AU597252B2

AU597252B2 - Fault current protective circuit breaker

Info

Publication number: AU597252B2
Application number: AU57786/86A
Authority: AU
Inventors: Gottfried Professor Dr Biegelmeier
Original assignee: Asea Brown Boveri AB
Current assignee: ASEA BROWN BOVERI AG
Priority date: 1985-04-16
Filing date: 1986-04-12
Publication date: 1990-05-31
Anticipated expiration: 2006-04-12
Also published as: EP0218648A1; ATE57448T1; AU5778686A; WO1986006222A1; ES553997A0; DE3674877D1; GB8609254D0; ES8703678A1; NZ215855A; GR860989B; GB2176069B; EP0218648B1; GB2176069A; AT383906B; ATA113785A

Abstract

The circuit breaker consists of a housing and contact apparatus (17) arranged with terminals, a fault current releasing device (15), a summation current converter (10), an electronic circuit (19) dependent of network voltage, and an energy storage circuit (13) independent of network voltage. For greater simplicity in assembling and manufacture, the device has only one summation current converter (10) and one fault current releasing device (15), which are used not only for release by the circuit dependent of the network voltage, but also by the circuit independent of the network voltage.

Description

bUA 7 7 86 il 6 pCT ~WELTORO AT FU7ST l U INTERNATIONALE ANMELDUNLE LIE N VERTRAG OBER DIE INTERNATIO NALE ZUSA MM ENARBET AB T WSES(PCT) (51) Internationale Patentklassifikation 4: 1 (11) Internationale Veroffentlichungsnummcr: WO 86/ 06222 H02H 3/33, 3/05 Al (43) Internationales Veriiffentlichungsda!umn± 23. Oktober 1986 (23.10.86) (21) Internationales Aktenzeichen: PCT/DE86/00161 (81) Restimmungsstaaten: AT (europiiisches Patent), AU, BE (europitisches Patent), CH (europfiisches Patent), (22) Internationtales Anmeldedatum: 12. April 1926 (12.04.86) DE (europflisches Patent), FR (europtfisches Patent), JP, LU (europtiisches Patent), NL (europilisches Pa- (31)Prioi ttsa tenelchn: 113/85 tent), SE (europaisches Patent), US.

(32) Prioritaitsdatum: 16. April 1985 (16.04.85) Veriiffentlicht A'fit internationalem Rech erchenberich r.

(33) Prioritiitsland: AT (71) Anmelder (MrT alle Besrtnmmungsstaaten ausser US): &G4;IAgI.4DQZDE]; Kallstadtcr Strasse 1, D-6800.

Mannheim-Kal'f rtal (DE).

(72) Erfinder; und Erfinder/Anmelder (nur filr US) BIEGELMEIER, Gottfried [AT/AT]; Kahlenbergerstrasse 2b, A-I1190 A. '0 J.P,1t 8 Wien AQJP i8 (74) Anwalt: DAHLMANN, Gerhard; Brown, Boveri Cie Aktiengesellschaft, ZPT/P, Postfach 351, D-6800 I AUSTRALIAN Miannh elm 1 NV18 PATENT OFFICE (54) Title: FAULT CURRENT POq9GqCIRCUIT BREAKER (54) Bezelchnung: FEHLERSTROMSCHUTZSCHALTER (57) Abstract The circuit breake.r consists of a housing and contact Li L 2 L 3 N apparatus (17) arrange~d with terminals, a fault current relea- I I IZ17 16 sing device a summation current converter an elec-- tronic circuit (19) dependent of' network voltage, and an en-. ZhL ergy storage circuit (13) independent of network voltage. ForL4J greater simplicity in assembling and manufacture, the device has only one summation current converter (10) and one ftault current releasing device which are used not only for release by the circuit dependent of the network voltage, but also by the circuit independent of the network voltage.

(57) Zusammenfassung 13 Emn Fehlerstromschutzschalter, bestehend aus einem in 10_ elnem Geh'duse mit Anschlussklemmen angeordnetemn Kontaktapparat einemn Fehlerstromausl6ser einemP Sumnmenstromwandler einer netzspannungsabhtlngigen111 Elektronikschaltung (19) und einer netzspannungsunabhfin- 712 gigen Energiespeicherschaltung besitzt zur Vereinfachung der Montage und der Herstellung nur eincn Summenstromwandler (10) und einen Fehlerstromausl~ser die 1 sowohl zur AusI~sung fiber die netzspan nungsu nab htngige- Schaltung als auch fiber die netzspanrnungsabhdngige Elek- ,trontkschaltung verwendet werden, 1-11-1 mm* S1 0* Ok *0

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Fault Current Protective Circuit Breaker The invention relates to a fault current protective circuit breaker.

