WO2010037424A1

WO2010037424A1 - Electric current limiting device

Info

Publication number: WO2010037424A1
Application number: PCT/EP2008/063291
Authority: WO
Inventors: Stephan Schoft; Jens Tepper; Felix Rager
Original assignee: Abb Technology Ag
Priority date: 2008-10-03
Filing date: 2008-10-03
Publication date: 2010-04-08

Abstract

Electric current limiting device comprising a repulsion drive (2) for actuating an actuation means (3a, 3b, 3c) of an primary switching element (1), the primary switching element (1) having at least one first electrical contact (4a, 4b, 4c, 4d, 4e) and at least one second electrical contact (5a, 5b, 5c, 5d, 6a, 6b, 6c, 6d), wherein at least the first contact (4a, 4b, 4c, 4d) is a solid electrode (4a, 4b, 4c, 4d) which can be actuated by the actuation means (3a, 3b, 3c). The current limiting device is characterized in that a reservoir (8) of liquid metal is contained in at least one of the contacts (4a-d; 5a-d; 6a-d) such that in an electrically conductive state of the primary switching element an electrical current path between the first (4a-d) and the second contact (5a-d; 6a-d) is provided by liquid metal of the reservoir (8).

Description

ELECTRIC CURRENT LIMITING DEVICE

D E S C R I P T I O N

Technical Field

The invention relates to the field of electric current limiting devices in particular to current limiting devices using an electromagnetic repulsion drive for actuation of switching contacts which commutate a fault current to commutation paths arcless and in particular relates to a current limiting devices for a system to limit and switch of currents arcless.

State of the Art In general circuit breakers for AC medium and high voltage application do not exhibit a current limiting effect during switching. Once the breaker is tripped solid contacts open and an arc is ignited. This arc normally extinguishes at the next current zero crossing. Thus the elements of the switchgear like busbars, insulating supports and others suffer from the mechanical and thermal impact of the first fault current impulse. Current limiters limit the maximum fault current peak well before current zero crossing. Therefore they prevent the installation from mechanical and thermal damage or facilitate the opening of circuit breakers.

The main recent increase in need of having fault current limiters installed in electric networks arises from the increasing installation of distributed energy generation (i.e. windmills, solar power, etc.) and from more and more coupled networks. Both, distributed energy generation and network coupling lead to increased short circuit currents which may exceed the short circuit ratings of the actual installation especially those of circuit breakers. Besides this, one can imagine other applications 5 of current limiters, e.g. for transformer protection and others.

At the time being fault current limitation/ protection at medium voltage level is mainly done 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 the fault. Current limiting reactors are huge, i o expensive and cause a lot of electric losses.

From EP1377995 an electric device is known which comprises an electric switch and a commutation path arranged in parallel. The electric switch is built of a plurality of solid contact members arranged in series to form a plurality of breaking points.

15 The contact surfaces are substantially flat and parallel. The electric switch may comprise a Thomson coil which serves as drive to open several movable contact members simultaneously. The device may be used as a current limiting switch. In order to provide electrical contact a significant contact force has to be applied to open and close the solid contact members. The contact force causes abrasion on

20 the contact surfaces and a limitation of switching velocity.

The paper "A DC Hybrid Circuit Breaker with ultra fast contact opening and integrated gate -commutated thyhstors (IGCT)" of Jean-M Meyer et al., Laboratory of Industrial Electronics, EPF Lausanne; describes a device consisting of

25 a mechanical switch driven by a electromagnetic repulsion drive and having a bidirectional static cell with two high power IGCTs connected in parallel, four diodes in a rectifier scheme and a Metal Oxyde Varistor (MOV) element. The diode bridge configuration allows this breaker to be used for both DC and AC. The usual load current is carried by the mechanical switch. In case of a short-circuit, a fault

30 detecting unit produces an opening signal for the moving contact and, at the same time, a turn-on signal for the IGCTs. A small arc discharge is drawn between the contacts after separation and an arc voltage appears. This arc voltage acts as a counter voltage and the current commutates rapidly and completely to the power electronics. When the distance between the contacts is sufficient (total recovery of 5 the dielectric strengh), the IGCTs interrupt the fault current upon receiving a turn-off signal. Energy remaining in the circuit is absorbed by the MOV which also acts as an overvoltage arrester.

DE10346201 discloses a liquid metal switch driven by a pneumatic piston drive for i o switching a current on and off. In a conductive state of the switch the movable electrode bridges two stationary electrodes which are separated by an electrically isolating gap.

