Current limiting circuit breaker mechanism

The invention concerns a very simple and effective current limiting circuit breaker of great versatility which is especially adaptable for motor control centers and combinations starters. That breaker can be used with various interchangeable trip units always with the same basic mechanism. (a) for instantaneous trip type circuit breakers of various current ratings having high interrupting capacity and low I.sup.2 t value to protect control equipment at high fault currents. (b) for high interrupting capacity thermal magnetic circuit breakers at various current ratings. (c) for circuit breakers with solid state tripping units to protect against overloads, short circuits, single phasing, underloads, etc.

BACKGROUND OF THE INVENTION 
The basic invented breaker mechanism is an improvement of a mechanism until 
now used only for residential type circuit breakers. This mechanism could 
not be combined with the requirements for interrrupting high fault 
currents at high voltages (for example, 50 KA at 480 volts). It was 
further not available in combination with various trip units and 
industrial type handles. 
The invention relates: 
(a) The possibility to use this basic mechanism for current limiting action 
so obtaining industrial type high interrupting capacity circuit breakers 
for example 50 KA 480 volts. Such basic mechanism without the 
improvements is, for example, described in the book Elektrische 
Niederspannungs Schaltgerate by Kussy (Technischer Verlag Cram Berlin, 
1969) on page 784. The mechanism has the advantage of great simplicity but 
in order to obtain current limiting action, the contact arms must be 
designed in such a way that the two arms or at least a large section of 
the arms be positioned parallel or nearly parallel in the closed position 
of the breaker with the current flowing in opposite direction in both 
arms, the arms having a close distance. 
(b) A further improvement over the basic mechanism described by Kussy can 
be obtained by making the second contact arm also spring loaded so 
obtaining at higher fault currents an additional contact opening and 
increased opening speed because both contact arms are moving. The second 
contact arm can be under influence of a heavier spring than the first 
contact arm. That allows improved bouncing characteristic at the closing 
of the circuit breaker. 
(c) The basic mechanisms described before was until now designed in such a 
way that the cradle was latched against a bimetal or magnet. The invented 
breaker latches the cradle against a lever which is pushed by a rotating 
teeter bar. This teeter bar is pushed by a magnet or a bimetal or a spring 
loaded lever operated by a magnetic latch (released permanent magnet). The 
rotating teeter bar is under influence of a small spring and may be used 
to push that armature of the magnetic latch toward the yoke of the 
permanent magnet by the unlatched cradle so that the circuit breaker can 
be later reset and latched by hand. This adaptation allows the mechanism 
to be used with interchangeable trip units. 
(d) The contact blows open under heavy fault conditions before the breaker 
trips. Fast rebounding could cause welding and must be prevented. If the 
negative spring action and two moving contact arms do not already prevent 
reclosing it may be desirable to unlatch the cradle with a blown open 
contact arm. A further advantage of the invention is that such a current 
limiting circuit breaker therefore does not need an antirebound latch. 
(e) The trip unit can be built in such a way that we can select trip units 
which trip first the one pole that carries the over current so requiring 
small tripping forces (adjustable magnetic trip unit or thermal trip unit) 
or use those which trip all poles at the same time by a cross-bar (solid 
state trip unit) in the trip unit. 
(f) Another advantage of such a mechanism for industrial type breakers is 
that it can be used with an industrial type handle to secure positive 
action that means opening a welded contact by pushing directly the contact 
arm with the handle into the open position mechanically and not alone by a 
spring so securing that the contact arm moves to the full open position. 
(g) Another advantage of the invention is that each pole is in a separate 
housing securing high strength, the cross-bar between poles not requiring 
an easily damageable cover such arrangement preventing a fault between 
poles due to hot gasses when interrupting high current.

