CA1051069A - Current limiting circuit breaker - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

In an electromagnetically operable circuit interrupting device comprising an outer molded case, a magnetic core disposed in the outer case, a conductor turn disposed in the outer case and associated with the magnetic core, an armature disposed in the outer case, normally in spaced relationship to the magnetic core, and attracted toward the magnetic core upon flow of a predetermined current in the conductor turn, an inner case disposed in the outer case adjacent the armature of an opposite side thereof from the magnetic core, wherein the im-provement consists of an armature pin secured to the armature and having a portion reciprocally mounted in the inner case, a first contact blade having a mounting end portion disposed in the inner case and a contact end portion disposed outwardly of the inner case, a second contact blade having a mounting end portion disposed in the inner case and a contact end portion disposed outwardly of the inner case, each of the contact blades having a contact mounted on the contact end portion thereof and engaged with the contact on the contact end portion of the other of the contact blades when the contact blades are is a closed position, means in the inner case on one side of a longitudinal axis of the armature pin pivotally mounting the first contact blade, means in the inner case on the other side of the long-itudinal axis of the armature pin pivotally mounting the second contact blade, means operatively connecting the armature pin with the contact blades, and spring means in the inner case bias-ing the contact blades towards the closed position.

Description

~S~ ;9 , I_ This invention relates to electxic circuit inter-rupting devices.
~ efore the present inyention, a commercially practi-cal current limiting circuit breaker suitable for use in low voltage power distribution systems of about 600 volts or less had been sought by the power distribution and c~ntrol industry for over thirtv years~ Various, sometimes conflicting require-ments have to be met. For example, a commercially practical current limiting circuit breaker (a) ~ust be repetitively oper-able at its maximum short circuit interrupting ratiny without repair or replacement of parts (This requirement precludes the use of fuses, fused switches, or fused circuit breakers ~or achieving current limiting.);~b~ must not have a temperature rise at the terminals of more than 50 degrees Centigrade at rated st~ady state current to meet appropriate standards of safety and performance established for circuit breakers used in po~er distribution systems of 600 volts or less ~This re~uire-ment precludes the use of a large built-in resistance to limit current.); ~c) must havP a design applicable to a wide range of steady state current ratings, from a few amperes to hundreds of amperes; (d) must have current limiting capabilities competi-tive with tho~e of the best available other current limiting devices including fuses (This requires that the deviCe will operate in a fraction of a millisecond when the available short circuit current is 100,000 amperes or more.);(e) must be compact enough to fit into existing circuit breaker panelboa~ds (This requires that the ratio of interrupting rating to vol~me be equal to or greater than that for any prior circuit brea~er.);
(f) mu.st use non-toxic, non-hazardous materials;(g~ must have a response time which decreases proportionately as much as or faster than availab~e short circuit ~uxrent is increased;(h) must be economically competitive with present circuit protec-tive devices; and ~i) must function without inducing severe transient voltages. None of tpe prior ~urrent limiting circuit breakers meets all of the above re~uirements.

~L~5it~

~ ccording to one aspect of the present invention, there is provided in an electormagnetically operable circuit interrupting device comprising an out~r molded case, a magnetic core disposed in the outer case, a ~onductor turn disposed in the outer case and associated with the magnetic core, an armature disposed in the outer case t normally in : :
spaced relationship to the magnetic core, and attracted toward the magnetic core upon flow of a predetermined current :~
in the conductor turn, an inner case disposed in the outer case adjacent the armatu~e of an opposite side thereof from the magnetic core, wherein the improvement consists of an :1 armature pin secured to the armature and having a portion ~ :~
. .
: reciprocally mounted in the inner case, a first contact blade having a mounting end portion disposed in the inner case and a contact end portion disposed outwardly o the inner case, a second contact blade having a mounting end portion :' disposed in the inner case and a contact end portion disposed outwardly of the inner case, each of the contact blades 'j haviny a contact mounted on the contact end portion thereof and :~1 20 engaged with the contact on the contact end portion of the other .~ .' o the contact blades when the contact blades are in a closed 'i position, means in the inner case on one side of a longitudinal ::
: axis of the armature pin pivotally mounting the first contact ', blade, means in the inner case on the other side of ~he long-itudinal axis of the armature pin pivotally mounting the second contact blade, means operatively connecting the armature pin with the contact blades, and spring means in the inner case ~1 biasing the con~act ~lades towards the closed position. :

:, ' :

::~
-- 2 -- .
.

~--~51~6 BRIEF DESCRIPTION OF T~E DRAWINGS .
Fig. 1 is a longitudinal sec~ional view of a .
three-pole current limlting circuit breaker constructed ,:~
in accordance with the invention, taken generally along ~
the line 1-1 of Fig. 2 and showing a center pole thereof ~:
with parts in an ON position;
Fig. 2 is a cross sectional view of the current lil~ting circuit breaker of' Fig. 1, ta~en generally along ~-.~ the line 2-2 of Fig. l; : ::
Fîgs 3, 4, 5, and 6 are enlarged perspective, l top, sidf~, and outer end views, respectively, of a line ~:
~ terminal and stationary contact support assembly of any .~ one of ~le poles of the current limiting circuit breaker :jl of Fig. l; .,.

~! Fig. 7 is an enlarged end view of an operating ::~
~j mechanism in the center pole of the current limiting circuit 3 breaker of Fig. 1, with:portions broken away and the parts .. ~ .
~ being s~own in TRIPPED position;
`,~7~ Fig. 8 is a side view of the operating mechanism ~:
. 20 of Fig. 7, with portions bxoken away;
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2 FIG. 9 ls an enlarged cross sectional view through a blade

3 cross bar of the current limiting circuit breaker of FIG. 1, taken

4 between two blades;
FIG. 10 is an enlarged cross sectional view 5imilar to FIG 9~ ~ ~ :
6 but taken at a blade of the center pole; : :
FIG. 11 is an enlarged fragmentary longitudinal view of a 8 thermally actuated common trip bar and a fragmentary edge view of :~. an associated thermal trip lever of the current limiting circuit 10 breaker of FIG. l;
~ 11 FIG. 12 is an actual size cross sectional view of the therm-: 12 ally actuated common trip bar taken substantially along the line .`~
~ 13 12-12 of FIG. 11 and a side view o~ the associated thermal trip .i 14 lever; ~ `
~, 15 FIGS. 13, 14, 15, and 16 are perspective, left end, side, 16 and rlght end views, respectively, of an assembly of electrical ~.
17 conductors associated with an electromagnet in a current limiting 18 portion of any one of the poles of the current limiting circuit breaker of FIG. 1, portions being broken away or omitted in FIGS.
14~ 15, and 16.
; ~21 FIGS. 17, 18, and 19 are perspective, side, and end views, :-~
22 respectively, of an electromagnet and contact blade assembly of ~:, 23 any one of the poles of the current limiting circuit breaker of 4 FIG. 1, the electromagnet being associated with the conductor assembly of FIGS. 14-16 and having portions broken away in FIGS, ;~ 26 18 and 19; .
:. 27 FIG. 20 is a plan view of an unfinished current limiting 28 resistor for any one of the poles of the current limiting circuit 29 breaker of FIG. 1, the unfinished resistor including end portions .
;. 3 to be cut off after electroplating;
. 31 FIG. 21 is a plan view of the end portion of the resistor ~`
`; ~ 32 within the dotted enclosure 21 of FIG. 20, the broken line portion ~:

