Title of Invention	AUTOMATICALLY QUENCHING SURGE ARRESTER ARRANGEMENT AND USE OF SUCH A SURGE ARRESTER ARRANGEMENT
Abstract	The invention relates to an automatically triggering surge arrester arrangement (20) with a surge arrester (22) which, on exceeding a given first voltage, transforms from a non-conducting into a conducting state and returns to the non-conducting state only when a much smaller second voltage is dropped below and with a switch mechanism (26,..31), reacting to current flow through the surge arrester (22), interrupting the current flow through the surge arrester (22) and then automatically returning to the rest condition thereof. A simple, robust and compact assembly suitable for HF applications for such a surge arrester arrangement is achieved, whereby the switch mechanism (26,...31) reacts reversibly to the heat generated in the surge arrester (22) by the current flow.

Title of Invention

AUTOMATICALLY QUENCHING SURGE ARRESTER ARRANGEMENT AND USE OF SUCH A SURGE ARRESTER ARRANGEMENT

Abstract

The invention relates to an automatically triggering surge arrester arrangement (20) with a surge arrester (22) which, on exceeding a given first voltage, transforms from a non-conducting into a conducting state and returns to the non-conducting state only when a much smaller second voltage is dropped below and with a switch mechanism (26,..31), reacting to current flow through the surge arrester (22), interrupting the current flow through the surge arrester (22) and then automatically returning to the rest condition thereof. A simple, robust and compact assembly suitable for HF applications for such a surge arrester arrangement is achieved, whereby the switch mechanism (26,...31) reacts reversibly to the heat generated in the surge arrester (22) by the current flow.

