Secondary circuit breaker for distribution transformers

A circuit breaker having a fixed current contact (12,14), a movable current contact (16,18), a mechanism (20,22,54,66,68) for displacing the movable current contact (16,18) between a circuit closing position and a circuit opening position, and a latching member (32,34) disposed to cooperate with the mechanism (20,22,54,66,68) and movable in response to the magnitude of current flowing through the circuit to be controlled in order to cause the mechanism (20,22,54,66,68) to move the movable contact (16,18) in a manner to open the circuit when the magnitude of current flow exceeds a certain value, movement of the latching member (32,34) being controlled by a memory metal element (40,42) which is mechanically connected to the latching member (32,34) and electrically connected in the circuit to be heated by current flowing through the circuit to cause the latching member (32,34) to release the mechanism (20,22,54,66,68) when the current flowing through the circuit exceeds a given value for a selected period of time. The circuit breaker is further provided with a remotely located control unit (140-166 ) which is coupled to the circuit breaker mechanism (20,22,54,66,68) by a cable (78). The circuit breaker is further provided with an emergency locking device (180,188) which is manually movable into a locking position for preventing the mechanism (20,22,54,66,68) from moving upon being released by the latching member (32,34).

BACKGROUND OF THE INVENTION 
The present invention relates to circuit breakers, and particularly 
secondary circuit breakers for distribution transformers. 
While there are many types of circuit breakers available for such systems, 
the available circuit breakers have relatively complex thermal tripping 
and manual actuating mechanisms. Moreover, while there are many 
conventional circuit breakers which can be reset to a higher thermal 
tripping temperature, existing breakers do not possess a simple mechanism 
which permits the thermal tripping function to be entirely disabled. 
SUMMARY OF THE INVENTION 
It is a primary object of the present invention to simplify the thermal 
tripping mechanism of such circuit breakers. 
Another object of the invention is to provide a simple arrangement for 
manually operating such a circuit breaker from a location remote from the 
circuit breaker itself. 
A further object of the invention is to provide a simple mechanism which 
enables the thermal tripping function of such a circuit breaker to be 
entirely disabled. 
The above and other objects are achieved, according to the present 
invention, in a circuit breaker including a current conducting path, a 
fixed current contact and a movable current contact connected in the 
current path, a mechanism supporting the movable current contact for 
movement between a contact closing position in which the movable current 
contact is in contact with the fixed current contact to complete the 
current path and a contact opening position in which the movable current 
contact is separated from the fixed current contact to open the current 
path, latch means movable between a latching position for engaging the 
mechanism to enable the mechanism to be in the contact closing position 
and a release position for releasing the mechanism to allow the mechanism 
to move to the contact opening position, and latch actuating means coupled 
to the latch means for moving the latch means between the latching and 
release positions, by the improvement wherein the latch actuating means 
comprise: a memory metal element mechanically connected to the latch means 
and electrically connected in the current conducting path to be heated by 
current flowing through the path, the memory metal element being formed to 
place the latch means in the latching position when the current through 
the path is below a selected magnitude and to place the latch means in the 
release position when the current through the path is above the selected 
magnitude. 
Objects according to the invention are further achieved by the provision, 
in a circuit breaker of the type described above, of biassing means for 
urging the mechanism into its contact closing position and circuit breaker 
control means disposed at a location remote from the current path, the 
mechanism and the latch means and movable between a circuit breaker 
opening position and a circuit breaker closing position; and a first 
flexible cable connected between the control means and the mechanism for 
moving the mechanism in response to movement of the control means such 
that movement of the control means to the circuit breaker opening position 
moves the mechanism to the contact opening position and movement of the 
control means to the circuit breaker closing position permits the 
mechanism to move, under the influence of the biassing means, into the 
contact closing position. 
In further accordance with the invention, such a circuit breaker is 
provided with emergency locking means operatively associated with the 
mechanism and movable into a locking position for preventing the mechanism 
from moving to the contact opening position in response to movement of the 
latching means to the release position.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
FIG. 1 shows the basic components of a circuit breaker embodying the 
present invention mounted on a molded plastic base 2, the circuit breaker 
providing two independent load current paths, each defined by a respective 
entry lead 4, 6 and a respective exit lead 8, 10. Each current path 
further includes a stationary contact assembly 12, 14 and a respective 
movable contact assembly 16, 18. 
Each movable contact assembly 16, 18 is pivotally supported at one end of a 
respective contact arm 20, 22. The opposite end of each arm 20, 22 is 
formed to contact a latching finger 24, 26, each latching finger normally 
being engaged by a respective latch 28, 30, each forming part of a 
respective latch arm 32, 34 each pivotally mounted on base 2 via a 
respective pivot pin 36, 38. 