:~: - 4 ~

5~ ;9 in ~ig. 21 indicating a portion which is cu~ away after electroplatiny;
Fig. ~2 is an edye view of the resistor end portion;
Figs. 23, 24 and 25 are p~rspective, end, and side views, respectively, of a field magnet assembly of any one of the poles of the current limiting circuit breaker of Fig. l;
Fig~. 26, 27, 28 and 29 are perspective, top, inner end, and side views, ~spectively, of ~ electrical conductor : and load erminal assembly of any one of the poles of the current limiting circuit breaker ~ Fig. l;
Figs. 30 and 31 are perspective and front views~
respectively, of an arc chute adjacent the load terminal :
assembly of any one of ~he poles of the current limiting circuit breaker of Fig~ l;
Fig. 32 is a ~ectional view taken generally along the line 32-32 of Fig. 31;
, Fig. 33 is a perspective view of one of the arc plates in the arc chute of Figs. 30~32; and .
Fig. 34 is a longitudinal ~ectional view of the current limiting circuit breaker of Fig. 1, taken generally along the line 34-34 of Fig. 2 and showing an outer pole thereof with parts in an ON position,.
, : DETAILED DESCRIPTION OF PREFERRED EUnODIUENT
With reference to the drawings, a ~hree-pole current limiting circuit breaker 40 constructed in accordance with the invention is shown in Fig~. 1, 2 and 34. The circuit bxeaker 40 includes a molded case comprising a molded base 41 an:d a complementary molded cover 42 each having a pair of outer side walls and a pair of spaced intexmediate walls to provide three compartmen~s 44, 45,and 46 (~igO 2). The structure of a center pole of the circuit breaker 40 disposed in the center compartment 45 is shown in Fig. 1.
A line terminal and sta~nary contact ~sen~ay 48 ~ ~wn ., .

' ;

~S~069 1 ad~acent the le~t end of FIG. 1. The assembly 48 is better shown 2 in FIGS. 3-6 and includes a terminal member 49 and a stationary 3 contact mounting member 50 pivotally connected by a pin 51 and 4 electrically interconnected by a braided wire cable 52. The terminal member 49 has a bight portion 49a and a pair of spaced

6 leg portions 49b and 49c as a first U-shaped portion, the leg

7 portiQns 49b and 49c merging respectively with a pair o~ spaced

8 extending leg portions 49d and 49e of a second U-shaped portion g having a split bight portion formed by two tabs 49r and 49g 10 extending respectively from the leg portions 49d and 49e. A ~ ~-11 mounting tab 49h having an aperture 49i extending therethrough 12 pro~ects at right angles from the bight portion 49a oppositely i 13 from the leg portions 49b and 49c.
14 The member 50 has a bight portion 50a and a pair o~ spaced leg portions 50b and 50c as a first U-shaped portion, the leg 16 portions 50b and 50c respectively having laterally extending ears 17 50d and 50e, a leg portion 50f of a second U-shaped port~on 18 extending from the bight portion 50a to a bight portion 50g, and 19 a leg portion 50h opposite the leg portion 50f. The leg portions 49d and 49e and the ears 50d and 50e are apertured to receive the 21 pin 51. The cable 52 has one end welded to the tab 49f, one end 22 welded to the tab 49g, and a central portion welded to the bight , portion 50a. A stationary main contact 53 and an arcing contact 24 54 are secured to the leg portion 50h in abutting relationship to each other. The leg portion 50f is provided with a threaded 26 aperture 50i for receiving a retaining screw 56 (FIG. 1) ~or a , 27 contact pressure spring 57.
`I 28 An internally threaded sleeve 58 is staked to the mounting 29 tab 49h at the aperture 49i and disposed in an apertured mounting pad portion 41a of the base 41. A screw 59 threaded into the 31 sleeve 48 secures an apertured connector body 60 to the tab 49h.
32 The connector body 60 has suitable wire or cable receiving holes ', _ ~_ :, :~051069 1 ¦ and is ovided with an internally threaded hole for recelving a 2 clamping screw 61.

3 Similar terminal and stationary contact assemblies 48 are provided in the outer poles of the compartments 44 and 46.

A blade crossbar 63 extends transversely through the center 6 compartment 45 into the outer comparments 44 and 46. The inter-7 mediate walls of the base 41 are slotted to receive the crossbar8 63, but a bracket 64 (FIGS. 2 and 34) secured to the base 41 in q the compartment 44 and an oppositely ~ormed bracket 55 (FIG. 2) secured to the base 41 in the compartment 46 are provided to sup-11 port the crossbar 64 for pivotal movement. ~hree movable contact 12 blades 67, one in each pole, are mounted directly in the crossbar 13 63, which is made of molded plastic material and provided with a 14 metallic reinforcing insert 68 (FIGS. 9 and 10). Tooling recesses such as recess 63a and recess 63b (FIG. 9) are provided at 16 appropriate places in the crossbar 63 to hold it while the blades 17 67 are being assembled therein Each blade 67 is provided with 18 a pair of shouldered portions 67a and 67b (FIG. 10) which abut the 19 crossbar 63 and from which a tapered mounting tongue portion 67c extends through the crossbar 63 and through a retaining plate 69 21 staked thereto. A movable contact 70 is provided on each blade 22 67 for engagement principally with an associated one of the main 23 stationary contacts 53.
24 Operating mechanism for the crossbar 63 and blades 67 is disposed in the center compartment 45 (FIG. 1). Portions of the 26 operating mechanism are best shown in FIGS. 7 and 8, and are there 27 shown in a TRIPPED position. Two oppositely formed frame members 28 72 and 73 (FIGS. 2, 7 and 8) are secured to the base 41 and 29 contoured as at 73a (FIG. 8) which together with brackets64 and 66 support the crossbar 63 for pivotal movement. The frame member 73 31 is provided with an arm portion 73b (FIG. 7) extending toward the frame member 72 and having a bent mounting ear 73c at its free end ~ 7 -~ V5~)1E;9 A pin 74 is mounted adjacent one end in the ear 73c and adjacent the other end in a corresponding mounting ear (not shown) of ~he frame m~mber 72 ~ A releasably latchable cradle member or trip lever 76 is pivotally mounted adjacent csne end on the pin 74.
Two inner toggle link.~ 78 and 79 are pivotally mounted adjacent their inner ends respectively on oppo~ite end portions of a pin `~
80 mounted in the blade 67 of the Genter pole. Two outer toggle links 82 and 83 are pivotally mounted adjacent their outer ends respectively on opposite end portions of a pin 84 mounted in the trip lever 76. The outer end portions of the links 78 and 79 and the inner end portions of the links 82 and B3 are pivotally interconnected by an elongated toggle pin 85~ the inner end portions of ~he links 82 and 83 being offset to straddle the outer end portions of the links 78 and 79.
A handle extension is formed by two handle plate members 86 and 87 pi~otally mounted re~pectively on a pair of pins 88 and 89 disposed respectively in the frame members 72 `. and 73. The handle plate members are joined by a pair of spring anchoring pins 91 and 92 and a reset pin 93. The toggle pin 85 has a pair o spring hook members 95 and g6 pivotally mounted thereon respectively adjacent opposite ends thereof A tension spring 97 ~Fig. 2) is secured at an outer end to the pin 91 and , at an inner end (not shown) to the member 95 on one side of :; `
.:, the toggle pin 85, and a t~nsion spring 98 (Fig. 7) i5 secured at an outer end to the pin 92 and a~ an inner end to the member 95 on the other side of the toggle pin 85. Similarly, a tension spring 99 (Figs. 2 and 8) is secured at an outer end to the pin ~ :
gl and at an inner end to the member 96 on one side of the toggle ~.
pin 85, and a tension spring 100 (Figs. 7 and 8) is secured at an outer end to the pin 92 and at an inner end (not shown) to ~he me~ber 96 on ~he other side of the toggle pin 85. ~he springs 97, 98, 99 and 100 maintain the toggle pin 85 in ~. :
, . , op~n-slotted inner ends of the outer toggle links 82 and 83.

