DE1465799C3 - Arrangement for the protection of telecommunication lines against the influence of high voltage systems - Google Patents

Description

Telecommunication lines, ie telecommunication cables or other bundles of telecommunication lines, are often and under certain circumstances over long distances in the area of the magnetic fields generated by high-voltage systems, in particular by the contact wires of electric railways or overhead lines. Corresponding to the frequency of the alternating current, these are mostly alternating magnetic fields of 50 or 16 _^2/3 Hz which induce stresses in the elongated conductors of the telecommunication line. If the telecommunication line is routed in parallel to the power line, such external voltages can occur at dangerous levels, even at a distance of 100 m and more, and can take on orders of magnitude of several thousand volts.

In addition, there is often a. Endangerment of the telecommunication systems by the fact that with short circuits In neighboring power systems, the earth potential is raised and so-called voltage funnel develop. The telecommunication cables running out of such a voltage funnel drag the potential of the Voltage funnel over the isolated telecommunication wires in areas of a "distant earth", so that there Hazardous voltages arise.

Various means are known for suppressing or reducing external voltages. For example, telecommunication cables with a metal sheath are used and, if the metal sheath is insufficient for shielding, this is also provided with a ferromagnetic armouring, for example wrapped with steel bands. The reduction factor r / c is given as a measure of the reduction in the voltages induced in the cores of the telecommunication cable, ie the ratio of the core voltage E _a reduced by the protective measure to the originally induced core voltage Ei. For cables with a metal jacket, the reduction factor is obtained from the following simplified mathematical relationship

r _k = R / \ ^: R * + ω ^ν Z ² = Ea / Ei.

R is the ohmic resistance and L is the

ίο Self-induction of the metal cable sheath, which is equal to the mutual inductance to the telecommunication wires. The reduction factor is always less than 1 and should be as small as possible, which means that the cable sheath should have the lowest possible resistance R and the highest possible inductance L. To achieve this, it is known (German patent specification 1 113 488 and ETZ, 1964, H. 16, p. 470 to 474), the telecommunication wires with their metallic cable sheath in several at at least one point inside or outside the inductive area of influence of the high-voltage system Winding around a magnetic core and thereby increasing the inductance point by point. These reduction transformers have proven their worth, but the prerequisite for their use is that a cable with a metal jacket is available.

Another means of reducing the external voltages in the cable cores as much as possible, that they are no longer disruptive or even dangerous, consists in the ends of the individual cable cores - "to earth via special circuits and to this Way to divert the currents caused by the external voltages to earth, whereby the Voltages at least at the ends of the cables are approximated to the earth potential. This grounding takes place in a known manner either by surge arresters or by having high-voltage safe at the cable ends Transformers are connected, the windings of which are grounded on the line side.

If the grounding is carried out by a surge arrester, when the surge arrester responds, the Wire directly earthed and therefore unusable for the duration of the response for telecommunication transmission. Grounding through transformers avoids this disadvantage, but it occurs in both cases high induced voltages and correspondingly high currents as a result of the unavoidable earth transmission resistances of the earth lines still have considerable residual stresses at the cable ends.

The purpose of the invention is to create a protective arrangement to allow communication cables without Metal jacket or with a metal jacket that is ohmic due to insufficient insulation or too high Resistance is unsuitable for switching on a reduction transformer or otherwise Conductor bundles to create protection against induced overvoltages that eliminates the disadvantages of the known Avoids arrangements. According to the invention, the wires of the telecommunication cable or other conductor bundles connected in parallel by earthing via impedances at both ends and the cable or conductor bundle placed in at least one place in one or more turns around a magnetic core. This gives the advantages of the reduction transformer without the disadvantages associated with the Earthing of the individual cable cores are connected via special circuits, have to be accepted have to. While with the grounding of the cable cores over