According to a particular feature of the present invention, movement of 
each latch arm 32, 34 is effected by a respective memory metal actuator 
40, 42, each mounted at one end to a respective fixed support 44, 46 
secured to base 2 and at the other end to a movable support 48, 50 
fastened to respective ones of latch arms 32, 34. 
Each fixed support 44, 46 is connected to a respective movable contact 16, 
18 by a respective current lead 52, 53 and each exit lead 8, 10 is 
connected to a respective one of latch arms 32, 34 and the current path 
between each fixed support 44, 46 and its associated latch arm 32, 36 is 
constituted by the respective actuator 40, 42. 
Each actuator 40, 42 is constructed and treated to be in the configuration 
illustrated in FIG. 1 while at normal operating temperature but to be 
deflected, upon being heated to a higher, preselected temperature, in a 
manner to pivot its respective latch arm 32, 34 in a counter-clockwise 
direction, thereby releasing the associated latching finger 24, 26. 
Because of the inherent properties of memory metals, actuator 40, 42 will 
directly generate a force sufficient to pivot the associated latch arm 32, 
34 by the amount required to release latching finger 24, 26. Thus, the 
complicated lever and latch arrangements required with bimetal actuators 
can be eliminated. 
While the illustrated actuators 40, 42 are in the form of cantilever bars, 
actuators according to the present invention could alternatively take the 
form of torsion bars or coil springs, or could have other configurations, 
it only being required that the actuator be configured and treated to 
pivot each latch arm 32, 34 by the required amount when heated to a given 
temperature. 
Moreover, actuators made of a memory metal will have a much lower 
resistance than conventional bimetal actuators, so that circuit breakers 
according to the present invention will have lower power losses than 
conventional breakers. 
Contact arms 20, 22 are pivotally mounted at opposite ends of a connecting 
link 54 by means of pivot pins 56 and 58 each passing through circular 
passages in arms 20 and 22 and link 54. Pins 56 and 58 are guided in guide 
slots 60 and 62 provided on base 2. 
Movement of connecting link 54 is controlled by a toggle mechanism composed 
of an upper toggle link 66, a lower toggle link 68 and a cable connector 
70. The upper end of toggle link 66 is pivoted to base 2 by a pivot pin 
72, while the lower end of link 66, the upper end of link 68 and connector 
70 are connected together by a pivot pin 74 and the lower end of link 68 
is pivotally connected to pin 56. 
Movement of the toggle mechanism is controlled by a toggle operating cable 
78 secured to connector 70 and a compression spring 80 interposed between 
connector 70 and an abutment member 82 which is secured to base 2. In view 
of the biassing action performed by spring 80, cable 78 need only perform 
a pulling movement and therefore need not be enclosed in a restraining 
sheath that would have to be fastened at booth ends. 
Each movable contact 16, 18 is composed of a copper contact member 86 and a 
refractory contact member 88. Each contact 86 is supported by an insulator 
90 carried by a respective one of arms 20 and 22. Each copper contact 86 
is connected to a respective one of current leads 52 and 53. 
Each stationary contact assembly 12, 14 is composed of a load current 
contact 94 and an arcing contact 96 provided with a refractory contact 
member. Each of contacts 94 and 96 is mounted in an insulating support 
secured to base 2 in such a manner as to be movable over a short distance 
in the direction toward and away from its associated movable contact 
assembly 16, 18, each of contacts 94 and 96 being provided with a biasing 
spring urging that contact in the direction toward its associated movable 
contact assembly. In addition, contacts 94 and 96 are constructed to 
permit each arcing contact 96 to be movable over a slightly greater travel 
path than its associated load current contact 94. When the circuit breaker 
is closed, each copper contact member 86 contacts its associated load 
current contact 94 and each refractory contact member 88 contacts the 
refractory member of its associated arcing contact 96. During opening 
movement of each movable contact assembly 16, 18, contact between copper 
contact member 86 and load current contact 94 will be broken first so that 
a current flow of reduced amplitude can continue to flow between 
refractory contact member 88 and arcing contact 96. When contact 
therebetween is subsequently broken, the resulting arc occurs between the 
refractory members and thereby causes minimal damage. 
In order to assure that the contacts associated with both current paths 
will open at the same, the contact arm 20, 22 associated with each current 
path is coupled to the latch arm 32, 34 associated with the other current 
path by a respective one of two trip links 98, 100. Trip link 98 is 
pivotally connected at one end to latch arm 32 and at its other end 
engages slidably in a slot 102 provided in contact arm 22. 
Correspondingly, trip link 100 is pivotally connected at one end to latch 
arm 34 and engages via its other end in a slot 104 formed in contact arm 
20 and identical in configuration to slot 102. 
Each contact arm 20, 22 is biased in a clockwise direction relative to its 
associated link 56, 58 by a bias spring 106 secured to base 2, only the 
spring 106 associated with contact arm 20 being shown. 