The impetus for the invention is given by the experience, which has been obtained during the application of fault current protective circuits and which requires novel technological solutions for the purpose of closing the gaps in the extent of protection which have become known in this protective device, which is being used nowadays in many countries.

The three basic circuits possible in the construction of fault current protective switches have been quoted twenty years ago already (Ref. The FI-prote:rive (where "FI" stands for "Fault-Current") circuit breakers, used first in Austria and incorporating impulse or energy storage tripping, were a landmark invention (AT-PS 197,468), have been installed in large numbers and have proved themselves to be reliable. A glow discharge lamp was used initially as a switching device of the energy 20 storage circuit, which made this solution expensive (large number of secondary turns in the summation current transformer) and required too much space. Semiconductor technology however makes available nowadays integrated circuits, which are capable of replacing the glow discharge lamp as a switching device cheaply and with small dimensions. Using switching voltages in the vicinity of 10 volts, they allow relatively small numbers of secondary turns in the summation current transformer and practically any desired tripping characteristic of the protective 30 circuit breaker. For the purpose of maintaining the storage capacitor small as well, permanent magnet triggers are being advantageously used for tripping purposes, which may be set less critically and which can be made to operate with larger triggering forces than in the case of 315< mains voltage independent circuits without any electrical la

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*5 S S energy storage. A modern concept of a fault current protective circuit breaker must however be also able to cater for tripping in the case of fault currents, which may occur in the form of pulsating or smoothed direct currents It has of course always been known, that FI-protective circuit breakers could be effective only in the case of alternating fault currents. If the fault current has direct current components, then this will exert an unfavourable influence onto the tripping sensitivity of the protective circuit breaker.

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i n^&aegccA-ec electronic Jldjag- -leew,4-ts- are being used in domestic appliances, it will be necessary to also resolve the direct current problem. It has been thought for a long time, that in the case of a snort circuit to frame: and in the case of the circuits used in practice for electric domestic appliances, the flowing fault current may occur only in the form of a pulsating direct current It is possible to construct for such fault currentj such as these may occur for example during half-wave rectification without smoothing capacitor, fault curre'lt protective sucsindependent of mains voltage using the classical circuits, therefore also with the energy storage tripping (GB-PS 2 08 408). It has been found however to be hardly possible to impose restrictions upon the manufacturers of electrical appliances with respect to the selection of the electronic circuits required for their appliances c\rcuW- brceA.-e.s because of the FI-protective 0.witches. It will be necessary to specifically mention here in that regard half-wave rectification with smoothing capacitors and 3-phase rectifications.

Mains voltage independent circuits, including those with electrical energy storage, are however unable, because of the transformer type tripping principle, to recognise fault currents in the shape of smoothed direct currents The use of electronic circuits will be required in those cases, which are naturally dependent of the mains voltage and are able to process direct fault currents of all shapes through summation current transformers.

Such circuits are described for example in the US-PS 3,768,011 and the DE-OS 27 30 874. The question arises therefore as to what hazards may arise from the use of the mains as an auxiliary voltage supply for the tripping of fault current protective switchs. If the auxiliary voltage is only derived from an active conductor and from the neutral conductor, then the 'rcit hre.eer .s itch may fail, when the corresponding active conductor o the neutral conductor fails (such as for example a fuse operates in the active conductor Sor the neutral conductor breaks) and fault voltages, which may be generated by short circuits to mass of the other two active conductors, can no longer be recognised. But even if all three active conductors of the 3-phase mains system are used for the supply of the auxiliary voltage, there still always remains the break of the neutral conductor. An attempt has therefore been made to find a remedy by the means, that the FI-sw-tchktrips when the neutral conductor breaks (DE-OS 28 25 881). If an additional connection is S used for this purpose, for example the earth conductor, then this will entail the drawback, that the installation will thus be made more complicated and that the earth potential is being introduced into thesui. This however I I r mr -3will make the circuit more sensitive with respect to overvoltages, which do occur of course mainly with respect to earth. Mains voltage dependent tripping systems suffer however mainly from the drawback, that in the case of short circuits to earth in the protected installation, the magnitude of the voltage for the supply of the auxiliary voltage depends on the ratio of the mains loop resistance between transformer and the connecting points of the auxiliary voltage supply with respect to the total resistance of the fault loop.

