Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01T—SPARK GAPS; OVERVOLTAGE ARRESTERS USING SPARK GAPS; SPARKING PLUGS; CORONA DEVICES; GENERATING IONS TO BE INTRODUCED INTO NON-ENCLOSED GASES
  • H01T4/00—Overvoltage arresters using spark gaps
  • H01T4/08—Overvoltage arresters using spark gaps structurally associated with protected apparatus

Definitions

• the present invention relates to the technical field of terminal block over ⁇ voltage protectors.
• the invention relates to an overvoltage protector for such terminal blocks which have a plurality of individually insulated connectors for connecting a plurality of electrical conductors and includes at least ne earth electrode and a plurality of protection electrodes, which are arranged mutually insulated and with intermediate spark air gaps.
• the overvoltage protector is utilizable as lightening protector for cable networks withstanding an overvoltage in the order of magnitude 10 kV or more.
• overvoltage protectors of different kinds for protecting cable networks and connected equipment against overvoltages caused, inter alia, by lightning.
• Several different types of overvoltage protector for connection to different connection points in a cable network are known.
• Such overvoltage protectors function well, in general, and can have a nominal d.c. excitation voltage in the order of magnitude 300-600 V.
• a disadvantage with such protectors is that in some cases they can be comparatively expensive.
• Terminal blocks in cable networks are normally formed for elecrically connecting a plurality of first conductors to their individual second conductors.
• terminal blocks in cable networks there are, for example, elongate terminal blocks with connectors arranged in rows for connecting ten pairs of incoming conductors to ten pairs of outgoing conductors. In such a case there can be overvoltages occurring between adjacent conductors in different pairs, there being a need to protect the terminal block and other equipment against such overvoltages.
• overvoltage protectors for such terminal blocks which have a plurality of connectors insulated from each other for connection to a plurality of electrical conductors, the overvoltage protectors having a substantially lower d.c. excitation voltage than the voltage at which flash-over normally takes place in the terminal block.
• Protectors using inert gas tubes have been regarded as too expensive in certain connections, while protectors with spark air gaps have been too unreliable and difficult and/or expensive to manufacture.
• the invention has the object of solving this problem and providing an overvoltage protector which is sufficiently reliable, simple and cheap to manufacture together with being well suited to terminal blocks and cables of modern kind.
• the overvoltage protector is based on the air gap principle, i.e- the protector includes at least one earth electrode for connection to an earth conductor and a plurality of protective electrodes for connection to the connectors of the terminal block, the earth electrode and protective electrodes being arranged mutually insulated and with intermediate air gaps, which are determining for the nominal d.c. excitation voltage of the protector.
• the earth electrode and protective electrodes are implemented and situated relative each other in the overvoltage protector such that the nominal d.c. excitation voltage between the earth electrode and any one of the
• protective electrodes is substantially equally as great as the nominal d.c. excitation voltage between the protective electrode and at least one other protective electrode.
• the nominal d.c. excitation voltage between a protective electrode and an earth electrode is substantially equally as great as the nominal d.c. excitation voltage between the protective electrode and each of two other protective electrodes, while the nominal d.c. excitation voltage between the protective electrode and still further other protective electrodes apart from the two mentioned is substantially higher.
• the protective electrodes are arranged in rows, the nominal d.c. excitation voltage between any two adjacent protective electrodes in a row being substantially equally as great as the nominal d.c. excitation voltage between the protective electrode and earth electrode.
• the earth electrode is elongate, with its longitudinal direction in that of the block, the protective electrodes being on the same side of the earth electrode, seen in the longitudinal direction of the latter.
• the earth and protective electrodes are preferably fabricated from a metal alloy, which at least in the areas of the electrodes where flash-over can take place has a coating of nickel, there being a layer of tin on the coating.
• the nominal d.c. excitation voltage is preferably about 4 kV.
• Implementing an overvoltage protector in accordance with the invention results in advantages from the aspects of cost, manufacture and reliability, these advantages being particularly salient in preferred embodiments.
• the primary and perhaps most important advantage is that the air gaps, which are determining for the nominal d.c. excitation voltage, can be made comparatively large in ' relation to the maximum permitted voltage between pairs of conductors in the terminal block, about 0.6-0.8 mm for about 4 kV.
• the comparatively large air gaps permit manufacture and fitting of the electrodes with comparatively large tolerances. Manufacturing and fitting the electrodes in an overvoltage protector with comparatively large spark air gaps and large tolerances will be substantially cheaper than corresponding manufacture with spark air gaps which are small or have small tolerances. If the earth electrode is implemented elongate, and if the protective electrodes with their air gaps determining the d.c. excitation voltage are solely arranged on one side of the earth electrode, the earth electrode and protective electrodes can be given an implementation which is particularly simple and cheap in manufacture.
• the comparatively large spark air gaps reduce the risk of short-circuiting bridges across the gaps by material from the electrodes in conjunction with flash-over. This risk becomes particularly small if the electrodes are manufactured from a metal alloy with a coating of nickel, there being a layer of tin applied over this coating ⁇ The reliability of the overvoltage protector will thus be increased.
• Figure 1 illustrates a terminal block mounted on an earthed block holder, an overvoltage protector in accordance with the invention being connected to the terminal block.
• Figure 2 illustrates how protective electrodes in an overvoltage protector can be electrically connected to connectors in a terminal block according to Figure 1.
• Figure 3 illustrates a preferred embodiment and a preferred implementation of an elongate earth electrode and protective electrodes in an elongate over ⁇ voltage protector, seen in the longitudinal direction thereof.