., ~ .

~ t~inln~ olip 102 Is secured to the arm port~on 73b of the¦
2 frame me~be~ 73 and to the corresponding arm portion (not shown) 3 of the frame member 72 for holding shock absorbing material 103 4 (FIG. 8) for the blade 67 of the center pole at the end o~ the `
opening movement.
6 The frame member 73 includes an arm portion 73d (FIG. 8) 7 having a semicircular recess 73e therein. The frame member 72 is similarly formed. A thermally actuated common trip bar 105 (FIGS.
1~ 2) 11, 12, and 34) is pivotally mounted in the frame member 73 at the recess 73e and in the frame member 72 at a similar recess 11 in an arm portion 72d (FIG. 2) of the frame member 72. A
12 ge~erally L-shaped thermal trip lever 106 best shown in FIG. 12 13 is provided with an aperture 106a by which it is pivotally mounted 14 on a pin 107 (FIGS. 1, 2, 7 and 8) having opposite end portions disposed respectively in the frame members 72 and 73. A pin 108 16 (FIG. 8) having an enlarged head portion 108a (FIG. 7) is received 17 in an aperture 106b (FIG. 12) of the thermal trip lever 106 and 18 mounted in the frame member 72 to limit pivotal movement of the 19 trip lever 106 and prevent movement thereof axially along the pin 107. -21 A molded plastic operating handle 110 (FIGS. 1 and 2) extends 22 through an aperture in the cover 42 and is recessed in an enlarged 23 inner end portion to receive the pins 91 and 92 and the outer end 24 portions of the handle plate members 86 and 87.
Each of the outer two poles is provided with a pin 107 (FIGS.2G 2 and 34) identical to the pin 107 of the center pole but having 27 one end portion mounted in an appropriate groove in an outer wall 28 portion of the base 41 and an opposite end portion mounted in a 29 respective one of the brackets 64 and 66. Each of the three pins ;
3 107 has a magnetic core holder 111 and an armature plate 112 31 pivotally mounted thereon. Each holdèr 111 carries a generally 32 U-shaped magnetic core 113 having opposite leg portions secured _g_ ~ ~' ., .' - . ~ . . . ., .

respectively to spaced opposite side portions of the holder. As viewed in FIGS. 1 and 34, each side portion (only one being vis-ible) of the holder 111 is generally in the shape of an inverted "Y" having one leg pivotally mounted on the pin 107 and the other leg co~nected to a corresponding leg of the other side por-tion by a rear plate portion having an air gap adjusting screw 115 threaded therein. Each sCrew 115 extends through a rear wall portion of the base 41 and has a compression spring 116 mounted thereon. Turning of a screw 115 adjusts the air gap between the free ends of the leg portions of the respective magnetic core 113 and armature plate 112.
Each of the armature plates 112 is provided with a pair of opposite bent-over ears 112a~ each ear 112a being spaced inwardly o a side portion of the respective magnetic core holder 111 and having an opening aligned with that of the opposite ear for re-ceiving the respective pin 107. As shown in FIG. 2, a right-hand side portion of each holder 111 is outwardly offset at the por-tion mounted on the respective pin 107, and a right hand ear of each of the armature plates 112 is similarly offset so as to be hidden by the holder 111. Thus, only the left-hand ear 112a of each armature plate 112 is visible in FIG. 2. A free end portion of each armature plate 112 is secured by a pair of rivets 117 ~FIG. 2) to a con~non trip bar 118 of molded plastic extending through the center compartment 45 into the outer compartments 44 and 46. The armature plate 112 of the center pole is apertured to receive a free end portion of the trip lever 76 and thereby releasably latch the trip lever, as shown in FIG. 1. The three armature plates 112 and the common trip bar 118 are biased to-ward latching position for the trip lever 76 by a pair of tension j 30 springs 120 ~FIGS~ 2 and 34) disposed respectively in the two outer compartments 44 and 46 and each secured at one end to a ~ ~;
r~spective armature plate 112 and at the other end to a respective .~ .

~ s~
one of the brackets 64 and 66.
Each of the c~mpartments 44, 45, and 46 has a barrier plate 122 tFIGs~ 1 and 34) mounted in appropriate grooves in the walls of the base 41 and extending into the cover 42 adjacent the com-mon trip bar 105 on the op~osite side thereof from the respec- ~"
tive armature plate 112. As best shown in FIGS. 11 and 12, a latch plate 123 is secured to the common trip bar 105 by a rivet 124. The thermal trip lever 106 is provided with a hole 106c and a lanced portion 106d, the hole being partly in the lanced portion. A tension spring 125 ~FIGS. 1 and 2) is anchored at one end on the lanced portion 106d at the hole 106c and at the other end on the barrier plate 122 in the center compartment 45 to bias the thermal trip lever 106 clockwise a~out the pin 107, the barrier plates 122 being omitted in FIG. 2. Each barrier , plate 122 is provided with a hook portion 122a (FIGS. 1 and 34), and in each of the two outer compartments 44 and 46 a compres-sion spring 126 (FIG. 34) is seated at one end on the respective hook portion 122a and at the other end on an appropriate portion of the common trip bar 105 to bias the trip bar 105 and the latch ~;
plate 123 mounted thereon toward latching position with respect to the thermal trip lever 106.
A push-to-trip button 128 (FIG. 34), more completely shown and described in U.S. Patent No. 3,895,205, issued July 15, 1975, and assigned to the assignee of this application, has a com- ;
~ pression spring 129 mounted thereon to normally maintain the l button flush with the surface of the cover 42 and is engageable with the common trip bar 118 upon being pushed inwardly to move ~, the armature plate 112 of the center compartment 45 clockwise in FIG. 1 toward unlatching position with respect to the trip lever 76.
Each of the compartments 44, 45, and 46 is provided with a laminated field magnet assembly comprising a plurality o~ generally ' . , ' .