Summary of the invention

1 5

The object of the present invention is to provide a fast, cheap, small and resettable (multi shot) current limiting device with low nominal current losses. The problem is solved by an electric current limiting device with characteristics of independent claims.

20

According to the invention the electric current limiting device comprises a primary switching element which is actuated by an electromagnetic repulsion drive e.g. a Thomson Drive and comprises at least one commutation path. The primary switching element having electrical contacts which can be divided in a group of first

25 electrical contacts and in a group of second electrical contacts wherein at least a first contact is made from a solid electrode and can be moved by the actuation means of the repulsion drive in order to force the electrical current to flow through at least one commutation path. The electric current limiting device is characterised in that a reservoir of liquid metal forms or is contained in or alongside of at least one of

30 the contacts such that in an electrically conductive state of the primary switching element an electrical current path between the first and the second contact is provided. A liquid metal reservoir which is in physical contact with one of the contacts should also be understood by the expression liquid metal reservoir contained in one of the contacts. In other words, the reservoir can be in close 5 vicinity to one of the contacts. The primary switching element carries the nominal current flowing in an electric circuit. The switching contacts force a fault current either to commutate to at least one commutation path that is connected in parallel to at least one switching contact or to flow through at least one additional current path that is connected in series to the at least one switching contact. An electric current i o limiting device designed in this manner provides a very fast and reliable device in order to commutate and limit high currents in case of a fault. Advantageously the device requires no or negligible contact forces between the first and second electrical contacts during opening, closing operation and during nominal current flow due to the liquid -solid interface between the first and second contacts. Thus_.,

15 opening and closing of the contacts occur almost free from friction and wear. In a preferred embodiment the actuation means is a piston which is part of the Thomson drive.

In a preferred embodiment the at least one liquid metal reservoir is formed on a side 20 of the first contact facing the second contact. Alternatively or in addition a liquid metal reservoir can be formed on a side of the second contact facing the first contact. Providing the liquid metal reservoir in such a way an electrically conducting state between the first and second contacts can be achieved by a straight-path first or second contact travel.

25

In another preferred embodiment the current limiting device contains the reservoir in the first or second contact or forms one of the contacts. The reservoir is arranged as a recess. The shape of the reservoir can be e.g. spherical or cubical. It can also be of any other shape suitable to keep a certain quantity of liquid metal.

30 The first contacts slide along a direction which is in an angle orthogonal to the current path of the contacts of the support and that the piston carries several first contacts arranged in stacks, and the electrical current paths are arranged in the support in corresponding stacks.

5

In other preferred embodiments the electric current limiting device comprises pairs of first and second contacts which pairs are connected electrically in series with each other. Thus, the voltage drop at each single contact during switching is decreased and advantageously an arcless switching can be achieved in this way. i o The moveable part of the switch which can be e.g. the piston or the rotator carries several first contact members arranged in a stack. With the movement of the first contacts into the closing position each first contact member is in contact with an adjacent second contact. In this way many switching contacts can be closed and opened simultaneously. The second contacts are contained in the support and

15 provide the electrical current paths within the support element.

In another preferred embodiment the electric current limiting device is equipped with two arrays of first contacts which are actuated simultaneously by the Thomson drive. In this way a very compact design of a current limiting device with an important 20 number of series and or parallel connections of several switching contacts can be realized. In other embodiments the current limiting device has three, four or more movable arrays of first contacts.

In another preferred embodiment the electric current limiting device has second 25 contacts which comprise two contact members belonging together. The first contacts have the function of bridging contacts and bridge two second contact members belonging together.

In another preferred embodiment the current limiting device comprises at least one 30 first contact and a plurality of second contacts which are arranged in a stack. The second contacts provide alternative electrical commutation paths. During current limitation the at least one first contact is moved along the second contacts such that the it makes contact to at least one second contact and thereby activates the corresponding commutation path. More and more commutation paths are enabled 5 during the travel of the at least one first contact along the stack of second contacts. More and more commutation path elements are connected in series and are inserted as additional impedance in the electric grid. In this way the specific limiting behaviour of the device can be designed and adapted to individual application.

i o In a variant of the current limiting device the piston can be left out and the opening and closing movement of the contacts in the current limiter is realised by means of a rotator. Depending on the angle of the rotation connecting, bridging or disconnecting of first and second electrical contacts can be realized.

15 According to another aspect of the invention a system comprises the electric current limiting device and a circuit breaker. The circuit breaker is arranged in series connection with the electric current limiting device and arc less switching of high currents can is feasible. In a first step the current will be limited by the limiting device and in a second step the limited current can be switched off by the first circuit

20 breaker.

