CA2266560A1 - Current limiting circuit breakers with ptc (positive temperature coefficient resistivity) elements and arc extinguishing capabilities - Google Patents
Current limiting circuit breakers with ptc (positive temperature coefficient resistivity) elements and arc extinguishing capabilities Download PDFInfo
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- CA2266560A1 CA2266560A1 CA002266560A CA2266560A CA2266560A1 CA 2266560 A1 CA2266560 A1 CA 2266560A1 CA 002266560 A CA002266560 A CA 002266560A CA 2266560 A CA2266560 A CA 2266560A CA 2266560 A1 CA2266560 A1 CA 2266560A1
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- switch
- current
- line
- ptc
- circuit breaker
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01H—ELECTRIC SWITCHES; RELAYS; SELECTORS; EMERGENCY PROTECTIVE DEVICES
- H01H9/00—Details of switching devices, not covered by groups H01H1/00 - H01H7/00
- H01H9/30—Means for extinguishing or preventing arc between current-carrying parts
- H01H9/42—Impedances connected with contacts
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01H—ELECTRIC SWITCHES; RELAYS; SELECTORS; EMERGENCY PROTECTIVE DEVICES
- H01H9/00—Details of switching devices, not covered by groups H01H1/00 - H01H7/00
- H01H9/30—Means for extinguishing or preventing arc between current-carrying parts
- H01H9/32—Insulating body insertable between contacts
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- Emergency Protection Circuit Devices (AREA)
- Arc-Extinguishing Devices That Are Switches (AREA)
- Breakers (AREA)
Abstract
A Positive Temperature Coefficient Resistivity (PTC) element has a resistivity that increases as the temperature increases. Circuit breakers having PTC
elements can achieve better overload and short circuit protection than existing products. Circuit breakers hving PTC elements are also configured as current limiting devices for low, medium and high voltage applications wherein the amount of arcing is reduced and the arc is extinguished by interposition of an insulating body between the contacts.
elements can achieve better overload and short circuit protection than existing products. Circuit breakers hving PTC elements are also configured as current limiting devices for low, medium and high voltage applications wherein the amount of arcing is reduced and the arc is extinguished by interposition of an insulating body between the contacts.
Description
CA 02266~60 1999-03-23 CURRENT LIMITING CIRCUIT BREAKERS WITH PTC
(POSITIVE TEMPERATURE COEF~ICIENT RESISTIVIl~Y) ELEMENTS AND ARC EXTINGUISHING CAPABILITIES
FIELD OF THE INVENTION
The invention relates to the use of mechanical means and elements with Positive Temperature Coefficient E~esistivity (PTC) elements in circuit breakers to limit the arcing that results from the operation of a circuit breaker under short circuit conditions.
BACKGROUND OF THE INVENTION
Circuit breakers are widely used in residential and industrial applicaitons for the interruption of electrcal current in power lines upon conditions of severe overcurrent caused by short circuits or by ground faults. One of the problems associated with the process of interruption of the current during severe overcurrent conditions is arcing.
Arcing occurs between the contacts of circuit breakers used to interrupt the current, which is highly undersirable for several reasons. Arcing causes deterioration of the contacts of the breaker and it causes gas pressure to build up. It also necessitates circuit breakers with larger separation between the contacts in the open position to ensure that the arc does not persist with the contacts in the fully open position.
Prior art devices have used a number of approaches to limit the occurrent of arcing. In heavy duty switchgear, the contact may be enclosed in a vacuum or in an atmosphere of SF6. Both of these approaches are expensive. Besides, SF6 has been identified as a greenhouse gas.
SUt~ 111 ~JTE SHEET (RULE 26) Another approach that has been used to limit the amount of arcing is the use of a resistor co~nccle~l in parallel with the main cor-t~ct~ of the circuit breaker. Upon opc~ng of the main cont~cts, current can still flow through the shunt resistor, effectively reduçing the arnount of arcing in the main contacts. The current flowing through the resistor is less than the short circuit current that would flow through the main contacts in the ~bs~r nce of the resistort and the opening of a second pair of cont~ctc connected in series with the resistor can be açcGI,.rliched with less arcing than would occur in the ahsence of the shunt resistor.
T~r~a et al., teach a circuit breaker in which a resistor-provided UH~I breaker has a tank sealing an inc~ ting gas, a main contact and a resistor unit co~ e~,led in parallel to the main contacts also located in the tank. ~eçh~nicms are provided so that the resistor contact is made before and broken after the main contact is made and broken. The resistor has to be rated to withct~n~l the high currents and te.l~pe.~L~res during short circuit conditions.
Khalid teaches a current limiting circuit breaker in which the current limitin~ contacts are in series with the main co~t~cts of a breaker. Opening of the limiting contacts shunts high fault current through the resistor. The resistor is an iron wire resistor with a positive te.l.pe.~L~lre coefficient (PTC) of recict~nce The flow of the short circuit current through the resistor heats the resistor, thereby increasing its resict~ce and limiting the buildup of the short circuit current.
Perkins et al. describe a PTC resistor that utilizes the metal-inc~ tor solid state SUBSmUTE SHEET (RULE 26) W O 99/10903 PCT~US98/17543 ~rS~c;~ion in (V,Cr)2O~ . At a transition temperature of 80~ C, the resistivity of a ceramic body in~ ding (V,Cr)2O3 increases to a value !~~ times tne value at 20~ C. They ~icclose the use of a PTC element for overcurrent prote~,lion as a s~lbstitute for a bimet~llic strip for overcurrent protection. The switch is connected to a PTC rlo....e.~l that is sh~nted by the actl~tine coil for the switch. During normal operating conditions, the current flows through the PTC resistor. During short circuit conditions, the rapid heating of the PTC resistor leads to an increased r~osict~nce and voltage across the PTC resistor, diverting current through the t~tin~ coil which then trips the switch.
Hansson et al. (U.S. Patent 5,382,938) disclose a PTC cle.~ that is capable of withct~n~iinE short circuit currents without damage, thereby enabling it to be reused. Figure 1 shows a disclosure by Hansson '938 on the use of a PTC ~lPment 22 as an overcurrent protection device for a motor 25. The PTC element is connecte~ in series with a switch 23 and in parallel with an excitation coil 24 that operates the switch 23. An overcurrent in the circuit heats the PTC element 22 and at a certain temperature, its recict~nce rises sharply.
The voltage across the PTC element 22 is then sllfficient to cause the excitation coil 24 to trip the switch 23. ~ansson et al (WO 91/12643) discloses a more complicated invention for motor and short circuit protection using a PTC cl~,nenl. A switch is connected in series with a tli~pillg circuit con~ictin~ oftwo parallel connecte~ current branches. One ofthese branches has the excitation coil for the switch while the other branch has two PTC resistors.
Overcurrent conditions cause a buildup of voltage across the PTC resistors that then activates the eYcit~tion coil for the switch.
SU~ JTE SHEET (RULE 26) W O 99/10903 PCT~US98/17543 Chen (!J.S. Patent 5,629,658) cliscloses a number of devices in which PTC el~ \,r~
are used in conj--nction with two or more switches to limit the current under short circuit conditions and thereby reduce the associated arcing.