~o~o~9 O-shaped plates 130 and a plnrality of generally U-shaped plates 131 disposed around the respective stationary contacts 53-54 and movable contacts 70 of each pole. The field magnet assemblies are coated with an arc extinguishing material such as one of , ;
those disclosed in Canadian Patent 1,014,725, issued October 2, 1977, and assigned to the assignee of ~his application. Further, each compartment is provided with an arc chute 133 including a plurality of metal arc plates 134 best shown in FIG. 33 and a pair of venting plates 135 and 136 formed of insulating -material.
The arc extinguishing material referred to above is used to ~ ;~
coat other elements of this invention hereinafter described.
Its function is to help create a medium in the arc chamber which brings about a rapid rate of dielectric strength recovery of the gap. A suitable material by way of example is a filler of be-tween 40% to 56% by weight of hydrated zinc borate in a dimethyl silicone resin. A more complete description of such arc ex-tinguishing material, and additional examples, are set ~orth in the Canadian Patent referred to above and hereinafter by its Patent No. 1,014,72S. ~ -In each compartment, the movable contact blade 67 is con- ' nected by a flexible braided cable 138 (FIGS. 1 and 34) to one leg of generally U~shaped conductor 139 secured at a bight por-tion to the base 41 by a pair of screws 140 and 141. The other I leg of conductor 139 is secured to a conductor 142 secured to the base 41 by a screw 143 and extending between the leg portions of the U-shaped magnetic core 113 and alon~ the barrier plate 122.
gen~rally L-shaped bimetallic strip 145 is secured at one end to the bight portion of the U-shaped conductor 139. The common trip , 30 bar 105 is provided with three actuating legs 105a, one in each of the compartments 44, 45, and 46, only the center actuating leg 105a disposed in the compartment 45 being shown in FIGS. 11 and 12.

1~151~69 The free end portion of the bimetallic strip 145 in each compart-ment is engageable with the respective actuating leg 105a, and upon sustained moderate overload current flow in the conductor 139, the bimetalliC strip 145 is heated sufficiently to pivot the actuating leg 105a counterclockwise as viewed in FIGS. 1 and 34, the high expansion side of the bimetallic strip being on the inside of the ~-shape. The thermal trip lever 106 in the cen-ter compartmPnt 45 is thereby released from the latch plate 123 on the thermally actuated common trip bar 105 and strikes th~
common trip bar 118 under the influence of the tension spring 125 to pivot the armature plates 11~ about their respective pins 107 clockwise as viewed in FIGS. 1 and 34. The trip lever 76 in the center compartment 45 is thereby released to ef~ect open-ing movement of the three movable contact blades 67. If a fault ~; current higher than the moderate overload current flows through I any of the conductors 142, the respective magnet 113 attracts `~ its associated armature plate 112 and all three of the armature ; plates 112 are pivoted clockwise to release the trip lever 76 and open the contact blades 67. Pushing the button 128 also pivots the common trip bar 118 and the three armature plates 112 clockwise to release the trip levex 76 and open the contact blades 67.
The end of each conductor 142 opposite the end secured by the screw 143 is connected by a screw 146 (FIGS. 1, 2, and 34) to a flatwise L-shaped strap portion 148a of a box-like conductor 148 best shown in FIGS. 13-16. The conductor 148 includes the strap portion 148a, an end portion 148b, a pair of spaced side portions 148c and 148d, and a split end portion including a tab portion 148e extending from the side portion 14Bc and a tab portion 148f extending from the side portion 148d. The side portions axe ;~
generally square, except that the side portion 148c includes a mounting tab 148g extending toward the base 41 when assembled.
In each of the compartments 44, 45, and 46, a conductor 150 .; ~

~s~
includes an edgewise L-5haped portion 150a secured at an e~d of a longer leg thereo to a tab extending from a shor~er leg of the strap portion 148a and joined at an end of a shorter leg thereof to an end of a strap portion 150b having an opposite end secured to the tab po~tions 148e and 148f. A flexible braided cable 151 is secured at one end to the conductor 150 and at the other end to auxiliary contact means for current limit-ing, including a mo~able contact blade 152 ~FIGS. 1 and 34) having a contact 153 mounted thereon. The blade 152 cooperates with another movable contact blade 154 having a contact 155 ~;
mounted thexeon.
In each of the compartments 44, 45, and 46, the mechanism by which the blades 152 and 154 are operated is best shown in FIGS. ~-17-19. A generally U-shaped laminated magnetic core 156 is dis-posed in an outer portion of the box-like conductor 148 (FIGS.
1 and 34~ with a pair of spaced leg portions 156a and 156b thereof ~FIG. 17) stradling the strap portion 148a and a pair of oppositely extending shoulder portions 156c and 156d thereof (FIG. 17) respectively engaging the side portions 148c and 148d ~ --(FIG. 13). A generally V-shaped laminated armature 158 ~FIGS.
~, 17-19) is disposed in an inner portion of the box-like conductor 148 (FIGS. 1 and 34) with a pair of spaced relatively short leg portions 158a and 158b thereof (FIGS. 17 and 19) disposed re~
spectively opposite and in spaced relationship to the leg por-tions 156a and 156b. An armature pin support plate 160 is dis~
posed between the leg portions 158a and 158b. The armature 158 , is provided with a hole disposed centrally of a bight portion ,I thereof and aligned with a hole in the support plate 160 for receiving an outer threaded stud portion of an armature pin 161 having a nut 162 threaded thereon to secure an inner, enlarged shouldered portion of the pin 161 against an inner side of the - armature 158. The armature pin 160 is provided with a pair of opposed flats at its inner end and two spaced links 163 and 164 ~ 14 -~5~0~;~
are pivotally mounted thexeon by a pin 165. The links 163 and 164 carry a pin 166 engaged in a ~otch in an edge of the hlade 152 facing the blade 154 and a pin 167 normally engaged with an edge of the blade 154 facing the blade 152. The blade 152 is pivotally mounted on a pin 168 received in a hole 169 (FIG. 17) and the blade 154 is pivotally mounted on a pin 170 received in a hole 171. The pivot pins 168 and 170 are disposed on opposite `~ sides of the armature pin 161 and opposite end portions thereof are xeceived respectively in a pair of molded inner casing por-tions 173 and 174 tFIG. 19) secured together by a plurality of ,~
rivets 175. A compression spring 176 disposed in the casing poxtions 173 and 174 encircles the armature pin 161 and bears on the blade 152 to urge it clockwise in FIG. 18 toward closed position. The blade 152 bears on the pin 166 and causes the pin ,-, 167 to bear on the blade 154 to urge it counter-clockwise in FIG. 18 toward closed position. The spring 176 is also a re-, turn spring for the armature 158 and armature pin 161. A shield 177 (FIGS. 18 and 19) having a forked end portion straddling the links 163 and 164 is disposed between the blades 152 and 154 and ~J
mainly within the casing portions 173 and 174. Appropriate ;~
openings are provided in the casing formed by the casing portions 173 and 174 for the armature pin 161, the cable 151, the contact . .
blades 152 and 154, and a flexible braided cable 178 secured to the blade 154. The sides 148c and 148d of the box-like con-ductor 148 respectively engage the casing portions 173 and 174, and the mounting tab 148g (FIGS. 15 and 16) is disposed between , a pair of bosses on the caslng portion 173, one such boss 173a being shown in FIG. 19. The contact end portions of the blades ~, 152 and 154 are disposed outwardly of the casing 173-174 and a '` 30 piece of shock absorbing material 180 (FIG. 18) is mounted in ;;
the casing adjacent the blade 152 to cushion opening movement thereof.
, ~ A magnetic core structure 181 generally in the orm of a - ~ 15 -':', ~51~
rectangular tube surro~-ds ~he contact ~nd por~ions of the blades 152 and 154 extending outwardly of the casing 173-174.
The magnetic core structure 181 is best shown in Figs. 23-25 and comprises two identical, generally L-shaped, laminated magnetic cores 182 and 183 arranged as shown with an end of a long leg portion 182a of the core 182 abutting an inner side ~ ,~
of a short leg por~ion 183b of he core 183 and an and of a long leg portion 183a of the core 183 abutting an inner side of a short leg portion 182a of ~he core 182. ~ach of the cores 182 and 183 is coated with an arc extinguishing material such as disclosed in the aforesaid Canadian Patent 1,014,725 and ~ ;~
additional pieces of such material are adhesively secured re~
, spectively to inner sides of the L-shaped assemblies as shown in Figs. 23 and 24. Alternati~ely, the cores 182 and 183 could be generally U-shaped, C-shaped or J-shaped. ~ :
:, .
In each of the compartments 44, 45 and 46, the cable 178 connected to the blade 154 is electrically connected at an opposite end to one end of a terminal strap 184 best ~hown in ~
Figs. 26-29 and having a terminal member 186 secured to an oppo- ~ -site end. ~he terminal me~ber 186 is similar to th~ terminal membex 49 and has a bight portion 186a and a pair of spaced :~
leg portions 186b and 186c as a fir-~t U-shaped portion, the leg portions 186b and 186c merging at right angles respectively with a pair of spaced leg portions 186d and 186e of a second U-shaped portion having a split bight portion formed by two tab~ 186f and 186g extending respectively from the leg portions :
186d and 186e. The tabs lB6f and 186g are secured to the terminal strap 184. A mounting tab 186h having an aperture , 186i extending there~hrough projects at right angles from the , 30 bight portion 186a oppositely from the leg portions 186b and ~ 6c. :