Full Text	FIELD OF INVENTION The present invention relates to an automatically quenching surge arrester arrangement and use of such a surge arrester arrangement. More particularly, this invention relates to the field of electrical protection of electrical devices from permanent damage due to dangerous voltage spikes. BACKGROUND OF THE INVENTION AND PRIOR ART Lightening strikes or other brief phenomena can result in dangerous voltage spikes occurring in electrical and electronic circuits, or on electrical cables, which are connected to exposed apparatuses such as radio antennas, and these can lead to permanent damage to the electrical devices or to a total failure. In order to render such voltage spikes safe, surge arresters of various designs and methods of operation have for a very long time been installed at suitable points on the device to be protected, which are non-conductive in normal circumstances but are switched through when dangerous overvoltages occur, equalizing out the potential differences that occur. One possible type of surge arrester is formed by voltage-dependent resistors, for example metal-oxide varistors (MOVs), which are connected between two conductors between which dangerous voltage spikes can occur. At normal operating voltages, the resistance of the varistors is high, so that only a small leakage current flows between the two conductors. When high voltage spikes occur, the resistance of the varistors decreases drastically, so that the desired equalization current can flow. However, problems result in the case of varistors when greatly increased leakage currents flow in them even in normal conditions as a result of internal changes, which load the circuit to be protected and can lead to changes in their operation. It has therefore already been proposed for a switching device which can be activated thermally to be connected in series with a varistor, which interrupts the current through the varistor as the varistor is heated as a result of a major leakage current, and, as a substitute for this, introduces a spark gap as additional overvoltage protection into the disconnected connection (US-A-4,288,833). The switching device which can be activated thermally is provided by an elastic switching arm which is soldered by one end to the varistor such that it is mechanically prestressed, and which produces an electrical connection to the varistor. When the varistor is heated severely as a result of excessive leakage currents, the solder of the soldered joint melts, and the electrical switching arm is lifted off the varistor by its prestressing, interrupting the current flow through the varistor. As the switching arm is lifted off, a spark gap comes into effect, which is formed between the varistor and the raised switching arm . or conductor tips which are provided specifically for this purpose. This surge arrester arrangement has the disadvantage that the change in the arrangement when the switching device is triggered is irreversible. The switching process of the surge arrester which is provided with an external short-circuit device, from the document DE-A1-197 31 312 is also irreversible, in the same way. If the surge arrester is heated excessively, two insulating spacers melt, so that an elastically prestressed short-circuiting bracket can short the two or three connecting contacts of the surge arrester and can thus take over . the current flow through the surge arrester. Another type of surge arrester is formed by gas capsule arresters, in which an overvoltage results in a gas discharge being triggered in a closed gas-filled capsule with two or three electrodes. These arresters are subject to the problem that, once a gas discharge has been triggered, it is maintained at a comparatively low burning voltage. If, for example, a supply voltage for remote electronics which is greater than or equal to the burning voltage, or a high RF power, is applied during normal operation to the gas capsule arrester which is installed in a circuit or cable, the gas discharge continues to burn after the occurrence of a triggering overvoltage spike, and loads the circuit or cable. Additional irreversible switching devices have also already been proposed for gas capsule arresters, which react to excessive heat being created in the arrester and then permanently interrupt the current supply to the arrester (US-A-4,051,546) or permanently short the arrester by means of a bypass (US-A-3,755,715 or US-A-4,132,915). The thermally activated switching devices can be integrated in the surge arrester (see the abovementioned documents), although they could also be formed separately and can be thermally coupled to the surge arrester from the outside (US-A-4,275,432). Thermally activated, irreversible shorting devices are also known in conjunction with gas capsule arresters for coaxial cables (US-A-5,724,220, Figures 24 and 25). A reversible switching device for interruption of the discharge current through a gas capsule arrester is known from US-A-4,068,277. In this case, a separate contactor is provided, which is equipped with a bimetallic element, operates thermally and whose heating element is connected in series with the arrester. If a discharge, once it has been triggered, remains in existence for a certain time in the arrester, the contactor trips and interrupts the current through the arrester and one line. Once the contactor has cooled down again sufficiently after a relatively long time of, for example, 20-30 seconds, it automatically reconnects the current through the arrester and the one line, thus restoring the initial state. This solution has the disadvantage that a compact and space-saving arrangement is not possible, because of the separate contactor. Furthermore, interruption in one line is unsuitable for applications in which a supply current for other circuit parts is passed via the lines. Surge arrester arrangements which are integrated in a coaxial conductor arrangement for radio frequencies and therefore have to be suitable not only for very high frequencies but should furthermore also be physically compact, functionally reliable, robust and requiring little maintenance, are ' subject to particular requirements. Examples of coaxial conductor arrangements with an integrated surge arrester arrangement but without any additional switching device are disclosed in CH-A5-660 261, EP-A1-0 855 756, or EP-A1-0 938 166 from the same . applicant. In order to allow the gas capsule arresters to be reliably switched to the non-conductive state even when a DC voltage or a radio-frequency signal is applied, in the case of a defect with surge arrester arrangements such as these, WO-A1-2004/032276 from the same applicant proposes an additional switching arrangement, which comprises an inductance, an electromagnetically operated interrupter switch, and a diode. This switching arrangement interacts with a series circuit comprising two identical gas capsule arresters. The configuration and method of operation of the arrangement can be found in the cited document. The switching arrangement which is known from WO-A1-2004/032276 protects the gas capsule arrester reliably against continuous loading, and is automatically reconnected after quenching of the gas discharge in the gas capsule arresters. This arrangement has been proven in practice and can be integrated in coaxial conductor arrangements provided that they are designed from the start for this purpose. FR 2848353 (A1) discloses an overvoltage protection, provided with an electric current interrupter opened by a spring and held closed by a catch. When the temperature exceeds a threshold value a bimetallic strip adjacent to the overvoltage protection bends sufficiently away from the catch to allow the circuit to open. CH 660261 (A5) discloses a surge arrester arrangement which has a radially arranged threaded hole or the attachment of a hollow screw. The screw is located in a cylindrical housing which is provided with an external thread for screw connections. A conventional gas-discharge overvoltage suppressor is inserted into the hollow screw. However, there is an urgent need to have an automatically quenching surge arrester arrangement which can be used in particular over a broad bandwidth, is of simple design and can be produced at low cost, but which can also be retrofitted to existing coaxial conductor arrangements with an integrated surge arrester, as described in CH-A5-660-261, without having to make any physical modifications to the coaxial conductor arrangement itself. DESCRIPTION OF THE INVENTION The object of the invention is thus to create an automatically quenching, broad bandwidth and low-cost surge arrester arrangement, which is of simple and robust design, is highly functionally reliable, can be implemented in an extremely space-saving manner, and in particular can be retrofitted to existing coaxial conductor applications without physical modifications. This is achieved by the totality of the features of claim 1. The essence of the invention is to provide a switching mechanism which responds reversibly to the heat which is produced by the current flow through the surge arrester when a current flows through the surge arrester and interrupts the current flow through the surge arrester, and then automatically returns to its initial state again. In the simplest case, this can be achieved by purely electronic means, for example by using a resistor with a positive temperature coefficient (PTC) or a negative temperature coefficient (NTC) to monitor the heat in the surge arrester, and to interrupt the gas discharge as a result of its change in resistance. The switching mechanism preferably has switching means as well as operating means, which are thermally coupled to the surge arrester, for operation of the switching means, which operating means - in contrast to the melting soldered joints from the prior art - respond reversibly to the heat which is produced by the current flow through the surge arrester. The direct thermal coupling of the operating means to- the surge arrester allows the two to be physically combined, thus resulting in a very compact arrangement. The response of the operating means to the heat which is produced in the surge arrester ensures that the interruption is carried out with a certain delay and only when the arrester is actually subject to a continuous load. When the heating of the arrester decays again after the interruption of the current flow through the surge arrester, the operating means automatically return to their initial state, so that the surge arrester arrangement is ready for use again after a certain time delay. By way of example, memory metals or bimetallic strips may be used as the operating means, which change their shape as a result of being heated and either operate separate switching means or are themselves part of the switching means. One preferred refinement of the invention is distinguished in that the operating means have expansion means which convert the heat produced by the current flow in the surge arrester to a switching movement, by means of thermal expansion. The thermal expansion is a particularly simple, effective, functionally reliable and reproducible mechanism for the production of a switching movement, by means of which the current flow through the arrester can then be interrupted. When the surge arrester subsequently cools down again, the expansion is followed by a contraction, which returns it to the initial state. In principle, the thermal expansion of a gas, of a liquid or of a solid can be used. For simplicity and robustness, it is particularly advantageous, according to one preferred development, for the expansion means to have an expansion body composed of a solid material, whose thermal expansion on a first axis is used as a switching movement. This results in a linear switching movement which can be combined particularly easily with appropriate switching means. In particular, in this case, the thermal expansion of the expansion body on the first axis can be amplified by suitable shaping of the expansion body or by the expansion body material having an anisotropic behavior. One example of suitable shaping is an angled shape in the form of a toggle lever (acting in the opposite direction). The expansion body is preferably composed of a heat-resistant rubber-elastic material, in particular a silicone rubber or a fluoroelastomer, and the expansion body is preferably surrounded by a limiting element, which limits the radial expansion, and thus amplifies the axial expansion. The limiting body limits the thermal expansion radially with respect to the first axis, and results in considerable amplification of the expansion in the direction of the first axis as a result of the "quasi-hydrostatic" behavior of the expansion body. If, according to one development, the expansion body is in the form of a circular disk which is axial with respect to the first axis, and a hollow-cylindrical, coaxial, electrically and thermally insulating insulator sleeve, in particular composed of polytetrafluoroethylene, is provided as the limiting element, this makes it possible to prevent the heat which has flowed into the expansion body flowing away which is not wanted, as a result of the lateral limit. In principle, the current flow through the surge arrester can be interrupted by opening a series-connected switch or by closing a parallel-connected switch. The design of the surge arrester arrangement is particularly simple and compact if the switching means have a switch which is connected in series with the surge arrester and is closed in the initial state, and which is opened when the operating means respond to the heat which is produced by the current flowing through the surge arrester. However, it is also feasible within the scope of the invention for the switching means to have a switch which is connected in parallel with the surge arrester and is open in the initial state, and which is closed when the operating means respond to the heat which is produced by the current flow through the surge arrester. The switch preferably has two metallic contact elements, which are pressed against one another by a spring element and can be disconnected from one another against the pressure of the spring element, with one of the contact elements being connected to the surge arrester arrangement, in particular being soldered to it, and with the operating means and/or the expansion means being arranged between the two contact elements. The contact elements are surface-treated in order to prevent wear, in particular by being coated with silver. The surge arrester arrangement is very simple and is particularly suitable for use in coaxial radio-frequency cables when the surge arrester, the metallic contact elements, the spring element and the operating means and/or the expansion means are arranged one behind the other axially with respect to a first axis in a common housing, when the housing is electrically conductive and is used as a supply line to the surge arrester, and when contact springs are provided in order to make the contact with the housing. The metallic contact elements, the spring element and the operating means and/or the expansion means may in this case be arranged on one side of the surge arrester. However, the metallic contact elements and the operating means and/or the expansion means can also be arranged on one side of the surge arrester, with the spring element being arranged on the other side of the surge arrester. The housing may be in . the form of a housing which is open on one side and can be screwed in. However, it is also feasible for the housing to be in the form of a housing which is open on one side, and for connecting pins for insertion of the surge arrester arrangement into a printed circuit to be provided on the open side of the housing. The surge arrester is preferably in the form of a gas capsule arrester and has a cylindrical shape with electrical connections arranged on the end faces. According to the invention, a surge arrester arrangement in which the surge arrester, the metallic contact elements, the spring elements and the operating means and/or the expansion means are arranged one behind the other coaxially with respect to a first axis in a common housing, in which the housing is electrically conductive and is used as a supply line to the surge arrester, and in which contact springs are provided in order to make the contact with the housing, is used in a coaxial conductor arrangement. In particular, the coaxial conductor arrangement has an inner conductor which runs on a second axis and an outer conductor which coaxially surrounds the inner conductor, with the surge arrester arrangement being attached to the coaxial conductor arrangement with the first axis at right angles to the second axis, in particular being screwed to it, and with the housing being electrically conductively connected to the outer conductor, and with a second supply line to the surge arrester being electrically conductively connected to the inner conductor. Further embodiments are specified in the dependent claims. BRIEF EXPLANATION OF THE FIGURES The invention will be explained in more detail in the following text with reference to exemplary embodiments and in conjunction with the drawing, in which: Fig.1 shows a longitudinal section through a coaxial conductor arrangement having a screwed-in surge arrester arrangement according to one preferred exemplary embodiment of the invention; Fig.2 shows the configuration of the surge arrester arrangement from Figure 1, fitted with a gas capsule; Fig.3 shows a surge arrester arrangement according to another exemplary embodiment of the invention, which is suitable for installation in a printed circuit; Fig. 4 shows an exemplary embodiment, comparable to Figure 3, with axial connecting wires for "flowing" wiring, and Fig. 5 shows a cross section through an expansion body which, by virtue of its shape as a toggle lever, carries out an amplified thermal expansion movement on one axis. APPROACHES TO IMPLEMENTATION OF THE INVENTION Figure 1 shows a longitudinal section through a coaxial conductor arrangement having a screwed-in surge arrester arrangement according to one preferred exemplary embodiment of. the invention. The configuration and external dimensions of the coaxial conductor arrangement 10 shown in Figure 1 are comparable to those of known gas capsule lightening- protection devices, such as those which are marketed by the same applicant and are used in particular in mobile radio base stations. Gas capsule lightening-protection devices such as these normally have an impedance of 50 Q, can be used for frequencies up to several GHz, and can be loaded with single current pulses up to 30kA and . with multiple current pulses up to 20kA. Typical external dimensions are axial lengths of 100 mm and external diameters of about 30 mm. The invention allows gas capsule lightening-protection devices such as these to be fitted retrospectively with a switching device which is suitable for self-quenching, without any need to carry out significant modifications. The coaxial conductor arrangement 10 has a metallic outer conductor 11 (made from surface-treated brass or the like) which is used as a housing at the same time and has a stepped internal diameter, and an inner conductor which is composed of a plurality of inner conductor sections 12,..., 15. The inner conductor 12,..., 15 is arranged and fixed coaxially in the outer conductor 11 by means of insulating holders 16, 17 in the form of disks. The inner conductor sections 14 and 15 at the ends are in the form of slotted bushes and are part of screw-type plug connections. The outer conductor 11 has external threads 18, 19 on it for screw connection. The outer conductor 11 and its internal diameter are enlarged in a central section of the coaxial conductor arrangement 10. An inner conductor section 30 with a reduced external diameter is provided at the same time in this section. A threaded hole 23 is incorporated on one side (at the top in Figure 1) in the outer conductor and/or the housing 11 at right angles to the axis 35 of the coaxial conductor arrangement 10, and a surge arrester arrangement 2 0 according to the invention can be screwed into this threaded hole 23. The surge arrester arrangement 20 contains a (cylindrical) surge arrester 22 which is known per se and is in the form of a two-pole gas capsule arrester or gas discharge arrester, whose cylinder axis