This is shown in Figure 1 for the case of the short circuit to earth in an installation with an earthed neutral point.

If one designates: ZL Conductor impedance of the active conductor from the transformer to the fault current protective swr-tch; Z Conductor impedance of the PEN (earthed neutral) conductor from PEN Circu-v bsre es the Transformer to the fault current protective sws h; Z Conductor impedance of the active conductor beyond the fault current SCircu- IbreoskeC protective sw4c-h ntil the location of the fault;

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2 Conductor impedance of the protective conductor from the location of the faut as far as the PEN (earthed neutral) conductor; UN Mains voltage between the active (phase) conductor and the PEN (earthed neutral) conductor; U Supply voltage of the mains votage dependent electronic circuitry; then the following applies for the magnitude of the supply voltage: U a "N L PE 2 2 If therefore the short circuit to frame occurs in the vicinity CvC-c^* brecder of the place of installation of the FIj4ikt w then the auxiliary voltage may become zero, which makes tripping impossible. In those cases the overcurrent protective devices must clear the short circuit to frame, the FI-wi4-. has become inoperative. For this reason, only a so-called "supplementary protection" is achieved through the Fl- in those countries, which use/ w.tes.

with mains dependent tripping systems and it is intended to provide appropriate restrictions into the international regulatory system (Refs. 2 and 3).

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4 It is also of no use if, such as this is stated in the DE-OS 28 25 881, the voltage of the neutral conductor is monitored with respect to the earth conductor. The circuit will namely fail, if a short circuit occurs at the same time as a short circuit to frame. It can be seen from Figure 2, that in CeCu it- brew, er that case the output terminals of the FI-satch are short circuited together crco-C'- bree'her- crcui bfrecKer k with the protective switeh-, the swi4eh is unable to trip and yet, the protected parts of the installation will assume a fault voltage of for example 110 V.

Thi can be seen in Figure 2 with the designation: ZL Conductor impedance of the active conductor from the transformer Circu- bre-c ar to the fault current protective swc-kh; Z Conductor impedance of the neutral conductor from the transformer i ,.TCC)IC C o brs-iker to the faulrcurrent protective sw4ith; ZL" Conductor impedance of the active conductor from the fault current C',r-cuit breeker protectve witch bo the point of short circuit; ZN Conductor impedance of the neutral conductor from the fault current c N 'cui' breer protective swi.tchI Lo the point of short circuit; S= Mains voltage between active conductor and neutral conductor; vo I-tc- e Ua Supply voltage of the mains ependent electronic circuitry; PE Connecting terminal for the earth conductor in the fault current protective/Fwi-tc; Ik Short circuit current; I Fault current; RA Earth resistance of the protected installation; R Earth resistance of the neutral conductor in the transformer substation

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c r 1 If therefore the short circuit occurs in the vicinity of the fault current protectivd wi4-te- then the supply voltage will collapse and the PE-terminal will also assume the potential of the short circuit location.

Crc v brectc-Pr The s.w-4c-lis thus unable to trip under any circumstance. The short circuit current Ik flows through the active conductor and the neutral conductor and the voltage drop in the neutral conductor which is caused by it becomes effective as a fault voltage In the ratio of the installation earth R, to the? system earth RR. The fault current I flowing because cf the fault voltage Art- brec-rl-, is unable however to trip the l.ith because of the absence of the auxiliary voltage UA The following conditions need therefore to be satisfied for the purpose of using a fault current protective switeh for the protection in the case of indirect personal contact (fault protection): C.ircuit \rcocAker The .SwAtE.irl st trip in the case of normal mz.JnE voltage supply in case of the occurance of alternating current fault current and/or direct current fault currents. If it trips in the case of alternating fault currents at the rated value of the tripping fault current I, then it will be adequate for physiological remasors (Ref. if tripping takes place in the case of pulsating direct fault currenis at ha.f-wave rectification at 21x I in the case of full-wave rectification at 2 x I/ 7 hand in the case of smoothed direct fault current at 2.8 x I1. Mains voltage dependent electronic circuits are required to achieve this. Other auxiliary voltage sources, such as for example iatteries, cannot be considered for practical reasons for this application.

c(rcu reo-er- The swt must trip even in the case of a failure (break) of the active (phase) conductors and/or of the newuri-a conductor, as well as in the case of simultaneous (phase) short circuits and short circuits to frame in the case of alternating fault currents. In those cases it does not need to remain functional in the case of direct fault currents since, in the first instance, the simultaneous occurarce of a rnmins su.pp djsturbance and of a direct fault current t-vtpresents a negligible safety risk and in the second instarnco, in the cae of shot ctircuits, the fault potential remains be'cow 120 V with respect to earth due to the potential division betweenc active conductor and neutral conductor in networks of up to 240 V and thus the conventional touch potentii !Jnit, which is 120 V in the case of direct curr!ent is not being exceeded.

