Overvoltage Arrester With Several Electrodes

Abstract

In order to avoid transverse voltages between associated conductor pairs without additional deflectors, particularly in the case of symmetrical wiring of telecommunication lines with overvoltage arresters, a gas discharge lightning arrester is proposed comprising two principal electrodes and one secondary electrode, as well as a ground electrode located symmetrically with respect to the principal electrodes, the ground electrode together with the two principal electrodes forming two principal discharge paths whose response for which is higher than that of a secondary discharge path defined by the principal electrodes. BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to an overvoltage arrester having several electrodes facing each other in a gas-tight discharge vessel, the electrodes electrically insulated and spaced from one another and defining at least two discharge paths. 2. Description of the Prior Art In order to protect electrical installations, particularly telecommunication systems, it is generally known to utilize gas-filled overvoltage arresters, commonly called button arresters. Generally, such overvoltage arresters comprise two spaced metallic electrodes insulated from one another and facing each other in a gas-tight discharge vessel. In addition, so-called multiple path arresters are known which contain at east three electrodes which define several discharge paths (compare for example German Pats. 729,803 and 930,400). In these multiple path arresters of the prior art, all discharge paths have substantially the same response voltage. The purpose of a multiple path arrester resides in the fast ignition of the discharge paths in response to a pre-ionization caused by a first discharge over one of the paths. When wiring telecommunication conductors with overvoltage arresters, one arrester is placed between the individual conductors to be protected against overvoltages, and the ground. Because the ignition voltages of the arresters do not precisely agree, so that in case of a voltage surge they will not ignite simultaneously, transverse voltages can occur for a short time between the two conductors associated as a conductor pair, like the A and B conductors of telephone lines. To avoid such transverse voltages which have particularly harmful effect in telephone lines, particularly those telephone lines which have transistor amplifiers connected thereto, steps must be taken to compensate the voltages between the conductor pairs. For that purpose, protective circuits have been disclosed, all of which require at least three arresters (see for example German published application 1,462,168). It also has been attempted to avoid the occurrence of transverse voltages by utilizing multiple path arresters. However, transverse voltages cannot be eliminated completely with the multiple path arresters of the prior art, because in spite of the pre-ionization following ignition of the first discharge path, the remaining discharge paths respond with a certain ignition delay. In practice, therefore, when wiring telephone lines with multiple path arresters, an additional arrester having a low response voltage, for example, a 90-volt arrester, is connected between the A and B conductors. SUMMARY OF THE INVENTION The present invention therefore has as it primary object the provision of an overvoltage arrester which protects conductors associated in pairs both against voltage surges and against transverse voltages without the need of additional arresters or circuit members. The foregoing objective is realized through the design of an overvoltage arrester of the kind mentioned above wherein a ground electrode is arranged symmetrically with respect to two principal electrodes, wherein the two principal electrodes form a secondary discharge path therebetween, and wherein the two principal electrodes together with the ground electrode form two principal discharge paths whose response voltage is higher than that of the secondary discharge path. A protective spark gap with two stationary principal electrodes insulated from each other within a chamber that is placed under a high vacuum and surrounded by stationary trigger electrodes has been disclosed in the German published application 1,463,149. However, in that structure, the one principal electrode is to be connected with a conductor to be protected and the other principal electrode is to be connected to ground in contrast with the structure of the present invention wherein both principal electrodes are placed electrically parallel with a ground electrode. The present invention makes it possible to effectively protect conductors associated in pairs, on which voltage surges are to be expected, with a single overvoltage arrester in such a manner that as voltage surges occur between the conductors, harmful transverse voltages are avoided. An overvoltage arrester according to the invention is intended in particular for use in telephone installations having input and intermediate amplifiers equipped with transistors. Therefore, the two principal electrodes of the arrester are associated in each case with the A and B conductors of a telephone line, while the ground electrode is connected to a reference potential, usually ground. As soon as the telephone or telecommunication line is subjected to an inadmissibly high voltage surge, one of the two principal discharge gaps ignites. Unless it just so happens that at precisely the same time the second principal discharge path or gap also responds, transverse voltages between the A and B conductors of the conductor pair affected are compensated by way of a secondary discharge path which has a lower response voltage, whereby the accomplished ignition of a principal discharge path causes the secondary discharge path to ignite at an accelerated rate by pre-ionization thereof. As it is known, the response voltage of a gas discharge over-voltage arrester substantially depends on the electrode distances, the composition of the electrode surfaces and on the gas load. Since the discharge gaps of an overvoltage arrester according to the invention are all placed in the same discharge vessel, the desired differential response voltages of the principal discharge gaps on the one hand and of the secondary discharge gap on the other hand are accomplished by differential electrode distances and/or different activations of the electrodes. To prevent the ignition operation of a principal discharge path from influencing the secondary discharge gap, it is recommended to physically separate the secondary discharge gap from the principal discharge gaps. A detrimental influence of the principal discharge gaps upon the secondary discharge gap must be taken into consideration, particularly in high performance arresters, where physically extended principal electrodes are needed to arrest powerful current surges. Therefore, if a principal discharge gap ignites at a point located at a great distance from the secondary discharge path, a pressure wave in the direction toward the secondary discharge gap not yet ignited must be anticipated because of the heating of the gas present in the arrester. This pressure wave could lead, without physical separation of principal and secondary discharge gaps, to an increase of the response voltage of the secondary discharge gap. A separation of the discharge gaps is easily accomplished by appropriate electrode design. For example, in an arrester having a concentric structure, where the ground electrode coaxially surrounds two pin-shaped principal electrodes, the ends of the secondary discharge gap will be decreased between the principal electrodes defining the gap by providing tapered ends of the principal electrodes.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects, features and advantages of the invention, its organization, construction and operation will best be understood from the following detailed description of preferred embodiments thereof taken in conjunction with the accompanying drawing, in which:

FIG. 1 is a sectional elevational view of an overvoltage arrester having a coaxial electrode arrangement, according to the present invention;

FIG. 2 is a sectional elevational view of an overvoltage arrester according to the present invention having tongue-shaped electrodes; and

FIG. 3 is a sectional elevational view of an embodiment of an overvoltage arrester according to the present invention in the form of a so-called button arrester.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIG. 1, a gas discharge overvoltage arrester comprises a pair of cylindrical pin electrodes 1, hereinafter called principal electrodes, facing each other on a common axis and having flat facing surfaces. The principal electrodes 1 are coaxially surrounded by a hollow cylindrical electrode 2, hereinafter called the ground electrode. The ground electrode 2 together with a pair of insulating bodies 3 and a pair of metal terminal caps 4 form a gas-tight discharge vessel. The annular insulating bodies 3 are preferably made of a ceramic material. The metal terminal caps 4 receive and are connected to respective ones of the principal electrodes 1.

The discharge vessel is loaded with a gas, particularly a rare gas. Depending on the gas charge, a discharge takes place in the annular gap 5 located between the principal electrodes 1 and the ground electrode 2 upon application of an electric voltage between the principal electrodes 1 on the one hand and the ground electrode 2 on the other hand when a certain value (response voltage) of the electrical voltage is exceeded. The space in which a discharge takes place will hereinafter be called the principal discharge gap.

Another discharge gap, called a secondary discharge gap, is located between the principal electrodes 1 where the ends thereof are in proximity to each other, that is, in an area 6 between opposite ends of the pin-shaped principal electrodes 1. To avoid reciprocal influencing of the principal discharge gaps 5 on the one hand and the secondary discharge gap 6 on the other hand, the ends of the pin-shaped principal electrodes 1 facing each other are separated from their jacket surfaces defining the annular gap with the principal discharge gaps 5, the jacket surfaces being coated with a substance (activating substance) for promoting electron emission ability, if necessary.

According to the invention, the distance of the principal electrodes 1 defined in the secondary discharge gap 6 and the electrode activation layers 7 applied thereto, which comprise a substance of high electrode emission capability, should be so dimensioned that the response voltage of the secondary discharge gap 6 is lower than the response voltage of both principal discharge gaps 5 located in the area between the principal electrodes 1 and the ground electrode 2. For example, the principal discharge gaps 5 will be dimensioned for a rated response of 230 volts, and the secondary discharge gap 6 for a response voltage of 90 volts. If such an overvoltage arrester is inserted with its principal electrodes 1 connected to the respective A and B conductors of a telecommunication line and if the ground electrode 2 is connected to ground, a compensation of harmful transverse voltages takes place via the secondary discharge gap 6, as soon as one of the principal discharge gaps 5 has ignited in response to the presence of a voltage surge exceeding the response voltage of the principal discharge gaps 5. As a result, it is possible to eliminate the overvoltage arresters with correspondingly lower response voltage, for example, 90 volt deflectors, which are customarily placed in addition between the A and B conductors of a telecommunication line.