is located on the axis 34 of the surge arrester arrangement 20. Gas discharge arresters such as these, available for example from the Epcos Company, have response voltages from 70 V to several kV, and have an arc burning voltage of 10-30 V in the triggered state. The internal resistance in the triggered state falls to values of state) it is > 1 GΩ. The capacitance is only a few pF, and this is particularly advantageous for RF applications. The external dimensions (length x external diameter) are in the order of magnitude of 6 mm x 8 mm. The surge arrester 22 is held detachably in the surge arrester arrangement 20, and has two contact surfaces at the end, which are connected to the internal gas discharge path and are isolated from one another by the ceramic housing in between. The lower free end of the surge arrester 22 is seated in an insulating cup 21. Its lower contact surface rests on an electrically conductive connecting piece 24, which makes contact with the inner conductor section 13 through a hole in the bottom of the insulating cup 21. The surge arrester arrangement 20 illustrated in Figure 1 is shown enlarged in Figure 2 in its own right. This has a housing 25 which is open at the bottom and holds the surge arrester or gas capsule arrester 22 (capsule holder housing) . On the outside, the housing 25 is provided with key surfaces and has a screw thread 32, by means of which it can be screwed into the threaded hole 23 in the outer conductor 11 (Figure 1). Initially, the housing 25 is also designed to be open on the other side, in order that the functional elements 22 and 26, ..., 31 accommodated in the housing can be introduced into the interior of the housing. A bolt 33 is then used to (permanently) close the upper opening. The surge arrester 22, a center contact 30, an expansion body 29, a contact disk 27 with contact springs 28 (which are fitted at the edge on the upper circumference and project upwards) and a spring element 26 in the form of a spring washer are arranged one behind the other - from the bottom upwards - along the axis 34 of the surge arrester arrangement 20 in the housing 25. The center contact 30 has a base plate 40 in the form of a circular disk, on which a cylindrical contact bolt 39 with reduced diameter is integrally formed pointing upwards. The external diameter of the base plate 40 is somewhat larger than the external diameter of the surge arrester 22. By way of example, the center contact 30 is composed of brass and is surface-treated, in particular by being coated with silver, in order to improve the contact characteristics and, in particular, in order to prevent wear. The expansion body 29 is in the form of a circular disk and is preferably composed of a heat-resistant, rubber-elastic material, in particular a silicone rubber or a f luoroelastomer. In the center, it has a coaxial hole 38, whose diameter is matched to that of the contact bolt 39 of the center contact 30. In the assembled state (Figure 2) the center contact 30 with the contact bolt 39 actually passes through the hole 38 in the expansion body 2 9 to such an extent that, at the operating temperature, the end surface of the contact bolt 39 is adjacent to and flush with the upper face of the expansion body 29, and at the same time makes an electrical contact with the lower face of the contact disk 27, which is arranged above the expansion body 29. The circular contact disk 27 is likewise composed of surface-treated, in particular silver-plated, brass. The contact springs 28 which are fitted, distributed over the circumference, to the upper edge of contact disk 27, extend in the axial direction and are bent slightly outwards, make a sliding contact with the inner wall of the housing 25. The housing 25 is at the same time used as a supply line to the surge arrester 22. In order to prevent the center contact 30 and the contact disk 27 from being shorted via the housing 25, the center contact 30 is surrounded on the outside by a coaxial insulator sleeve 31, which also surrounds the expansion body 29 and the lower part of the contact disk 27. The insulator sleeve 31 is in the form of a hollow cylinder and is composed of an electrically and thermally insulating, heat-resistant material, preferably of polytetrafluoroethylene. The insulator sleeve 31 has an outer projection 41 which engages behind an undercut in the housing 25. The center contact 30 with the base plate 40 is itself supported on an undercut 42 in the insulator sleeve 31. The surge arrester 22, whose upper contact surface is soldered to the base plate 40 of the center contact, is thus held in the housing 25. A spring element 2 6 is arranged between the upper face of the contact disk 27 and the housing 25 or the bolt 34 and, in the illustrated example, is in the form of a spring washer, although it may also assume different shapes (cup spring, spiral spring or the like) . The spring element 2 6 and the axial dimensions of the individual components of the surge arrester arrangement 20 are designed such that the contact bolt 39 and the contact disk 27 are pressed against one another, such that they make contact, by spring pretension in the normal state (at the operating temperature). The surge arrester arrangement 20 operates as follows: In the normal state, when the surge arrester 22 has not been triggered and the arrangement is essentially at the operating temperature, the switching contact which is formed by the center contact 30 and the contact disk 27 remains closed. The surge arrester 22 is thus electrically conductively connected at its first end to the. inner conductor section 13, and at its other end via the elements 30, 27, 28 and the housing 25, to the outer conductor 11. If a lightening strike or some other brief voltage pulse which is greater than the triggering voltage of the surge arrester 22 is now applied to the coaxial conductor arrangement 10, the surge arrester 22 is triggered, and the potential difference is largely equalized. When the voltage falls, after the voltage pulse has decayed, back below the burning voltage of the surge arrester 22, the latter is quenched, and resumes the initial state. There is no significant heating of the surge arrester 22 and thus of the expansion body 29. If, in contrast, a voltage which is above the burning voltage still remains on the surge arrester 22 even after the voltage pulse has decayed, with currents still flowing through the surge arrester 22, this current produces heat as a result of the internal resistance of the arrester, leading to heating of the surge arrester 22. The heat which is created in the surge arrester 22 flows axially via the base plate 40 and radially via the contact bolt 39 of the center contact 30 into the expansion body 29, heats the latter and results in thermal expansion with a rapid radial outflow of the heat into the housing 25 being prevented by the thermally insulating insulator sleeve 31. In this case, the thermal expansion of the expansion body 29 takes place virtually exclusively in the axial direction, because the expansion body 29 is bounded by the insulator sleeve 31 in the radial direction and the pressure which is created by this constriction acts in the axial direction owing to the "quasi-hydrostatic" material characteristics of the expansion body 29. This results in the expansion body 29 expanding axially by more than 3 times the isotropic expansion, thus representing a considerable amplification effect. Provided that a sufficiently high temperature of, for example, 100°C or more has been reached, the axial thermal expansion of the expansion body 2 9 between the two contacts 30 and 37 results in the two contacts being disconnected from one another, against . the pressure of the spring element 26. When the contacts 30 and 27 are disconnected, the current flow through the surge arrester 22 and thus also 'the heat that is produced are interrupted (self-quenching). As soon as sufficient heat has flowed out of the expansion body 29 again after the interruption and the expansion body 29 has cooled down and contracted again, the switch which is formed from the center contact 30 and the contact disk 27 is closed again, and returns to the initial state. It is self-evident that the described switching process operates better the greater the thermal coefficient of expansion of the material used for the expansion body 29. At the same time, however, the material should also be thermally resistant up to temperatures > 200 °C and should have sufficient resistance to ageing. Finally, it should also have advantageous dielectric characteristics for use in the coaxial cable arrangement. The dielectric characteristics of the expansion body 29 are particularly important when the aim is to retrospectively install a switching device such as this in a coaxial lightening-protection device which is equipped with a surge arrester without a self- quenching switching device, as is advantageously possible in the case of the surge arrester arrangement according to the invention. Various measurements have been carried out in the laboratory with a coaxial conducting arrangement and a surge arrester arrangement as shown in Figure 1, using gas capsule arresters of the type described above with triggering voltages of 230 V and 90 V. Pulses of 4 kV/2kA (in accordance with IEC 61000-4-5) resulted in capsule burning times in the order of magnitude of 10 s to 20 s, and reactivation times in the order of magnitude of 1-2 minutes. However, the surge arrester arrangement according to the invention may not only be advantageously used in conjunction with a coaxial conductor arrangement of the type shown in Figure 1, but can also be used whenever gas capsule arresters are used for over voltage protection. For example, it is normal practice to solder gas capsule arresters which are equipped with connecting wires or solder pins (see DE-Al-197 31 312) into printed circuits. Figure 3 shows a comparable surge arrester arrangement that has been modified according to the invention. The surge arrester arrangement 46 in Figure 3 has a surge arrester 22 in the form of a gas capsule, which is accommodated in a housing 43 which is open on one side. The series- connected switching device in turn comprises the center contact 30, which is soldered to the capsule 22, the expansion body 29, which is in the form of a disk, and a contact plate 36, and these items are isolated from the housing 43 by an insulation sleeve 31'. The switching device is in this case arranged underneath the surge arrester 22, while the contact springs 28 with the contact disk 27 are located above the surge arrester 22. On one side (at the bottom), the surge arrester 22 is connected via central connecting means 45 and the switch 30, 36. On the other side (at the top) , the connection is provided via the outer connecting means 44, the housing 43 and the contact disk 27 with the contact springs 28. The connecting means 44, 45 can advantageously be used for connection of the surge arrester arrangement 46 in a printed circuit. However, it is also feasible within the scope of the invention in the case of a surge arrester arrangement of the type illustrated in Figure 3 to provide axial (or also radial) connecting wires 37 on both sides, instead of the connecting means 44, 45 arranged on one side, as is shown in Figure 4. The surge arrester arrangement 46 can thus be provided with "flowing" wiring, that is to say it can be installed in any desired circuit. It is also feasible within the scope of the invention, instead of using the flat expansion body 29 in the form of a circular disk as described above, to use an expansion ' body which carries out an amplified thermal expansion movement by virtue of its special shape or the fact that its material has an anisotropic behavior. One example of a specially shaped expansion body is shown in Figure 5. The expansion body 4 8 in Figure 5 uses the mechanical principle of a toggle lever by being formed either as a conically shaped disk or as a strip with a bend in the center. The outer edge of the expansion body 48 is supported on an opposing bearing 47. Thermal expansion as indicated by the double-headed arrows in Figure 5 results, because of the special shaping, in a reverse toggle-lever effect, that is to say an amplified thermal expansion movement on the axis 34 (arrow), which can advantageously be used as a switching movement. LIST OF REFERENCE SYMBOLS 10 Coaxial conductor arrangement 11 Outer conductor (housing) 12,...,15 Inner conductor section 16,17 Holder 18,19 External thread 20,46 Surge arrester arrangement 21 Insulating cup 22 Surge arrester (gas capsule arrester) 23 Threaded hole 24 Connecting piece 25 Housing (capsule holder housing) 26 Spring element (spring washer) 27 Contact disk 28 Contact spring 29,48 Expansion body 30 Center contact 31,31' Insulator sleeve 32 Screw thread 33 Bolt 34 Axis (expansion body) 35 Axis (coaxial conductor arrangement) 36 Contact plate. 37 Connecting wire 38 Hole 39 Contact bolt 40 Baseplate 41 Projection 42 Undercut 43 Housing 44,45 Connecting means 47 Opposing bearing WE CLAIM 1. An automatically quenching surge arrester arrangement (20,46) having a surge arrester (22), which changes from a non-conductive state to a conductive state when a predetermined first voltage is exceeded and returns to the non-conductive state only when a very much lower second voltage is undershot, and having a switching mechanism (26, , 31, 31'), which responds when a current flows through the surge arrester (22) and interrupts the current flow through the surge arrester (22), and then automatically returns to its initial state again, characterized in that the switching mechanism (26, 31) responds reversibly to the heat which is produced by the current flow in the surge arrester (22). 2. The surge arrester arrangement as claimed in claim 1, wherein the switching mechanism (26, 31, 31') has switching means (26, 27, 30 and 26, 30, 36), as well as operating means (29, 31, 31',48) which are thermally coupled to the surge arrester (22) for operation of the switching means (26, 27, 30 and 26, 30, 36), with the operating means (29, 31, 31', 48) responding reversibly to the heat which is produced by the current flow in the surge arrester (22). 3. The surge arrester arrangement as claimed in claim 2, wherein the operating means (29, 31, 31') have expansion means (29,48) which convert the heat produced by the current flow in the surge arrester (22) to a switching movement, by means of thermal expansion. 4. The surge arrester arrangement as claimed in claim 3, wherein the expansion means have an expansion body (29, 48) composed of a solid material, whose thermal expansion on a first axis (34) is used as a switching movement. 5. The surge arrester arrangement as claimed in claim 4, wherein the expansion body (29) is composed of heat-resistant rubber-elastic material, in particular a silicone rubber or a fluoroelastomer, and in that the expansion body (29) is surrounded by a limiting element (31, 31'), which limits the radial expansion, and thus amplifies the axial expansion. 6. The surge arrester arrangement as claimed in claim 5, wherein the expansion body (29) is in the form of a circular disk which is axial with respect to the first axis (34), and a hollow-cylindrical, co-axial, electrically and thermally insulating insulator sleeve (31,31'), in particular composed of polytetrafluoroethylene, is provided as the limiting element. 7. The surge arrester arrangement as claimed in one of claims 1 to 6, wherein the switching means have a switch (27,30 or 30, 36), which is connected in series with the surge arrester (22) and is closed in the initial state, and which is opened when the operating means (29,31,31') respond to the heat which is produced by the current flow in the surge arrester (22). 8. The surge arrester arrangement as claimed in one of claims 1 to 6, wherein the switching means have a switch which is connected in parallel with the surge arrester (22) and is open in the initial state, and which is closed when the operating means respond to the heat which is produced by the current flow in the surge arrester (22). 9. The surge arrester arrangement as claimed in claim 7, wherein the switch has two metallic contact elements (27, 30 and 30, 36), which are pressed against one another by a spring element (26) and can be separated from one another against the pressure of the spring element (26), in that one of the contact elements (30) is connected, in particular soldered, to the surge arrester arrangement (22), and in that the operating means (29,31,31') and/or the expansion means (29) are/is arranged between the two contact elements (27,30 and 30, 3'6). 10. The surge arrester arrangement as claimed in claim 9, wherein the contact elements (27, 30 and 30, 36) are surface-treated, in particular being coated with silver. 11. The surge arrester arrangement as claimed in claim 9 or 10, wherein the surge arrester (22), the metallic contact elements (27,30 and 30, 36), the spring element (26) and the operating means (29, 31, 31') and/or the expansion means (29) are arranged one behind the other axially with respect to a first axis (34) in a common housing (25,43), in that the housing (25,43) is electrically conductive and is used as a supply line to the surge arrester (22), and in that contact springs (28) are provided in order to produce the contact with the housing (25,43). 12. The surge arrester arrangement as claimed in claim 11, wherein the metallic contact elements (27,30 and 30, 36), the spring element (26) and the operating means (29,31, 31') and/or the expansion means (29) are arranged on one side of the surge arrester (22). 13. The surge arrester arrangement as claimed in claim 11 or 12, wherein the housing (25, 25') is in the form of a housing which is open on one side can be screwed in. 14. The surge arrester arrangement as claimed in claim 11, wherein the metallic contact elements (27,30 and 30, 36) and the operating means (29,31, 31') and/or the expansion means (29) are arranged on one side of the surge arrester (22), and the spring element (26) is arranged on the other side of the surge arrester (22). 15. The surge arrester arrangement as claimed in claim 11 or 14, wherein connecting means (37, 44, 45) for connection of the surge arrester arrangement (46) in a circuit, in particular a printed circuit, are provided on the housing (43). 16. The surge arrester arrangement as claimed in one of claims 9 to 15, wherein the spring element (26) is a spring washer. 17. The surge arrester arrangement as claimed in one of claims 1 to 16, wherein the surge arrester (22) is a gas capsule arrester and has a cylindrical shape with electrical connections arranged on the end faces. 18. The surge arrester arrangement as claimed in claim 1, wherein the switching mechanism has a resistance element with a positive or negative temperature coefficient (PTC or NTC). 19. The surge arrester arrangement as claimed in claim 1, wherein the switching mechanism has a bimetallic or memory-metal element. 20. The surge arrester arrangement as claimed in claim 3, wherein the expansion means are in the form of a gas or a liquid whose thermal expansion is used to produce a switching element. 21. The surge arrester arrangement as claimed in claim 4, wherein the thermal expansion of the expansion body (48) on the first axis (34) is amplified by suitable shaping of the expansion body. 22. The surge arrester arrangement as claimed in claim 4, wherein the thermal expansion of the expansion body on the first axis (34) is amplified by the expansion body material having an anisotropic behavior. ABSTRACT AUTOMATICALLY QUENCHING SURGE ARRESTER ARRANGEMENT AND USE OF SUCH A SURGE ARRESTER ARRANGEMENT The invention relates to an automatically triggering surge arrester arrangement (20) with a surge arrester (22) which, on exceeding a given first voltage, transforms from a non-conducting into a conducting state and returns to the non-conducting state only when a much smaller second voltage is dropped below and with a switch mechanism (26,..31), reacting to current flow through the surge arrester (22), interrupting the current flow through the surge arrester (22) and then automatically returning to the rest condition thereof. A simple, robust and compact assembly suitable for HF applications for such a surge arrester arrangement is achieved, whereby the switch mechanism (26,...31) reacts reversibly to the heat generated in the surge arrester (22) by the current flow.

