CH684036A5 - Electrical overload protection unit - Google Patents

Abstract

An electrical equipment overload protection unit comprises a metal shell (1,2) containing two electrodes (4,5), one at each end of a surge suppressor (3), an electrically conducting, meltable component (8) and a low m.pt. insulator (9), pref. polyethylene wax acting as a flow aid.On overloading of the suppressor (3) the component (8) melts flows along the outside of the suppressor (3) and forms a connection between the electrodes (4,5).Both ends of the unit are protected by a plastic flange and the metal shell (1,2) is wrapped in a shrink-wrap film, pref. PETP, PE or PVC. The unit is enclosed in a plastic housing filled with PU.

Description

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CH 684 036 A5

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description

The invention relates to a gas-filled isolating spark gap according to the preamble of patent claim 1 and a method for its production. Such isolating spark gaps are generally known. Their main task is to protect devices against overvoltages caused by lightning, high-voltage line contact or similar. protect or prevent that in underground metal structures that are cathodically protected against corrosion, e.g. In natural gas lines, underground tank systems etc., induced currents occur which destroy the insulation of the lines or endanger people.

They can fulfill this task in that, in principle, they consist of two electrodes, which face each other at short intervals in an insulated housing and which normally separate electrically conductive system parts. If overvoltages occur that could endanger the system, the spark gap ignites and the system parts are temporarily conductively connected to one another.

However, the occurrence of a sustained overload can cause high currents to pass through the isolating spark gap, which can destroy the overvoltage protection device and pose a considerable fire risk.

To avoid this danger, fusible elements are used that melt when such overloads occur and either cause a permanent short circuit on or in the surge arrester or trigger another mechanism, e.g. a spring-loaded short-circuit bar, that establishes the short-circuit connection; these devices are referred to as “failsafe devices”.

An example of a failsafe device in which a short-circuit connection is created within a gas-filled surge arrester is DE-A1 2 828 591, in which at least one of the electrodes arranged at a distance from one another is provided with a metal plate which melts when overloaded and establishes a galvanic connection between the electrodes.

Another example of a surge arrester with an internal short-circuit connection is DE-A1 2 621 074, in which the one electrode at the lead-through point is surrounded by the covering by a material which softens when overloaded, so that the electrode is exposed to the outside air lower internal pressure is pulled inwards and forms a short circuit with the other electrode. According to a preferred embodiment, at least one of the electrodes can additionally be provided with a metallic material that melts when overloaded.

A failsafe device with an outer short-circuit mechanism is described in DE-A 2 738 077. In this device, an additional air gap device is placed parallel to the ionizable gap, which has a melting device made of meltable material, which melts in the event of a persistent overvoltage and which creates a melted path of current-conducting material between the electrodes of the overvoltage protection device.

DE-A1 1 922 823 describes a further failsafe device with an outer short-circuit mechanism. In this device, a soft solder pill is arranged next to the one electrode and holds a bracket, which is in electrically conductive connection with the other electrode, in the operating state at a distance from the first electrode. When the surge arrester heats up due to overload, the soft solder pill melts and the bracket causes the external short circuit by contact with the first electrode.

Instead of a soft solder pill, a solder plate can also be used. For example, DE-U1 8 910 382 describes a button conductor for discharging overvoltages, which is inserted in a holder with opposing contact springs and in which a solder plate is arranged at least on one side between the metallic end piece of the button conductor and the contact spring. The latter failsafe devices have in common that the short-circuit connection is not made by the material of the metallic solder, but that an additional device causes the electrical contact by melting the solder.

A major disadvantage of the previously known isolating spark gaps is that they do not give a safe short circuit at small (<20A) and large currents (> 2 kA).

On the basis of this prior art, the object of the invention is to create an isolating spark gap which avoids the disadvantages of the known isolating spark gaps and, in particular, to create an isolating spark gap which, with a simple construction, gives a safe short circuit even at currents <20 A and> 2 kA.

This object is achieved in an isolating spark gap of the type mentioned at the outset by the characterizing features of patent claim 1. Preferred embodiments of the invention and refinements are defined in the dependent claims.

A preferred embodiment of the isolating spark gap according to the invention consists in producing the device producing the external electrically conductive connection between the electrodes from a brass sleeve and a solder mass applied to the metal electrode as the melting body and the free space between the surge arrester, the electrode and the melting body one side and the brass sleeve on the other side to be filled with a slightly melting, insulating material, preferably made of a polyethylene wax. This insulating material prevents the formation of a microclimate inside the spark gap; it also serves as a flux for the melting body.

The invention is explained below with reference to the embodiment shown in the drawings. Show it

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Fig. 1 an inventive separation spark path and

2 an isolating spark gap according to the invention in an explosion-protected design.

The gas-filled isolating spark gap shown in FIG. 1 essentially consists of a brass casing, which consists of a pot-shaped part 1 and an attached cover part 2. In the brass sheath 1, 2, a conventional gas-filled surge arrester 3 is inserted so that it fits on one side exactly in the pot-shaped part 1 of the brass sheath, but on the other side, however, between the surge arrester 3 and the upper part of the pot-shaped part 1 and the Cover of the brass casing 1, 2, a space remains.

The surge arrester consists of two metal electrodes 4, 5, which are provided with an emission-promoting coating and are installed in a ceramic tube which is filled with an inert gas. If overvoltage conditions occur, a current-conducting path is formed between the electrodes in a known manner. However, this is not the subject of the present patent and is therefore not shown in detail.