• Figure 4 illustrates a preferred embodiment and a preferred implementation of an elongate earth electrode and protective electrodes in an elongate over ⁇ voltage protector, seen from one long side of the latter.
• Figure 5 illustrates a preferred embodiment and a preferred implementation of an elongate earth electrode and protective electrodes in an elongate over- voltage protector seen from above, i.e. in a direction towards the terminal block.
• Figure 1 there is illustrated a terminal block 1, which is attached to an earthed block holder 2.
• the block is of a known type marketed by Ericsson Network Engineering under the type designation NER 25101, or which is described in the Swedish Patent Application 8702766-0.
• the holder is of the _ ' type marketed by Ericsson Network Engineering under the type designation NBH 12301.
• An overvoltage protector 3 is connected to the terminal block.
• the former has an elongate exterior configuration with approximately the same outside dimensions as a known overvoltage protector marketed by Ericsson Network
• the overvoltage protector includes an elongate earth electrode 4 and a plurality of protective electrodes 5 mounted in a protective body of electrically insulating plastics. On the upper side of the protective body the protector has a plastics cover 7. For connection of the earth electrode to earth conductors or the block holder, the overvoltage protector has two contact means 8, said means projecting out dependently from the bottom of the protective body at either end of the overvoltage protector.
• the contact means 8 are thus situated in a similar way as corresponding contact means in the known overvoltage protector NFD 25111.
• the protective body and lid are not shown in Figures 2-5, but only the earth electrode and the protective electrodes, for more clearly illustrating the configuration of the electrodes, their position and orientation in relation to each other.
• the earth electrode 4 is elongate and, apart from its end portions, substantially has the form of a straight strip of rectangular cross section. At either end this electrode has end portions including the contact means 8.
• the terminal block 1 is intended for the connection of up to 20 incoming conductors 9, each a conductor of up to 20 outgoing conductors 10.
• the terminal block has connectors 11 arranged in rows and insulated from each other, for connecting the conductors.
• Each connector consists of two parts 11a and lib.
• the overvoltage protector has 20 protective electrodes 5 implemented for connection each to a connector by engaging against opposing sides of a leg of the part 11a.
• the protective electrodes are commonly alike, each one including a substantially strip-like longitudinal portion 12 extending right through the protective body. In the elongate portion there is a slot for the leg of the connector part 11a.
• Each protective electrode also includes a substantially U- shaped portion 13 of substantially the same thickness as the elongate portion. The U-shaped portion 13 joins up with the elongate portion 12 at one leg 14. The configuration of the U-shaped portion has preferably been achieved by folding a straight, strip-like portion.
• the protective electrodes are fastened in the plastics protective body such that their elongate portions extend substantially parallel to each other, and so that these portions are arranged in a row in the longitudinal direction of the overvoltage protector on one side of the earth electrode.
• the protective electrodes are fastened in the plastics protective body so that the U- shaped portions are free, and are arranged in a row in the longitudinal direction of the overvoltage protector with substantially parallel legs 14 and 15 substantially at right angles to the longitudinal direction of the protector.
• the webs 16 of the U-shaped portions are substantially straight and oriented substantially parallel to each other and the earth electrode 4 on one side of this electrode.
• the least distance between two adjacent protective electrodes is the distance between the leg 14 of one and the leg 15 of the other. This distance is substantially equal for all these electrodes.
• the least distance between the earth electrodes and a part of a protective electrode not completely covered by the protective body is the distance between the web 16 and the earth electrode. This distance is substantially equal for all the protective electrodes and substantially equally as • great as the least distance between two adjacent, protective electrodes, and can preferebly attain to 0.6-0.8 mm.
• the nominal d.c. excitation voltage between the earth , electrode and any protective electrode is thus substantially equally as great as the nominal d.c. excitation voltage between the protective electrode and at least one other protective electrode.
• the nominal d.c. excitation voltage can preferably be about 4 kV.
• the protective and earth electrodes preferably have a somewhat rounded-off configuaration at their edges facing towards each other, for avoiding field concentration effects.
• they are manufactured from a tin- bronze alloy, which is then nickel plated and provided with a layer of tin, at least in the areas of the electrodes where the distance between them is least.
• the entire electrodes are preferably nickel plated and covered by a layer of tin.
• the latter can have recesses 17 at their upper edges, and the cover 7 have on its under side a stiffening flange, which is formed for engagement in the recesses.
• the invention is not restricted to overvoltage protectors entirely agreeing with what is illustrated in Figures 1-5, or to overvoltage protectors which can solely be used with the known terminal block NER 25101.
• the inventive overvoltage protector can to advantage be also used in other elongate terminal blocks with connectors arranged in rows for a plurality of conductors.

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• Emergency Protection Circuit Devices (AREA)

Priority Applications (6)

Applications Claiming Priority (2)

Publications (1)

Family

ID=20369124

Family Applications (1)

Country Status (7)

Citations (2)

Family Cites Families (4)

• 1987
  • 1987-07-14 SE SE8702865A patent/SE455908B/sv not_active IP Right Cessation
• 1988
  • 1988-06-13 DE DE3890896A patent/DE3890896C2/de not_active Expired - Fee Related
  • 1988-06-13 WO PCT/SE1988/000318 patent/WO1989000780A1/en active IP Right Grant
  • 1988-06-29 IE IE196888A patent/IE62273B1/en not_active IP Right Cessation
• 1989
  • 1989-02-20 FI FI890814A patent/FI88555C/sv not_active IP Right Cessation
  • 1989-02-21 GB GB8903854A patent/GB2218581B/en not_active Expired - Lifetime
  • 1989-03-10 DK DK118589A patent/DK168902B1/da not_active IP Right Cessation

Patent Citations (2)

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