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9 9 99 9 Mains supply voltage independent circuits, such as this has already been explained, are unable to recognise smoothened direct currents mains supply voltage dependent designs will fail on the other hand again in the case of a break of the active (phase) conductors and/or of the neutral conductor and in the case of short circuits, if these occur simultaneously with short circuits to frame. The technological requirements with respect to the protection in the case of indirect manual contact thus exclude both mains supply voltage independent circuits as well as mains supply voltage dependent circuits. These apparently contradictory requirements with respect to a fault current protection/circuit breaker for the protection in the case of indirect manual contact (fault (leakage) protection) are advantageously resolved with a favourable economical expenditure by the invention described below.

It would be of course possible, to utilise two FI circuit breakers connected in series, one with a mains 20 voltage dependent circuit to satisfy the protective requirements stipulated in (2 above and a mains voltage dependent design for the protective requirements stipulated in above. This expenditure cannot however be justified on economic grounds. Also the installation 25 of the two systems into a circuit breaker with two summation current transformers and/or two fault current triggers is not possible for economical reasons and because of the required space. This is the reason, why Patent DE-PS 23 48 8il was never applied in practice. It describes a fault current protective circuit breaker with a summation current transformer arrangement with a secondary winding, which is connected with the excitation winding of the fault current trigger, whereby a quiescent current is fed into the secondary winding from an external alternating current source for the purpose of 9999 Si 99 9 9 4 4r 9 9999 9* 9

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S S A fault current protective circuit breaker has become known aui EP-OS 0 113 026 in which a relay is connected simply only through a rectifier circuit to the secondary winding of the summation current transformer. To increase the sensitivity of the tripping circuit it is possible to utilise a capacitor which, together with the inductance residing in the tripping circuit (relay or secondary winding), will form an LC-circuit tuned to the frequency on the secondary side. This known circuit is not an energy storage.

An energy storage circuit has not become known from the US-PS 4 320 433 either.

The present invention provides a fault current c'ircuit breaker, comprising a summation current transformer having primary windings arranged for connection to an electricity supply, and secondary windings, a first fault detection means connected to said secondary windings and comprising a capacitor arranged to be charged on the occurrence of a current fault in the 20 form of an a.c. signal or pulsed a second fault detection means connected to said secondary windings and comprisng an electronic circuit powered by electricity from said electricity supply, said second fault detection means being arranged to detect fault currents having a d.c. component, and a fault current trigger responsive to detection of a fault current by either of the first and second fault detection means to operate a switch to disconnect the electricity supply.

Advantageously the invention gives a fault current 30 protective circuit breaker which is suitable both for alternating fault current as well as for direct fault currents and also for ioternating fault currents incorporating a direct current component and which at the same time is of a simpler construction than, for example, the circuit breaker in accordance with r(-PS 23 48 881.

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7a En contrast with the circuit in accordance with DE-PS 23 48 881 only one summation current transformer is Ibeing used in the arrangement described here in accocdance with the invention and the fault current tripping device, which preferably assume2 the form of a permanent magnet trip, utilised for the mains supply voltage dependent energy storage circuit, is being used also for the tripping through the voltage dependent electronic circuit. This can take place either by means, that a trip coil of the tripping device is triggered through the electronic circuit directly by alternating current or by direct current using energy drawn directly from the supply mains or alternatively the electronic circui- causes the charging of the storage capacitor from the mains when an appropriate fault current flows, whereby the tripping impulse occurs wheni the appropriate charging a 6 voltage has been reached. It is there possible to dimension in accordance with the invention the electronic circuitry in such a manner, that the circuit breaker has 4*as 20 the same tripping characteristic both during mains supply Voltage dependent tripping through the electronic circuitry during the occurrence of direct fault current as well as during mains supply voltage independent tripping through the energy storage circuit, which means therefore, that the same rated values apply for both tripping systems.