One problem with PTC resistors is their durability: they have to be desigred to with.ct~ntl the heating that accompanies short circuit currents. This can make their use more e,~p~,..s;~e unless arrangements are made to limit this he~tin~
Yet another approach used to reduce arcing in switchgear involves the use of meçh~ni~ l means to break the arc. Belbel et al. (U.S. Patent 4,562,323) discloses a switch in which an electrically in~nl~tinp screen is inserted between the contacts during the opening of the con~ac,Ls. The control of the movement of the screen is obtained by propulsion means separate from those causing the separation of the contacts. Belbel et al. (U. S. Patent 4,677,266) disclose another switch that has an in.c~ tirtg screen that adapts the breaking speed as the current increases. Brak~rwsh et al. (U.S. Patent 4,801,772) disclose a current limiting circuit interrupted in which an incul~ting wedge is inserted between the contact arms as they open.
Most ofthe prior art methods ~iscl~ssed above are addressed towards industrial applic~tion~. For re~ nti~l use, even though the voltage and the loads are smaller, co~ ,;ally available circuit breakers still have a significant amount of arcing accompanying their operation. The present invention achieves interruption of electrical currents with a S~a~ TE SHEET(RULE 26) W O 99/10903 PCT~US98/17543 reduction in arcing, noise and gas venting. The present invention also reduces the cost and enClos~lre requiren~e.l~s for residenti~l circuit breakers and increases the switching capacity of a normal relay.
~ -~dition~lly~ the invention improves the operation of circuit breakers when a ground fault is detected without a mesh~nic~l linkage between the ground fault circuit and the circuit breaker. For heavy duty and high voltage devices, the invention replaces SF6 and vacuum switcllg~r by air circuit breakers while accomplishing many of the objectives listed above.
SUMMARY OF T~E INVEN~ION
One aspect of the invention uses a PTC element in a circuit breaker in series with a power line. The voltage increase across the PTC element during an overload is used to drive a relay coil for opening the main contzlcts In order to prevent heat d~m~e to the PTC
~Ir....f..ll ~ during a short circuit, one or more metal oxide varistors are in parallel with the PTC
component. This limits the m~6mllm voltage (and hence the amount of heating) that occurs in the PTC el~ nt Another aspect of the invention is the ability of a circuit breaker incorporating a PTC element to respond to ground faults. A ground fault interrupter circuit is used to en~ e a trip coil wound on the same core as the relay coil. In another embo~lim~nt the trip coil is elimin~ted and the full line voltage is applied to the relay coil.
Another embodiment of the invention uses a switching device that is triggered by a SUBS 1 l 1 UTE SHEET (RULE 26) CA 02266560 l999-03-23 W O 99/10903 PCT~US98/17543 ground fault sensing circuit to short the line; the r~s~lting short circuit current operates the circuit breaker having a PTC elt,. . .l'~ .1 Another aspect of the invention is the use of PTC elPments in a current limiting circuit breaker. The current limiting breaker could be used in low, medil1~ and high voltage switching devices. Two pairs of contacts are provided in series with the line and in parallel vvith each other. The main contacts are provided with an inc~ ting wedge that breaks the arc.
The inclll~ting wedge is driven by the m~gnetic forces caused by the short circuit line current.
Upon opening of the main contacts, the current flows through the secondary contacts that are provided with a PTC PIPmPnt; the pl esence of the secondary contacts limits the arcing in the main cQnt~cts while the PTC elemPnt limits the current that has to be interrupted by the secon.i~ry contacts. In an alternate embodiment, the secondary contacts are ~ ted and the invention is used as an accessory module in conjunction with another circuit breaker.
Examples ofthe more important features ofthe invention have been s~mm~rized rather broadly in order that the det~iled description thereofthat follows may be better understood, and in order that the contributions to the art may be appreciated. There are, of course, a(l~lition~l features of the invention that will be described hereinafter and which will form the subject of the claims appended hereto.
BRIEF DESCRIPTION OF THE FIGURES
SUb~~ TE SHEFT(RULE 26) W O 99/10903 PCT~US98/17543 For dç~ ed unde. ~n'3;~8 of the present invention, r~fcre. ce should be made to the following det~iled desc.il,lion of the p,~,fe..ed embo~iment, taken in conjunction with the acco...l ~nying drawings, in which like ~1~..,~".,l~ have been given like numerals, and wherein:
Figure I (prior art) shows the use of a PTC element as an overcurrent protection device for a motor.
Figure 2 shows the use of a PTC pl~mPnt in accordance with this invention Figure 3 shows a n~gn~;c relay that can be used to operate the invention of figure 1.
Figure 4 shows one way in which the invention can be adapted to respond to ground faults.
Figure 5 shows a second manner in which the invention can be used to respond to ground faults.
Figure 6 illustrates the use of a PTC breaker in association with a shorting switch to respond to ground fault currents Figures 7 and 8 illustrate a current limiting PTC circuit breaker provided with a wedge ...c;.h~-;c... for breaking the arc.
Figure 9 illustrates a current limitin~ PTC module provided with a wedge mech~ni~m for breaking the arc.
DETAILED DESCRIPTION OF T~IE INVENTION
Figure 1 shows a prior art device that uses a PTC element 22 as an overcurrent protection device for a motor 25. The PTC element is connected in series with a switch 23 and in parallel with an excitation coil 24 that operates the switch 23. An overcurrent in the SUBSTITUTE SHEET~RULE 26) CA 02266~60 1999-03-23 circuit heats the PTC ele~ 22 snd at a certain te..,~e.aL~lre, its recict~n~e rises sharply.
The voltage across the PTC ele~nent 22 is then s~fficiç~t to cause the excitation coil 24 to trip the switch 23.
One drawback of the prior art device of figure 1 is that there is nothing to limit the voltage across PTC element. This problem is overcome in one embodiment of the present invention shown in figure 2. The circuit breaker 100 is connected in series to the line 99.
Internal to the circuit breaker are the co~t~cts 101. In series with the contacts are the PTC
cl~....P...~ 103 .chlmted by one or more varistors. The PTC components could be made from conductive polymers, ceramic BaTiO3, or any other PTC material having a resistivity greater than 0. l n cm. at room temperature. In order to limit the complexity of the figure, only one varistor, 105, is shown. The purpose of the varistor 105 is to protect the PTC component.
The rated voltage of the varistor has to be equal to or smaller than the rated voltage of the PTC component. In other words, the clarnping voltage of the varistor has to be equal to or smaller than the transient failure voltage of the PTC component. The pair of separable co~t~ctc, 101, in line ~,vith the PTC components are driven to open by a coil connected in parallel with the PTC component. A meCh~nicm similar to the m~netic l~tching relay shown in figure 3 could be used for the purpose.
The magrletic l~tçhing device of figure 3 comprises, a stiffcopperblade 117 att~chPd to a base 110 by means of suitable support, 111. The free end ofthe copper blade 117, carries the movable contact 101a. A pe.",anellt magnet, 113, and tension spring, 115, keep SUBSTITUTE SHEET (RULE 26) CA 02266~60 1999-03-23 the cont- ,tc closed under norrnal co~ tions. The coil 107 is wound on a core 121. Under short circuit con~iti~nc, the coil 107 is el~er~i~e~ and the magnetic field produced therein moves the contact 101a away from the fixed contact 101b, thus breaking the circuit. A novel feature of the device in figure 3 is shown by the body 117a of the stiff copper blade forming the moveable contact and 117b ofthe fixed contact 101b: these form a reverse current loop such that during short circuit conditions, there is a repulsive force between portions 117a and 117b that forces the contact 101a away from the fixed contact 101b. Once the contacts have opened, the pe..llane,lL magnet 113 serves to keep contacts latched in the open position.