Brief Description of the Drawings

25 Below, the invention is illustrated in more detail in the following more detailed description of preferred embodiments, which are shown in the included drawings. The figures show: Fig. 1 a schematic wiring diagram of a current limiting device including a series connection of n fast opening contacts with and one commutation path element connected in parallel each;

Fig. 2 a schematic wiring diagram of a current limiting device including a

5 series connection of n fast opening contacts and one single commutation path element connected in parallel to the entire series connection of opening contacts Fig. 3 a schematic wiring diagram of a current limiting device comprising a series connection of m current limiting devices according Fig. 2: i o Fig. 4 a schematic wiring diagram of a current limiting device with an alternating arrangement of contacts and commutation path elements; Fig.5 an illustration of the Thomson Drive setup;

Fig.6 a schematic illustration of a current limiting device having a primary switching element with two movable pistons and a Thomson Drive 15 actuator and a commutation path with a resistive element in parallel;

Fig.7 a perspective view of primary switching element actuated by two pistons;

Fig. 8 a diagram of the performance of a current limiting device;

Fig. 10a, b a schematic illustration of a switch with contacts that dip in a liquid 20 metal reservoir and a Thomson Drive actuator;

Fig 1 1 a,b a schematic top view of primary switching element in closed (a) and opened (b) position with a contact turned by a rotator; Fig. 12a, b a schematic top view of primary switching element in closed (a) and opened (b) position with two movable contacts in series connection 25 and both contacts actuated by one rotator;

Fig. 13 a schematic illustration of primary switching element having several movable contacts arranged in a stack and actuated by one rotator.

The reference symbols used in the figures and their meaning are summarized in the 30 list of reference symbols. Generally, alike or alike-functioning parts are given the same reference symbols. The described embodiments are meant as examples and shall not confine the invention.

Ways to implement the invention

Fig. 1 to Fig. 3 show exemplary schematic diagrams of electric current limiting i o devices comprising opening contacts S of the nominal current path and resistive elements Z_com of commutation paths 13. At no fault condition all contacts S are closed. In case of a fault the contacts are opened simultaneously by means of a Thomson drive 2 and the current commutates to the commutation paths 13. As indicated, the nominal voltage U_N is then split into the voltage drop U_ZN on the line 15 impedance Z_N and the voltage drop Uι_ιm on the current limiting device. Once the current is commutated the commutation path 13 represents an additional impedance in the electric grid. In this way a current limiting device is performed.

Arcing at the fast opening contacts and therefore contact degradation may be 20 avoided by connecting a plurality of contacts in series and by choosing commutation paths with significantly low impedance at current commutation. Thus the voltage drop at each switching contact can be limited to below the minimum arcing voltage of about 20 V.

25 The current limiting device according Fig. 1 comprises the series connection of n fast opening contacts S of the nominal current path with one commutation path element Z_com in parallel each. Fig. 2 shows the implementation of a current limiting device with a series connection of n fast opening contacts S and one single commutation element Z_com connected in parallel to the entire series connection of opening contacts. Fig. 3 exhibits a current limiting device comprising a series connection of m current limiting devices as shown in Fig. 2.

Fig. 4 shows exemplary a current limiting device with an alternating arrangement of 5 T₁ to T_n commutation path contacts and resistive elements Z_com of the commutation path. Under no fault condition contact S₀ of the nominal current path is closed. In case of a fault, contact S₀ opens just after contact T₁ of the commutation path is closed. In the following contact T₂ closes and T₁ opens right afterwards and so on. Thus more and more commutation path elements Z_comi to Z_comn are inserted into the i o electric grid.

The commutation path can contain ordinary resistors, positive temperature coefficient materials (PTC), Thyristors, IGCTs, diodes, vahstors or any other impedance or a combination thereof. The use of PTCs within the commutation path 15 is advantageous.

In the case that a PTC is applied to the commutation path, ceramic, polymer, metallic or any other PTC material may be used. In the moment of current commutation into the PTC, the PTC still has its "low" cold resistance which helps to 20 prevent the opening contacts from arcing (first stage of current limitation). In the following the fault current flows through the PTC and heats it up. The PTC increases its resistance and leads (quasi in a second stage of current limitation) to further significant current limitation.

25 The commutation path may be made from a serial and/ or parallel connection of more than one current path in the way that the commutated current splits up in the different paths or commutates from one to another commutation path.