3 4

Impedances without the simultaneous use of one or more places magnetic cores. 4, 5 are provided in the cable cores and a reduction transformer, around which the telecommunication cable is wound. These coils, the earth lines at high induced voltages, have the inductances L _S4 , L ₈₅ and the high currents flow, which on the one hand the cable cores total inductance EL _S. The total resistance of all can endanger, on the other hand due to the ohmic 5 parallel-connected cores of the telecommunication resistance of the earth line at the cable ends high cables and the finite earth resistances, which generate voltages to earth, are denoted by Re , together with the value earlier Use of a reduction transformer ER . The inductance of the cable cores is small and the currents in the cable cores due to the counter voltages generated by the additional inductance reduction transformer when switched on would do and can therefore be neglected. When kept low so that no harmful voltages ohmic resistances is reversed the occurrence. The magnetic core can be located within the position R _s of the cable wound around the magnetic core or outside the area of influence of the heavy current system. This results in the reduction factor />, i.e.

The earthing of the two ends of the wires must be 15 for the ratio of the residual voltage E _a to the original

be done so that the telecommunications transmission borrowed induced voltage Et

is affected as little as possible. You can νοι \ Ιί ^ Ί ^ Λ'Ί '~ ζ7Ψϊ ~ \ ϊ

in a known way by surge arresters r _k -ZK / \ '(ZK) + ω (2-.L ₈ ).

take place, with the wires only in the event of interference. From this it can be seen that the reduction factor is around

after ignition, the surge arrester grounded 20 becomes smaller, that is, the larger it becomes, the cheaper it is

are, or in a likewise known manner thereby, the value of EL _S is.

that paired cores of the remote control In the event of interference, d. H. after igniting the

signaling cable through high-voltage-safe transformers Surge arrester, flows through the wires of the

are completed and the middle of the line-side telecommunication cable a total current

Windings of the transformer directly or via a 25 1? ιλ'ΓϋΊλϊ in the \ 2

Phantom circuitry are grounded. When applying I = Jn /] / (2.R) + ω [ZL ₃ ).

of surge arresters results in the further It can be seen that the current / is very strongly reduced

The advantage that, since the surge conductor is never adorned compared to the current in the known

respond exactly at the same time, after responding systems in which only surge arresters, but

the first surge arrester the induced 30 no magnetic cores around which the cable is wound,

Tensions in the other cable cores, which are foreseen. As can be seen without further ado

Surge arrester has not yet addressed the total self-induction a> EL _s a much greater one

ben, are reduced, so that depending on the amount are given value than the total value of the

of the induced voltage only a possibly ohmic resistance ER. The diminution of

small part of the surge arrester responds and 35 currents / in the wires also has the consequence that the

thus only a few cable cores during the response due to the finite earth contact resistances R _e

In addition, the surge conductors fail, the remaining voltages Ee = / · Re are harmless

Cable cores, however, remain unaffected. When values are reduced. Furthermore, it follows from the

Application of high-voltage safe transformers is the formula that the influence of the earth contact resistance

self- 40 Re resulting from the additional inductances to the value of the reduction factor fk far less

induction is of less importance due to the parallel connection of all cores,

equally effective for all individual cores. F i g. Fig. 2 shows a further embodiment that

Is it a telecommunication cable with a different from the embodiment according to FIG. 1 groove. A relatively small number of cores can be distinguished by the fact that the individual cores 2 Improvement of the effect an additional conductor, 45 are not earthed via surge arresters, otherwise there is the metal jacket, to the veins that two together at the end of the cable Grounding on both sides connected in parallel and associated wires through a high-voltage safe are also completed in several turns in the same winding transformer 7, the sense of conduction and is grounded with the same number of turns around the side winding 8 in the middle. Here too Magnetic core or the magnetic cores be placed. 50 the cable is back in one or more places

Wrapped around an impairment of the telecommunication over magnetic cores 4, 5.