Another embodiment of the invention, illustrated in figure 4, shows how a circuit breaker of the present invention can interrupt the flow of current when a ground fault occurs.
As would be known to those versed in the art, a ground fault interruption circuit is dçcig to interrupt the electric current to the load when a fault current to ground exceeds some predetermined value that is less than that required to operate the overcurrent protective device of the supply circuit. As in figure 2, the contacts 101 are in series with the live line, 99. The neutral line 121 is also in-liç~ted in figure 4. A ground fault detectio~ circuit, 123, is on the load side of the circuit breaker. The ground fault detection circuit, 123, sends a signal to a ground fault circuit board, 125, upon occurrence of a ground fault. The ground fault circuit board activates a trip coil, 127, that is also capable of operating the contacts 101. The trip coil 127 and the relay coil 107 could be wound on the sarne core. The relay coil will be ene.gized to trip the breaker whenever there is an overload or short circuit. The trip coil will be energized to trip the circuit breaker whenever there is a ground fault in the circuit.
SIJtlS ~ TE SHEET (RULE 26) .. . . . ~
W O 99/10903 PCT~US98/17543 An alternate embo~ nt of the circuit breaker of the present invention e~ ina~rQ the use of a second coil for ground fault interruption. It is illustrated in figure 5. As in the embodiment of figure 4, the cort~ctc are on the live line 99. The ground fault detection circuit, 123, sends a signal to the ground fault circuit board, 125, upon detection of a ground fault. The ground fault circuit board in~ des an SCR, 129, that closes upon detection of a ground fault. The effect of this is to apply the full line voltage across the relay coil, 107, thus activating it; the PTC el~ nt 103 and the varistor 105 are bypassed. The diodes 130 ensure that there will be no short circuit current flowing through the PTC el~oment 103 in the event of a ground fault. The embodiment of the invention shown in figure S is mec.h~nic~lly simpler than the one of figure 4 in that there is only one coil to operate the switching.
An alternate embodiment of the invention, illustrated in figure 6, elimin,ttes the diodes 127 in figure 5. The switch, 131, shorts the line to ground, causing a large short circuit current to fiow through the line. The breaker then operates as a short circuit protection device: the current cause heating of the PTC element, 103, leading to a buildup of voltage across the coil 107, causing the contacts to operate. The switch 131 could be an SCR as in figure 5. An advantage of this system is that no linkage is required between the ground fault detection circuit and the circuit breaker. This allows the m~tr~l~f~ct~lre of'Lstandard circuit breakers" using high volume, cost effective m~tt~nf~ctttt ing, without the loss of offering a Ground Fault Interruption (GFI) product; the GFI product could be sold as an ~cce.~so-y that could be either factory or field installed.
S~ UTE SHEET~RULE 2~) CA 02266~60 1999-03-23 The embo~iments discl~c~se~l above are particularly suit~hle for use in residenti~l applie.,l;ons with small ampere ratings. However, for industrial circuit breakers with large ampere ratings, embo~im~ntc of the invention diccl~esed below are particularly useful.
Figure 7 shows a s~l-P ..~tic diagram of a type of circuit breaker that is a current limiter. The breaker is provided with a pair of main cont~cts, 145a and 145b, and a pair of seCQnr~ry contacts, 147a and 147b. The line tenr~nal, l4l~iscQrm~cted by a first flexible co~ e~,ler ("pig tail" ) to a movable magnetic plate, 149. The m~gnetic plate, 149,is co~ e~,led by means of a second pig tail, 153, to a fixed m~gnetic plate, 157. The fixed ma~etiC plate, 157,isconnçcterl to one ofthe the main contacts, 145a, and one ofthe secondal~cont~c~s,l47a Contacts 145a and 147a are the fixed contacts. The movable main contact 145bis connecled through the main blade, 169 and pig tail 165, to the load terminal 143. The movable secondary contact, 147b,is connected through the secondary blade, 168 to a PTC element 167. In the preferred embodiment, the PTC element 167is made of t.-ng.cte.n The p,~,fe..~d shape ofthe PTC ele."ent is the se~.,Li~le shape shown in the figures: this reduces the inrll~ct~nce of the PTC ek....~.nt The PTC elementl67is, in turn col~ne~led to the load terminal 143.
The movable m~gr etic plate 149iS provided with a spring 159 to control its operation and is l..ec~ ;c~lly coupled to an ins~ ting wedge 161, disposed so as to be capable of insertion between the main contacts 145a and 145b The wedge is preferably made of glass filled nylon. In the ~left..ed embodiment, a conventional mech~nicm, not shown, can move SU85nTUTE SHEET (RULE 2~) .. . .
btades 167 and 169 and open the main cont~ctc 145a and 145b and the seco~ry co~t~ctc 147a and 147b. Other mçch~nicmc could also be used and are consi~ered to be within the scope of the invention. For keeping the figures simple, these meçh~nismc are not shown.
The operation of the circuit breaker is best understood by concidering what happ~,n when a short circuit occurs. The fixed m~gnetic plate 157 and the movable m~8r ÇtiG plate 149 form a reverse current loop, carrying current in opposite directions. During short circuit con-litionc, this produces a strong repulsive force on the movable m~gnetic plate, 149, causing it to move the inc.ll~tinE wedge 161 bet ,veen the main contacts 145a and 145b. The wedge, 161, extin~iches the arc between the main contacts. The reverse current loop should preferably be designed to provide a driving force that can accelerate the wedge at at least 5000 m/s2. The wedge, being quickly driven between the main contacts 145a and 145b, causes the arc to be çxtin~lichecl in less than t~,vo milliseconds. The current then flows through the seconda,y contacts, 147a and 147b, and the PTC element 167. It is preferable that the voltage drop across the PTC ele~ be less than 15 volts at the IIlOlllf ~-L of opening of the main co~t~ctc 145a and 145b.
The recict~nce ofthe PTC elernent 167 is increased to at least 10 times its room te...~ re value as the PTC element is heated by the current The PTC elf mf~nt is specially desi~ed to urithct~n-l the he~ting The secondary contacts then open to interrupt the circuit.
Under norrnal operations, most of the current goes through the main contacts. The SlJ~ UTE SHEFT (RULE 26) , . .. . .
cliG force produced by the current in the reverse loop is not large enough to drive the wedge and the contact force between the main contacls is not arr~,eled by the wedge. Since the cold r~Cispnce of the tlmgcten wire used as a PTC cle.--e..l is at least ten times greater than the main contact reCict~n~e~ Iittle current is chllnted through the tl~ngcten wire, lceeping its t~ ~lp~ahlre low.
An alternate arr~ng~mPnt, shown in figure 8, ~ ).h-~tes the reverse current loop. The line terminal 181 is co.-l-e~,le(1 to the st~tion~ly main contact 187a and the st~tion~ry secondary contact 185a. The movable main contact 187b is connected to the load terminal 183 by means of a flexible connector 196 while the movable secondary contact 185b is connected to the PTC elemrnt 199 by a flexible connector 197. The PTC element 199 is, in turn, col-l-P~,Iecl to the load terminal 183.
The wedge 193, adapted to be driven between the main contacts, is mec.h~njcally ~ttnchPd to the movable m~netic plate 191. The movable m~gnetic plate 191 is simply placed close to a current carrying bus 195. A short circuit current flowing through the bus is sllffiri~.nt to cause motion ofthe m~etic plate 191 which, in turn, causes the wedge 193 to eYtin~.ich the arc between the main contacts 187a and 187b.