Full Text

FIELD OF INVENTION
The present invention relates to an automatically quenching surge arrester
arrangement and use of such a surge arrester arrangement. More particularly,
this invention relates to the field of electrical protection of electrical devices
from permanent damage due to dangerous voltage spikes.
BACKGROUND OF THE INVENTION AND PRIOR ART
Lightening strikes or other brief phenomena can result in dangerous voltage
spikes occurring in electrical and electronic circuits, or on electrical cables,
which are connected to exposed apparatuses such as radio antennas, and
these can lead to permanent damage to the electrical devices or to a total
failure. In order to render such voltage spikes safe, surge arresters of various
designs and methods of operation have for a very long time been installed at
suitable points on the device to be protected, which are non-conductive in
normal circumstances but are switched through when dangerous overvoltages
occur, equalizing out the potential differences that occur.
One possible type of surge arrester is formed by voltage-dependent resistors,
for example metal-oxide varistors (MOVs), which are connected between two
conductors between which dangerous voltage spikes can occur. At normal
operating voltages, the resistance of the varistors is high, so that only a small
leakage current flows between the two conductors. When high voltage spikes
occur, the resistance of the varistors

decreases drastically, so that the desired equalization
current can flow. However, problems result in the case
of varistors when greatly increased leakage currents
flow in them even in normal conditions as a result of
internal changes, which load the circuit to be
protected and can lead to changes in their operation.
It has therefore already been proposed for a switching
device which can be activated thermally to be connected
in series with a varistor, which interrupts the current
through the varistor as the varistor is heated as a
result of a major leakage current, and, as a substitute
for this, introduces a spark gap as additional
overvoltage protection into the disconnected connection
(US-A-4,288,833). The switching device which can be
activated thermally is provided by an elastic switching
arm which is soldered by one end to the varistor such
that it is mechanically prestressed, and which produces
an electrical connection to the varistor. When the
varistor is heated severely as a result of excessive
leakage currents, the solder of the soldered joint
melts, and the electrical switching arm is lifted off
the varistor by its prestressing, interrupting the
current flow through the varistor. As the switching arm
is lifted off, a spark gap comes into effect, which is
formed between the varistor and the raised switching
arm . or conductor tips which are provided specifically
for this purpose. This surge arrester arrangement has
the disadvantage that the change in the arrangement
when the switching device is triggered is irreversible.
The switching process of the surge arrester which is
provided with an external short-circuit device, from
the document DE-A1-197 31 312 is also irreversible, in
the same way. If the surge arrester is heated
excessively, two insulating spacers melt, so that an
elastically prestressed short-circuiting bracket can
short the two or three connecting contacts of the surge
arrester and can thus take over . the current flow
through the surge arrester.