-8- The secondary winding of the summation current transformer serves both to charge up the storage capacitor during mains vc .age independent tripping during the occurance of alternating fault current or pulsating direct fault currents, as well as for the control of the electronic circuit, which caters for smooth direct fault current but also pulsating direct fault currents, should the energy storage circuit have been designed for 6an ea r eOm en rne O= alternating fault current only. If, in accordance with the invention, the summation current transformer is equipped both with a secondary winding and with a tertiary winding, then the secondary winding can be utilised for the energy storage circuit and the tertiary winding can be utilised for the control of the electronic circuit. By means of this solution it is possible to galvanically separate the energy storage circuit, if the fault current trigger is equipped in accordance with the invention with two tripping coils.

It is possible to fufrther influence the characteristic tripping CFr T bre or curve of the FI-protective swi h in a'simple and known manner (AT-PS 205 574) by means of generating continuously an artificial fault current through the electronic circuit in the secondary winding or the tertiary winding of the summation current transformer, the magnitude of which is below the response limit of the protective switch. The summation current transformer will then also be pre-excited by this fault current and this will cause the storage capacitor to be partially charged. If now a genuine fault current occurs in the installation, which exceeds the tripping current of the 4-ts then this will cause the residual charging up of the storage capacitor up to the tripping of the energy storage circuit.

This can be achieved in accordance withjhe invention by the means, that the signal current with a suitable frequency and generated by the mains supply voltage dependent electronic circuit, which of course flows through the secondary winding or the tertiary winding of the summation current transformer, induces a voltage in those and thus causes through the rectifier circuit an energy pre-storage of the storage capacitor, The solutions in accordance with the invention will be described below on the basis of examples.

Based on the drawings, which show appropriate circuits and implementation examples of the invention appropriate to the state of technology, it is desired to explain the invention in greater detail and describe it.

YI_ -9- Figures 1 and 2 show two known circuits, which have already been described above; Figures 3, 4 and 5 show each an implementation example of a cr'iM'rt braoilerfault current protective sw4-tc4 n accordance with the invention.

The (active) phase conductors L L 3 and the neutral conductor N of a distribution network are fed as primary windings through the summation current transformer (Item 10). The summation current transformer (Item 10) carries a secondary winding (Item 11), which is feeding a rectifier circuit (Item 12) which is connected in parallel with an energy storage device in the form of a capacitor (Item 13), which capacitor (Item 13) upon reaching a specified charging voltage, renders a threshold switch (Item 14) conductive. In parallel with the energy storage device (Item 13) there is connected a permanent magnet trigger device (Item 15), which trips a latch (Item 16), which opens contacts (Item 17) in the conductors

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I to L 3 and N. By means of the supply lines (Item which are connected to the (active) phase conductor L, and the neutral conductor N, an electronic monitoring device (Item 19) is fed with a voltage, which detects direct fault currents in the secondary winding and is connected with the energy storage device by means of the connecting leads (items 20, 21).

The secondary winding (Item 11) serves therefore both for the charging of the capacitor (Item 13) when alternating fault currents flow and possibly also in the case of pulsating direct fault currerts, as well as for the control of the mtins voltage dependent electronic clcult (Item 19) which, for example, is connected in such a manner, that it is connected in parallel with the capacitor (Item 13), and thus functions also during triggering with tripping impulses through the voltage dependent semiconductor element (Item 14) and the tripping coil of the fault current trip (Item The swUtG.arrangement In accordance with Figure 4 differ.

from that shown in Figure 3 only in that the summation curren tmer (Item 10) has both a secondary winding (Item I1) as well A ii 7 i winding (Item 22)9 whereby the secondary winding is being used for the energy storage circuit and the tertiary winding (Item 22) is being used for the control of the electronic circuit. The fault current trigger (Item 15) incorporates for example two tripping coils (items 15a and 15b). Thus the tripping circuit is separated galvanically from the tripping circuit of the electronic circuit and thus from the supply mains.

A more detailed implementation of the invention can be seen in Figure 5. One can recognise again the (active) phase conductors Lj, L 2 L 3 as well as the neutral conductor N, which are fed in the manner of primary conductors through the summation current transformer (Item The secondary winding (Item 11) feeds the energy storage circuit, which is indicated by a time delay circuit (Item 13) and by a threshold switch or a trigger circuit (Item 14). The output of the circuit (Item 13/14) is fed into the relay (Item 15) and then, when alternating fault currents do occur, the capacitor (Item 13) will be charged and then discharged through the threshold switch (Item 14) into the relay (Item 15) upon reaching a specific charging condition, whereby the contacts (Item 17) will open.