As noted above, the merh~nicm for causing the movement ofthe main and second~ry breaker cont~ctC is not diccncsed here. A variety of methods could be used. The sequence of operations is important. Proper operation of the invention requires that the secondary SUBS I I I UTE SHEET (RULE 26) . .
W O 99/10903 PCTrUS98/17543 contacts open after the wedge has opened the main cont~cts during a short circuit interruption.
A portion of the dev~ce of figures 7 or 8 could be used as a current limiting mo~lle This is illustrated in figure 9, where such a module, designed to be used in senes with another circuit breaker, is shown.
The module is provided with a pair of main contacts, 215a and 215b. The line terminal, 201, is co~ne~,led by a first pig tail to a movable m~gnetic plate, 203. The m~ netic plate, 203, is connected by means of a second pig tail, 207, to a fixed m~gnetic plate, 209.
The fixed m~etic plate, 209, is connected to the fixed contact 215a, and the PTC element 219. The movable contact 215b is co.-ne~te~l through the blade, 217 and pig tail 221, to the load terminal 223. In the p-t;iel,ed embodiment, the PTC çlement 219 is made of tnng~t~rt The p-efe.led shape ofthe PTC cl~.,.c.,~ is the serpentine shape shown in the figures: this reduces the in~uct~nce of the PTC elçm~nt The PTC cle...~ 219 is, in tum connected to the load terrninal 223.
The movable m~e,netic plate 203 is provided with a spring 211 to control its operation and is ~IC~ I,Anic~lly coupled to an in~nl~ting wedge 213, disposed so as to be capable of insertion bet~,veen the collt~ctc 215a and 215b. The wedge is preferably made of glass filled nylon. In the p.ef~,.,ed embo~im~nt~ insertion ofthe wedge also causes a m.~nh~nism, not shown, to move blade 217 and open the contacts 215a and 215b. It is also possible to have a SUBS 111 UTE SHEET (RULE 26) "~ h~ c~ in~ep~nl1pnt ofthe ~,vedge, for sensing overcurrents and causing the opc,~ing of the movable cQîltacts; this would lead to a more e.~e,-s;~e device. Other mer.h~ni.cmc could also be used and are considered to be within the scope of the invention. For simplifying the figure, these merh~ni$mc are not shown.
The main di~I~. cnce, between the operation of the module shown in figure 9 and of the circuit breaker of figure 8 is the ~bsence of the seCo~ry cQn~cts in the former. The device of figure 9 acts as a current lirniter and col.lplete interruption is pc.ro."lcd by a breaker for which the device of figure 9 is an accessory.
The filn~mpnt~l concept of the devices of figures 7 - 9 is to convert most of the interruption energy into heating the PTC Plement, instead of generating an arc and gas pressure during a short circuit interruption, as happens in conventional prior art devices. In existing mPtlinnl and high voltage circuit breakers, SF6 or a vacuum has to be used to suppress the arcing. In the present invention, the arcing is greatly reduced, so that SF6 or a vacuum are no longer nf.ce.~s~. y. This makes it possible to build air circuit breakers to perform the same fimction This reduces the cost considerably.
Several embo-limPnts of the invention have been described. It will be obvious to those skilled in the art that various ~h~ngPs and modifications may be made therein ~,vithout departing from the intent of the invention, and the purpose of the claims is to cover all such çh~ng~s and modifications as fall within the true spirit and scope of the invention.
SUBSTrrUrE S~EET(RULE 26) . . ,
(POSITIVE TEMPERATURE COEF~ICIENT RESISTIVIl~Y) ELEMENTS AND ARC EXTINGUISHING CAPABILITIES
FIELD OF THE INVENTION
The invention relates to the use of mechanical means and elements with Positive Temperature Coefficient E~esistivity (PTC) elements in circuit breakers to limit the arcing that results from the operation of a circuit breaker under short circuit conditions.
BACKGROUND OF THE INVENTION
Circuit breakers are widely used in residential and industrial applicaitons for the interruption of electrcal current in power lines upon conditions of severe overcurrent caused by short circuits or by ground faults. One of the problems associated with the process of interruption of the current during severe overcurrent conditions is arcing.
Arcing occurs between the contacts of circuit breakers used to interrupt the current, which is highly undersirable for several reasons. Arcing causes deterioration of the contacts of the breaker and it causes gas pressure to build up. It also necessitates circuit breakers with larger separation between the contacts in the open position to ensure that the arc does not persist with the contacts in the fully open position.
Prior art devices have used a number of approaches to limit the occurrent of arcing. In heavy duty switchgear, the contact may be enclosed in a vacuum or in an atmosphere of SF6. Both of these approaches are expensive. Besides, SF6 has been identified as a greenhouse gas.
SUt~ 111 ~JTE SHEET (RULE 26) Another approach that has been used to limit the amount of arcing is the use of a resistor co~nccle~l in parallel with the main cor-t~ct~ of the circuit breaker. Upon opc~ng of the main cont~cts, current can still flow through the shunt resistor, effectively reduçing the arnount of arcing in the main contacts. The current flowing through the resistor is less than the short circuit current that would flow through the main contacts in the ~bs~r nce of the resistort and the opening of a second pair of cont~ctc connected in series with the resistor can be açcGI,.rliched with less arcing than would occur in the ahsence of the shunt resistor.
T~r~a et al., teach a circuit breaker in which a resistor-provided UH~I breaker has a tank sealing an inc~ ting gas, a main contact and a resistor unit co~ e~,led in parallel to the main contacts also located in the tank. ~eçh~nicms are provided so that the resistor contact is made before and broken after the main contact is made and broken. The resistor has to be rated to withct~n~l the high currents and te.l~pe.~L~res during short circuit conditions.
Khalid teaches a current limiting circuit breaker in which the current limitin~ contacts are in series with the main co~t~cts of a breaker. Opening of the limiting contacts shunts high fault current through the resistor. The resistor is an iron wire resistor with a positive te.l.pe.~L~lre coefficient (PTC) of recict~nce The flow of the short circuit current through the resistor heats the resistor, thereby increasing its resict~ce and limiting the buildup of the short circuit current.
Perkins et al. describe a PTC resistor that utilizes the metal-inc~ tor solid state SUBSmUTE SHEET (RULE 26) W O 99/10903 PCT~US98/17543 ~rS~c;~ion in (V,Cr)2O~ . At a transition temperature of 80~ C, the resistivity of a ceramic body in~ ding (V,Cr)2O3 increases to a value !~~ times tne value at 20~ C. They ~icclose the use of a PTC element for overcurrent prote~,lion as a s~lbstitute for a bimet~llic strip for overcurrent protection. The switch is connected to a PTC rlo....e.~l that is sh~nted by the actl~tine coil for the switch. During normal operating conditions, the current flows through the PTC resistor. During short circuit conditions, the rapid heating of the PTC resistor leads to an increased r~osict~nce and voltage across the PTC resistor, diverting current through the t~tin~ coil which then trips the switch.
Hansson et al. (U.S. Patent 5,382,938) disclose a PTC cle.~ that is capable of withct~n~iinE short circuit currents without damage, thereby enabling it to be reused. Figure 1 shows a disclosure by Hansson '938 on the use of a PTC ~lPment 22 as an overcurrent protection device for a motor 25. The PTC element is connecte~ in series with a switch 23 and in parallel with an excitation coil 24 that operates the switch 23. An overcurrent in the circuit heats the PTC element 22 and at a certain temperature, its recict~nce rises sharply.