Now referring to the figures: 
In FIG. 1, the metallic shaft 1 connects the three poles, 2 and 3 are 
mounting screws, 4 is a guard for the load side terminals 5 which connect 
to the trip unit here not drawn, 6 the line side, 7 the load side 
terminals of the breaker, 8, 9, and 10 are the three poles, 11 is the trip 
indicator, 12 the trip button, 15 are rivets, 13 plug in jaws, 14 the trip 
bar which after the first pole has tripped trips the other poles. 
In FIG. 2 are 16 the line side terminals which are connected to the load 
side terminals 5 of the breaker mechanism, 17 are the three studs which 
can be plugged into the jaws 13. The positions 1, 2, 3 of adjustment knob 
18 indicate the tripping current range of the trip unit, the dotted lines 
the position of the shunt trip which functions through hole 19 and the 
armature arm of the adjustable magnetic trip unit, 20 is the cover, 21 
various base subassemblies for different current ranges, 22 tubular rivet 
assemblies. 
In FIG. 3 is 23 a molded first lever which rotates with the shaft 1 (FIG. 
1). This lever is a bearing for the first movable contact arm and provides 
the necessary clearing and air space to the shaft. The first movable 
contact arm 24 is divided in two sections 24a from the bearing point to 
the point where the tension spring is hooked into the contact arm and a 
section 24b between said point and the point of contact (FIGS. 4, 5). The 
point of contact 100 is not shown in FIG. 2. The pigtail 65 connecting 24 
to 5 is partly shown. Contact spring 25 is held in cradle 26, cradle 26 
turns around shaft 27. By turning shaft 1 we turn first lever 23 from the 
"ON" position (FIG. 4) to the "OFF" position (FIG. 5.) When the breaker 
trips the contact arm is in the position shown in FIG. 3. By turning from 
ON to OFF, we slide first the contact attached to arm 24 against the other 
contact until spring 25 crosses the center line, quick break is obtained. 
The center line is reached when the contact arm 24 and the hook 101 point 
of spring 25 and hole 28 in cradle 26 is in one line. A second movable 
contact arm 30 is pivoted around a shaft 102 and under influence of spring 
29. A large section of this contact arm is in the closed position of the 
breaker approximately parallel to the section 24b of the first movable 
contact arm 24 with a partly shown pigtail, the second movable contact arm 
is connected to the line side terminal 6. An insulating barrier 32 
separates the two contact arms. Not shown is a fixed L-shaped line side 
contact arm which could be used instead of the second movable contact arm 
for breakers having a somewhat lower interupting capacity. Compression 
spring 29 pushes the contact arm against a cushion 34 made, for example, 
of rubber. In case a fault current is interrupted, the contact arms 24 and 
30 blow apart, the contact arm 4 is blown against an energy absorbing 
cushion 33. Generally, the presence of 33 and the second movable contact 
arm 30 are sufficient to avoid that the contacts reclose together before 
the breaker trips and therefore an antirebound latch is not necessary with 
this mechanism. In case that test results should show that a rebound of 
the contact arm with the consequence of contact welding under extremely 
high fault current occurs, a nose 36 could be attached to contact arm 24. 
This nose pushes trip lever 35 only in case the contacts blow open. The 
contact arm position for that case is shown in FIG. 6. When the trip unit 
functions teeter bar 37 is pushed by the not shown trip unit and turns 
latch lever 38, 38 is after unlatching cradle 26 turned back by spring 39, 
in catch spring cap 39A, teeter bar 37 pushes when operated trip plate 40 
spring 41 resets 40 and 37. When the cradle collapses it pushes trip lever 
35, 35 turns clockwise, it is connected through the trip bar 14 to the 
other poles. 14 is made of laminated material. Now the other trip levers 
35 in the other poles move the latch lever in each pole unlatching the 
cradles in the other poles. This arrangement insures low tripping force 
and that the pole which is subjected to highest current trips first. In 
cases this feature is not desirable, for example, for solid state trip 
units having only one magnetic latch for all poles, the trip unit can be 
built with one tripper bar tripping all poles simultaneously. 
The line side terminals of the trip unit 16 (FIG. 2) are fastened to the 
load terminals of the breaker mechanism 5 and the load side studs 17 of 
the trip unit to the jaws 13. The jaws are connected to the load side 
terminals 7 of the circuit breaker. A spring loaded (42A) lever 42 trips 
the breaker mechanism if the trip unit is removed. The upper right corner 
is a space for an auxiliary switch operated from the auxiliary switch 
lever 43 with guide plate 43A. The button with spring 44 serves to trip 
the breaker manually, 45 is a captive nut to attach the auxiliary switch. 
59 is a cover for each pole. 60, the base (FIG. 1). 61 is the arc chute 
assembly. 62, the arc chute cover. 63, the metal screen. 64, the vented 
barrier. 
FIG. 7 shows an alternate tripping mechanism. A second latch lever 46 is 
fastened to the cradle 26 when the lever 38 is turned by teeter bar 37 the 
cradle unlatches the latch lever 46 turns the teeter bar back by sliding 
over edge 47 which is held in one direction by the teeter bar 47 can turn 
counter clockwise against a not shown torsion spring. The teeter bar has a 
slight overtravel. 
In any case the mechanism is reset by reengaging the cradle. The cradle is 
pushed back by turning the molded lever to the "OFF" or reset position, 
hereby resetting the cradle through reset pin 48 (FIG. 5). 
A nose 49 at cradle pushes the movable contact arm 24 in case the contacts 
are slightly welded when the breaker trips. 
FIG. 8 shows the arc chute assembly 61 in greater detail. A large number of 
deion blades 66 are stacked between 2 cover plates 67 and 68 of insulating 
material, each blade is clamped on one side in the center slot on the 
other side in 2 slots. 
Although there have been described preferred embodiments of this novel 
invention, many variations and modifications will now become apparent to 
those skilled in the art. Therefore, this invention is to be limited not 
by the specific disclosure herein but only by the appending claims.