Another type of surge arrester is formed by gas capsule
arresters, in which an overvoltage results in a gas
discharge being triggered in a closed gas-filled
capsule with two or three electrodes. These arresters
are subject to the problem that, once a gas discharge
has been triggered, it is maintained at a comparatively
low burning voltage. If, for example, a supply voltage
for remote electronics which is greater than or equal
to the burning voltage, or a high RF power, is applied
during normal operation to the gas capsule arrester
which is installed in a circuit or cable, the gas
discharge continues to burn after the occurrence of a
triggering overvoltage spike, and loads the circuit or
cable. Additional irreversible switching devices have
also already been proposed for gas capsule arresters,
which react to excessive heat being created in the
arrester and then permanently interrupt the current
supply to the arrester (US-A-4,051,546) or permanently
short the arrester by means of a bypass (US-A-3,755,715
or US-A-4,132,915). The thermally activated switching
devices can be integrated in the surge arrester (see
the abovementioned documents), although they could also
be formed separately and can be thermally coupled to
the surge arrester from the outside (US-A-4,275,432).
Thermally activated, irreversible shorting devices are
also known in conjunction with gas capsule arresters
for coaxial cables (US-A-5,724,220, Figures 24 and 25).
A reversible switching device for interruption of the
discharge current through a gas capsule arrester is
known from US-A-4,068,277. In this case, a separate
contactor is provided, which is equipped with a
bimetallic element, operates thermally and whose
heating element is connected in series with the
arrester. If a discharge, once it has been triggered,
remains in existence for a certain time in the
arrester, the contactor trips and interrupts the

current through the arrester and one line. Once the
contactor has cooled down again sufficiently after a
relatively long time of, for example, 20-30 seconds, it
automatically reconnects the current through the
arrester and the one line, thus restoring the initial
state. This solution has the disadvantage that a
compact and space-saving arrangement is not possible,
because of the separate contactor. Furthermore,
interruption in one line is unsuitable for applications
in which a supply current for other circuit parts is
passed via the lines.
Surge arrester arrangements which are integrated in a
coaxial conductor arrangement for radio frequencies and
therefore have to be suitable not only for very high
frequencies but should furthermore also be physically
compact, functionally reliable, robust and requiring
little maintenance, are ' subject to particular
requirements.
Examples of coaxial conductor arrangements with an
integrated surge arrester arrangement but without any
additional switching device are disclosed in CH-A5-660
261, EP-A1-0 855 756, or EP-A1-0 938 166 from the same .
applicant. In order to allow the gas capsule arresters
to be reliably switched to the non-conductive state
even when a DC voltage or a radio-frequency signal is
applied, in the case of a defect with surge arrester
arrangements such as these, WO-A1-2004/032276 from the
same applicant proposes an additional switching
arrangement, which comprises an inductance, an
electromagnetically operated interrupter switch, and a
diode. This switching arrangement interacts with a
series circuit comprising two identical gas capsule
arresters. The configuration and method of operation of
the arrangement can be found in the cited document.

The switching arrangement which is known from WO-A1-2004/032276
protects the gas capsule arrester reliably against continuous loading, and is
automatically reconnected after quenching of the gas discharge in the gas
capsule arresters. This arrangement has been proven in practice and can be
integrated in coaxial conductor arrangements provided that they are designed
from the start for this purpose.
FR 2848353 (A1) discloses an overvoltage protection, provided with an electric
current interrupter opened by a spring and held closed by a catch. When the
temperature exceeds a threshold value a bimetallic strip adjacent to the
overvoltage protection bends sufficiently away from the catch to allow the
circuit to open.
CH 660261 (A5) discloses a surge arrester arrangement which has a radially
arranged threaded hole or the attachment of a hollow screw. The screw is
located in a cylindrical housing which is provided with an external thread for
screw connections. A conventional gas-discharge overvoltage suppressor is
inserted into the hollow screw.
However, there is an urgent need to have an automatically quenching surge
arrester arrangement which can be used in particular over a broad bandwidth,
is of simple design and can be produced at low cost, but which can also be
retrofitted to existing coaxial conductor arrangements with an integrated surge
arrester, as described in CH-A5-660-261, without having to make any physical
modifications to the coaxial conductor arrangement itself.
DESCRIPTION OF THE INVENTION
The object of the invention is thus to create an automatically quenching, broad
bandwidth and low-cost surge arrester arrangement, which is of simple and
robust design, is highly functionally reliable, can be implemented in an
extremely space-saving manner, and in particular can be retrofitted to existing
coaxial conductor applications without physical modifications.
This is achieved by the totality of the features of claim 1. The essence of the
invention is to provide a switching mechanism which responds reversibly to the
heat which is produced by the current flow through the surge arrester when a
current flows through the surge arrester and interrupts the current flow
through the surge arrester, and then automatically returns to its initial state
again. In the simplest case, this can be achieved by purely electronic means,
for example by

using a resistor with a positive temperature
coefficient (PTC) or a negative temperature coefficient
(NTC) to monitor the heat in the surge arrester, and to
interrupt the gas discharge as a result of its change
in resistance.
The switching mechanism preferably has switching means
as well as operating means, which are thermally coupled
to the surge arrester, for operation of the switching
means, which operating means - in contrast to the
melting soldered joints from the prior art - respond
reversibly to the heat which is produced by the current
flow through the surge arrester. The direct thermal
coupling of the operating means to- the surge arrester
allows the two to be physically combined, thus
resulting in a very compact arrangement. The response
of the operating means to the heat which is produced in
the surge arrester ensures that the interruption is
carried out with a certain delay and only when the
arrester is actually subject to a continuous load. When
the heating of the arrester decays again after the
interruption of the current flow through the surge
arrester, the operating means automatically return to
their initial state, so that the surge arrester
arrangement is ready for use again after a certain time
delay.
By way of example, memory metals or bimetallic strips
may be used as the operating means, which change their
shape as a result of being heated and either operate
separate switching means or are themselves part of the
switching means. One preferred refinement of the
invention is distinguished in that the operating means
have expansion means which convert the heat produced by
the current flow in the surge arrester to a switching
movement, by means of thermal expansion. The thermal
expansion is a particularly simple, effective,
functionally reliable and reproducible mechanism for

the production of a switching movement, by means of
which the current flow through the arrester can then be
interrupted. When the surge arrester subsequently cools
down again, the expansion is followed by a contraction,
which returns it to the initial state.
In principle, the thermal expansion of a gas, of a
liquid or of a solid can be used. For simplicity and
robustness, it is particularly advantageous, according
to one preferred development, for the expansion means
to have an expansion body composed of a solid material,
whose thermal expansion on a first axis is used as a
switching movement. This results in a linear switching
movement which can be combined particularly easily with
appropriate switching means. In particular, in this
case, the thermal expansion of the expansion body on
the first axis can be amplified by suitable shaping of
the expansion body or by the expansion body material
having an anisotropic behavior. One example of suitable
shaping is an angled shape in the form of a toggle
lever (acting in the opposite direction).
The expansion body is preferably composed of a
heat-resistant rubber-elastic material, in particular a
silicone rubber or a fluoroelastomer, and the expansion
body is preferably surrounded by a limiting element,
which limits the radial expansion, and thus amplifies
the axial expansion. The limiting body limits the
thermal expansion radially with respect to the first
axis, and results in considerable amplification of the
expansion in the direction of the first axis as a
result of the "quasi-hydrostatic" behavior of the
expansion body.
If, according to one development, the expansion body is
in the form of a circular disk which is axial with
respect to the first axis, and a hollow-cylindrical,
coaxial, electrically and thermally insulating

insulator sleeve, in particular composed of
polytetrafluoroethylene, is provided as the limiting
element, this makes it possible to prevent the heat
which has flowed into the expansion body flowing away
which is not wanted, as a result of the lateral limit.
In principle, the current flow through the surge
arrester can be interrupted by opening a
series-connected switch or by closing a
parallel-connected switch. The design of the surge
arrester arrangement is particularly simple and compact
if the switching means have a switch which is connected
in series with the surge arrester and is closed in the
initial state, and which is opened when the operating
means respond to the heat which is produced by the
current flowing through the surge arrester. However, it
is also feasible within the scope of the invention for
the switching means to have a switch which is connected
in parallel with the surge arrester and is open in the
initial state, and which is closed when the operating
means respond to the heat which is produced by the
current flow through the surge arrester.
The switch preferably has two metallic contact
elements, which are pressed against one another by a
spring element and can be disconnected from one another
against the pressure of the spring element, with one of
the contact elements being connected to the surge
arrester arrangement, in particular being soldered to
it, and with the operating means and/or the expansion
means being arranged between the two contact elements.
The contact elements are surface-treated in order to
prevent wear, in particular by being coated with
silver.
The surge arrester arrangement is very simple and is
particularly suitable for use in coaxial
radio-frequency cables when the surge arrester, the