A rectifier (Item 30) is is connected to the (active) phase conductor L 4 and N by means of the conductors (Item 18), which rectifier (Item 30) serves to supply the electronic circuit (Item 19) cortained within the box drawn in broken lines. This electronic circuitr, incorporates essentially an amplifier stage (Item 31), a time delay circuit or an integrator (Item 32) and a threshold switch (Item 33) as well as an oscillator (Item 34). Corresponding to the hysteresis loop of the material of the summaion current transformer, the summation current transformer (Item 10) is being demagnetised or remagnetised with a frequency of preferably 500 Hz by means of the oscillator and through a conductor (item 35) at a tapping point (Item 36) of the secondary winding (Item 11). When a direct fault current or an alternating fnuit current with a direct current component occurs, then the summation current transformer is driven into the direction of saturation, that is therefore into non-symmetry and the thus occuring voltage drop is detected by the switching arrangement (Items 31/32/33) and processed and fed into the energy storage circuit (Items 13/14), which will cause a tripping of the relay (Item 15) and thus an opening of the contacts (Item 17).

I0 t A frequency essentially of from 1000 to 5000 Hz is used for the pre-magnetising of the core for the purpose of detecting direct fault current in the case of the known electronic circuit arrangement. So C'rbCet- bas rdetec that such a fault current protective swi-t-hwould be able to also detect alternating fault currents, it is necessary to generally provide a second summation current transformer, see for example the DE-PS 23 48 881. By the means of reducing the frequency of the oscillator to approx. 500 Hz, it is possible to utilise the summation current transformer as well, which is suitable for alternating iault currents. When thus the current transformer is manufactured from F80-material, then one requires 700 turns on the secdcdary side and the tapping point is made at approx. 100 turns, so that there are approx. 100 turns of the secondary winding between the connection (Item 4u) and the tapping conductor (Item 1

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|t .i 1 i 12 R e f e r e n c e s Biegelmeier, Modern fault current protection.

75th year (1958), No.8, pp. 157-164.

Biegelmeier, Thoughts about the neutral (star-point) earthing STN-system) as an .ptimum fault protection (protective measure for indirect personal contact) in electrical installations, dZE, 37th year (1985), No.12, p.483.

IEC 64 (Central Office) 15'1, 3anuary 1985, IEC Publ. 364 Part 4, Oapter 53 switchgear and controlgear.

fEC-Report 479, second Edition: Effects of electric shock on the human body, Part 2, Chapter

Claims

1. A fault current circuit breaker, comprising a summation current transformer having primary windings arranged for connection to an electricity supply, and secondary windings, a first fault detection means connected to said secondary windings and comprising a capacitor arranged to be charged on the occurrence of a current fault in the form of an a.c. signal or pulsed a second fault detection means connected to said secondary windings and comprising an electronic circuit powered by electricity from said electricity supply, said second fault detection means being arranged to detect fault currents having a d.c. component, and a fault current trigger responsive to detection of a fault current by either of the first and second fault detection means to operate a switch to disconnect the electricity supply.

2. A fault current circuit breaker in accordance with claim i, wherein said second fault detection means is arranged to charge said capacitor of said first fault detection means in response to the occurrence of a fault current having a d.c. component, when the capacitor has been charged to a predetermined threshold voltage it excites a tripping coil of the fault current trigger to disconnect the electricity supply.

3. A fault current circuit breaker in accordance with claims 1 or 2, wherein said electronic circuit is arranged such that the tripping of the fault current circuit breaker takes place with the same characteristic tripping curve as for tripping via the first fault detection means.

4. A fault current circuit breaker in accordance with claims 1, 2 or 3, wherein the secondary windings comprise secondary and tertiary coils of the summation current transformer, the secondary coils being connected to the first fault detection means and the primary coils being connected to the second fault detection means.

Cl x /n -7 -14 A fault current circuit breaker in accordance with any preceding claim, wherein the fault current trigger comprises two tripping coils, one tripping coil being excited in response to the first fault detection means, and the other tripping coil being excited in response to the second fault detection means.

6. A fault current circuit breaker in accordance with any preceding claim, wherein said electronic circuit is arranged to provide an exciting current of a predetermined frequency to the secondary windings of the summation current transformer, causing a pre-charging of said capacitor. DATED this 24 day of October 1989 seeo BROWN BOVERI CIE AKTIENGESELLSCHAFT Patent Attorneys for the Applicant: F.B. RICE CO. 6* 00* 0 5*