NZ237923A

NZ237923A - Telecommunication line protector with varistor and gas discharge tube

Info

Publication number: NZ237923A
Application number: NZ237923A
Authority: NZ
Inventors: John Morton; Benjamin Wright
Original assignee: Australian Telecomm
Priority date: 1990-04-26
Filing date: 1991-04-23
Publication date: 1993-11-25
Also published as: WO1991016752A1; MY105433A

Description

237 9 2 Priority Date(s): Complete Specification F;^d: .^-.V.Sh"5U | AWUMJpv*;, A.W^J.Wvv;..... j rtoilteta,-. .1"^.

Publication Date: .?!?}( .??? P.O. Journci, No: .. /v ', 2" • '^23 APRl99i'~! ""tic ,, v ««/ Patents Form No. 5 NEW ZEALAND PATENTS ACT 1953 COMPLETE SPECIFICATION A CIRCUIT PROTECTION DEVICE WE, AUSTRALIAN TELECOMMUNICATIONS CORPORATION, -ef- ^o^Wulo* 199FWillTam tftreei, ^pl^ournc^ Viator<=f ^ 159 V\j,l\;©.~ Srt^Md, rOe.lU=.e><_>v*va/ vicAosloy Awfetv- AUSTRALIAN hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: (followed by page la) 23 7 92 3 - 1^3" A CIRCUIT TO PROTECT A TELECOMMUNICATIONS SYSTEM TROM LIGHTNING STRIKE FIELD OF THE INVENTION The present Invention relates to two devices to protect electrical equipment from lightning strikes and more particularly but not exclusively to protect telephone equipment such as facsimile machines.

BACKGROUND ART Gas arrestors 1n the past have been commonly used to protect telephone circuits by discharging the lightning to ground. However these arrestors are relatively slow and are therefore not totally successful.

One attempt to overcome the above problem 1s described In Australian Patent 590 491. This particular patent teaches the use of Zener diodes, In series with a parallel arrangement of capacitor and resistor. However this particular arrangement has the disadvantage that 11 Is frequency-dependent. More particularly, It Is only effective during rapid changes In voltage. In this regard It should be appreciated that the problem 1s high voltages, not high rates of change 1n voltage.

OBJECT OF THE INVENTION It 1s the object of the present Invention to overcome or substantially ameliorate the above disadvantages.

SUMMARY OF THE INVENTION There Is disclosed herein a protective circuit for a telecommunications system, the circuit comprising; a pair of signal lines to be attached to the telecommunications system; a gas filled protector operatlvely connected to each line and to an earth line means; a first and second varlstor, each varlstor being connected to a respective signal line and to a further earth line means; a first resistor In each signal line between said protector and the associated varlstor; and a second resistor 1n each signal line to connect each first resistor and its associated varistor to the telecommunications system.

Preferably, there would be a plurality of said protective circuits, arranged 1n parallel. It Is still further preferred that the earth line means are earth lines having a total cross-sectional area greater than the cross-sectional area of the signal lines, so that the signal lln^^lllo^x fall prior to the earth lines. •=27 SEPIW * * (followed by page 2) JLH/LMM/422t 23 7 92 3 It 1s still further preferred that the protective circuit is of a three or more layered construction, with the first layer consisting of the first resistors and the protector , a further layer consisting of the earth line means, and the third layer consisting of the second resistors, with the third layer being adapted to be attached to the telecommunications system.

BRIEF DESCRIPTION OF THE DRAWING A preferred form of the present Invention will now describe by way of example with reference to the accompanying drawing, which schematically depicts a protective circuit for a telecommunications system.

BEST MODE AND OTHER EMBODIMENTS OF THE INVENTION In the accompanying drawing, there Is schematically depicted a protective circuit 10 for a telecommunications system. The circuit 10 Includes a plurality of subclrcults 11, with the subclrcults 11 being arranged In parallel.

The circuit 10 Includes signal lines 12 and 13 between which extends a gas filled protector 14. The gas filled protector has the object of clamping the voltage at 230 volts. Once the voltage rises to a certain level, the protector 14 starts to Ionize and operatlvely connects the signal lines 12 and 13 to an earth line 15.

There Is further provided 1n each line 12 and 13, resistors 19 and 16, with each resistor 19 being approximately 4.7 ohms, and each resistor 16 being 2.2 ohms.

Also extending between the lines 12 and 13 1s a pair of varlstors 17, which are preferably metal oxide varlstors. The varlstors attached to an earth line 18.

Preferably, the total sum of the cross-sectional areas of the earth lines 15 and 18 Is greater than the cross-sectional area of each of the lines 12 and 13 so that the lines 12 and 13 will destruct prior to the earth lines 15 and 18.

In the abovedescrlbed circuit 10, the first stage of protection 1s provided by the varlstors 17. They are effective for voltage surges above 140 volts. If the varlstors 17 fall to clamp the voltage at 140 volts, the second stage of protection comes Into operation. The second stage of protection 1s provided by the gas filled protectors 14 which act to clamp the voltage to 230 volts. If this second stage of protection falls, tjie^fT^V "sacrificial" design 1n respect of the relative cross-sectional areas'^ the earth lines 15 and 18 relative to the lines 12 and 13 comes 1ntov \27SEPmz <~s JLH/LMM/422t ^ti\! 23 7 92 3 operation. That Is the lines 12 and 13 will fuse. Accordingly, any overwhelming strike on any one of the ten subclrcults 11, will "take out" the lines 12 and 13, leaving the untouched lines 12 and 13 still guarded. If all the lines 12 and 13 were struck at the same time, again the lines 12 and 13 would fall before the earth link.

A desirable construction for the circuit 10, 1s a multi-layered construction, including three or more layers. For example the first layer could include the protector 14, and resistors 19. The second layer would include the earth lines 15 and 18. The third layer would Include the resistors 16. 3LH/LMM/422t < o / 0 r \ vJ 2 j V ' 0 7. ^ i - (. J

Claims

WHAT WE CLAIM IS:

1. A protective circuit for a telecommunications system, the circuit comprising; a pair of signal lines to be attached to the telecommunications system; a gas filled protector operatively connected to each line and to an earth line means; a first and second varistor, each varlstor being connected to a respective signal line and to a further earth line means; a first resistor in each signal line between said protector and the associated varistor; and a second reslslor 1n each signal line to connect each first resistor and its associated varistor to the telecommunications system.

2. The circuit of claim 1, wherein said circuit consists of a three or more layered construction, with a first layer consisting of the first resistors and the protector, and a further layer consisting of the earth line means, and a third layer consisting of the second resistors, with the third layer being adapted to be attached to the telecommunications system.

3. The circuit of claim 1 or 2, wherein the first and second varistors are metal oxide varistors.

4. A circuit protection device including a plurality of protective circuits according to claim 1, 2 or 3, wherein said circuits are arranged in parallel, and wherein the earth line means are earth lines, with the total cross sectional area of the earth lines being greater than the cross sectional area of the signal lines, so that the signal lines will fail prior to the earth lines.

5. A protective circuit for a telecommunications system, substantially as hereinbefore described with reference to the accompanying drawing. j i.Z, 4 2 7 SEp •v 0LH/LMM/422t