The voltage across the PTC element 22 is then sllfficient to cause the excitation coil 24 to trip the switch 23. ~ansson et al (WO 91/12643) discloses a more complicated invention for motor and short circuit protection using a PTC cl~,nenl. A switch is connected in series with a tli~pillg circuit con~ictin~ oftwo parallel connecte~ current branches. One ofthese branches has the excitation coil for the switch while the other branch has two PTC resistors.
Overcurrent conditions cause a buildup of voltage across the PTC resistors that then activates the eYcit~tion coil for the switch.
SU~ JTE SHEET (RULE 26) W O 99/10903 PCT~US98/17543 Chen (!J.S. Patent 5,629,658) cliscloses a number of devices in which PTC el~ \,r~
are used in conj--nction with two or more switches to limit the current under short circuit conditions and thereby reduce the associated arcing.
One problem with PTC resistors is their durability: they have to be desigred to with.ct~ntl the heating that accompanies short circuit currents. This can make their use more e,~p~,..s;~e unless arrangements are made to limit this he~tin~
Yet another approach used to reduce arcing in switchgear involves the use of meçh~ni~ l means to break the arc. Belbel et al. (U.S. Patent 4,562,323) discloses a switch in which an electrically in~nl~tinp screen is inserted between the contacts during the opening of the con~ac,Ls. The control of the movement of the screen is obtained by propulsion means separate from those causing the separation of the contacts. Belbel et al. (U. S. Patent 4,677,266) disclose another switch that has an in.c~ tirtg screen that adapts the breaking speed as the current increases. Brak~rwsh et al. (U.S. Patent 4,801,772) disclose a current limiting circuit interrupted in which an incul~ting wedge is inserted between the contact arms as they open.
Most ofthe prior art methods ~iscl~ssed above are addressed towards industrial applic~tion~. For re~ nti~l use, even though the voltage and the loads are smaller, co~ ,;ally available circuit breakers still have a significant amount of arcing accompanying their operation. The present invention achieves interruption of electrical currents with a S~a~ TE SHEET(RULE 26) W O 99/10903 PCT~US98/17543 reduction in arcing, noise and gas venting. The present invention also reduces the cost and enClos~lre requiren~e.l~s for residenti~l circuit breakers and increases the switching capacity of a normal relay.
~ -~dition~lly~ the invention improves the operation of circuit breakers when a ground fault is detected without a mesh~nic~l linkage between the ground fault circuit and the circuit breaker. For heavy duty and high voltage devices, the invention replaces SF6 and vacuum switcllg~r by air circuit breakers while accomplishing many of the objectives listed above.
SUMMARY OF T~E INVEN~ION
One aspect of the invention uses a PTC element in a circuit breaker in series with a power line. The voltage increase across the PTC element during an overload is used to drive a relay coil for opening the main contzlcts In order to prevent heat d~m~e to the PTC
~Ir....f..ll ~ during a short circuit, one or more metal oxide varistors are in parallel with the PTC
component. This limits the m~6mllm voltage (and hence the amount of heating) that occurs in the PTC el~ nt Another aspect of the invention is the ability of a circuit breaker incorporating a PTC element to respond to ground faults. A ground fault interrupter circuit is used to en~ e a trip coil wound on the same core as the relay coil. In another embo~lim~nt the trip coil is elimin~ted and the full line voltage is applied to the relay coil.
Another embodiment of the invention uses a switching device that is triggered by a SUBS 1 l 1 UTE SHEET (RULE 26) CA 02266560 l999-03-23 W O 99/10903 PCT~US98/17543 ground fault sensing circuit to short the line; the r~s~lting short circuit current operates the circuit breaker having a PTC elt,. . .l'~ .1 Another aspect of the invention is the use of PTC elPments in a current limiting circuit breaker. The current limiting breaker could be used in low, medil1~ and high voltage switching devices. Two pairs of contacts are provided in series with the line and in parallel vvith each other. The main contacts are provided with an inc~ ting wedge that breaks the arc.
The inclll~ting wedge is driven by the m~gnetic forces caused by the short circuit line current.
Upon opening of the main contacts, the current flows through the secondary contacts that are provided with a PTC PIPmPnt; the pl esence of the secondary contacts limits the arcing in the main cQnt~cts while the PTC elemPnt limits the current that has to be interrupted by the secon.i~ry contacts. In an alternate embodiment, the secondary contacts are ~ ted and the invention is used as an accessory module in conjunction with another circuit breaker.
Examples ofthe more important features ofthe invention have been s~mm~rized rather broadly in order that the det~iled description thereofthat follows may be better understood, and in order that the contributions to the art may be appreciated. There are, of course, a(l~lition~l features of the invention that will be described hereinafter and which will form the subject of the claims appended hereto.
BRIEF DESCRIPTION OF THE FIGURES
SUb~~ TE SHEFT(RULE 26) W O 99/10903 PCT~US98/17543 For dç~ ed unde. ~n'3;~8 of the present invention, r~fcre. ce should be made to the following det~iled desc.il,lion of the p,~,fe..ed embo~iment, taken in conjunction with the acco...l ~nying drawings, in which like ~1~..,~".,l~ have been given like numerals, and wherein:
Figure I (prior art) shows the use of a PTC element as an overcurrent protection device for a motor.
Figure 2 shows the use of a PTC pl~mPnt in accordance with this invention Figure 3 shows a n~gn~;c relay that can be used to operate the invention of figure 1.
Figure 4 shows one way in which the invention can be adapted to respond to ground faults.
Figure 5 shows a second manner in which the invention can be used to respond to ground faults.
Figure 6 illustrates the use of a PTC breaker in association with a shorting switch to respond to ground fault currents Figures 7 and 8 illustrate a current limiting PTC circuit breaker provided with a wedge ...c;.h~-;c... for breaking the arc.
Figure 9 illustrates a current limitin~ PTC module provided with a wedge mech~ni~m for breaking the arc.
DETAILED DESCRIPTION OF T~IE INVENTION
Figure 1 shows a prior art device that uses a PTC element 22 as an overcurrent protection device for a motor 25. The PTC element is connected in series with a switch 23 and in parallel with an excitation coil 24 that operates the switch 23. An overcurrent in the SUBSTITUTE SHEET~RULE 26) CA 02266~60 1999-03-23 circuit heats the PTC ele~ 22 snd at a certain te..,~e.aL~lre, its recict~n~e rises sharply.
The voltage across the PTC ele~nent 22 is then s~fficiç~t to cause the excitation coil 24 to trip the switch 23.
One drawback of the prior art device of figure 1 is that there is nothing to limit the voltage across PTC element. This problem is overcome in one embodiment of the present invention shown in figure 2. The circuit breaker 100 is connected in series to the line 99.
Internal to the circuit breaker are the co~t~cts 101. In series with the contacts are the PTC
cl~....P...~ 103 .chlmted by one or more varistors. The PTC components could be made from conductive polymers, ceramic BaTiO3, or any other PTC material having a resistivity greater than 0. l n cm. at room temperature. In order to limit the complexity of the figure, only one varistor, 105, is shown. The purpose of the varistor 105 is to protect the PTC component.
The rated voltage of the varistor has to be equal to or smaller than the rated voltage of the PTC component. In other words, the clarnping voltage of the varistor has to be equal to or smaller than the transient failure voltage of the PTC component. The pair of separable co~t~ctc, 101, in line ~,vith the PTC components are driven to open by a coil connected in parallel with the PTC component. A meCh~nicm similar to the m~netic l~tching relay shown in figure 3 could be used for the purpose.
