Note: Descriptions are shown in the official language in which they were submitted.
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CURRENT LIMITING CIRCUIT BREAKER
WITH INSULATING BARRIERS AND BAFFLES
BACKGROUND OF THE INVENTION
The invention relates generally to circuit
interrupters and, more particularly, to circuit inter-
rupters operating under short clrcuit conditions to limit
the flow of current throuyh the interrupter to a value
lower than the available fault current which the circuit
is capable of supplying.
Circuit breakers are widely used in industrial,
residential, and commercial installations to provide
protection against damage due to overcurrent conditions.
As the usage of electrical energy has increased, the
capacity of sources supplying this electrical energy has
increased correspondingly. Therefore, extremely large
currents can flow through distribution circuits should a
~5 short circuit condition occur. Under these conditions
conventional circuit interrupters are incapable of pre-
ventiny severe damage to apparatus connected downstream
from the interrupter.
Current limiting circuit interrupters were
developed to provide the degree of protection necessary on
circuits connected to power sources capable of supplying
very large fault currents. One type of circuit inter-
rupter provides such current limiting action by operating
to achieve extremely rapid separation of -the contacts
during short circuit conditions. This action produces an
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arc voltage across the contacts which quickly approaches
the system voltage, thus limiting the current flow between
the contacts. Although the performance of prior ar-t
current limiting circuit interrupters of this type was
ade~uate in certain applications, it would be desirable to
provide a circuit breaker providing an even higher degree
of current limiting action. Furthermore, it would be
desirable to extend the uses of current limiting circuit
interrupters to higher vol-tage ranges on the order of 1000
volts or more, and into different locations such as in the
mining industry where their use would be beneficial.
SUMMARY OF THE INVENTION
In accordance with this invention, there is
provided a circuit interrupter comprising an insulating
base which has a plurality of insulating walls separating
the base into a plurality of adjacent pole unit compart-
ments. A pair of spaced-apart terminals are disposed on
the base within each pole unit compartment, with a pair of
separable contacts being electrically connected to the
spaced-apart terminals. An insulating cover is secured to
tLe base, which toge-ther with the base forms an insulating
housing in which is disposed an operating mechanism for
effecting movement of the separable contacts between open
and closed positions. Insulating barriers are disposed
between adjacent pole unit terminals to enable the circuit
interrupter to operate at higher voltage levels. The
insulating barriers extend outwardly from the cover a
distance sufficient to prevent the gases at each pole
terminal generated during an opening operation from mixing
with the gases at adjacent pole unit terminals until such
time as these gases aL-e deionized suf~iciently to prevent
conduction between the two terminals.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure l is a side sectional view of a multi-
pole current limiting circuit interrupter constructedaccording to the principles of the present invention, the
contacts being shown in the closed position (open position
in dashed lines);
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Fig. 2 is a top view of one outside pole of the
circuit interrupter shown in Fig. 1;
Fig. 3 is a view similar to Fig. 1 with the
circuit interrupter shown in the tripped condition;
Fig. 4 is a view similar to Figs. 1 and 3, with
the circuit interrupter shown in the current limiting
position;
Fig. 5 is a perspective view illustrating the
circuit interrupter of this invention with the cover in
place on the base;
Fig. 6 is a detailed cross-sectional view look-
ing at the front of the insulating barriers and baffles;
Fig. 7 is a top view of the barriers and baf-
fles;
Fig. 8 is a rear view of the barriers and baf-
fles; and
Fig. 9 is a cross-sectional view taken along
line IX-IX of Fig. 6.
DESCRIPTION OF THE PREFERRED EMBODIMENT
___ _
Referring now to the drawings, Fig. 1 shows a
three pole circuit breaker 3 comprising an insulating
housing 5 and a high-speed circuit breaker mechanism 7
supported in the housing 5. The housing 5 comprises an
insulating base 9 having a generally planar back, and an
insulating front cover ll secured to the base 9 which
together form the housing 5. The housing 5 includes
insulating walls 4 separating the base 9 into three adja-
cent side-by-side pole unit compartments.
The circuit breaker mechanism 7 comprises a
single operating mechanism 13 and a single latch mechanism
15 mounted on the center pole unit. The circuit breaker
mechanism 7 also comprises, in each of the three pole
units, a separate thermal trip device 16 and a high-speed
electromagnetic trip device 17. The high-speed electro-
magnetic trip device is more completely described in U.S.Patents 4,255,732 and 4,220,935.