;~ An internaIly threaded sleeve 58 OEigs 1 and 34~ identical to those staked b~ the tabs 49h is staked to the m~u$ing ~ 186h . , .

,,-1 ! ~051C~
1 ¦ of each of the terminal members 186 at the aperture 186i therein 2 ¦ and disposed in an apertured mounting pad portion 41b of the base 3 ¦ 41. A screw 59 threaded into the sleeve 58 secures an apertured 4 ¦ connector body 60 to the tab 186h. The connector body 60 is 5 ¦ identical to those secured to the tabs 49h and is provided with 6 ¦an internally threaded hole for receiving a clamping screw 61.
7 ¦ In each of the compartments 44t 45, and 46, a conductor 188 8 ¦ (FIGS. 13-16) has a tab 188a secured to the end of the strap por-; 9 tion 150b adjacent the tabs 148e and 148f, a strap portion 188b (FIGS. 1 and 34) extending between the leg portions 156a and 156b 11 of the magnetic core 156, an offsetting portion 188c extending ~ 12 generally parallel to the tab 188a, and a strap portion 188d i 13 extending through the magnetic core assembly 181 formed by the two 14 L-shaped magnetic cores 182 and 183 along the inner side of the short leg portion 182b. A strip 189 of arc extinguishing material 16 such as disclosed in the aforementioned Canadian Patent, No.
17 1,014,725, is adhesively secured to the side of the strap ~`
18 portion 188d facing the contact blade 152. A conductor 190 19 includes a tab portion 190a secured to an end of the strap portion 188d and extending and bent from a strap portion 190b. The strap 21 portion l9Ob extends parallel to an end face of the magnetic core 22 182 and is joined at right angles to a strap portion 190c extend- ;
23 ing somewhat diagonally across the outer side of the long leg 24 portion 182a. The strap portion 190c is joined at right angles to a strap portion 190d extending along a rear wall of the base ~l 26 41 and having an apertured offset connecting tab portion 190e `;1 27 disposed in a hole extending through the rear wall of the base 41.
28 An internally threaded fastener 191 is secured to the connecting 29 tab portion 190e.
Opposite the compartments 44, 45, and 46, the rear wall of 31 the base 41 is provided on the rear side with three shallow 32 recesses 44a, 45a, and 46a (FIG. 2) each having a resistor 192 .~` . , ~: ' D
~OS~i9 ~ 5' 1 potted therein with potting material 193,preferably a ceramic compound having properties o~ good thermal conductivity, such as 3 alumina or silica based ceramics. A thin plastic cover 194 is 4 recessed 1n the base 41 and adhesively secured in place to cover 5 the potting material in all three of the recesses 44a, 45a, and 1 6 46a. The resistor 192 in each recess is made of material having 7 a positive temperature ccefficient of resistance, is preferably 8 chromium-plated substantially pure iron wire, and is best shown