The electromagnetic repulsion drive is schematically shown in Fig. 5. A charging 30 unit 18 stores energy in a capacitor c. In case of a fault current the discharge switch S_Th is closed and the capacitor C is discharged to the Thomson coil 14. The steep current pulse i_Th through the Thomson coil 14 causes a steep pulse of a magnetic field near to the coil. This magnetic field pulse induces eddy currents in a conductive plate 15 arranged in direct vicinity to the top of the coil. These eddy 5 currents again cause a magnetic field that interacts with the magnetic field of the Thomson coil 14. As a result the conductive element 15 is moved upwards rapidly and therefore drives the primary switching element 1 within the electric current limiting device.

i o Fig. 6 schematically shows an arrangement of the electrical contacts 4a, 4b, 4c, 4d, 5a, 5b, 5c, 5d, 6a, 6b, 6c, 6d of the primary switching element 1 of the electric current limiting device. The primary switching element 1 comprises two pistons 3a, 3b of e.g. of cylindrical shape and made of electric isolating material for example PTFE (polytetrafluoroethylene). Both pistons 3a, 3b are simultaneously driven by

15 the Thomson drive 2. As a result the pistons 3a, 3b are accelerated and move upwards into the support 10 of the primary switching element 1. Thus the primary switching element 1 initiates current commutation within several hundreds of microseconds to a few milliseconds.

20 Within the piston 3a, 3b the nominal current path is established by solid first contacts 4a, 4b, 4c and 4d. The current path and the sliding direction of the pistons 3a and 3b are at an angle, preferred orthogonal. In the embodiment shown in Figure 6 the first solid contacts 4a, 4b, 4c and 4d extends over the diameter of piston 3a and 3b, but does not have the full length of the piston diameter. Therefore

25 the contacts are located within the piston 3a and 3b. To provide electrical contact between the first contacts 4a, 4b, 4c and 4d and its adjacent pair of second contacts 5a 5 b, 5c, 5d, 6a, 6b, 6c and 6d in the closing state of the primary switching element 1 recesses in the piston 3a, 3b are formed that contain reservoirs of liquid metal 8. Two recesses in the piston 3a, 3b are on the opposite sites of each first

30 contact 4a, 4b, 4c and 4d to form a current path over the full diameter of the piston 3a and 3b. The recesses do not have to be necessary in horizontal plane with the first contacts 4a, 4b, 4c and 4d. They can be located above or underneath the horizontal plane formed by the movable first contacts 4a, 4b, 4c and 4d. Important is to provide a current path over the diameter of the piston 3a and 3b in order to 5 establish electrical contact between first and second contacts 4a, 4b, 4c, 4d, 5a 6 b, 5c, 5d, 6a, 6b, 6c, 6d. In other preferred embodiments the recess is a circumferential recess in the piston or in the support of the switch containing the liquid metal reservoir.

i o Series connections between the contacts in different layers are realized by means of a linking conductor 17 between two adjacent second contacts e.g. between 5b and 5c. In this way a meandering of the current path within the switch is performed and the commutation voltage splits up to the sum of voltage drops on all opening contacts. Thus arcing at the opening contacts can be avoided during current

15 commutation in case that an appropriate commutation path is provided.

Optional the contacts 5a 5 b, 5c, 5d, 6a, 6b, 6c and 6d can be connected in parallel in order to increase the current rating of the current limiting device. Thus the number of contact layers can be adapted accordingly to the current and voltage ratings of 20 the current limiting device.

As can be seen in Fig. 6 sealings 9 are provided to keep the device tight and to hinder liquid metal from pouring out when the piston 3a and 3b is actuated within the support 10. Sealings 9 are located below and above each movable first contact 4a, 25 4b, 4c and 4d and can be e.g. performed as a sealing ring surrounding the piston 3a and 3b. Therefore the sealings are contained in circumferential recesses of the piston 3a and 3b.

A single resistive element Z_com e.g. PTC electrically connected to the second 30 contact members 5a and 5d establishes a commutation path 13 in parallel to the nominal current path. In case of fault the nominal current path will be interrupted by opening movement of the pistons 3a, 3b of the primary switching element 1 and the fault current commutates into the PTC Z_com of the commutation path 13.

5 Fig. 7 shows a perspective illustration of the primary switching element 1 as shown in Fig.6. The support 10 is composed of five isolating plates 16 having two central bores of diameter of the pistons 3a, 3b. The fixed second contacts 5a, 5b, 5c, 5d and 6a, 6b, 6c, 6d are guided between two adjacent support plates 16. Optional either the contacts 5a, 5 b, 5c, 5d can be electrically connected to form a parallel i o current path or neighbouring contacts 6a-6b, 5b-5c, 6c-6d can be electrically connected to form a serial current path.

Fig. 8 shows a diagram of the principal performance of a Thomson drive limiter according to the invention. The current I, the voltage U and the resitance R are

15 plotted as function of the time T.