The magrletic l~tçhing device of figure 3 comprises, a stiffcopperblade 117 att~chPd to a base 110 by means of suitable support, 111. The free end ofthe copper blade 117, carries the movable contact 101a. A pe.",anellt magnet, 113, and tension spring, 115, keep SUBSTITUTE SHEET (RULE 26) CA 02266~60 1999-03-23 the cont- ,tc closed under norrnal co~ tions. The coil 107 is wound on a core 121. Under short circuit con~iti~nc, the coil 107 is el~er~i~e~ and the magnetic field produced therein moves the contact 101a away from the fixed contact 101b, thus breaking the circuit. A novel feature of the device in figure 3 is shown by the body 117a of the stiff copper blade forming the moveable contact and 117b ofthe fixed contact 101b: these form a reverse current loop such that during short circuit conditions, there is a repulsive force between portions 117a and 117b that forces the contact 101a away from the fixed contact 101b. Once the contacts have opened, the pe..llane,lL magnet 113 serves to keep contacts latched in the open position.
Another embodiment of the invention, illustrated in figure 4, shows how a circuit breaker of the present invention can interrupt the flow of current when a ground fault occurs.
As would be known to those versed in the art, a ground fault interruption circuit is dçcig to interrupt the electric current to the load when a fault current to ground exceeds some predetermined value that is less than that required to operate the overcurrent protective device of the supply circuit. As in figure 2, the contacts 101 are in series with the live line, 99. The neutral line 121 is also in-liç~ted in figure 4. A ground fault detectio~ circuit, 123, is on the load side of the circuit breaker. The ground fault detection circuit, 123, sends a signal to a ground fault circuit board, 125, upon occurrence of a ground fault. The ground fault circuit board activates a trip coil, 127, that is also capable of operating the contacts 101. The trip coil 127 and the relay coil 107 could be wound on the sarne core. The relay coil will be ene.gized to trip the breaker whenever there is an overload or short circuit. The trip coil will be energized to trip the circuit breaker whenever there is a ground fault in the circuit.
SIJtlS ~ TE SHEET (RULE 26) .. . . . ~
W O 99/10903 PCT~US98/17543 An alternate embo~ nt of the circuit breaker of the present invention e~ ina~rQ the use of a second coil for ground fault interruption. It is illustrated in figure 5. As in the embodiment of figure 4, the cort~ctc are on the live line 99. The ground fault detection circuit, 123, sends a signal to the ground fault circuit board, 125, upon detection of a ground fault. The ground fault circuit board in~ des an SCR, 129, that closes upon detection of a ground fault. The effect of this is to apply the full line voltage across the relay coil, 107, thus activating it; the PTC el~ nt 103 and the varistor 105 are bypassed. The diodes 130 ensure that there will be no short circuit current flowing through the PTC el~oment 103 in the event of a ground fault. The embodiment of the invention shown in figure S is mec.h~nic~lly simpler than the one of figure 4 in that there is only one coil to operate the switching.
An alternate embodiment of the invention, illustrated in figure 6, elimin,ttes the diodes 127 in figure 5. The switch, 131, shorts the line to ground, causing a large short circuit current to fiow through the line. The breaker then operates as a short circuit protection device: the current cause heating of the PTC element, 103, leading to a buildup of voltage across the coil 107, causing the contacts to operate. The switch 131 could be an SCR as in figure 5. An advantage of this system is that no linkage is required between the ground fault detection circuit and the circuit breaker. This allows the m~tr~l~f~ct~lre of'Lstandard circuit breakers" using high volume, cost effective m~tt~nf~ctttt ing, without the loss of offering a Ground Fault Interruption (GFI) product; the GFI product could be sold as an ~cce.~so-y that could be either factory or field installed.
S~ UTE SHEET~RULE 2~) CA 02266~60 1999-03-23 The embo~iments discl~c~se~l above are particularly suit~hle for use in residenti~l applie.,l;ons with small ampere ratings. However, for industrial circuit breakers with large ampere ratings, embo~im~ntc of the invention diccl~esed below are particularly useful.
Figure 7 shows a s~l-P ..~tic diagram of a type of circuit breaker that is a current limiter. The breaker is provided with a pair of main cont~cts, 145a and 145b, and a pair of seCQnr~ry contacts, 147a and 147b. The line tenr~nal, l4l~iscQrm~cted by a first flexible co~ e~,ler ("pig tail" ) to a movable magnetic plate, 149. The m~gnetic plate, 149,is co~ e~,led by means of a second pig tail, 153, to a fixed m~gnetic plate, 157. The fixed ma~etiC plate, 157,isconnçcterl to one ofthe the main contacts, 145a, and one ofthe secondal~cont~c~s,l47a Contacts 145a and 147a are the fixed contacts. The movable main contact 145bis connecled through the main blade, 169 and pig tail 165, to the load terminal 143. The movable secondary contact, 147b,is connected through the secondary blade, 168 to a PTC element 167. In the preferred embodiment, the PTC element 167is made of t.-ng.cte.n The p,~,fe..~d shape ofthe PTC ele."ent is the se~.,Li~le shape shown in the figures: this reduces the inrll~ct~nce of the PTC ek....~.nt The PTC elementl67is, in turn col~ne~led to the load terminal 143.
The movable m~gr etic plate 149iS provided with a spring 159 to control its operation and is l..ec~ ;c~lly coupled to an ins~ ting wedge 161, disposed so as to be capable of insertion between the main contacts 145a and 145b The wedge is preferably made of glass filled nylon. In the ~left..ed embodiment, a conventional mech~nicm, not shown, can move SU85nTUTE SHEET (RULE 2~) .. . .
btades 167 and 169 and open the main cont~ctc 145a and 145b and the seco~ry co~t~ctc 147a and 147b. Other mçch~nicmc could also be used and are consi~ered to be within the scope of the invention. For keeping the figures simple, these meçh~nismc are not shown.
The operation of the circuit breaker is best understood by concidering what happ~,n when a short circuit occurs. The fixed m~gnetic plate 157 and the movable m~8r ÇtiG plate 149 form a reverse current loop, carrying current in opposite directions. During short circuit con-litionc, this produces a strong repulsive force on the movable m~gnetic plate, 149, causing it to move the inc.ll~tinE wedge 161 bet ,veen the main contacts 145a and 145b. The wedge, 161, extin~iches the arc between the main contacts. The reverse current loop should preferably be designed to provide a driving force that can accelerate the wedge at at least 5000 m/s2. The wedge, being quickly driven between the main contacts 145a and 145b, causes the arc to be çxtin~lichecl in less than t~,vo milliseconds. The current then flows through the seconda,y contacts, 147a and 147b, and the PTC element 167. It is preferable that the voltage drop across the PTC ele~ be less than 15 volts at the IIlOlllf ~-L of opening of the main co~t~ctc 145a and 145b.
The recict~nce ofthe PTC elernent 167 is increased to at least 10 times its room te...~ re value as the PTC element is heated by the current The PTC elf mf~nt is specially desi~ed to urithct~n-l the he~ting The secondary contacts then open to interrupt the circuit.
Under norrnal operations, most of the current goes through the main contacts. The SlJ~ UTE SHEFT (RULE 26) , . .. . .
cliG force produced by the current in the reverse loop is not large enough to drive the wedge and the contact force between the main contacls is not arr~,eled by the wedge. Since the cold r~Cispnce of the tlmgcten wire used as a PTC cle.--e..l is at least ten times greater than the main contact reCict~n~e~ Iittle current is chllnted through the tl~ngcten wire, lceeping its t~ ~lp~ahlre low.