metallic contact elements, the spring element and the
operating means and/or the expansion means are arranged
one behind the other axially with respect to a first
axis in a common housing, when the housing is
electrically conductive and is used as a supply line to
the surge arrester, and when contact springs are
provided in order to make the contact with the housing.
The metallic contact elements, the spring element and
the operating means and/or the expansion means may in
this case be arranged on one side of the surge
arrester.
However, the metallic contact elements and the
operating means and/or the expansion means can also be
arranged on one side of the surge arrester, with the
spring element being arranged on the other side of the
surge arrester.
The housing may be in . the form of a housing which is
open on one side and can be screwed in. However, it is
also feasible for the housing to be in the form of a
housing which is open on one side, and for connecting
pins for insertion of the surge arrester arrangement
into a printed circuit to be provided on the open side
of the housing.
The surge arrester is preferably in the form of a gas
capsule arrester and has a cylindrical shape with
electrical connections arranged on the end faces.
According to the invention, a surge arrester
arrangement in which the surge arrester, the metallic
contact elements, the spring elements and the operating
means and/or the expansion means are arranged one
behind the other coaxially with respect to a first axis
in a common housing, in which the housing is
electrically conductive and is used as a supply line to

the surge arrester, and in which contact springs are
provided in order to make the contact with the housing,
is used in a coaxial conductor arrangement.
In particular, the coaxial conductor arrangement has an
inner conductor which runs on a second axis and an
outer conductor which coaxially surrounds the inner
conductor, with the surge arrester arrangement being
attached to the coaxial conductor arrangement with the
first axis at right angles to the second axis, in
particular being screwed to it, and with the housing
being electrically conductively connected to the outer
conductor, and with a second supply line to the surge
arrester being electrically conductively connected to
the inner conductor.
Further embodiments are specified in the dependent
claims.
BRIEF EXPLANATION OF THE FIGURES
The invention will be explained in more detail in the
following text with reference to exemplary embodiments
and in conjunction with the drawing, in which:
Fig.1 shows a longitudinal section through a coaxial
conductor arrangement having a screwed-in surge
arrester arrangement according to one preferred
exemplary embodiment of the invention;
Fig.2 shows the configuration of the surge arrester
arrangement from Figure 1, fitted with a gas
capsule;
Fig.3 shows a surge arrester arrangement according to
another exemplary embodiment of the invention,
which is suitable for installation in a printed
circuit;

Fig. 4 shows an exemplary embodiment, comparable to
Figure 3, with axial connecting wires for
"flowing" wiring, and
Fig. 5 shows a cross section through an expansion body
which, by virtue of its shape as a toggle
lever, carries out an amplified thermal
expansion movement on one axis.
APPROACHES TO IMPLEMENTATION OF THE INVENTION
Figure 1 shows a longitudinal section through a coaxial
conductor arrangement having a screwed-in surge
arrester arrangement according to one preferred
exemplary embodiment of. the invention. The
configuration and external dimensions of the coaxial
conductor arrangement 10 shown in Figure 1 are
comparable to those of known gas capsule lightening-
protection devices, such as those which are marketed by
the same applicant and are used in particular in mobile
radio base stations. Gas capsule lightening-protection
devices such as these normally have an impedance of
50 Q, can be used for frequencies up to several GHz,
and can be loaded with single current pulses up to 30kA
and . with multiple current pulses up to 20kA. Typical
external dimensions are axial lengths of 100 mm and
external diameters of about 30 mm. The invention allows
gas capsule lightening-protection devices such as these
to be fitted retrospectively with a switching device
which is suitable for self-quenching, without any need
to carry out significant modifications.
The coaxial conductor arrangement 10 has a metallic
outer conductor 11 (made from surface-treated brass or
the like) which is used as a housing at the same time
and has a stepped internal diameter, and an inner
conductor which is composed of a plurality of inner

conductor sections 12,..., 15. The inner conductor
12,..., 15 is arranged and fixed coaxially in the outer
conductor 11 by means of insulating holders 16, 17 in
the form of disks. The inner conductor sections 14 and
15 at the ends are in the form of slotted bushes and
are part of screw-type plug connections. The outer
conductor 11 has external threads 18, 19 on it for
screw connection. The outer conductor 11 and its
internal diameter are enlarged in a central section of
the coaxial conductor arrangement 10. An inner
conductor section 30 with a reduced external diameter
is provided at the same time in this section. A
threaded hole 23 is incorporated on one side (at the
top in Figure 1) in the outer conductor and/or the
housing 11 at right angles to the axis 35 of the
coaxial conductor arrangement 10, and a surge arrester
arrangement 2 0 according to the invention can be
screwed into this threaded hole 23.
The surge arrester arrangement 20 contains a
(cylindrical) surge arrester 22 which is known per se
and is in the form of a two-pole gas capsule arrester
or gas discharge arrester, whose cylinder axis is
located on the axis 34 of the surge arrester
arrangement 20. Gas discharge arresters such as these,
available for example from the Epcos Company, have
response voltages from 70 V to several kV, and have an
arc burning voltage of 10-30 V in the triggered state.
The internal resistance in the triggered state falls to
values of state) it is > 1 GΩ. The capacitance is only a few pF,
and this is particularly advantageous for RF
applications. The external dimensions (length x
external diameter) are in the order of magnitude of
6 mm x 8 mm.
The surge arrester 22 is held detachably in the surge
arrester arrangement 20, and has two contact surfaces

at the end, which are connected to the internal gas
discharge path and are isolated from one another by the
ceramic housing in between. The lower free end of the
surge arrester 22 is seated in an insulating cup 21.
Its lower contact surface rests on an electrically
conductive connecting piece 24, which makes contact
with the inner conductor section 13 through a hole in
the bottom of the insulating cup 21.
The surge arrester arrangement 20 illustrated in Figure
1 is shown enlarged in Figure 2 in its own right. This
has a housing 25 which is open at the bottom and holds
the surge arrester or gas capsule arrester 22 (capsule
holder housing) . On the outside, the housing 25 is
provided with key surfaces and has a screw thread 32,
by means of which it can be screwed into the threaded
hole 23 in the outer conductor 11 (Figure 1).
Initially, the housing 25 is also designed to be open
on the other side, in order that the functional
elements 22 and 26, ..., 31 accommodated in the housing
can be introduced into the interior of the housing. A
bolt 33 is then used to (permanently) close the upper
opening.
The surge arrester 22, a center contact 30, an
expansion body 29, a contact disk 27 with contact
springs 28 (which are fitted at the edge on the upper
circumference and project upwards) and a spring element
26 in the form of a spring washer are arranged one
behind the other - from the bottom upwards - along the
axis 34 of the surge arrester arrangement 20 in the
housing 25. The center contact 30 has a base plate 40
in the form of a circular disk, on which a cylindrical
contact bolt 39 with reduced diameter is integrally
formed pointing upwards. The external diameter of the
base plate 40 is somewhat larger than the external
diameter of the surge arrester 22. By way of example,
the center contact 30 is composed of brass and is

surface-treated, in particular by being coated with
silver, in order to improve the contact characteristics
and, in particular, in order to prevent wear.
The expansion body 29 is in the form of a circular disk
and is preferably composed of a heat-resistant,
rubber-elastic material, in particular a silicone
rubber or a f luoroelastomer. In the center, it has a
coaxial hole 38, whose diameter is matched to that of
the contact bolt 39 of the center contact 30. In the
assembled state (Figure 2) the center contact 30 with
the contact bolt 39 actually passes through the hole 38
in the expansion body 2 9 to such an extent that, at the
operating temperature, the end surface of the contact
bolt 39 is adjacent to and flush with the upper face of
the expansion body 29, and at the same time makes an
electrical contact with the lower face of the contact
disk 27, which is arranged above the expansion body 29.
The circular contact disk 27 is likewise composed of
surface-treated, in particular silver-plated, brass.
The contact springs 28 which are fitted, distributed
over the circumference, to the upper edge of contact
disk 27, extend in the axial direction and are bent
slightly outwards, make a sliding contact with the
inner wall of the housing 25. The housing 25 is at the
same time used as a supply line to the surge arrester
22. In order to prevent the center contact 30 and the
contact disk 27 from being shorted via the housing 25,
the center contact 30 is surrounded on the outside by a
coaxial insulator sleeve 31, which also surrounds the
expansion body 29 and the lower part of the contact
disk 27. The insulator sleeve 31 is in the form of a
hollow cylinder and is composed of an electrically and
thermally insulating, heat-resistant material,
preferably of polytetrafluoroethylene. The insulator
sleeve 31 has an outer projection 41 which engages
behind an undercut in the housing 25. The center