In graph a) the increase and drop down of the Thomson drive 2 current I is plotted. Graph b) shows the limited short circuit current l_hm and graph c) shows the unlimited short circuit current l_Sc- In graph d) the resitance of a Ba TiO3 PTC element is plotted. In graph e) the charctehstic of the voltage drop of the current limiting device

20 is shown.

Fig. 9a and Fig. 9b show an embodiment of primary switching element 1 coupled with an alternating arrangement of contacts 20a-21 a... 20i-21 i and commutation paths elements 12 according to wiring schematic of Fig. 4. The piston 3a is guided

25 in a support 10 which comprises an alternating stacked order of conducting and isolating material, i.e. of commutation path contact members 20a...2Oi; 21 a..21 i and isolating material of the support 10. Neighbouring contact members 20a-20b, ..., 20i-5a and 21 a-21 b,..., 21 i-6a are electrically connected to each other via a commutation path element 12 e. g. a PTC element. The piston 3a carries a single

30 first contact 4a and two liquid metal reservoirs 8 sealed by sealings 9 in order to establish a nominal current path between the second members 5a and 6a and between the commutation path contact members 2Oi and 21 i, ...20a and 20b respectively. The piston 3a is actuated by a Thomson drive 2. Under normal operation conditions nominal current I flows over the contacts 5a and 6a bridged by 5 the first contact 4a being in a first position as it is illustrated in Fig. 9a. In case of a detected fault current the piston 3a is moved by means of the Thomson Drive 2 along the stack of commutation path contact members 20i-21 i,...20a-20a into a transient or steady second position at an elaborated height or plane in the stack. Successively it makes and opens electrical contact between the pair of second i o contacts 20i-21 i... 20a-21 a as shown in Fig. 9b. With increasingly shifted position of the piston 3a an increasing number of commutation path elements 12 are inserted in the electric grid. The increasing shifted position of the piston 3a along 20i-21 i to 20a-21 a corresponds to successive open and close of the switching elements S1 to Sn in Fig.4. A commutation path actuated in such elevator like manner has the

15 advantage that in occurrence of a fault an increasing number of commutation path elements successively are inserted into the commutation path 13.

The capacity of the capacitor for the Thomson Drive in Fig. 6-8 measures typically some millifarads to some tenths of millifarads. The charging voltage is some 20 hundreds to few thousands of volts whereas the number of turns of the Thomson coil is in the single digit order of range. The peak of the current pulse through the Thomson coil is in the kA range and rises within some tenth of microseconds to several hundreds of microseconds. By means of a Thomson Drive contact switching occurs within several hundreds of microseconds to a few milliseconds.

25

The voltage drop Uι_ιm on a medium voltage (MV) electric current limiting device during current limitation measures typically several kV. The resistance of the limiter during limitation measures typically in the range of 100 mOhm or more. In accordance with the embodiments in Fig.6-8 the metallic PTC materials nickel (Ni) or iron-cobalt-nickel alloys as well as the ceramic PTC material BaTiO3 may be used in the commutation path.

Nickel and iron-cobalt-nickel alloys e.g. are metallic PTC with an almost constant 5 resistance coefficient. BaTiO3 is a ceramic PTC with a highly non linear resistance coefficient. BaTiO3 changes its resistivity by orders of magnitude when the so called Curie-temperature is reached. Thus using BaTiO3 within the commutation path of a current limiting device is particularly interesting. It can provide a significant low cold resistance at current commutation in order to prevent arcing at the switching i o contacts. Afterwards it forms a fast increasing impedance in order to limit the commutated current (non linear commutation path).

Alternatively a third or more commutation paths, among others a varistor e. g. (not shown) can be installed which e. g. limits the maximum voltage drop on the PTC.

1 5

Fig. 10a and Fig 10b show another embodiment of simultaneously switching contacts of a primary switching element 1. Several second contacts 5a..5f are permanently fixed in bores within the insulating support 10. Above each second contact 5a..5f within the bores there is a liquid metal reservoir 8. A set of moveable

20 first contacts 4a...4f is inserted into the bores from the opposite side. In the closed position, as shown in Fig. 10a, the first electrical contacts 4a..4f dip into the liquid metal reservoirs 8 and therefore form conducting paths to the second contacts 5a...5f. Under operating conditions the nominal current I flows through the meandering contact arrangement 4a-5a...5a-5f. If a fault occurs the first contacts