9 in FIGS. 20-22. An important feature of the resistor 192 is that its resistance is transformable from a relatively low value to a 11 relatively much higher value. Other materials which have a posi- ~`
12 tive temperature coefficient o~ resistance and can be used for the ;~
resistor 192 in place of substantially pure iron include tungsten, 14 nickel, cobalt, and alloys or metallic compounds of these and other elements such as cobalt-iron and zirconium diboride. In 16 these materials, the resistance is a direct function of tempera-17 ture.
18 As shown in FI~. 20, the resistor 192 terminates at each end 19 in a flattened, generally P-shaped portion which includes a straight portion of length "X" to which an electrode is attached 21 for electroplating in a solution containing chromium. A~ter 22 electroplating, the electrode terminal portions, as shown in 23 broken lines for one of the end portions in FIG. 21, are cut off, 24 and the remainder of the flattened end is aligned with the plane containing the axis of the circular wire, as shown in FIG. 22.
26 In each of the recesses 44a, 45a, and 46a, a screw 195 (FIGS.
27 1 and 34) secures an end portion 192a of the respective resistor 28 192 (FIG. 20), modified as described above, to the tab portion 29 192e IFIG. 13) of the conductor 190. A screw 196 secures an 30 opposite end portion 192b, modified as described, to an apertured ;;~
31 connecting tab portion 197a of a conductor 197 (FIGS. 26-29). An internally threaded fastener 198 is secured to the connecting tab , ' 1 portion 197a. The conductor 197 includes a ~trap portion 197b 2 extending at right angles to the connecting tab portion 197a along 3 an end of the short leg portion 183b of the magnetic core 183 and joined at right angles to a strap portion 197c extending along an end face of the core 183. A bent tab 197d extending from the 6 strap portion 197c is secured to a conductor 199 having a strap 7 ¦ portion l99a extending through the magnetic core structure 181 8 1 along the inner side of the short leg portion 183b of the magnetic g I core 183. An ofsetting poxtion l99b joins the strap portion l99a lO ¦ to a tab portion l99c secured to the terminal strap 184 and having the cable 178 secured thereto. A strip 200 of arc extin-12 ¦ guishing material such as disclosed in the aforesaid Canadian ~`
13 ¦ Patent No. 1,014,725, issued October 2, 1977, is adhesively 14 ¦ secured to the side of the strap portion l99a facing the contact 15 ¦ blade 154.
16 ¦ In each of the compartments 44, 45, and 46, an arc chute 202 17 ¦ (FIGS. 1 and 34~ for the contacts 153 and 155 is disposed adjacent 18 ¦ the magnetic core structure 181. The arc chute 202 is best shown 19 ¦ in FIGS. 30-32 and includes a pair of molded casing portions 203 20 ¦ and 204 secured together by a plurality of rivets 205. Eaah of ;
21 I the casing portions 203 and 204 is provided with a pair of ~ ;
22 ¦ recesses on a side thereof facing the other casing portion, such 23 ¦ as an inner recess 203a and an outer recess 203b (FI~. 32~ in the 24 ¦ casing portion 203, to provide a pair of passageways through the 25 ¦ arc chute 202. Each of the casing portions is grooved on a wall 26 ¦ of each recess facing the other casing portion and each groove has 27 ¦ one of the arcing plates 134, best shown in FIG. 33, adhesively 28 ¦ secured therein. A venting plate 206 is adhesively secured to the ;
29 ¦ casing portions 203 and 204 and is disposed in the base 41 rear-wardly fo the respective connector body 60. A venting plate 207 31 is adhesively secured to the cas~ng portions 203 and 204 and is 32 disposed in the cover 42 of the assembled circuit breaker 40 for-~3 wardly of the respective connector body 60. From the contact side -~ 19 - , '~'' ~C~5~
of the arc chute, ~he arc plates 134 in the inner re~es~ 203a slant ~oward the rear wall of the base 41, and those in the outer ;~ -recess 203b slant toward the front wall of the cover 42. The arc plates 134 in the ca~ing portion 204 slant in a similar ~ :
fashion, but as best shown in Fiy. 31, they are staggered with respect to those in the casing portion 203. :
In each of the co~artr~nts 44, 45 and 46, when the ~-contacts 153 and 155 are closed, part of the current from the conductor 142 fLows through the ~-shaped portio~ 150a of the .
conductor 150 to the cable 151 and the remainder 10ws by way of the strap portion 148~ through the box~like conductor 148 and the strap portion lSOb of the conductor 150 to the cable 151. `
-1 From the cable lSl the total or recombined current flows through the contact blade 152, contacts 153 and 155, contact blade 154, cable 178, and the terminal strap 184 to the terminal member 186. ~.
~ The strap portion 148a and the magnetic core 156 in ;~
;~l each compartment form an electromagnet. Upon flow of a fault current through the strap portion 148a greater than that at which the magnetic core 113 at~racts the armature plate 112, the magnetic core 156 at~racts the armatuxe 158 alo~g with the i : plate 160, armature pin 161, nut 162, links 163 and 164, and pins 165, 166, and 167. The pin 166 pivots the blade 152 about -~
~he pin 168 toward a~ open position, and the pin 170 releases the blade 154 so that it is free to pivot about the pin 170 ¦ toward an open position under the influence of a repul~ion force 1 between the two blades due to the current path through the -,J blades. The blade~ 152 and 154 are also moved apart by magnetic forces induced by the current flow therethrough, it being no~e~
1 that they constitute partial conductor turns for the magnetic.1 30 core structure 181. The contacts 153 and ~55 are thus separated ~, to switch the current path through the resistor }92. ~:

~:~`. The parallel circuits between conductorl42 and cab}e 151, !

,.1 ~ ~:
1 comp~is:lng a circuit through conductor 15~a in parallel wlth the 2 circuit through conductors 148a, 148, and 150b, provides by-pass 3 means ~or sufficlent current to prevent opening the current limit-4 ing contacts 153 and 155 until a threshold fault current above a selected rnagnitude is present for magnetic core 155 to attract 6 armature 158 which opens contacts 15~ and 155. By way of example, 7 this circuit arrangement and electromagnet characteristics may be -~
8 adapted to prevent separation of the limiting contacts 153 and 155 below a threshold of 1,000 amps.
When the contacts 153 and 155 are separated, part o~ the 11 current from the conductor 142 ~lows through the L-shaped portion 12 150a and also through the strap portion 150b of the conductor 13 150 to the conductor 188, and the remainder flows by way Or the 14 strap portion 1~8a through the box-like conductor ~8 to the conductor 188. The recombined current then flows through the 16 conductors 188 and 190, through the resistor 192~ through the 17 conductors 197 and 199, and through the terminal strap 184 to the 18 terminal member 186.
19 The current limiter contacts preferably do not operate in the thermal overload range but only at relatively higher ranges of 21 fault current or short circuit conditions. Within the thermal 22 overload range, one or more of the bi-metallic strips 145 are 23 operable to trip the circuit breaker and open the sets of main 24 contacts 53 and 54 as previously described. Immediately above the thermal overload range, fault currents are still relatively low 26 but are of sufficient magnitude to cause at~raction of one or more 27 o~ the armature plates 112 and open the sets of main contacts 53 28 and 54 as previously described. Immediately above the thermal ; -29 overload range, fault currents are still relatively low but are of sufficient magnitude to cause attraction of one or more of the 31 armature plates 112 and open the sets o~ main contacts 53 and 54 32 as previously described. Such fault currents are below the ~ 21 -: . ~ . -- ~ .-- ,-, ~ , ~ - . . ,, , , . :. ;

~S~
interrupting ability of the sets of main contacts 53 and 54. Fault currents immediately above this range are just sufficient to cause magnetic core 156 to attract armature 158 and pin 161 which cause limiter contacts 153 and 155 to open.
As the current decays, the magnetic forces also decay. The com- `
pression spring 176 in urging contacts 153 and 155 to a closed position tends to dominate over the decaying current causing those contacts to reclose while a short arc still exists in a ; small air gap between them. This action often leads ~o contact welding. To solve this problem, an additional or supplemental magnetizing turn 188b is provided in series with current limit~
ing resistor 192. Thus, while fault current still flows in re-, sistor 192, magnetic core 156 ~ill be sufficiently energized to attract armature 158 to hold contacts 153 and 155 apart.
In each compartment, the strap portion 148a is the only ef-fective conductor turn for the magnetic core 156 when the con-tacts 153 and 155 are closed, and only part of the current flows therethrough, the remainder flowing through the by-pass con-ductor provided by the L-shaped portion 150aO When the contacts i ~ 153 and 155 are open, the strap portion 188b provides an addi-i 20 tional conductor turn, and it carries the total current while the strap portion 148a is effective as a conductor turn carrying l part of the current. The additional conductor turn 188b enables -; the blades 152 and 154 to~be maintained in an open position with less current than is required to move them to an open position originally. By the time the blades 152 and 154 move back to ~closed position under the influence of the spring 176, the fault current will have been dissipated in the resistor 192 and the j blades 67 will have been opened.
~i In each of the compartments 44, 45, and 46, the strap por- ;~
tions 188d and l99a are conductor turns for the magnetic core structure 181. Further, portions of the contact blades 152 and 154 are partial conductor turns for the magnetic core .~ .
~ ~ - 2~ -.~