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A pair of separable contacts l9 and 2i attached
to upper and lower pivoting contact arms 20 and 22, respec-
tively, are provided in each pole unit of the breaker. An
arc extinguishing unit 23 is also provided in each pole
S unit. The upper contact 19 is electrically connected,
throuyh the upper contact arm 20, constructed of conduct-
ing material to a shunt 24 which is in turn connected
through a conducting strip 25 and the thermal and magnetic
trip devices 16 and 17 to a terminal connector 26. The
lower contact 21 is connected through the lower contact
arm 22, also constructed of conducting material, through a
shunt 27 and conducting strip 28 to a similar terminal
connector 29. With the circuit breaker 3 in the closed
position as is shown in Fig. 1, an electrical circuit thus
exists from the terminal 26 through the conducting strip
25, the shunt 24, the upper contact arm 20, the upper
contact 19, the lower contact 21, the lower arm 22, the
shunt 27, and the conducting strip 28 to the terminal
connector 29.
The upper contact arm 20 is pivotally connected
to the point 30 to a rotating carriage 32, which is fixed-
].y secured to an insulating rotatable tie bar 35 by a
staple 34. A tension spring 36 connected between the left
end of the upper contact arm 20 and a bracket 37 attached
to the carriage 32 serves to maintain the upper contact
arm 20 in the position shown in Fig. 1, with respect to
the carriage 32. The upper contact arm 20 and carriage 32
thus rotate as a unit with the crossbar 35 during normal
current conditions through the circuit breaker 3.
The single operating mechanism 13 is positioned
in the center pole unit of the three pole circuit breaker
and is supported on a pair of spaced metallic rigid sup-
porting plates 41 that are fixedly secured to the base 9
in the center pole unit of the breaker. An inverted
U-shaped operating lever 43 is pivotally supported on the
spaced pla-tes 41 with the ends of the legs of the lever 43
positioned in U-shaped notches 56 of the plates 41.
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The U-shaped operating lever 43 includes a
member 44 extending through a hole in a slide plate 46.
The slide plate 46 is slidingly attached to the cover 11
by a support plate 47, and includes a member 48 seated in
a molded handle 149.
The upper contact arm 20 for the center pole
unit is operatively connected by means of a toggle, com-
prised of an upper toggle link 53 and a lower toggle link
55, to a releasable cradle member 57 that is pivotally
supported on the plates 41 by means of a pin 59. The
toggle links 53 and 55 are pivotally connected to each
other by means of a knee pivot pin 61. The lower toggle
link 55 is pivotally connected to the carriage 32 of the
center pole unit by means of a pin 65 and the upper toggle
link 53 is pivotally connected to the releasable cradle
member 57 by means of a pin 63. Overcenter operating
springs 67 are connected under tension between the knee
pivot pin 61 and the bight portion of the operating lever
43. The lower contact arm 22 is pivotally mounted at the
point 18 to the base 9.
A leaf spring 31 urges the lower contact arm 22
in a counterclockwise direction about the pivot point 18,
the counterclockwise travel of the lower contact arm 22
being limited by a pin 40. Since the clockwise force upon
the upper arm 20 in the closed position is greater than
the counterclockwise force on -the lower arm 22, a degree
of overtravel is provided from the first point of contact
between the arms until the fully closed position. This
allows for the effect of contact wear.
The contacts 19 and 21 are manually opened by
movement of the handle 149 in a leftward direction as seen
in Fig. 1 from the O~l position to the OFF position. This
movement causes the slide plate 46 to rotate the operating
lever 43 in a counterclockwise direction. The rotating
movement of the operating lever 43 carries the line of
action of the overcenter operating springs 67 to the left
causing a collapse, to the left, of the toggle linkage 53,
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55. The collapse of the toggle linkage 53, 55 causes the
crossbar 35 to rotate in a counterclockwise direction to
simultaneously move the upper contact arms 20 of the three
pole units to the open position, opening the contacts of
the three pole units. The operating mechanism 13 is then
in the position shown in dashed lines in Fig. 1.
The contacts are manually closed by reverse
movement of the handle 149 from the OFF to the ON posi-
tion, which movement moves the line of action of the
overcenter springs 67 to the right to move the toggle
linkage 53, 55 to the position shown in Fiy. 1. This
movement rotates the crossbar 35 in a clockwise direction
to move the upper contact arms 20 of the three pole units
to the closed position.
