Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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SAFETY CIRCUIT SYSTEM FOR
OVERVOLTAGE PROT~CTION OF
HULTIVIRE LINES
A sa~ety circuit system ~or overvoltage protection of multiwire
lines (an, bn), in particular, of lines for telecommunication and
the like.
The protective system comprises a device (P1) for dispersing the
overvol~age energy, connected between the various line wires (an,
bn) and1 respectively, between each line wire (an, bn) and earth
wire (T) by means of a composite bridge of diodes (Dk, Dr, Dt,
D't) or overvoltage-activated solid-state switch means in which
the energy dispersing device (P1) lies on a common diagonal of
the bridge.
This invention concerns a safety circuit system ~or protecting
two-wire or multiwire lines against overvoltage, for example or
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protecting telecommunication lines and the like.
It is a known fact that modern electronic equipment, especially
when it is connected to very long metal lines (as in the case of
telecommunication`equipment and the like) can be quite easily
damaged by any overvoltage which may occur on-the lines.
This due to the fact that, whilst on the one hand the latest elec-
tronic components used in manu~acturing the equipment offer bet
ter and better performances thanks to their increasing integra-
tion and the reduction in cost for each single ~unction, on th~
other hand they are are becoming more and more vulnerable to
overvoltages due to the continuous reduction in the însulating
distances as a result of greater miniaturi~ation, and to an in-
crease in the response rates.
Overvoltages are generally caused by atmospheric phenomena, for
example, by electric discharge between clouds and the earth or
between one cloud and another, and can also be caused by varia-
tions in the electromagnetic ~ield produced by adjacent electric
lines during operations or breakdowns on the lines themselves.
Whenever the line subjected to overvoltage is made up o~ two or
more conductors, it is possible to distinguish "differential mode
overvoltages", that is to say, between conductor and conductor,
and "common mode overvoltages", that is to say, between the same
conductors and the earth.
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In order to prevent the above-mentioned problems, use is made o~
suitable protective devices or the purpose of absorbing the ener-
gy which accompanies overvoltages, or ~or enabling it to be ab~
sorbed by the portion o~ the line upstream to the device itsel,
thereby preventing their output voltages from reaching values
which could cause damage to the adjoining equipmentO
Among the know protective devices, for electronic circuits7 men-
tion can be made, ~or example, of: gas arresters~ variable resi-
stors (varistors~, semiconductor suppressors (normal or special,
unidirectional or bidirectional Zener diodes, integrated circuits
with the ~unction of crowbar-type discharger and other functions).
According to the circumstances and the desired degree of protec-
tion, these devices are situated between one conductor and ano-
ther and between the conductor and the earth.
However, the use o~ protective devices, in the per sè known man-
ner, gives rise to considerable problems~ both Prom the point o~
view of higher costs and also ~rom the point of view of Pull and
adequate protection. In Pact, in the case of a line with only
two conductors, at least three overvoltage energy dispersing de-
vices must be used. ~oreover, the various protective devices
used on the same line usually have characteristics which are not
perPectly identical, with the disadvantage o~ giving rise to
cross components even in the presen~e of longitudinal overvoltages.
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Consequently, in the case o~ lines with several pairs or with a
great number o conductors, it would be necessary to use an ex-
tremely large number of energy dispersing devices, resulting in
considerably high costs and lengthy installation times.
A scope of this invention is to provide a saPety circuit system
for protecting two-wire and multiwire lines against overvoltages
which is capable oP remedying the drawbacks o~ known devices.
A ~urther scope o~ this inventi~n is to provide a ci:rcuit system
~or protecting against overvoltage which, although it makes use
of known ~ypes of energy dissipating devices~ is extremely in-
expensive, can be m~de in the Porm of an integrated circuit and
provides the best possible protection on lines with two or more
conductors Por telecommunication and the like.