~15~LO~j~
structure 181. When the contact blades 152 and 154 are moved to open position and an arc 208 forms between the open contacts 153 and 155, the magnetic field set up as a result of current flow through the partial conductor turn portions of the contact blades 152 and 154 acts on the arc 208 to force it toward the arc chute 202 with its staggered, slanting arc plates 134. Once the arc is interrupted, the current flow shifts to the previously de- ~
scribed path through the resistor 192, and the flow through the -conductor turns 188d and l99a maintains the magnetic field, aids the dielectric strength recovery of the gap, and thereby guards against re-ignition. Any re-ignition of the arc would also take place in a magnetic field, which would force the arc out again.
The device of this invention is compact enough to fit into existing circuit breaker panelboards and yet it is capable of repeatedly ir.terrupting currents in exc~ss of 100,000 amperes root-mean-square (RMS) symmetrical. With such currents avail-able, the arc which forms between the contacts 153 and 155 upon :, ~
their opening must be extinguished in about a millisecond or less.
This is accomplished by the generation of a sustained arc voltage which reaches the magnitude of the impressed supply voltage in about a millisecond or less. The structure used to accomplish this result includes the fast operating mechanism for opening the blades 152 and 154 with their contacts 153 and 155, the magnetic core structure 181, the coating of the arc chamber with arc ex-tinguishing material, and the resistor 192 connected in parallel with the contacts L53 and 155.
! The magnetic core structure 181 encloses the contacts 153 and 155 and a substantial portion of the blades 152 and 154 and provides a magnetic field with the maximum practical value of magnetic flux density normal to the blades 152 and 154 and also normal to the arc. The magnetic field exerts a force on each ~ - 23 -~;
.-~051~
blade tending to "blow" them apart; and also ex~rts a force onthe arc 208 tending to "blow" the arc out toward the arc chute 202. The force is proportional to the product of the current and the magnetic flux density. Since the magnetic flux density is derived from the current, the orce i8 p~oportional to the square of the current, and the higher the available current is, the faster the blades open and the aster the arc is blown out.
The xesponse of the current limiting device is thus proportional to the severity of the ~hort circuit. ~he magnetic core lQ stxucture 181 and blades 152 and 154 are so arranged that the lines o force in the magnetic field intersect blades 152 and 153/ through which current flows in opposite directions, from the direction which will force said blades apart. As viewed in Fig. 1, when current flows in the direction from cable 151, ! forward through contacts 153 and 155, then fromthe contact end of blade 154 back through blade 154 and out through cable 178, then during such current flow the magnetic flux and lines of . , , ; force in the transverse magnetic field extend from leg 183a (Fig. 23) of magnetic core 183 to leg 182a ~Fig. 23) of magnstic ~i 20 core 182 (Figs. 1 and 23). This arrang~m~nt of current flow through blades 152 and 154, and magnetic flux across said blades tends to force blades 152 and 154 apart.
Furthermore, when blades 152 and 154 separate and an arc 208 forms between contac~s 153 and 155, current 1~ws through said arc from contact 153 to contact 155. The transverse ma~netic field, wi~h lines of force from leg 183a to leg 182a, acting on such arc with current flow as described, will there-fore "blow" the arc forward toward arc plates 134. This .1 "bl~wing" action effectively increases ~he arc length and ~ 30 resistance and therefore arc voltage, consequently limlting ;~ the current as well as extinguishing the arc. The magnetic . :. .
field also aids the rate of dielectric strength recovery of the gap across contacts 153 and lS5 following arc extinction and the subsequent continued rise of the impressed ~. ~
~ - 24 -;'' "

105~L0Ei9 1l ~ voltage cross the gap after current trans~er. It sho~ld also be 2 noted that by increasing arc voltage the transverse magnetic field 3 has the effect of' increasing the power ~actor of` the circult by 4 inserting resistance into the essentially inductive short circuit 5 thereby reducing the lag o~' current behind voltage. The power 6 factor is increased almost to unity.

Blades 152 and 154 are elongated and pivotally mounted at 8 respective points 151 and 170, which provides leverage effect to 9 increase speed and resistance at the contact ends thereof when actuated by magnetic core 156. Thus~ when core 156 is energized 11 to raise armature pin 161 a given distance within a given time, 12 the contact ends of blades 152 and 154 and respective contacts 153 13 and 155, will move apart a greater distance within a shorter time 14 than the corresponding displacement and rate of speed or armature pin 161.
16 The contact blades 152 and 154, and contacts 153 and 155, are 17 shaped and dimensioned to provide structures o~ relatively low 18 mass and minimum inertia to respond quickly and open rapidly when 19 the electromagnet is energized.
The contact blades 152 and 154 are constructed, dimensioned 21 and mounted with respect to the actuating electromagnet (magnetic 22 core 156, armature 158) to provide a gap on the order o~ one-23 quarter inch within one sixteenth cycle o~ current flow or about 24 0.001 seconds (within one millisecond).
25 The electromagnetic means (magnetic core 156, armature 158, :
26 pln 161, and connecting links), the field magnet structure 181, 27 blades 152 and 154, and the particular way in which they are 28 positioned and associated as described, serve to open the current -?9 limiting contacts 153 and 155 in about 0.0002 seconds (.2 o~ a millisecond) rrom initiation of a fault current in the circuit 31 above the threshold selected ~or operation of the current limiting 32 section, or within one-eightieth cycle of current ~low.
:' ~05~ ~1 ;g Under conditions of high available short circuit currents, the limiter contacts 153 and 155 are open in as little a time as .2 milliseconds (one-eightieth of a cycle) from current initia-tion. As the contacts open an arc is formed between them. The arc between the limiting contacts is ordinarily extinguished `~ within one millisecond by the structure and mechanism of this invention. It should be borne in mind that the mechanism de-scribed responds with the square of the magnitude of fault cur-xent so the larger the fault current, the faster the current limiting response. This accelerating responsiveness includes not - only the speed of contact separation, but the effective respon-siven~ss of the transverse magnetic field generated by field ~-magnet structure 181 on the arc formed between contacts 153 and 155 which raises the arc voltage almost instantaneously to equal the voltage of the source by the means described (essentially by lengthening the arc through faster and greater contact separa-tion plus bowing forwardly, plus cooling, all of which increase resistance of the axc and arc voltage). When the arc voltage equals the supply voltage, current can no longer continue to rise and is forced to transfer completely into the current limiting , resistor 192 where its energy is dissipated.
! The main breaker contacts 53 and 70 open within 0.004 seconds ~ of fault current initiation, or within 1/4 cycle of current flow 3 at 60 cycles per second by which time the fault current has been fully shunted into current limiting resistor 192 and its energy dissipated. The main contacts 53 and 70 being opened, current has ceased to flow in the protected circuit in less than 1/4 cycle or less than 4 milliseconds after appearance of the fault ~; current above the threshold selected for the limiting section of the circuit breaker to become operable.
The effective current limiting responsiveness of the follow-ing combination, (1) speed of contact separation plus ~2) in-creasing arc voltage to equal source voltage, occurs within a~out ~5~
a millisecond or less by means of the invention described herein.
This is important because symmetrical short circuit currents have their maximum growth rate during the first millisecond immediate-ly following current zero. The current limiting means in accord-ance with this invention intercepts the short circuit current befoxe it achieves a significant growth following current zero and shunts it into limiting resistance 192 having a positive temperature coefficient of resistance.
The mechanism as described ca~ be mounted in compact cases to fit in standard panelboards. The compactness may be measured in terms of the ratio of short circuit amperes of interrupting ; rating to circuit breaker ~olume. The table bel~w provides a ~-reasonable illustration of the volumetric efficiency o short circuit interruption of the subject breaker. The volume of five representative circuit breakers is given in the second column and the interrupting rating shown in column 3. The first circuit '~ breaker in the ~ollowing table is the subject matter of this application.