The releasable cradle 57 is latched in the
position shown in Fig. 1 by means of the latch mechanism
15. The latch mechanism 15 comprises a primary latch
member 71 and an insulating trip bar 73 pivoted at the
point 70. The primary latch member 71 comprises a gener-
ally U-shaped latch lever 75 and a roller member 77 mov~
ably supported for limited travel in a pair of slots 78 in
opposite legs of the lever 75. A torsion spring 81 biases
the roller member 77 to one end of the slots. The primary
latch member 71 is pivotally supported on the supporting
plates 41 by means of a pin 83. The free end of the
cradle 57 moves within a slot in the bight portion of the
lever 75.
The trip bar 73 is a molded insulating member
pivotally supported in the support plates 41, an~ is
provided with a secondary latch member 89 for engaging the
bight portion of the latch lever 75 of the primary latch
member 71 to latch the primary latch member 71 in the
position seen in Fig. 1. The releasable cradle 57 is
provided with a hook portion 58 serving as a primary
latching surface for engaging the roller 77 to latch the
cradle 57 in the position seen in Eig. l.
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The primary latch member 71 includes a bias
spring 72 secured at the upper end thereof, with the other
end of the bias spring 72 being seated against the trip
bar 73. The bias spring 72, in compression, urges the
primary latch member 71 in a clockwise direction about its
pivot point 83. Thus, as soon as the trip bar 73 is
rotated in the counterclockwise direction raising the
secondary latch 89 away from the top of the latch lever
75, the bias spriny 72 will rotate the primary latch
member 71 in a clockwise direction allowing the cradle 57
to be released from the roller 77. The action of the bias
spring 72 is overcome during a resetting operation as will
be described hereinafter.
Included in each pole unit is a separate high-
speed electromagnetic trip device 17. Each of the electro-
magnetic trip devices 17 comprises a generally U-shaped
pole piece 95, the legs of which extend around the con-
ducting strip 25. An armature structure 97 is pivotally
supported in the housing 5 and includes a laminated mag-
20 netic clapper 101 and an actuating member 103.
A separate thermal trip device 16 is also in-
cluded in each pole unit. The thermal device 16 includes
a bimetal element 105 welded to the conducting strip 25.
The upper end of the bimetal element 105 includes an
25 adjusting screw 107 threaded therein. The magnetic 17 and
thermal 16 trip devices may also be of the electronic type
illustrated in Figure 5, instead of the mechanical types
described herein.
When the circuit breaker is in the latched
position as seen in Fig. 1, the springs 67 operate through
the toggle link 53 and pivot 63 to pivot the cradle 57 in
a clockwise direction about the pivot point 59. Clockwise
movement of the cradle member 57 is restrained by engage-
ment of the latching surface of the hook portion 58 under
the roller 77 of the primary latch member 71, with the
cradle member 57 pulling the primary latch member 71 in a
clockwise direction about the pivot 83. Clockwise move-
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ment of the primary latch member 71 about the pivot 83 isrestrained by engagement of the primary latch member with
the secondary latch part 89 on the trip bar 73. The force
of the primary latch member 71 against the secondary latch
89 of the trip bar 73 operates through the axis of the
pivot 70 of the trip bar 73 so that clockwise movement of
the primary latch member 71 is restrained by the trip bar
73 without tending to move the trip bar 73 about its axis.
Thus, the trip bar 73 is in a neutral or latching position
latching the primary latch member 71 and cradle member 57
in the latched position as seen in Fig. 1.
The circuit breaker is shown in the closed and
reset position in Fig. 1. Upon occurrence of a high
overload current above a predetermined value in any of the
pole units, the clapper 101 is attracted toward the asso-
ciated pole piece 95 whereupon the armature structure 97
pivots in a clockwise direction closing the air gap be-
tween the pole piece 95 and clapper 101 and pivoting the
armature actuating member 103 in a clockwise direction
against the extension 79 of the trip bar 73. This causes
rotation of the trip bar 73 in a counterclockwise direc-
tion moving the secondary latch 89 of the trip bar 73 out
of engac~ement with the latch lever 75. The upward force
of the cradle member 57 upon the roller 77 now rotates the
primary latch 71 in a clockwise direction, releasing the
hook portion 58 of the cradle member 57. The force of the
operating springs 67 upon the knee pin 61 is transmitted
through the upper toggle link 53 to cause the cradle
member 57 to rotate in a clockwise direction about the
point 59. Continued rotation of the cradle member moves
the upper toggle pin 65 to the riyht of the line of action
of the operating springs 67, causing col].apse of -the
toggle linkage 53, 55 which in turn rotates the carriage
32 and the attached crossbar 35 in a counterclockwise
direction and move all three upper contact arms 20 in a
counterclockwise direction to simultaneously open the
contacts of the three pole uits. During this movement,
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the handle 149 is moved to a TRIP position between the OFF
and ON positions to provide a visual indication that the
circuit breaker has been tripped.
