus, there is a large Lorentz force generated by the in^¬ duced eddy currents. In addition to this force (which is also present in conventional Thomson drives), the attrac^¬ tive force between the two coils is also used for accelerating the two switch members. This attractive force increases when the distance between the coils decreases, i.e. it increases during the process as the coils ap^¬ proach each other. Since this force is not of inductive nature, it is also present in the case of stationary currents .

In the following, some further embodiments of switches are described, which also implement at least part of these benefits. The respective figures only show the Thomson drive itself, while the remaining components of the switch can e.g. be similar to those of Fig. 1.

Second embodiment:

In the embodiment of Fig. 1, the coils 8a, 8b were arranged in the region between the first and the second metal parts 10a, 10b such that the two metal parts 10a, 10b were accelerated in opposite directions. This type of double-motion or double-acceleration provides for faster final velocities as described under the section "double motion" below.

Fig. 4 shows an alternative embodiment of the switch that is simpler in design than the one of Figs. 1 - 3, but it still exploits the advantages of double motion . In this embodiment, only a single coil 8a (in the claims designated as "first coil 8a") is arranged in the region between the two movable metal parts 10a, 10b. Again, coil 8a may be arranged within or on a coil carrier 9a and it may or may not be stationary within the frame of the switch.

When a current pulse is applied to coil 8a, eddy currents are generated in the metal parts 10a and 10b, which drives the metal parts 10a and 10b away from each other along the arrows shown in Fig. 4.

Third embodiment:

Yet another embodiment with a single coil 8a and a single metal part 10b, which exploits double motion, is shown in Fig. 5. Here, coil 8a forms part of the first movable switch member, while metal part 10b forms part of the second movable switch member. Both coil 8a and metal part 10b are movable independently from each other. Upon application of a current pulse, an eddy current is induced in metal part 10b, which leads to a repulsive force between coil 8a and metal part 10b and therefore to an acceleration of the two movable switch members away from each other, along the arrows shown in Fig . 5.

Fourth embodiment :

Fig. 6 .shows an embodiment with two non- movable coils 8a, 8b, which are arranged electrically in parallel to each other. Ά first metal part 10a is arranged adjacent to second coil 8b, while a second metal part 10b is arranged adjacent to first coil 8a. The metal parts 10a, 10b are movable independently in respect to each other and in respect to the frame of the switch.

Upon application of a current pulse, first metal part 10a is accelerated away from second coil 8b, while second metal part 10b is accelerated away from first coil 8a, along the arrows shown in Fig. 6. Double motion:

The present invention is based on the idea of a double-movement and a double-acceleration. The advantage of this scheme is that a larger distance between the two switch members can be reached, because the kinet^¬ ic energy depends on the square of the velocity.

In a conventional design, where only one switch member is accelerated to a velocity v, the resulting kinetic energy E is

E = m-v²/2. ·

Hence, for a given energy E, the final separation velocity v is limited to

In contrast to this, if two masses mi and are accelerated, we have

If the masses are the same, the process is symmetric and the masses are accelerated in opposite di^¬ rections, the final separation velocity v is limited to

which is better than the conventional solution by a factor of Hence, a faster contact separation can be achieved for a given energy. Notes :

As mentioned above, if the coil arrangement comprises at least two coils, it is advantageous to arrange these coils electrically in parallel during pulse generation. This decreases the pulse duration by a factor 2, because the time for discharging the capacitor of the pulse generator is proportional to the square root of the inductance of its load.

Further, since the inductance is proportional to the magnetic field energy, a compact design of the coil(s) allows to further reduce the pulse duration.

As mentioned, each metal part 10a, 10b forms at least part of a movable member of the switch. In the embodiment of Fig. 1, for example, first metal part 10a forms the first movable switch member 10a, while second metal part 10b forms the second movable switch member 10a. The switch members 10a, 10b may, however, also comprise further components. For example, in the embodiments above, the metal parts 10a, 10b are formed by solid metal plates or metal disks, but they may also e.g. be formed by a thin metal layer or a non-metallic support, in which case each switch member comprises a metal layer and its non-metallic support.