25 4a...4f are quickly moved out of the liquid metal reservoir 8 by the piston 3a of a Thomson Drive 2 and an electrically isolating gap is formed between facing first and second contacts 4a-5a,...4f-5f as shown in Fig. 10b. The piston 3d of the embodiment Fig. 10 can be a rod and has the function of an mechanical linkage between the movable contacts 4a,...4f and the actuator which is the Thomson drive

30 2. Sealings 9 on the first and second contacts and/ or within the support are provided to keep the device tight and to hinder liquid metal from pouring out. The current limiting device may me operated under air, in any other atmosphere or under vacuum. In case the current limiting device is not operated under vacuum ventilation holes 22 within the support and/ or the first and/ or the second contacts assure that 5 gas from the surrounding atmosphere can flow into the volume between the liquid metal reservoirs and the second contacts during contact opening.

Fig. 11 a and Fig. 11 b show a top view of primary switching element 1 similar to the embodiment shown in Fig. 6. The nominal current path is established by a pair of i o second contacts 5a and 6a bridged by a first contact 4e as shown in Fig. 11 a. At the interface between adjacent first contact 4e and the second contacts 5a and 6a liquid metal reservoirs 8 provide the electric conductive path. In difference to the embodiment of Fig.6 the first electrical solid contact 4e and the liquid metal reservoirs 8 are contained in a rotator 3c of cylindrical shape. The rotator 3c is

15 actuated by the Thomson drive 2. The linear movement of the repulsion drive is transmitted to the rotary motion of the rotator 3c e.g. by a rack and pinion drive (not shown) or other drive mechanism known in the art. In case of a fault current the rotator 3c is turned as indicated by the arrow and the nominal current path is interrupted (Fig.1 1 b). In Fig. 13 several first contacts 4a arranged in a stack in the

20 rotator 3c and several second contact members 5a, 6a are arranged in a stack in the support 10 allowing by rotation of the rotator 3c a parallel or serial switching of the several contacts arranged of the primary switching element 1.

Fig. 12a and Fig. 12b show a modification of the embodiment of Fig.11. Two first 25 contacts 4e are arranged in the rotator 3c and each of the contacts 4e bridges the second contact member 5a, 6a and 5b, 6b respectively. In this way the commutation voltage splits up to the sum of voltage drops on each opening contact. List of Reference Symbols

1 primary switching element

5 2 repulsion drive, Thomson drive

3a, 3b, 3d piston

3c rotator

4a,b,c,d,e first electrical contact

5a,b,c,d second contact member i o 6a,b,c,d second contact member

8 reservoir of liquid metal

9 sealing

10 isolating support

12 PTC, PTC element, commutation path element

15 13 commutation path

14 coil

15 conductive plate, plunger

16 support plate

17 linking conductor 20 18 charging unit

20a,b,c,d,...i second contact of commutation path

21 a,b,c,d,...i second contact of commutation path

22 ventilation holes

C capacitive element

25 F force lsc short circuit current lι_ιm limited short circuit current i_Th current supplying the Thomson coil

S₀, S-i, ...S_n opening contacts of the nominal current path

30 Scu switch to charge the capacitor S_Th discharge switch for discharging the capacitor

T₁, ...T_n contacts of the commutation path

Uhm voltage drop across all commutation paths

Usi,Uii,...Usnn voltage drop across a component

U-I, ...U_N voltage drop across resitive element Z_comi, - ..ZcomN

U_N nominal voltage

UZN voltage drop across line impedance Z_N

Z_N, Zcomi, Zcomn resistive element, commutation path element

Claims

- 19 -C L A I M S

1 . Electric current limiting device comprising a primary switching element (1 ) 5 having an electromagnetic repulsion drive (2) for actuating an actuation means (3a, 3b, 3c, 3d) and at least one commutation path (13), the primary switching element (1 ) having at least one first electrical contact (4a, 4b, 4c, 4d, 4e) and at least one second electrical contact (5a, 5b, 5c, 5d, 6a, 6b, 6c, 6d), wherein at least the first contact (4a, 4b, 4c, 4d, 4e) is i o a solid electrode (4a, 4b, 4c, 4d, 4e) which can be actuated by the actuation means(3a, 3b, 3c, 3d) in order to force the current to flow through the at least one commutation path (13), characterized in that a reservoir (8) of liquid metal is contained in or alongside of at least one of the contacts (4a-d; 5a-d; 6a-d) such that in an electrically conductive state

15 of the primary switching element (1 ) an electrical current path between the first (4a-4d) and the second contact (5a-5d; 6a-6d) is provided by liquid metal of the reservoir (8).

2. Electric current limiting device according to claim 1 , characterized in that 20 the actuating means (3a, 3b, 3d) is a piston.