In addition, a signal arm 110 is pivotally mounted on pivot pin 58 and is 
biased in a clockwise direction by a spring 112 fastened to base 2. Signal 
arm 110 is associated with a signal contact 114 in such a manner that a 
trip signal is produced when arm 110 strikes signal contact 114. Signal 
arm 110 is provided with a latching finger which is similar in shape to 
finger 26. However, as shown, finger 26 projects slightly beyond the 
latching finger on signal arm 110. 
Signal arm 110 is associated with a reset arm 116 which is pivotally 
mounted to base 2 at a pivot pin 118 and is spring biased into the 
position illustrated by a suitable return spring (not shown). Reset arm 
116 is connected to a signal reset cable 120 which can be actuated to 
pivot arm 116 in a counter-clockwise direction against an actuating finger 
of signal arm 110. 
The circuit breaker is shown FIG. 1 in its manually open position. In order 
to close the circuit breaker, the tension on cable 78 is released to 
permit connector 70 to move to the right, under the influence of spring 
80, to a position at which toggle links 66 and 68 lie in a straight line 
with connecting link 54. During this movement, link 54 is displaced 
downwardly, with pins 56 and 58 moving downwardly in guide slots 60 and 
62, respectively. This brings movable contact assemblies 16 and 18 into 
electrical contact with stationary contact assemblies 12 and 14. 
At this time, the circuit breaker is closed and can be opened either 
manually or in response to heating of either one of actuators 40 and 42, 
due to a current overload in either current path. If, for example, such an 
overcurrent occurs in the path between entry lead 4 and exit lead 8, 
actuator 40 will be heated sufficiently to pivot latch arm 32 
counter-clockwise until latching finger 24 is released. Then, under the 
influence of spring 106, contact arm 20 pivots clockwise causing the 
connection between stationary contact assembly 12 and movable contact 
assembly 16 to be broken, in the manner described above. 
Near the end of travel of contact arm 20, the upper end of trip link 100 
reaches the upper end of slot 104, after which further pivotal movement of 
contact arm 20 produces a downward movement of link 100, which causes 
latch arm 34 to pivot counter-clockwise, thereby releasing both latching 
finger 26 and the latching finger of signal arm 110. Thus, connection 
between stationary contact assembly 14 and movable contact assembly 18 is 
broken and signal arm 110 comes into contact with signal contact 114. 
During this opening movement, insulators 90 come into contact with 
associated abutments 122. 
The circuit breaker can be reset after actuators 40 and 42 have cooled 
sufficiently to return latch arms 32 and 34 to their latching positions, 
as shown in FIG. 1. Then, cable 78 is pulled to the left to bring the 
toggle mechanism into the position shown in FIG. 1. During this movement, 
while insulators 90 remain in contact with abutments 122, latching fingers 
24 and 26 move past latches 28 and 30, performing a camming action which 
pivots latch arms 32 and 34 slightly in the clockwise direction against 
the restoring force of actuators 40 and 42, until latch arms 24 and 26 
move past latches 28 and 30, after which latch arms 32 and 34 pivot back 
to bring latches 28 and 30 to their latching position. 
In order to reset signal arm 110, cable 120 is pulled upwardly to pivot 
reset arm 116 in a direction to rotate signal arm 110 back into the 
position shown in FIG. 1, during which movement, the right-hand end of 
signal arm 110 moves past latch 130. While this movement will pivot latch 
arm 34 through a small distance in the counter-clockwise direction, this 
movement will not be sufficient to release latching finger 26 because that 
latching finger projects slightly beyond the free end of signal arm 110. 
Then, cable 78 is displaced to the right, causing the toggle mechanism to 
move link 54 downwardly, thus re-establishing the connection between 
movable contact assemblies 16 and 18 and stationary contact assemblies 12 
and 14. At the same time, cable 120 is permitted to move downwardly in 
order to return reset arm to its inactive position, as shown in FIG. 1. 
Manual opening of the switch is effected simply by moving cable 78 to the 
left in order to bring the toggle mechanism and link 54 into the position 
shown in FIG. 1. 
One preferred embodiment of a remote operating mechanism according to the 
present invention is illustrated in FIG. 2. The operating mechanism is 
carried by a base 140 in which a shaft 142 is pivotally mounted. Shaft 142 
is fixed to a manual operating handle 144 and a first control arm 146. A 
second control arm 148 is mounted on shaft 142 in a manner to be pivotable 
relative to shaft 142. Each of arms 146 and 148 carries a respective 
support plate 150, 152 which is pivotally mounted in an opening provided 
at the free end of the respective control arm 146, 148. 
A rod 156 extends between plates 150 and 152, being slidably mounted in an 
opening provided in each support plate, and a compression spring 158 is 
disposed around rod 156 and compressed between plates 150 and 152. 