An overvoltage arrester according to the invention does not require a coaxial design according to FIG. 1. In FIG. 2, there is illustrated an embodiment of an overvoltage arrester according to the invention with tongue-shaped electrodes (so-called tongue arresters). The principal electrodes 1 thereby comprise two tongues inserted into a housing 8 of insulating material, made from glass or ceramic, and the tongues extend parallel and are juxtaposed. In their respective central areas, the tongues are proximal each other to form a secondary discharge gap 6. A ground electrode in the shape of an additional tongue 2 extends into the area between the tongue-shaped principal electrodes 1 and together therewith forms the basis for two discharge gaps 5 of the principal type. The principal discharge gas 5 and the secondary discharge gap 6 are dimensioned in an analogy with the apparatus described in FIG. 1 and thus act in the same manner as there described. Preferably, the principal electrodes 1 on the one hand and the ground electrode 2 on the other hand are extended at opposite ends through the insulation material of the housing 8 to the exterior of the housing.

FIG. 3 illustrates an overvoltage arrester according to the invention constructed as a so-called button arrester. In this embodiment, the principal electrodes 1 are frusto-conical caps known as such from the prior art which are inserted in a gas-tight manner into the ends of a pair of tubular bodies 9 of insulation material. In contrast to the button arresters of the prior art, the principal electrodes 1 have a further curved tray-like portion in their centers with the curves 10 facing each other so that they form therebetween a secondary discharge gap 6 having a low response voltage. A metallic annular disk divides the body 9 of insulation material into two mirror-image halves and engages the area between the principal electrodes 1 outside the tray-shaped curves 10 and is utilized as a ground electrode 2. Again, principal discharge gaps 5 are provided between opposite surfaces of the ground electrode 2 and the principal electrodes 1, these surfaces being advantageously coated as in FIGS. 1 and 2 with a substance of high electron emission capacity. The response voltage of the principal discharge gaps 5 again is higher than that of the secondary discharge gap 6.

The present invention is not restricted to the embodiments represented herein. More specifically, an overvoltage arrester according to the invention may also comprise additional electrodes according to the principal of known multi-path arresters. Other changes and modifications of the present invention may become apparent to those skilled in the art without departing from the spirit and scope of the invention, and it is to be understood that I intend to include within the patent warranted hereon all such changes and modifications as may reasonably and properly be included within the scope of my contribution to the art.

Claims

I claim:

1. An overvoltage arrester having at least two discharge paths, comprising a ground electrode, at least two principal electrodes which with said ground electrode form said discharge paths, said ground electrode spaced from and symmetrically disposed with respect to said principal electrodes to define a first discharge path, said principal electrodes spaced apart and defining a second discharge path therebetween, said second discharge path having a response voltage that is less than that of said first discharge paths, and a gas-tight vessel connected to said electrodes and enclosing said discharge paths.

2. An overvoltage arrester according to claim 1, wherein said principal electrodes comprise a pair of cylindrical pins spaced from each other on a common axis and said second discharge path therebetween, and said ground electrode comprises a hollow cylinder concentric about and spaced from said cylindrical pins to define said first discharge paths therebetween.

3. An overvoltage arrester according to claim 2, wherein each of said pins includes a stepped down portion at its end which faces the other such pin.

4. An overvoltage arrester according to claim 2, wherein said housing includes a pair of end caps, and a pair of insulating hollow cylinders connecting respective ones of said end caps to said ground electrode.

5. An overvoltage arrester according to claim 1, wherein said principal electrodes comprise a pair of parallel extending juxtaposed elongate members, and said ground electrode comprises a pin disposed between said pair of elongate members defining therewith said first discharge paths, portions of said members extending toward and parallel one another in the centers of said members.

6. An overvoltage arrester according to claim 5, wherein said housing includes insulating material at least at its opposite ends, and said ground electrode and said principal electrodes extend through said insulating material through the respective ends.

7. An overvoltage arrester according to claim 1, wherein said principal electrodes are disposed nearer each other than they are to said ground electrode to render the response voltage relationship.

8. An overvoltage arrester according to claim 1, comprising material having a high electron emission capability coating the facing portions of said principal electrodes.

9. An overvoltage arrester according to claim 1, wherein said principal electrodes comprise a pair of frusto-conical caps each including a central portion further cupped in the same direction as the cupping of the frusto-conical cups, said electrodes disposed with said central portions facing each other, said ground electrode comprises a metal disc having a central aperture concentric with and disposed about and of a greater diameter than said central portions, and a pair of hollow insulating cylinders connecting respective ones of said principal electrodes to said ground electrode in a gas-tight manner forming said housing.

10. An overvoltage arrester according to claim 1, comprising a telephone line having a pair of line conductors connected to respective ones of said principal electrodes, and said ground electrode connected to a reference potential.