3. Electric current limiting device according to claim 1 or 2, characterized in that the liquid metal reservoir (8) is formed on a side of the first contact (4a, 4b, 4c, 4d, 4e) facing the second contact (5a, 5b, 5c, 5d, 6a, 6b, 6c,

25 6d) and/or is formed on a side of the second contact (5a, 5b, 5c, 5d, 6a,

6b, 6c, 6d) facing the first contact (4a, 4b, 4c, 4d, 4e).

4. Electric current limiting device according to one of the claims 2 or 3, characterized in that the form of the reservoir (8) is a recess in the first

30 contact (4a, 4b, 4c, 4d, 4e,) or in the second contact (5a, 5b, 5c, 5d, 6a, - 20 -

6b, 6c, 6d) or in the piston (3a, 3b, 3c).

5. Electric current limiting device according to one of the claims 2 to 4, characterized in that the primary switching element (1 ) comprises a support (10) for electrical current paths connecting the second contacts

(5a, 5b, 5c, 5d, 6a, 6b, 6c, 6d) and a guidance for movably accommodating the piston (3a, 3b), wherein the piston (3a, 3b, 3d) is a rod of electric isolating material and carries the at least first contact (4a, 4b, 4c, 4d) and is slideable along its axis in the guidance of the support (10).

6. Electric current limiting device according to claim 5, characterized in that the electrical current paths in the support (10) and the sliding direction of the piston (3a, 3b, 3d) are at an angle, in particular orthogonal, to each other, and that the piston (3a, 3b) carries several first contacts (4a, 4b, 4c, 4d) arranged in stacks, and the electrical current paths are arranged in the support (10) in corresponding stacks.

7. Current limiting device according to claim 2 and 4 and in particular any of the claims 3, 5 and 6, characterized in that each first contact (4a, 4b, 4c, 4d) comprises the reservoir (8) arranged in the recess in the piston (3a,

3b), and, in particular, that sealings (9) between the piston and the guidance are provided on the piston (3a, 3b) below and above each reservoir (8) for maintaining the liquid metal in each reservoir (8) during piston actuation.

8. Electric current limiting device according to claim 2 and 4 and in particular any of the claims 3, 5 and 6, characterized in that each second contact (5a, 5b, 5c, 5d, 6a, 6b, 6c, 6d) comprises the reservoir (8) arranged in the recess in the support (10), and, in particular, that sealings (9) between the piston and the guidance are provided on the support (10) below and above each reservoir (8) for maintaining the liquid metal in each reservoir - 21 -

(8) during piston actuation.

9. Electric current limiting device according to one of the claims 2 to 9, characterized in that the primary switching element (1 ) comprises pairs of 5 first and second contacts (4a, 4b, 4c, 4d, 5a, 5b, 5c, 5d, 6a, 6b, 6c, 6d) which pairs are connected electrically in series with each other and are arranged in such a way that the piston (3a, 3b, 3d) actuates the first contact members (4a, 4b, 4c, 4d) simultaneously.

i o

1 0. Electric current limiting device according to any of the claims 2 to 9 characterized in that several pistons (3a, 3b, 3c, 3d) are actuated simultaneously by the electromagnetic repulsion drive (2) to form a series and / or parallel connection of the first and the second contact members (4a, 4b, 4c, 4d, 4e, 5a, 5b, 5c, 5d, 6a, 6b, 6c, 6d).

1 5

1 1 . Electric current limiting device according to one of the preceding claims, characterized in that the second electrical contact (5a, 5b, 5c, 5d, 6a, 6b, 6c, 6d) is a solid electrode.

20 1 2. Electric current limiting device according to one of the preceding claims, characterized in that the second contact comprises two contact members (5a-6a; 5b-6b; 5c-6c; 6d-6d) and in that the first contact (4a, 4b, 4c, 4d, 4e) is a bridging contact bridging the two contact members respectively (5a-6a; 5b-6b; 5c-6c; 6d-6d).

25

1 3. Electric current limiting device according to anyone of the claims 2 to 12, characterized in that the first contact members (4a, 4b, 4c, 4d) are arranged in a stack of parallel planes forming the piston (3a), in that pairs of the second contact members (5a, 6a; 5b, 6b; 5c, 6c; 5d, 6d) are 30 arranged in a stack forming a support (10) of parallel planes and in that the piston (3a, 3b) and the stack of second contact members (10) are - 22 -

arranged in movable relation to each other in such a way that in a electrically conductive state each first contact member (4a, 4b, 4c,4d) is in electrical contact with its adjacent pair of the second contact members (5a, 6a; 5b, 6b; 5c, 6c; 5d, 6d).