contact 30 with the base plate 40 is itself supported
on an undercut 42 in the insulator sleeve 31. The surge
arrester 22, whose upper contact surface is soldered to
the base plate 40 of the center contact, is thus held
in the housing 25.
A spring element 2 6 is arranged between the upper face
of the contact disk 27 and the housing 25 or the bolt
34 and, in the illustrated example, is in the form of a
spring washer, although it may also assume different
shapes (cup spring, spiral spring or the like) . The
spring element 2 6 and the axial dimensions of the
individual components of the surge arrester arrangement
20 are designed such that the contact bolt 39 and the
contact disk 27 are pressed against one another, such
that they make contact, by spring pretension in the
normal state (at the operating temperature).
The surge arrester arrangement 20 operates as follows:
In the normal state, when the surge arrester 22 has not
been triggered and the arrangement is essentially at
the operating temperature, the switching contact which
is formed by the center contact 30 and the contact disk
27 remains closed. The surge arrester 22 is thus
electrically conductively connected at its first end to
the. inner conductor section 13, and at its other end
via the elements 30, 27, 28 and the housing 25, to the
outer conductor 11. If a lightening strike or some
other brief voltage pulse which is greater than the
triggering voltage of the surge arrester 22 is now
applied to the coaxial conductor arrangement 10, the
surge arrester 22 is triggered, and the potential
difference is largely equalized. When the voltage
falls, after the voltage pulse has decayed, back below
the burning voltage of the surge arrester 22, the
latter is quenched, and resumes the initial state.
There is no significant heating of the surge arrester
22 and thus of the expansion body 29.

If, in contrast, a voltage which is above the burning
voltage still remains on the surge arrester 22 even
after the voltage pulse has decayed, with currents
still flowing through the surge arrester 22, this
current produces heat as a result of the internal
resistance of the arrester, leading to heating of the
surge arrester 22. The heat which is created in the
surge arrester 22 flows axially via the base plate 40
and radially via the contact bolt 39 of the center
contact 30 into the expansion body 29, heats the latter
and results in thermal expansion with a rapid radial
outflow of the heat into the housing 25 being prevented
by the thermally insulating insulator sleeve 31. In
this case, the thermal expansion of the expansion body
29 takes place virtually exclusively in the axial
direction, because the expansion body 29 is bounded by
the insulator sleeve 31 in the radial direction and the
pressure which is created by this constriction acts in
the axial direction owing to the "quasi-hydrostatic"
material characteristics of the expansion body 29. This
results in the expansion body 29 expanding axially by
more than 3 times the isotropic expansion, thus
representing a considerable amplification effect.
Provided that a sufficiently high temperature of, for
example, 100°C or more has been reached, the axial
thermal expansion of the expansion body 2 9 between the
two contacts 30 and 37 results in the two contacts
being disconnected from one another, against . the
pressure of the spring element 26. When the contacts 30
and 27 are disconnected, the current flow through the
surge arrester 22 and thus also 'the heat that is
produced are interrupted (self-quenching). As soon as
sufficient heat has flowed out of the expansion body 29
again after the interruption and the expansion body 29
has cooled down and contracted again, the switch which
is formed from the center contact 30 and the contact

disk 27 is closed again, and returns to the initial
state.
It is self-evident that the described switching process
operates better the greater the thermal coefficient of
expansion of the material used for the expansion body
29. At the same time, however, the material should also
be thermally resistant up to temperatures > 200 °C and
should have sufficient resistance to ageing. Finally,
it should also have advantageous dielectric
characteristics for use in the coaxial cable
arrangement. The dielectric characteristics of the
expansion body 29 are particularly important when the
aim is to retrospectively install a switching device
such as this in a coaxial lightening-protection device
which is equipped with a surge arrester without a self-
quenching switching device, as is advantageously
possible in the case of the surge arrester arrangement
according to the invention.
Various measurements have been carried out in the
laboratory with a coaxial conducting arrangement and a
surge arrester arrangement as shown in Figure 1, using
gas capsule arresters of the type described above with
triggering voltages of 230 V and 90 V. Pulses of
4 kV/2kA (in accordance with IEC 61000-4-5) resulted in
capsule burning times in the order of magnitude of 10 s
to 20 s, and reactivation times in the order of
magnitude of 1-2 minutes.
However, the surge arrester arrangement according to
the invention may not only be advantageously used in
conjunction with a coaxial conductor arrangement of the
type shown in Figure 1, but can also be used whenever
gas capsule arresters are used for over voltage
protection. For example, it is normal practice to
solder gas capsule arresters which are equipped with
connecting wires or solder pins (see DE-Al-197 31 312)

into printed circuits. Figure 3 shows a comparable
surge arrester arrangement that has been modified
according to the invention. The surge arrester
arrangement 46 in Figure 3 has a surge arrester 22 in
the form of a gas capsule, which is accommodated in a
housing 43 which is open on one side. The series-
connected switching device in turn comprises the center
contact 30, which is soldered to the capsule 22, the
expansion body 29, which is in the form of a disk, and
a contact plate 36, and these items are isolated from
the housing 43 by an insulation sleeve 31'. The
switching device is in this case arranged underneath
the surge arrester 22, while the contact springs 28
with the contact disk 27 are located above the surge
arrester 22. On one side (at the bottom), the surge
arrester 22 is connected via central connecting means
45 and the switch 30, 36. On the other side (at the
top) , the connection is provided via the outer
connecting means 44, the housing 43 and the contact
disk 27 with the contact springs 28. The connecting
means 44, 45 can advantageously be used for connection
of the surge arrester arrangement 46 in a printed
circuit.
However, it is also feasible within the scope of the
invention in the case of a surge arrester arrangement
of the type illustrated in Figure 3 to provide axial
(or also radial) connecting wires 37 on both sides,
instead of the connecting means 44, 45 arranged on one
side, as is shown in Figure 4. The surge arrester
arrangement 46 can thus be provided with "flowing"
wiring, that is to say it can be installed in any
desired circuit.
It is also feasible within the scope of the invention,
instead of using the flat expansion body 29 in the form
of a circular disk as described above, to use an
expansion ' body which carries out an amplified thermal

expansion movement by virtue of its special shape or
the fact that its material has an anisotropic behavior.
One example of a specially shaped expansion body is
shown in Figure 5. The expansion body 4 8 in Figure 5
uses the mechanical principle of a toggle lever by
being formed either as a conically shaped disk or as a
strip with a bend in the center. The outer edge of the
expansion body 48 is supported on an opposing bearing
47. Thermal expansion as indicated by the double-headed
arrows in Figure 5 results, because of the special
shaping, in a reverse toggle-lever effect, that is to
say an amplified thermal expansion movement on the axis
34 (arrow), which can advantageously be used as a
switching movement.
LIST OF REFERENCE SYMBOLS
10 Coaxial conductor arrangement
11 Outer conductor (housing)
12,...,15 Inner conductor section
16,17 Holder
18,19 External thread
20,46 Surge arrester arrangement
21 Insulating cup
22 Surge arrester (gas capsule arrester)
23 Threaded hole
24 Connecting piece
25 Housing (capsule holder housing)
26 Spring element (spring washer)
27 Contact disk
28 Contact spring
29,48 Expansion body
30 Center contact
31,31' Insulator sleeve
32 Screw thread
33 Bolt
34 Axis (expansion body)
35 Axis (coaxial conductor arrangement)

36 Contact plate.
37 Connecting wire
38 Hole
39 Contact bolt
40 Baseplate
41 Projection
42 Undercut
43 Housing
44,45 Connecting means
47 Opposing bearing

WE CLAIM
1. An automatically quenching surge arrester arrangement (20,46) having a
surge arrester (22), which changes from a non-conductive state to a
conductive state when a predetermined first voltage is exceeded and
returns to the non-conductive state only when a very much lower second
voltage is undershot, and having a switching mechanism (26, , 31,
31'), which responds when a current flows through the surge arrester
(22) and interrupts the current flow through the surge arrester (22), and
then automatically returns to its initial state again, characterized in that
the switching mechanism (26, 31) responds reversibly to the heat
which is produced by the current flow in the surge arrester (22).
2. The surge arrester arrangement as claimed in claim 1, wherein the
switching mechanism (26, 31, 31') has switching means (26, 27, 30
and 26, 30, 36), as well as operating means (29, 31, 31',48) which are
thermally coupled to the surge arrester (22) for operation of the switching
means (26, 27, 30 and 26, 30, 36), with the operating means (29, 31,
31', 48) responding reversibly to the heat which is produced by the
current flow in the surge arrester (22).
3. The surge arrester arrangement as claimed in claim 2, wherein the
operating means (29, 31, 31') have expansion means (29,48) which
convert the heat produced by the current flow in the surge arrester (22)
to a switching movement, by means of thermal expansion.