Cable 120 is secured to shaft 142 and extends therearound in the manner 
illustrated so that when shaft 142 is rotated in the clockwise direction, 
cable 120 will be pulled upwardly. 
Arm 148 is provided with first and second projecting members and 160 and 
162. Projecting member 160 cooperates with abutment members 164 and 166 to 
limit the range of pivotal movement of arm 148. Second projecting member 
162 is secured, at its free end, to the end of cable 78 remote from cable 
connector 70 (FIG. 1). 
In the position shown in FIG. 2, the operating mechanism maintains the 
circuit breaker in its closed position in which, referring to FIG. 1, link 
54 is in its lower most position and reset arm 116 is in its retracted 
position. 
The operating mechanism shown in FIG. 2 is an over-center type mechanism in 
that when arm 146 is pivoted clockwise to a point just past the point at 
which arms 146 and 148 come into alignment, spring 158 will act to pivot 
arm 148 in the Counter-clockwise direction, thus drawing cable 78 upwardly 
and moving projecting member 160 into contact with abutment member 164. 
In FIG. 2, the operating mechanism is shown in its circuit breaker closing 
position. In order to manually open the circuit breaker, handle 144 is 
manually moved in the clockwise direction until arm 146 moves past arm 
148. During this movement, cable 120 is pulled upwardly in order to pivot 
reset arm 116 in the counter-clockwise direction from the position shown 
into a position where it has moved past the portion of signal arm 110 with 
which it would engage in order to reset signal arm 110. When arm 146 moves 
past arms 148, arm 148 is pivoted by the action of spring 158 in order to 
pull cable 78 upwardly and thus bring the toggle mechanism to the position 
shown in FIG. 1. 
Subsequent closing of the circuit breaker is effected by moving handle 144 
back to the position shown in FIG. 2. 
If a condition should occur in which the circuit breaker remains closed, 
but signal arms 110 has tripped, the signal arm can be reset by moving 
handle 144 in the clockwise direction over only a portion of its travel 
path to a point at which arm 146 does not come into alignment with arm 
148. Under these conditions, cable 120 is moved sufficiently to cause 
reset arm 116 to return signal arm 110 to the position shown in FIG. 1, 
without displacing cable 78. 
After the circuit breaker has been thermally tripped, and latch arms 32 and 
34 have returned to the latching positions shown in FIG. 1, the circuit 
breaker can be reset simply by moving handle 144 in the clockwise 
direction relative to that shown in FIG. 2 to the manual opening position, 
and then moving handle 144 back to the circuit breaker closing position. 
Then, signal arm 110 can be reset in the manner described above. 
According to a further feature of the present invention, the circuit 
breaker shown in FIG. 1 can be equipped with an emergency control 
mechanism which can be positioned to prevent the circuit breaker from 
tripping thermally, while permitting it to continue to be manually opened. 
A preferred embodiment of such a mechanism is shown in FIG. 3 in position 
relative to contact arms 20 and 22. The emergency control mechanism 
includes an emergency control slide 180 provided with guide slots 182. 
Slide 180 will be mounted outside of the circuit breaker case, for example 
behind base 2 of FIG. 1 and will be supported by, for example, rivets 
secured to base 2 and extending through slots 182, thereby limiting slide 
180 to movement only in the direction of its length. Slide 180 carries two 
actuating pins 184 each engaging in an inclined slot 186 in a respective 
one of two emergency control arms 188. 
Arms 188 extend through openings in base 2 (not shown) to engage in slots 
190 in arms 20 and 22. Each control arm 188 is disposed between two guide 
members 192 (shown only for the lower control arm) secured to base 2 in 
order to permit each control arm 188 to move only in a direction 
perpendicular to the direction of movement of control slide 180. 
Movement of control slide 180 is controlled by a cable 194 mounted in a 
sheath 196 that is also secured to base 2 so that cable 194 can be 
employed to displace control slide 180 in either direction parallel to its 
length. 
In the position shown in FIG. 3, control arms 188 engage in slots 190 to 
prevent thermal tripping of the circuit breaker. Downward movement of 
control slide 180 causes control arms 188 to retract from slots 190, thus 
permitting normal operation of the circuit breaker. The operating end of 
cable 194 can remain at the location of the circuit breaker or can be 
extended to the remote location of the operating mechanism shown in FIG. 
2. 
While the description above refers to particular embodiments of the present 
invention, it will be understood that many modifications may be made 
without departing from the spirit thereof. The accompanying claims are 
intended to cover such modifications as would fall within the true scope 
and spirit of the present invention. 
The presently disclosed embodiments are therefore to be considered in all 
respects as illustrative and not restrictive, the scope of the invention 
being indicated by the appended claims, rather than the foregoing 
description, and all changes which come within the meaning and range of 
equivalency of the claims are therefore intended to be embraced therein.