5

1 4. Electric current limiting device according to one of the preceding claims, characterized in that the primary switching element (1 ) contains the series connection of n opening first and second electrical contact members (5a- 6a; 5b-6b; 5c-6c; 6d-6d) with one electrical element (12) of the i o commutation path (13) in parallel each, wherein n = integer number.

1 5. Electric current limiting device according to one of the preceding claims, characterized in that the primary switching element (1 ) contains a series connection of n opening first and second electrical contact members (5a- 15 6a; 5b-6b; 5c-6c; 6d-6d) , wherein n = integer number, and one single commutation element connected in parallel to the entire series connection of opening contact members (5a-6a; 5b-6b; 5c-6c; 6d-6d).

1 6. Electric current limiting device according to one of the preceding claims, 20 characterized in that the primary switching element (1 ) comprises a series connection of m current limiting devices according to claim 15, wherein m = integer number.

1 7. Electric current limiting device according to one of the preceding claims, 25 characterized in that the commutation path (13), in particular a PTC, is connected in parallel with the primary switching element (1 ) and is providing an electrical current path in case of an electrically non conductive state of the primary switching element (1 ).

30

1 8. Electric current limiting device according to claim 5 and in particular to any - 23 -

of the claims 1 to 4 and 6 to 14, characterized in that a first commutation path (13), is connected in parallel with at least one pair of first and second contacts (4a, 4b, 4c, 4d, 4e, 5a, 5b, 5c, 5d, 6a, 6b, 6c, 6d) and in that a second commutation path (13) is connected in parallel with at least one 5 pair of first and second contacts (4a, 4b, 4c, 4d, 4e, 5a, 5b, 5c, 5d, 6a, 6b,

6c, 6d) and wherein the at least one pair of contacts connected to the first commutation path (13) is different from the at least one pair of contacts connected to the second commutation path (13).

i o

1 9. Electric current limiting device according to anyone of the proceeding claims, characterized in that the primary switching element (1 ) comprises a first contact (4a) and a plurality of pairs of second contacts (20a, 21 a; 20b, 21 b; 20c, 21 c; 2Od, 21 d) arranged in a stack, which pairs provide alternative electrical commutation paths (13) and wherein the means (3a,

15 3b) are moveable such that the first contact (4a) can make contact to at least one of the pairs of second contacts and thereby activates the corresponding commutation path (13).

20. Electric current limiting device according to claim 19, characterized in that 20 neighbouring second contacts (20a, 20b, 20c, 2Od, 2Oe; 21 a, 21 b, 21 c,

21 d, 21 e) are connected to each other via PTC elements (12) in such a way that commutation paths (13) with series connections of the PTC elements (12) are realized.

25 21 . Electric current limiting device according to claim 20, characterized in that the connections between the PTC elements (12) are electrically connected to one of the second contacts (20a, 20b, 20c, 20d,20e; 21 a, 21 b, 21 c, 21 d, 21 e), and that with increasingly shifted position of the piston an increasing number of the PTC elements is present in the active commutation path

30 (13). - 24 -

22. Current limiting electric device according to one of the preceding claims, characterized in that at least one commutation path (13) comprises a varistor.

5 23. Electric current limiting device according to claim 1 , characterized in that the actuating means is a rotator (3c).

24. Electric current limiting device according to claim 23, characterized in that the solid electrode (4e) is carried and rotatable by the rotator (3c) and i o bridges or disconnects the second electrical contacts (5a, 6a; 5b, 6b) depending on the value of the rotation angle of the rotator (3c).

25. Electric current limiting device according to any of the claims 23-24, characterized in that the second contact comprises two contact members

15 (5a, 6a) and in that the first contact (4e) is a bridging contact, which is carried and rotatable by the rotator (3c) and bridges or disconnects the second electrical contacts (5a, 6a; 5b, 6b) depending on the rotation angle of the rotator (3c).

20 26. Electric current limiting device according to any of the claims 23-25, characterized in that the primary switching element (1 ) comprises pairs of first and second contacts (5a, 6a; 5b, 6b) which pairs are connected electrically in series with each other and are arranged in such a way that the rotator (3c) actuates the first contact members (4e) simultaneously.

25

27. Electric current limiting device according to any of the claims 23-26, characterized by the characterizing features of any of the claims 4, 10, 1 1 , 15-20 and 22.

30 28. System comprising an electric current limiting device according to any of the preceding claims and a circuit breaker, characterised in that the circuit -25-

breaker is arranged in series with the electric current limiting device.