Before the circuit breaker can be manually
operated after an automatic tripping operation, as shown
in Fig. 3, the circuit breaker mechanism must be reset and
latched. This resetting operation is effected by movement
of the handle 149 from the intermediate TRIP position to
the left to the full OFF position. During this movement,
the slide plate 46 acts upon the member 44 of the operat-
ing lever 43 to rotate the operating lever 43 in a coun-
terclockwise direction about the pivot point at the notch
56 in the support plates 41. A lower extending member 45
of the operating lever 43 engages a corresponding surface
54 of the cradle member 57 to move the cradle member 57
from the position shown in Fig. 3 in a counterclockwise
direction about the point 59.
During this movement, the hook portion 58 of the
cradle member 57 moves down in the slot in the bight
portion of the latch lever 75 of the primary latch member
71 and the hook portion 58 of the cradle member 57 comes
in contact with the roller 77 to move the roller 77 to the
right in the slot 78 with the hook portion wiping past the
roller 77. Once the hook portion 58 of the cradle member
57 passes the roller 77, the spring 81 snaps the roller 77
back to the posi-tion seen in Fig. 1. As the primary latch
member 71 reaches the position seen in Fig. 1, the member
71 clears the latch part 89 of the trip bar 73, whereupon
the spring 72 biases the latch part 89 into latching
engagement with the primary latch member 71 to latch the
primary latch member 71 in the position seen in Fig. 1.
Thereafter, upon release of the handle 149 by the operator,
the springs 67 again act upon the toggle link 55 to bias
the cradle member 57 in a clockwise direction to move the
hook portion 58 up to engage the roller 77 in a latched
position seen in Fig. 1. The handle 149 can then be
manually moved back and forth between the ON and OFF
positions to close and open the contacts.
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51,137
With the circult breaker in the closed and
latched position as seen in Fig. 1, a low current overload
condition will generate heat in the conductor strip 25 and
cause the upper end of the bimetal member 105 to flex to
the right as seen in Fig. l. The adjusting screw 107
impinges on the armature actuating member 103 of the
armature structure 97. This causes counterclockwise
rotation of the trip bar 73 to initiate a tripping action
and achieve automatic separation of the contacts in all
three pole units as hereinbefore described with regard to
a magnetic trip.
As can be seen in Figs. 1, 2 and 3, the circuit
breaker also includes a slotted magnetic drive device 110.
The magnetic drive device 110 includes a housing 112
having a slot 118 within which are disposed the upper and
lower contact arms 20 and 22. The magnetic drive device
110 is described more completely in U.S. Patent 4,220,934.
A bumper member 120 is provided to limit the
travel of the upper contact arm 20 during current limiting
operations as will be described hereinafter. The bumper
member 120 is composed of shock absorbing material such as
polyurethane or butyl plastic. This type of material has
a very large mechanical hystere~is loop, thus absorbing a
maximum amount of energy and minimizing rebound. A simi-
lar member 121 mounted to the base 9 is provided for thelower arm 22.
Under short circuit conditions, extremely high
levels of overload current fl.ow through the circuit breaker
3. The current flow through the conductor member 28 and
lower contact arm 22 generates a large amount of magnetic
flux in the slotted magnetic drive device 110. This flux
and the current flow through the lower contact arm 22
produces a high electrodynamic force upon the lower contact
arm 22, tending to drive the arm 22 from the closed posi-
tion shown in dashed lines in Fig. 4 toward the bottom ofthe slot 118. ~n addition, the current flow through the
contact arms 20 and 22 in opposite directions generates a
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high electrodynamic repulsion force between the arms 20
and 22. This force builds up extremely rapidly upon
occurrence of a short circuit condition, causing the upper
contact arm 20 to pivot in a counterclockwise direction
about the pin 30, actiny against the tension force of the
spring 36, from the closed position shown in dashed lines
in Fig. 4 to the current limiting position shown in solid
lines. The upper contact arm 20 is thus driven with great
force into the bumper member 120, which is desic3ned so as
to minimize the amount of rebound of the upper contact arm
20. This rebound is undesirable since the established arc
which has been extinguished by the arc ex-tinguishing
device 23 may restrike if the contacts 19 and 21 return to
close proximity. The high-speed magnetic trip device 17
is therefore designed to operate the latch mechanism 15 to
release the operating mechanism 13 before the arms 20 and
22 can reclose. As the operating mechanism 13 moves from
the closed position shown in Fiy. 4 to the tripped position
shown in Fig. 3, the carriage 32 rotates in a counterclock-
wise direction to raise the pivot point 30 of the uppercontact arm 20 before the tension spring 36 returns the
upper contact arm 20 to the first position with respect to
the carriage 32 as shown in Fig. 1.