These scopes are achieved by the circuit system Por overvoltage
protection oP two-wire and multiwire electric lines, comprising
an overvoltage energy dispersing device, in which said energy
dispersing device is connected between the line conductors and,
respectively, between each line conductor and the ear-th, by means
o~ a composite bridge oP diode means, said energy dispersing de-
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vice being inserted in the common diagonal of said compositebridge~
The invention will be described in greater detail hereunder, with
re~erence to the accompanyi~ drawings, and maXing a comparison
with the known systems. In the drawings:
~ig. 1 shows the conventional use of known devices, in the case
o~ a line with only two conductors;
Fig. 2 shows the use of the protective system according to the
invention, also in the case o a line with only two conductors;
Fig. 3 shows the conventional use o known devices, in the case
of a line with several conductors;
Fig. 4 shows the use o~ the protective syste~ according to this
invention, in the case of a line with several conductors.
DESCRI ION Or~ly ~ L~
With reerence to ~igures 1 and 2, we will illustrate the case
o~ the protection o~ an apparatus or group of apparatuses U-con-
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nected to a line with only two conductors a and b; the reference
T in both ~igures indicates the ground or earth conductor, in a
per sè known way, whilst the re~erence P in Pigure 1 indicates
the devices Por dispersing or dissipating the overvoltage energy,
both in the direction o the earth and between conductors a and
b. In the same figure, it can be seen that the conventional
systems for a line with two conductors, require at least three
overvoltage energy dispersing devices P, inserted as shown in
the diagram.
Contrary to the above, and as shown by the continuous line in
Pig. 2, the circuit system according to this invention, also in
the case of a line with only two conductors, comprises only one
energy dispersing device P1, being identical or similar ~o the
devices P according to the known systems of figure 1, said ener-
gy dispersing device P1 being inserted in the common diagonal
oP a composite bridge oP diodes according to the wiring diagram
shown in Pigure 2.
The composite bridge o~ diodes comprisest respectively, on the
sides oP the device P1, a irst set oP line diodes D1, D2 on one
side and a second set oP line diodes D4, D5 on the other, oP
which the diodes D1 and D2 have their anode connected to the
conductors a and b respectively, and their cathode connected to
a Pirst common node, whereas the diodeq 4 and 5 are connected,
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in th~ opposite way9 that is to say~ with their cathodes to the
conductors a and bl and wi~h their anode connected ~o a second
common node. The bridge circuit also comprises the earth diodes
D3 and D6 o~ which the diode D3 forms part of the first set o~
diodes and is connected by its anode to the earth T and by its
cathode to the a~oresaid first node, whereas the earth diode D6
orms part of the second set of diodes and is connected by its
cathode to the earth T and by its anode to the aÇoresaid second
node, on the opposite sidP o~ the ove~voltage energy dispersing
device.
Comparing the ~igures 1 and 2, it can be seen that in the latter
case the same protection o~ the conductors a and b is achieved,
both against dl~ferential mode and common mode overvoltages, by
using just one energy dispersing device and six bridge-connected
diodes~ the aoresaid device P1 lying in the common diagonal of
the latter. Since it is possible to use low-cost common diodes
o a type capable of withstanding high impulsive currents, with
respect to the normal permanent currents for which the diodes
are normally designed, it is obvious that the solution shown in
figure 2 implies a considerable reduction in costs, an advantage
which is even more appreciated as the cost o~ the energy disper
sing devices continues to increase, as a result o~ the use o~
combined devicès, ~or example, gas arresters plus a variator.
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A further advantage derives ~rom the fact that, according to this
invention, it is possible to use energy dispersing or dissipating
devices P1, o~ the unidirectional type, even in the presence o~
alternative voltage signals in ~he two line conductors; lastly,
by using a single overvoltage energy dispersing device P1, the
circuit system o4 ~igure 2 eliminates any problems ~hich may
occur in the Xno~ systems, as a result o possible di~erences
in the characteristics o one protective device P and the other.
Furthermore, in the case o~ the device P1 being o~ the crowbar
type (liXe gas-arresters or integrated circuits with similar ~unc-
tion) a simultaneous common safety short-circuit between all the
involved conductors and earth takes place during overvoltage
transients, thereby granting the maximum degree o~ protection
for the electronic equipment.
This can also apply in the case in which several protective de-
vices are used in cascade, on the s~me line, as shown by the
dotted lines in ~igures 1 and 2; in order to achieve a more e~i-
cient protection. In this case, the ~nown system would be ~ound
to require the use o~ six overvoltage energy dispersing devices
P, as opposed to the two devices P1 of figure 2.