4. The surge arrester arrangement as claimed in claim 3, wherein the
expansion means have an expansion body (29, 48) composed of a solid
material, whose thermal expansion on a first axis (34) is used as a
switching movement.
5. The surge arrester arrangement as claimed in claim 4, wherein the
expansion body (29) is composed of heat-resistant rubber-elastic
material, in particular a silicone rubber or a fluoroelastomer, and in that
the expansion body (29) is surrounded by a limiting element (31, 31'),
which limits the radial expansion, and thus amplifies the axial
expansion.
6. The surge arrester arrangement as claimed in claim 5, wherein the
expansion body (29) is in the form of a circular disk which is axial with
respect to the first axis (34), and a hollow-cylindrical, co-axial,
electrically and thermally insulating insulator sleeve (31,31'), in
particular composed of polytetrafluoroethylene, is provided as the
limiting element.
7. The surge arrester arrangement as claimed in one of claims 1 to 6,
wherein the switching means have a switch (27,30 or 30, 36), which is
connected in series with the surge arrester (22) and is closed in the
initial state, and which is opened when the operating means (29,31,31')
respond to the heat which is produced by the current flow in the surge
arrester (22).

8. The surge arrester arrangement as claimed in one of claims 1 to 6,
wherein the switching means have a switch which is connected in
parallel with the surge arrester (22) and is open in the initial state, and
which is closed when the operating means respond to the heat which is
produced by the current flow in the surge arrester (22).
9. The surge arrester arrangement as claimed in claim 7, wherein the
switch has two metallic contact elements (27, 30 and 30, 36), which are
pressed against one another by a spring element (26) and can be
separated from one another against the pressure of the spring element
(26), in that one of the contact elements (30) is connected, in particular
soldered, to the surge arrester arrangement (22), and in that the
operating means (29,31,31') and/or the expansion means (29) are/is
arranged between the two contact elements (27,30 and 30, 3'6).

10. The surge arrester arrangement as claimed in claim 9, wherein the
contact elements (27, 30 and 30, 36) are surface-treated, in particular
being coated with silver.
11. The surge arrester arrangement as claimed in claim 9 or 10,
wherein the surge arrester (22), the metallic contact elements (27,30 and
30, 36), the spring element (26) and the operating means (29, 31, 31')
and/or the expansion means (29) are arranged one behind the other
axially with respect to a first axis (34) in a common housing (25,43), in
that the housing (25,43) is electrically conductive and is used as a
supply line to the surge arrester (22), and in that contact springs (28) are
provided in order to produce the contact with the housing (25,43).

12. The surge arrester arrangement as claimed in claim 11, wherein
the metallic contact elements (27,30 and 30, 36), the spring element (26)
and the operating means (29,31, 31') and/or the expansion means (29)
are arranged on one side of the surge arrester (22).
13. The surge arrester arrangement as claimed in claim 11 or 12,
wherein the housing (25, 25') is in the form of a housing which is open
on one side can be screwed in.
14. The surge arrester arrangement as claimed in claim 11, wherein
the metallic contact elements (27,30 and 30, 36) and the operating
means (29,31, 31') and/or the expansion means (29) are arranged on
one side of the surge arrester (22), and the spring element (26) is
arranged on the other side of the surge arrester (22).
15. The surge arrester arrangement as claimed in claim 11 or 14,
wherein connecting means (37, 44, 45) for connection of the surge
arrester arrangement (46) in a circuit, in particular a printed circuit, are
provided on the housing (43).
16. The surge arrester arrangement as claimed in one of claims 9 to
15, wherein the spring element (26) is a spring washer.
17. The surge arrester arrangement as claimed in one of claims 1 to
16, wherein the surge arrester (22) is a gas capsule arrester and has a
cylindrical shape with electrical connections arranged on the end faces.

18. The surge arrester arrangement as claimed in claim 1, wherein the
switching mechanism has a resistance element with a positive or
negative temperature coefficient (PTC or NTC).
19. The surge arrester arrangement as claimed in claim 1, wherein the
switching mechanism has a bimetallic or memory-metal element.
20. The surge arrester arrangement as claimed in claim 3, wherein the
expansion means are in the form of a gas or a liquid whose thermal
expansion is used to produce a switching element.
21. The surge arrester arrangement as claimed in claim 4, wherein the
thermal expansion of the expansion body (48) on the first axis (34) is
amplified by suitable shaping of the expansion body.
22. The surge arrester arrangement as claimed in claim 4, wherein the
thermal expansion of the expansion body on the first axis (34) is
amplified by the expansion body material having an anisotropic
behavior.

ABSTRACT

AUTOMATICALLY QUENCHING SURGE ARRESTER ARRANGEMENT AND USE
OF SUCH A SURGE ARRESTER ARRANGEMENT
The invention relates to an automatically triggering surge arrester arrangement
(20) with a surge arrester (22) which, on exceeding a given first voltage,
transforms from a non-conducting into a conducting state and returns to the
non-conducting state only when a much smaller second voltage is dropped
below and with a switch mechanism (26,..31), reacting to current flow through
the surge arrester (22), interrupting the current flow through the surge arrester
(22) and then automatically returning to the rest condition thereof. A simple,
robust and compact assembly suitable for HF applications for such a surge
arrester arrangement is achieved, whereby the switch mechanism (26,...31)
reacts reversibly to the heat generated in the surge arrester (22) by the current
flow.

Documents:

00204-kolnp-2007-correspondence-1.1.pdf

00204-kolnp-2007-correspondence-1.2.pdf

00204-kolnp-2007-correspondence-1.3.pdf

00204-kolnp-2007-correspondence-1.4.pdf

00204-kolnp-2007-form-1-1.1.pdf

00204-kolnp-2007-form-18.pdf

00204-kolnp-2007-form-26.pdf

00204-kolnp-2007-international search authority report.pdf

00204-kolnp-2007-others document.pdf

0204-kolnp-2007 abstract.pdf

0204-kolnp-2007 claims.pdf

0204-kolnp-2007 correspondence others.pdf

0204-kolnp-2007 description(complete).pdf

0204-kolnp-2007 drawings.pdf

0204-kolnp-2007 form-1.pdf

0204-kolnp-2007 form-2.pdf

0204-kolnp-2007 form-3.pdf

0204-kolnp-2007 form-5.pdf

0204-kolnp-2007 international publication.pdf

0204-kolnp-2007 pct form.pdf

204-KOLNP-2007-(24-10-2011)-PETITION UNDER RULE 137.pdf

204-KOLNP-2007-(25-01-2012)-CORRESPONDENCE.pdf

204-KOLNP-2007-ABSTRACT.pdf

204-KOLNP-2007-AMANDED CLAIMS.pdf

204-KOLNP-2007-AMANDED PAGES OF SPECIFICATION.pdf

204-KOLNP-2007-CORRESPONDENCE.pdf

204-KOLNP-2007-DESCRIPTION (COMPLETE).pdf

204-KOLNP-2007-DRAWINGS.pdf

204-KOLNP-2007-EXAMINATION REPORT REPLY RECIEVED.pdf

204-KOLNP-2007-EXAMINATION REPORT.pdf

204-KOLNP-2007-FORM 1.pdf

204-KOLNP-2007-FORM 18.pdf

204-KOLNP-2007-FORM 2.pdf

204-KOLNP-2007-FORM 26.pdf

204-KOLNP-2007-FORM 3 1.1.pdf

204-KOLNP-2007-FORM 3.pdf

204-KOLNP-2007-FORM 5.pdf

204-KOLNP-2007-GRANTED-ABSTRACT.pdf

204-KOLNP-2007-GRANTED-CLAIMS.pdf

204-KOLNP-2007-GRANTED-DESCRIPTION (COMPLETE).pdf

204-KOLNP-2007-GRANTED-DRAWINGS.pdf

204-KOLNP-2007-GRANTED-FORM 1.pdf

204-KOLNP-2007-GRANTED-FORM 2.pdf

204-KOLNP-2007-GRANTED-SPECIFICATION.pdf

204-KOLNP-2007-OTHERS 1.1.pdf

204-KOLNP-2007-OTHERS.pdf

204-KOLNP-2007-REPLY TO EXAMINATION REPORT.pdf

abstract-00204-kolnp-2007.jpg

« Previous Patent

Next Patent »

Patent Number

253496

Indian Patent Application Number

204/KOLNP/2007

PG Journal Number

30/2012

Publication Date

27-Jul-2012

Grant Date

25-Jul-2012

Date of Filing

17-Jan-2007

Name of Patentee

HUBER & SUHNER AG

Applicant Address

DEGERSHEIMERSTRASSE 14, 9100 HERISAU, SWITZERLAND,

Inventors:

#	Inventor's Name	Inventor's Address
1	GROTH, SIEGFRIED	RUSSIKERSTRASSE 20, 8320 FEHRALTORF,
2	GOEBEL, UHLAND	ESPISTRASSE 11, 8492 WILA
3	GANTER, MARKUS	OBERMÜLISTRASSE 45, 8320 FEHRALTORF
4	NUECHTER, PETER	RÄMSEN 487, 9063 STEIN.

PCT International Classification Number

H01T1/14; H01T4/08

PCT International Application Number

PCT/CH2004/000495

PCT International Filing date

2004-08-06

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1			NA