An alternate arr~ng~mPnt, shown in figure 8, ~ ).h-~tes the reverse current loop. The line terminal 181 is co.-l-e~,le(1 to the st~tion~ly main contact 187a and the st~tion~ry secondary contact 185a. The movable main contact 187b is connected to the load terminal 183 by means of a flexible connector 196 while the movable secondary contact 185b is connected to the PTC elemrnt 199 by a flexible connector 197. The PTC element 199 is, in turn, col-l-P~,Iecl to the load terminal 183.
The wedge 193, adapted to be driven between the main contacts, is mec.h~njcally ~ttnchPd to the movable m~netic plate 191. The movable m~gnetic plate 191 is simply placed close to a current carrying bus 195. A short circuit current flowing through the bus is sllffiri~.nt to cause motion ofthe m~etic plate 191 which, in turn, causes the wedge 193 to eYtin~.ich the arc between the main contacts 187a and 187b.
As noted above, the merh~nicm for causing the movement ofthe main and second~ry breaker cont~ctC is not diccncsed here. A variety of methods could be used. The sequence of operations is important. Proper operation of the invention requires that the secondary SUBS I I I UTE SHEET (RULE 26) . .
W O 99/10903 PCTrUS98/17543 contacts open after the wedge has opened the main cont~cts during a short circuit interruption.
A portion of the dev~ce of figures 7 or 8 could be used as a current limiting mo~lle This is illustrated in figure 9, where such a module, designed to be used in senes with another circuit breaker, is shown.
The module is provided with a pair of main contacts, 215a and 215b. The line terminal, 201, is co~ne~,led by a first pig tail to a movable m~gnetic plate, 203. The m~ netic plate, 203, is connected by means of a second pig tail, 207, to a fixed m~gnetic plate, 209.
The fixed m~etic plate, 209, is connected to the fixed contact 215a, and the PTC element 219. The movable contact 215b is co.-ne~te~l through the blade, 217 and pig tail 221, to the load terminal 223. In the p-t;iel,ed embodiment, the PTC çlement 219 is made of tnng~t~rt The p-efe.led shape ofthe PTC cl~.,.c.,~ is the serpentine shape shown in the figures: this reduces the in~uct~nce of the PTC elçm~nt The PTC cle...~ 219 is, in tum connected to the load terrninal 223.
The movable m~e,netic plate 203 is provided with a spring 211 to control its operation and is ~IC~ I,Anic~lly coupled to an in~nl~ting wedge 213, disposed so as to be capable of insertion bet~,veen the collt~ctc 215a and 215b. The wedge is preferably made of glass filled nylon. In the p.ef~,.,ed embo~im~nt~ insertion ofthe wedge also causes a m.~nh~nism, not shown, to move blade 217 and open the contacts 215a and 215b. It is also possible to have a SUBS 111 UTE SHEET (RULE 26) "~ h~ c~ in~ep~nl1pnt ofthe ~,vedge, for sensing overcurrents and causing the opc,~ing of the movable cQîltacts; this would lead to a more e.~e,-s;~e device. Other mer.h~ni.cmc could also be used and are considered to be within the scope of the invention. For simplifying the figure, these merh~ni$mc are not shown.
The main di~I~. cnce, between the operation of the module shown in figure 9 and of the circuit breaker of figure 8 is the ~bsence of the seCo~ry cQn~cts in the former. The device of figure 9 acts as a current lirniter and col.lplete interruption is pc.ro."lcd by a breaker for which the device of figure 9 is an accessory.
The filn~mpnt~l concept of the devices of figures 7 - 9 is to convert most of the interruption energy into heating the PTC Plement, instead of generating an arc and gas pressure during a short circuit interruption, as happens in conventional prior art devices. In existing mPtlinnl and high voltage circuit breakers, SF6 or a vacuum has to be used to suppress the arcing. In the present invention, the arcing is greatly reduced, so that SF6 or a vacuum are no longer nf.ce.~s~. y. This makes it possible to build air circuit breakers to perform the same fimction This reduces the cost considerably.
Several embo-limPnts of the invention have been described. It will be obvious to those skilled in the art that various ~h~ngPs and modifications may be made therein ~,vithout departing from the intent of the invention, and the purpose of the claims is to cover all such çh~ng~s and modifications as fall within the true spirit and scope of the invention.
SUBSTrrUrE S~EET(RULE 26) . . ,
Claims (19)
1. A circuit breaker for limiting the flow of electrical current in a line comprising:
(a) a first switch and a second switch, each of said switches having a pair of contacts movable with respect to each other defining an open position and a closed position, said first switch and said second switch being connected in parallel with each other and connected in series with the line, (b) a first device responsive to current in the line adapted to move the first switch and the second switch from their respective closed positions to the open positions;
(c) a second device responsive to current in the line, adapted to insert an insulating object between the pair of contacts of the first switch; and, (d ) a resistor having a positive temperature coefficient of resistivity (PTC
resistor) connected in series with the second switch.
(a) a first switch and a second switch, each of said switches having a pair of contacts movable with respect to each other defining an open position and a closed position, said first switch and said second switch being connected in parallel with each other and connected in series with the line, (b) a first device responsive to current in the line adapted to move the first switch and the second switch from their respective closed positions to the open positions;
(c) a second device responsive to current in the line, adapted to insert an insulating object between the pair of contacts of the first switch; and, (d ) a resistor having a positive temperature coefficient of resistivity (PTC
resistor) connected in series with the second switch.
2. The circuit breaker of claim 1 wherein the second device is adapted to insert the insulating object between the pair of contacts of the first switch prior to the first device moving the second switch from the closed position to the open position.
3. The circuit breaker of claim 1 wherein the PTC resistor is made of metallic tungsten.
4. The circuit breaker of claim 1 wherein the insulating object is a wedge.
5. The current limiting circuit breaker of claim 4 wherein the insulating wedge is made of glass filled nylon.
6. The circuit breaker of claim 4 wherein the first switch has a first resistance, the PTC
resistor has a second resistance said second resistance being greater than ten times said first resistance.
resistor has a second resistance said second resistance being greater than ten times said first resistance.
7. The circuit breaker of claim 1 further comprising a current reverse loop coupled to the second device for driving the second device.
8. The circuit breaker of claim 7 wherein the second device inserts the insulting object at an acceleration of greater than 5000 m/s 2 during a short circuit condition of the line.
9. The circuit breaker of claim 4 wherein the PTC resistor has a serpentine shape.
10. A current limiting module, connected in series to a main circuit breaker, for limiting the flow of electrical current in a line comprising:
(a ) a switch having a pair of contacts movable with respect to each other defining an open position and a closed position of the switch, said switch being connected in series with the line, (b ) a first device, responsive to current in the line, adapted to move the switch between the closed position and the open position;
(c ) a second device responsive to current in the line, adapted to insert an insulating object between the contacts of the switch; and, (d ) a resistor having a positive temperature coefficient of resistivity (PTC
resistor) connected in parallel with the switch.
(a ) a switch having a pair of contacts movable with respect to each other defining an open position and a closed position of the switch, said switch being connected in series with the line, (b ) a first device, responsive to current in the line, adapted to move the switch between the closed position and the open position;
(c ) a second device responsive to current in the line, adapted to insert an insulating object between the contacts of the switch; and, (d ) a resistor having a positive temperature coefficient of resistivity (PTC
resistor) connected in parallel with the switch.