The initial high opening acceleration of the
contact arms produces a high arc voltage resulting in
extremely effective current limiting action. The combina-
tion of the high speed electromagnetic trip device and
high speed operating mechanism assures that the contacts
will remain separated to prevent re-establishment of the
arc after it is extinguished.
The current limiting circuit interrupter 3 thus
far described has been a highly reliable and extremely
efficient interrupting device at its existing voltage
classifications. However, in extending the voltage inter-
rupting capability of this breaker to higher levels, sayon the order of 1000 volts or higher to, say, 1500 volts,
problems have arisen due to arcing between the line ter-
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minals 29 and between the line terminals 29 and the en-
closure 5. To prevent this from occurring, and to enable
the circuit interrupter to function properly at 1000 volts
or higher (at 25 ka or higher), the breaker 3 was modified
by redesigning the primary channels which direct the gases
generated by the arc interruption. The modifications made
were the inclusion of an increased length insulating
barrier and the provision of insulating baffles.
Referring now more particularly to Figs. 5-9,
therein is illustrated in greater detail the barriers 49
and baffles 51 utilized to increase the voltage rating of
the current limiting circuit interrupter. As illustrated,
the insulating barriers 49 are made of a molded insulating
material separate from the insulating cover 11, but attach-
ed thereto through the screws 10. ~lternatively, althoughnot illustrated, the barriers 49 and baffles 51 can be
molded integrally with the insulating cover 5.
As can be seen more particularly in Figs. 5 and
1, -the insulating barriers 49 extend heightwise in the
direction from the cover 11 to the base 9, and are dis-
posed between adjacent pole unit terminals 29 at the line
end of the circuit interrupter 3. This is the end of the
circuit interrupter closest to the separable contacts l9,
21. The insulating barriers 49 are extended in the length-
wise direction (vertically as illustrated in Fig. 5) adistance sufficient to prevent the gases, which are present
at each pole unit terminal 49 and which are generated
during an opening operation of the separable contacts 19,
21, from mixing with the gases which are present at adja-
cent pole unit terminals 29 until such time as said gasesare deionized sufficiently to prevent conduction. For a
circuit interrupter 3 in the voltage range of 1000 volts
or higher, this length should be at least 1.5 inches, and
preferably may extend a distance of approximately 1.7
inches beyond the terminal 29 in the lengthwise direction.
As can be readily appreciated from Fig. 8, the
insulating barriers 49 have a plurality of grooves 50
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disposed therein in the heightwise direction, that is, in
the direction from the base 9 towards the cover 11. The
presence of these grooves 50, which are disposed on both
sides of the insulating barriers 49, funnels the gases
away from the insulatiny housing 5. The barriers 49, as
illustrated, extend lengthwise outwardly farther than the
base 9 itself, aiding in the dispersion of the arcing
gases.
As can be seen from Figs. 5-9, between the
insulatiny barriers 49 are disposed molded insulating
baffles 51 which also func-tion to direct the arcing gases
away from the housing 5 and the adjacent terminals 29 to
thereby further increase the interrupting capability of
the circuit interrupter 3. In particular, these baffles
51 direct the arcing gases away from the insulating hous-
ing 5 to prevent arcing to ground. The baffles 51, as
shown, extend in a direction perpendicular to the insulat-
ing base walls 4, or in other words, extend in the width-
wise direction across each pole unit in the vicinity of
the terminals. The baffles 51, with their angular align-
ment 52 more particularly noticeable in Fig. 9, function
to direct the arcing gases outwardly away from the housing
5 and upwardly as shown in the drawings away from the
insulating housing 5.
With the inclusion of the insulating barriers
and the insulating baffles, herein is provided a current
limiting circui-t interrupter which is capable of function-
ing satisfactorily at extended voltage ranges of 1000
volts or higher at 25 ka or higher.