The metal electrodes 4, 5 of the gas-filled surge arrester 3 are each connected to electrical connections 6, 7, which are designed as compact metal connections for better heat dissipation. There is a melting body 8 on the electrode 2 facing the cover 2 of the brass sleeve, which covers the entire surface of the electrode 5 and has approximately the same diameter as the electrode 5. The melting body 8 consists of an electrically conductive, easily melting material, for example of a tin / lead alloy (Sn / Pb 60/40), which melts at approximately 185 ° C. By choosing a suitable material composition, any melting temperature for the melting body 8 can be achieved.

The free space between the surge arrester 3, the electrode 5 and the melting body 8 on one side and the brass sleeve 1, 2 on the other side is filled with a light-melting, highly insulating material 9. This material, e.g. a polyethylene wax (AL 61, AH3, EAS 1 or EVA 1 from BASF) has a lower melting point than the metal of the melting body. It is important that the insulating material 9 is in close spatial connection with the melting body 8, since an important task of this material is to serve as a flux for the melting body 8.

The free space between the opening in the lid 2 of the brass casing 2 and the metal connection 7 is closed with a seal 10 made of highly insulating plastic (e.g. polytetrafluoroethane). The highly insulating material 9 and the seal 10 made of insulating plastic ensure that in the normal state there is no electrically conductive connection between the electrode 5 and the brass sleeve 1, 2, which is in good electrical contact with the other electrode 4. Another function of the insulating material 9 is to prevent the formation of a microclimate within the spark gap; it also prevents sealant from entering the isolating spark gap.

To protect the spark gap against corrosion and as protection against contact, the metal sleeve 1, 2 is surrounded by a tight-fitting shrink tube 13 made of a thermoplastic film (e.g. based on polyethylene terephthalate [PETP] or polyvinyl chloride [PVC]). Since the shrink tube 13 can only be shrunk in a certain ratio, two plastic flanges 11, 12 are arranged at both ends of the spark gap around the metal connections 6, 7 in order to ensure that the shrink tube 13 is securely closed.

The functioning of an isolating spark gap according to the invention is explained below with reference to the exemplary embodiment shown in FIG. 1. If a sustained overload occurs, the surge arrester 3 heats up and the melting body 8 begins to melt. At the same time, the lightly melting, insulating material 9 also melts. As a result, an electrically conductive connection between the one electrode 5 and the brass sleeve 1, 2, and thus between the two electrodes 4, 5, is produced regardless of the position.

This ensures a safe short circuit with weak currents (<20 A) (failsafe), and even with strong currents (> 2 kA), a safe short circuit is formed and the environment is protected if the isolating spark gap is destroyed.

2 shows an isolating spark gap in an explosion-proof design. The two metal connections 6, 7 of the spark gap are screwed to two steel brackets 14, 15, and the whole is in a cylindrical housing 16 made of plastic (e.g. polypropylene oxide). One steel bracket 14 protrudes from the plastic housing 16 on the open side, and the second steel bracket 15 is guided through the bottom of the housing 16 with a steel sleeve 17. The housing 16 is completely filled with a casting compound 18, for example made of polyurethane [PU]. In this case, the closure of the opening in the cover 2 of the brass sleeve with a seal 10 can be dispensed with, since the sealing compound provides a sufficient seal between the inside of the brass sleeve 1, 2 and the outside atmosphere.

Modifications of the construction described above are possible within the scope of the invention according to the claims and are familiar to the person skilled in the art.

Claims (1)

Claims 1. isolating spark gap with a surge arrester (3) which in a gas-filled housing has electrodes 4, 5 which are at a distance from one another and between which an overvoltage arrester creates an electrically conductive connection, characterized in that outside the surge arrester 5 10th 15 20th 25th 30th 35 40 45 50 55 60 65 3rd 5 CH 684 036 A5 (3) if the overvoltage arrester (3) is overloaded, a galvanic connection between the two electrodes (4, 5) producing device (1, 2, 8) is provided, which consists of a device that envelops the overvoltage arrester (3) one of the electrodes in an electrically conductive contact with the metal sleeve (1, 2) and one of the metal sleeve (1, 2) electrically insulated and with the other electrode (5) in electrically conductive contact with the melting body (8), which in the event of a sustained overload of the Surge arrester melts, is formed. 2. isolating spark gap according to claim 1, characterized in that the external connection between the electrodes (4, 5) producing device (1, 2, 8) from a brass sleeve (1, 2) and one on the one metal electrode as a melting body (8 ) applied solder mass and that the free space between the surge arrester (3), the electrode (5) and the melting body (8) on one side and the brass sleeve (1, 2) on the other side with a light-melting, insulating material ( 9), preferably made of a polyethylene wax. 3. isolating spark gap according to claim 1, characterized in that the insulating material (9) is in close spatial connection with the melting body (8). 4. spark gap according to one of claims 1 to 3, characterized in that a plastic flange (12, 13) is attached as protection against contact on both ends of the spark gap and that the spark gap with a shrink tube (13), preferably made of polyethylene terephthalate, polyethylene or Polyvinyl chloride, is coated. 5. isolating spark gap according to one of claims 1 to 3, characterized in that it is located in a cylindrical housing (16) made of plastic, from which the electrical connections (6, 7) via steel brackets (14, 15) are guided to the outside and that the housing (16) is filled with a casting compound (18), preferably made of a polyurethane plastic. 5 10th 15 20th 25th 30th 35 40 45 50 55 60 65 4th