In some of the above embodiments, the coil or coils is or are movable. To feed current to such a movable coil, sliding contacts or flexible feeds can be used.

Simulations show that the first embodiment (Fig. 1 - 3) shows the fastest acceleration for a given pulse energy and pulse peak voltage.

While there are shown and described presently preferred embodiments of the invention, it is to be distinctly understood that the invention is not limited thereto, but may otherwise variously be embodied and practiced within the scope of the following claims. Reference numbers

1 : frame

2: current terminals

3: stationary contacts

4 : movable contacts

5 : conductor

6: actuator rods

7 : Thomson drive

8a, 8b: coils

9a, 9b: coil carriers

10a, 10b: metal parts (movable switch members)

11: bores

12a, 12b: first support members

13a, 13b: second support members

14: pulse generator

15: coil current terminals

A: axis

Claims

1. An electrical switch with a Thomson coil drive comprising:

a static frame (1),

a first and a second switch member movable with respect to each other,

a coil arrangement (8a, 8b) comprising at least a first electrical coil (8a) , and

a pulse generator (14) adapted to generate a current pulse in the coil arrangement (8a, 8b) and thereby to move the first switch member with respect to the second switch member,

characterized in that both the first and the second switch member are movable with respect to the frame (1), wherein the switch is adapted to accelerate both the first and the second switch member in opposite directions by means of the current pulse.

2. The switch of claim 1, wherein the first coil (8a) is movable with respect to the frame (1) and is adapted to be accelerated by the current pulse.

3. The switch of any of the preceding claims, wherein the coil arrangement {8a, 8b) comprises a second coil (8b) in addition to the first coil (8a) .

4. The switch of claim 3, wherein the first and the second coils (8b) are electrically arranged par^¬ allel to each other.

5. The switch of any of the claims 3 to 4, wherein the first and the second coil (8b) are movable towards each other and are located to be attracted to each other by the current pulse.

6. The switch of any of the preceding claims, wherein the first coil (8a) is arranged between a first metal part (10a) of the first member and a second metal part (10b) of the second member, wherein the first metal part (10a) and the second metal part (10b) are movable in respect to each other and are located to be accelerated away from each other by the current pulse.

7. The switch of the claims 5 and 6, wherein the first and the second coil {8a, 8b) are arranged in a region between a or the first metal part (10a) and a or the second metal part (10b),

wherein the first coil (8a) is mechanically coupled to the first switch member to exert a force on the first switch member when the first coil (8a) is accelerated towards the second coil (8b) , and/or wherein the second coil (8b) is mechanically coupled to the second switch member to exert a force on the second switch member when the second coil (8b) is accelerated towards the first coil (8a) .

8. The switch of claim 7 comprising a first coil carrier (9a) carrying the first coil (8a) and a second coil carrier (9b) carrying the second coil (8b) ,

at least one first support member (12a, 13a) structured to transmit a pushing force between the first coil carrier (9a) and the first switch member, and

at least one second support member (12b, 13b) structured to transmit a pushing force between the second coil carrier (9b) and the second switch member.

9. The switch of claim 8, wherein the first support member (12a, 13a) is further structured to transmit a pulling force between the first coil carrier (9a) and the first switch member, and/or the second support member (12b, 13b) is further structured to transmit a pulling force between the second coil carrier (9b) and the second switch member.

10. The switch of claim 1, wherein the first coil (8a) is non-movable with respect to the frame (1) .

11. The switch of any of the preceding claims, wherein the first coil (8a) is part of the first switch member and is adapted to accelerate in a direction opposite to an acceleration of the second switch member upon the current pulse.

12. Use of the switch of any of the preceding claims for switching a voltage of at least 1,5 kV, in particular in a commutation switch, especially in a fault current limiter.