In this arrangement, currents do not only flow when transfers are made in whole or with a very high number of pairs falling below a certain limit voltage, but with upright conductor bundles, but every external induction causes the assignment of the Cores, in the individual 55 a current through the telecommunication cores to earth, groups wound around the magnetic core. which is reduced by the coils L _x . For the

On the basis of FIG. 1 and 2 in the following reduction factor r * results here of course

the subject matter of the invention explained in more detail. the same relationship as with the execution

F i g. 1 shows schematically an embodiment example according to FIG. i.e., here too the reduction

with surge arresters. The cable 1 contains, 60 tion factor smaller and therefore cheaper, the larger the

as usual, a larger number of cores 2, of which the value ω is EL .

only one is drawn for the sake of simplicity. It turns out that the value of the reduction factor

The cores of the cable are the cheaper the overvoltage, the smaller the total resistance

arrester 3 earthed. Occur by influencing the mutually parallel connected to earth

voltages in the cores of the communication cable, 65 effective communication cores. With higher paired

The response voltage of the surge arrester cables is this resistance value ER in itself

exceed, a current flows through it / to earth. be small enough d. that is, the one aimed at by the invention

These currents are limited by the fact that one purpose is also used for cables without a metal jacket,

for example, with cables in which the telecommunication wire bundle is surrounded by a plastic jacket. A metal sheath is of course not harmful, and the arrangement according to the invention can also be used with cables with a metal sheath 5, the metal sheath being expediently also grounded at both ends so that the resistance of the metal sheath is also connected in parallel to the total resistance of the wires and thereby the value ZR is further reduced. In this case, the metal jacket can also be placed around the magnetic cores.

From the fact that a metal jacket is not required is, it follows that an additional iron band armoring is not required. In cases in where such a reinforcement is present, it is not disturbing, so that the arrangement according to the Invention is also applicable in such cases.

If the cable to be protected only has a relatively small number of cores with a small copper cross-section, the reduction factor ric may not be sufficient to reduce the induced voltages to the desired level. In this case, an additional conductor can be connected in parallel to the wires and also wound around the magnetic cores, although this conductor can be the metal cable sheath, if one is already present, but does not have to be. Rather, the cable can contain an additional conductor with the lowest possible ohmic resistance, for example a central conductor with a relatively large cross-section, or, if it is a finished cable with a plastic sheath, a suitably insulated copper tape can be laid parallel to the cable, which is grounded its ends are connected in parallel to the cable cores. Such additional conductors are particularly useful in the arrangements according to FIG. 1 is expedient, since in this arrangement the telephone wires are not connected in parallel even below the response voltage of the surge arresters and, as a result, the reduction factor is still relatively high. Due to the additional conductor, this may be a metallic cable sheath, an additional conductor in the cable or a parallel-laid metal strip, the ends of which are directly earthed, i.e. without the use of surge arresters, the reduction factor is significantly reduced, as in this case too below the response voltage ER is already reduced and the induced voltages in the additional conductor cause a current that generates a back EMF in the telecommunication wires wound around the core via the magnetic cores.

Another advantage of the arrangement according to the invention is that if the individual parts are correctly coordinated with one another, the system can more easily be given a time constant L _s / R which also takes transient processes into account, especially during induction by short circuits in high-voltage systems.

1 sheet of drawings

Claims (4)

Patent claims: 1. Arrangement for the protection of telecommunication lines against interference from high-voltage systems, characterized in that the wires of a telecommunication cable or other Conductor bundle are connected in parallel by grounding via impedances at both ends and that Cable or bundle of conductors around at least one point in one or more turns a magnetic core is placed. 2. Arrangement according to claim 1, characterized in that the grounding of the ends of the wires by surge arresters. 3. Arrangement according to claim 1, characterized in that pairs belonging together Cores of the telecommunication cable are terminated by high-voltage-safe transformers and the The transformers are grounded in the middle of the line-side windings. 4. Arrangement according to claim 1 and one of claims 2 and 3, characterized in that an additional conductor arranged in or outside the telecommunication cable, if necessary the metal jacket, connected in parallel to the wires by earthing on both sides and also is placed in several turns around the magnetic core or cores.