(1) (21 (3) (4) Breaker Maximum Breaker Volume Interrupting Volumetric Ampere Cubic Inches- Rating, 480V, Efficiency Ratin~* (T~pical Brkr.) 3~,K-Amps rms KVA/in.3 Instant Inven. 100 138 100-~00** 347-594 Representative ~ 100 85 25 142 Circuit ~ 225 131 35 -128 Breakers ( 400 273 35 61.5 for 11000 569 35 29.5 ~;
comparison (2500 1994 85 20 * This is the steady state current rating, all breakers listed are molded case circuit breakers.
** The 100 K~ rating is an established but not a ~ ,~
maximum figure.

:'.... ' ~L~51~6i9 An additiona} feature of this invention which aids in fitting a mechanism o~ high interrupting capacity within a circuit breaker of minimum volume, are plates 134 positioned forward of limiting contacts 153, 155 and blades 152, 1540 One of the current limiting features of thi~ invention is the rapid increase of arc voltaye to equal source voltageO However, when high arc energy is applied to the air slab in the arc ~' chamber, the air temperature rises ~ery rapidly which creates shock waves and large pressure gradients which must be dissi-

10 pated. The devices which have attempted to limit current by generating high arc voltage have accordingly been bulky. They have had to include a large volume chamber in which to dissi-pate the shock waves and pressure gradients created by this ', means of current limiting. The invention herein combines arc ~' voltage increase with other current limiting means, so the degrees of shock waves and pressure gradients are substantially less than in those devices which rely on the arc voltage means alone. Furthermore, plates 134 are particularly shaped, dimen~
sioned and mounted as described above with respect to the arc, 20 its path of movement, plus the direction of shock wave and s air pressure gradients created, to intercept and effectively dissipate such ~orces without re~uiring a relatively large volume chamber.
The arc extinguishing material which coats the mag-netic core structure 181 and lines the inside of the re¢tangu-lar tube formed thereby and the inner sides of the conductor '~ turns 18Bd and 199a to a large extend determines the rate of ' dielectric strength recovery across the con~acts during and ; immediately f,ollowing arc extinction. The dielectxic strength ' 30 recovery is essential to the current limiting process and is further aided by the magnetic field. The arc extinguishing material is selected in accordance with the disclosure of the above mentioned Canadian Patent No. 1,014,725.

:

~Q5~$~
1 The resistor 192 should have a positively transformable 2 resistance, capable o~ changing from an extremely low value to a 3 much hlgher value af'ter the arc across the contacts 153 and 155 4 is extinguished and the total current is forced to flow through the resistor and bypass the contacts. The transf`ormation of the 6 resistance increases the circuit power f'actor~ aids interruption, and limits the "through" i2t (product of the squa~ of the current 8 and the time) f'actor of the short circuit.
9 Various modifications may be made in the structure shown and 10 described without departing f'rom the spirit of the invention and ~-

11 scope of the attached claims.

12

13 ~' lg ~
;~ 22o . . ' '' , 22 '', 23 ' 2l~ , , 26 , 27 , 28 l 29 '~ 3 ,~ 31 j 32 - 29 ~ ~;

:,~

Claims (6)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows :

1. In an electromagnetically operable circuit interrupting device comprising an outer molded case, a magnetic core disposed in the outer case, a conductor turn disposed in the outer case and associated with the magnetic core, an armature disposed in the outer case, normally in spaced relationship to the magnetic core, and attracted toward the magnetic core upon flow of a predetermined current in the conductor turn, an inner case disposed in the outer case adjacent the armature of an opposite side thereof from the magnetic core, wherein the im-provement consists of an armature pin secured to the armature and having a portion reciprocally mounted in the inner case, a first contact blade having a mounting end portion disposed in the inner case and a contact end portion disposed outwardly of the inner case, a second contact blade having a mounting end portion disposed in the inner case and a contact end portion disposed outwardly of the inner case, each of the contact blades having a contact mounted on the contact end portion thereof and engaged with the contact on the contact end portion of the other of the contact blades when the contact blades are in a closed position, means in the inner case on one side of a longitudinal axis of the armature pin pivotally mounting the first contact blade, means in the inner case on the other side of the long-itudinal axis of the armature pin pivotally mounting the second contact blade, means operatively connecting the armature pin with the contact blades, and spring means in the inner case bias-ing the contact blades towards the closed position.

2. A circuit interrupting device as claimed in Claim 1 wherein the spring means is a compression coil spring encircling the armature pin.

3. A circuit interrupting device as claimed in Claim 1 wherein the means operatively connecting the armature pin with the contact blades includes a pair of spaced links disposed in the inner case respectively on opposite sides of the armature pin, a pin pivotally mounting the links to an end portion of the armature pin disposed in the inner case, a pin carried by the links and operatively connected to the first contact blade, and a pin carried by the links and operatively connected to the second contact blade.

4. A circuit interrupting device as claimed in Claim 3 wherein the pin carried by the links and operatively connected to the first contact blade has a one-way connection thereto in an opening direction therefor.

5. A circuit interrupting device as claimed in Claim 4 wherein there is no lost motion in the one-way connec-tion as the pin moves the first contact blade from the closed position to an open position.

6. A circuit interrupting device as claimed in Claim 3 wherein the pin carried by the links and operatively connected to the second contact blade has a one-way connection thereto in a closing direction therefor.