11. The current limiting module of claim 10 wherein the PTC resistor is made of metallic tungsten.
12. The current limiting module of claim 10 where the insulating object is a wedge.
13. The current limiting module of claim 12 wherein the insulating wedge is made of glass filled nylon.
14. The current limiting module of claim 10 wherein the first switch has a first resistance, the PTC resistor has a second resistance, said second resistance being greater than ten times said first resistance.
15. The current limiting module of claim 10 further comprising a current reverse loop coupled to the second device for driving the second device.
16. The current limiting module of claim 15 wherein the second device inserts the insulating object at an accceleration of greater than 5000 m./s 2 during a short circuit condition of the line..
17. The current limiting module of claim 11 wherein the PTC resistor has a serpentine shape.
18. A method for limiting the flow of electrical current in a line comprising:
(a ) using a circuit breaker having:
(i) a first switch and a second switch, each of said switches having a pair of contacts movable with respect to each other defining an open position and a closed position of the respective switches, (ii) a first device responsive to current in the line adapted to move the first switch and the second switch from their respective closed positions to the open positions, (iii) a second device responsive to current in the line, adapted to insert an insulating object between the pair of contacts of the first switch, and, (iv) a resistor having a positive temperature coefficient of resistivity (PTC
resistor) connected in series with the second switch; and (b) connecting the circuit breaker to the line so that said first switch and said second switch are in parallel with each other and in series with the line,
(a ) using a circuit breaker having:
(i) a first switch and a second switch, each of said switches having a pair of contacts movable with respect to each other defining an open position and a closed position of the respective switches, (ii) a first device responsive to current in the line adapted to move the first switch and the second switch from their respective closed positions to the open positions, (iii) a second device responsive to current in the line, adapted to insert an insulating object between the pair of contacts of the first switch, and, (iv) a resistor having a positive temperature coefficient of resistivity (PTC
resistor) connected in series with the second switch; and (b) connecting the circuit breaker to the line so that said first switch and said second switch are in parallel with each other and in series with the line,
19. A method of limiting the flow of electricity in a line comprising:
(a ) using a module having:
(i) a switch having a pair of contacts movable with respect to each other defining an open position and a closed position of the switch, (ii) a first device, responsive to current in the line, adapted to move the switch between the closed position and the open position;
(iii) a second device responsive to current in the line, adapted to insert an insulating object between the contacts of the switch; and (iv) a resistor having a positive temperature coefficient of resistivity (PTC
resistor) connected in parallel with the switch; and (b ) connecting the module in series with the line and a circuit breaker, the switch being in series with the line.
(a ) using a module having:
(i) a switch having a pair of contacts movable with respect to each other defining an open position and a closed position of the switch, (ii) a first device, responsive to current in the line, adapted to move the switch between the closed position and the open position;
(iii) a second device responsive to current in the line, adapted to insert an insulating object between the contacts of the switch; and (iv) a resistor having a positive temperature coefficient of resistivity (PTC
resistor) connected in parallel with the switch; and (b ) connecting the module in series with the line and a circuit breaker, the switch being in series with the line.
Applications Claiming Priority (3)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US91875597A | 1997-08-25 | 1997-08-25 | |
| US08/918,755 | 1997-08-25 | ||
| PCT/US1998/017543 WO1999010903A1 (en) | 1997-08-25 | 1998-08-25 | Current limiting circuit breakers with ptc (positive temperature coefficient resistivity) elements and arc extinguishing capabilities |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2266560A1 true CA2266560A1 (en) | 1999-03-04 |
Family
ID=25440913
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002266560A Abandoned CA2266560A1 (en) | 1997-08-25 | 1998-08-25 | Current limiting circuit breakers with ptc (positive temperature coefficient resistivity) elements and arc extinguishing capabilities |
Country Status (4)
| Country | Link |
|---|---|
| EP (1) | EP0934597A1 (en) |
| JP (1) | JP2001504983A (en) |
| CA (1) | CA2266560A1 (en) |
| WO (1) | WO1999010903A1 (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US9799423B2 (en) | 2014-09-18 | 2017-10-24 | Littelfuse, Inc. | Cable and method of manufacturing the same |
Families Citing this family (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US6414256B1 (en) * | 2000-12-20 | 2002-07-02 | Square D Company | Current limiting circuit breaker |
| JP2004014434A (en) | 2002-06-11 | 2004-01-15 | Uchiya Thermostat Kk | Dc current shut-0ff switch |
| US7742270B2 (en) | 2004-06-10 | 2010-06-22 | Invensys Systems, Inc. | System and method for limiting energy in an industrial control system |
| WO2010037424A1 (en) * | 2008-10-03 | 2010-04-08 | Abb Technology Ag | Electric current limiting device |
Family Cites Families (11)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3249810A (en) * | 1962-11-20 | 1966-05-03 | Westinghouse Electric Corp | Circuit interrupting apparatus |
| FR2540665B1 (en) * | 1983-02-04 | 1987-02-27 | Telemecanique Electrique | SWITCHING DEVICE PROVIDED WITH AN INSULATING SCREEN INTERPOSED BETWEEN THE CONTACTS WHEN SWITCHING OFF AND ARC SHEAR MEANS BETWEEN THIS SCREEN AND AN INSULATING WALL |
| US4583146A (en) * | 1984-10-29 | 1986-04-15 | General Electric Company | Fault current interrupter |
| FR2573912B1 (en) * | 1984-11-26 | 1987-01-09 | Telemecanique Electrique | ELECTRICAL SWITCH WITH SCREEN |
| FR2606929B1 (en) * | 1986-11-14 | 1989-02-10 | Telemecanique Electrique | SWITCHING DEVICE FOR PROTECTIVE APPARATUS |
| US4801772A (en) * | 1988-03-02 | 1989-01-31 | Westinghouse Electric Corp | Current limiting circuit interrupter with insulating wedge |
| SE465524B (en) * | 1990-02-08 | 1991-09-23 | Asea Brown Boveri | DEVICE FOR OVERLOAD AND SHORT-CUT PROTECTION IN ELECTRICAL EQUIPMENT |
| US5126517A (en) * | 1990-09-11 | 1992-06-30 | Square D Company | Arc suppressing current interrupter |
| US5382938A (en) * | 1990-10-30 | 1995-01-17 | Asea Brown Boveri Ab | PTC element |
| US5629658A (en) * | 1992-08-18 | 1997-05-13 | Chen; William W. | Methods of arc suppression and circuit breakers with electronic alarmers |
| FR2714520B1 (en) * | 1993-12-24 | 1996-01-19 | Telemecanique | Electric switch device with separable contacts. |
-
1998
- 1998-08-25 EP EP98942230A patent/EP0934597A1/en not_active Withdrawn
- 1998-08-25 CA CA002266560A patent/CA2266560A1/en not_active Abandoned
- 1998-08-25 JP JP51454799A patent/JP2001504983A/en active Pending
- 1998-08-25 WO PCT/US1998/017543 patent/WO1999010903A1/en not_active Application Discontinuation
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US9799423B2 (en) | 2014-09-18 | 2017-10-24 | Littelfuse, Inc. | Cable and method of manufacturing the same |
Also Published As
| Publication number | Publication date |
|---|---|
| WO1999010903A1 (en) | 1999-03-04 |
| JP2001504983A (en) | 2001-04-10 |
| EP0934597A1 (en) | 1999-08-11 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| FZDE | Discontinued |