As mentioned previously, the invention can easily be extended
to the case o lines with more than two conductors, as shown
schematically in Pig~re 4. In this igure, it can be seen that
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in the case in which there is any given number o~ pairs o~ con-
du~tors a1, b1, a2, b2, an, bn~ the layout oP the protective de-
vice remains substantially unchanged, with the overvoltage ener-
gy dispersing device P1 always inserted in ~he common diagonal
o the composite bridge of two sets of diodes, the only dif~er-
ence being that on both the input and the ou~put sides o~ this
device P1, there will be a number of line diodes DX and Dr equal
to the number o~ line conductors, each of which connected to its
respective conductor as indicated previously9 and a single earth
diode Dt, D't per side. In said figure 4, the references n, k,
and r may assume any given numerical value over two.
The comparison between Pigure 3 which shows a conventional sys-
tem for a line made up oP two pairs of conductors a1, b1 and
a2, b2, and ~igure 4 for the same number of pairs, shows that in
the ~irst case six overvoltage enFrgy dispersing devices P are
required, as opposed to the use o~ only one device P1 according
to this invention; in this case too, the cost of the diodes is
considerably lower than the cost o~ the various devlces P.
Moreover, it can be seen that the solution in figure 3 does not
o~er protection agalnst diPPerential mode overvoltages between
the conductors of one pair and the conductors of the other, un-
less a larger number o~ dispersing devices P are used. In the
case in ~igure 4, according to the invention, such protection
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between pairs o~ diferent conductors is achieved automatically
by means o~ the single device P1 and the t~o sets of diodes Dk
and Dr; in other wor~s, with the circuit system according to
this invention, cirtually total protection is achieved without
having to resort to additional devices.
According to a further scope and possible application of the pre-
viously described circuit, the invention can also be used in
place o ~nown protective devices, for telecommunication circuits
using self-piloting multiple gas arresters, usually o~ the tri-
polar type (two line and one earth electrodes) or pentapolar type
(four line and one earth electrodes, the latter sometimes dis~
tributed over two or more connecting elements).
Said arresters represent a technically advantageous solution, as
compared to the use of separate bipolar gas arresters inserted
between each wire and the earth, in that it enables the discharge
~rom any given electrode to "pilot" ~that is to say, to help) the
sparking off of the remaining electrodes, due to the fact that
thetemporary gas ionization produced by the initial discharge
gives rise to an immediate and considerable reduction in the
value of their break-down voltage.
So it is evident that a "self-piloting" effect also proves to
be intrinsically inherent in the circuit system embodied accord-
ing to the invention and represented in eigs. 2 and 4, since the
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break-down o~ the overvoltage energy despersing device P1 (device
consisting ~or example o~ a simple bipolar gas arrester) is si-
multaneously made use of by all the line conductors~ irrespective
o the pair of elements (wire/wire or wire/earth) in which the
overvoltaye which started the spark takes place.
Other embodiments are possible within the sphere of this inven-
tion, or example, the diodes o~ the two sets which constitute
the composite bridge connecting the overvoltage energy dispers-
ing device P1 to the line and earth conductors, may be replaced
by transistors or, more generally, by overvoltage-con~rolled so-
lid-state switch means, so as to enable the embodiment of the
entire circuit system claimed herein in the ~orm o~ an integra~
ted circuit. Alternatively, or in comhinatian, the earth diodes
D't or the controlled switch means connected to the earth, could
be replaced by other overvoltage energy dispersing devices.
According to a ~urther embodiment, it is also possible to use
two or more diodes or controlled switch means, connected parallel
with one another, ~or each line conductor and earth7 without de-
viating ~rom the innovatory principles o~ this invention.
It will be clear, ~rom what has been described and shown in the
accompanying drawings, that the invention consists in a particu-
lar system for protecting against overvoltages in lines with se-
veral conductcrs, comprising a single overvoltage energy dispers-
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ing device inserted in the common diagonal o~ a composite bridge
of diod~s, which ca~ be used irrespective of the number 0~ COn-
ductors making up ~he line. Therefore, wha~ has been described
and shown in the accompanying dr~wings, is given merely in order
to illustrate the invention and is understood as extended to all
the cases that may occur in practice.
