Contact assembly for low-voltage circuit breakers with a two-arm contact lever

A contact assembly is provided for current-limiting low-voltage circuit breakers. The contact assembly has a two-armed contact lever swivel-mounted on a central bearing pin whose lever arms are equipped at their ends with contact pieces. The contact lever is equipped with a slot for mounting on the bearing pin whose longitudinal axis extends approximately at a right angle to the longitudinal axis of contact lever. The contact lever has a stop extending at approximately a right angle to its longitudinal axis for a catch swivel-mounted on the bearing pin. The contact forces on both lever arms cannot be influenced by the swivel mount or by the drive mechanism of the contact lever, but are determined exclusively by the biasing springs.

BACKGROUND OF THE INVENTION 
This invention pertains to a contact assembly for low-voltage circuit 
breakers, specifically current-limiting circuit breakers with a two-arm 
contact lever which rotates around a central rotary axis, with the lever 
equipped at its ends on opposite sides of a longitudinal axis crossing the 
rotary axis with one contact piece on each side and having a biasing 
spring assigned to each lever arm. 
A contact assembly of the above specified said type is disclosed in German 
Offenlegungsschrift No. 2,157,927. This contact assembly, in principle, 
has the advantage that no flat flexible conductor is necessary in the 
current path of the switch, since the two-arm contact lever bridges two 
fixed-mounted counter-connection pieces. Thus, when switching, two 
disconnect points connected in series are created. In conjunction with the 
relatively low energy requirement of a rotating lever device, one has the 
prerequisites for a high breaking capacity. 
Even with these advantages, however, there are mechanical problems. In 
particular, it is difficult to assure the constancy of contact forces at 
the two disconnect points which is absolutely required for proper 
long-term operation. Moreover, fairly difficult problems are raised by the 
placement of the biasing springs and the transmission of the driving force 
into the contact lever. Accordingly, it will be appreciated that it would 
be highly desirable to provide a contact assembly which assures constancy 
of contact forces. 
It is an object of the present invention to provide a contact assembly for 
a circuit breaker. 
Another object of the invention is to provide a contact assembly which 
assures constancy of contact forces. 
SUMMARY OF THE INVENTION 
Briefly stated, in accordance with one aspect of the invention, a contact 
assembly is provided for a circuit breaker of the type which has a 
two-armed contact lever swivel-mounted on a central bearing and equipped 
with a contact piece at each end on opposite facing sides of a 
longitudinal axis which crosses the rotating axis of a swivel mount. Each 
lever arm is assigned a biasing spring. The bearing has a bearing pin and 
a slot enclosing the bearing pin whose longitudinal axis extends 
approximately at a right angle to the longitudinal axis of the contact 
lever. The contact lever has at least one stop extending approximately at 
a right angle to its longitudinal axis and is mateable with a catch 
swivelling on the rotary axis and moving the contact lever in the 
switch-off direction.

DESCRIPTION OF A PREFERRED EMBODIMENT 
Referring to FIG. 1, a contact assembly is shown mounted in a compartment 
of housing 1. This housing consists of an insulating material and can be 
designed with one or more sections. Housing 1 is shown in FIG. 1 in its 
general outline with the additional components required for a low-voltage 
circuit breaker, such as drive, latch mechanism, connecting assemblies and 
other well-known items which are not shown. The figure simply shows the 
main current path of one pole of a circuit breaker which extends from a 
first terminal or connecting bar 2 over a schematically shown release 
switch unit 3 to a first fixed-mounted contact piece 4. From the contact 
piece 4 current flows over a swivel-mounted contact lever 5 to another 
fixed-mounted contact piece 6 and a terminal or connecting bar 7. The 
contact lever 5 is fitted at its opposite ends with contact pieces 10, 11 
which work in conjunction with the fixed-mounted contact pieces 4, 6. 
Contact pieces 10 and 11 of the contact lever 5 are mounted on opposite 
sides of the longitudinal axis 12 of the contact lever. By rotating 
contact lever 5 counterclockwise, contact pieces 10 and 11 can be 
simultaneously separated from the fixed-mounted contact pieces 4 and 6. 
For mounting contact lever 5, there is a fixed-mounted bearing pin 13 which 
is either insulated or made of insulating material in the housing 1, in 
conjunction with a central slot 14 of contact lever 5. While the dimension 
of slot 14 in the direction of the longitudinal axis 12 is in accordance 
with the diameter of bearing pin 13 with a standard tolerance, contact 
lever 5 can shift transversely to its longitudinal axis 12 along bearing 
pin 13, since the longitudinal axis 15 of slot 14 also runs at right 
angles to the longitudinal axis 12 of the contact lever. The contact 
forces arising between contact piece 4 and 10 or 6 and 11 are then 
independent of the mounting of contact lever 5 and reflect only the effect 
of biasing springs 47 and 48, whose assembly will be explained below based 
on FIG. 2. 
FIG. 1 also shows that the contact lever 5 has two stops 16 and 17 facing 
the bearing shaft. These are designed for joint action along catches 20 
and 21 which are integral to a switching shaft 22 made of insulating 
material, which is rotary-mounted on bearing pin 13. The stops 16 and 17 
are positioned along the longitudinal axis 15 of slot 14. A shift of 
bearing pin 13 brought about by realignment of contact lever 5 thus has no 
effect on the interaction between stops 16 and 17 and catches 20 and 21. 
In the switch-on position shown the catches 20 and 21 are raised from 
stops 16 and 17 so that, aside from any bearing friction between bearing 
pin 13 and slot 14, only the biasing springs have any effect. 
Between catch 20 and arm 8, as well as between catch 21 and arm 9, there is 
adequate space to create play so that contact lever 5 can rotate with 
switching shaft 22 in an unchanged position under the impact of current 
forces. For that purpose the central section of contact lever 5, which is 
overlapped by catches 20 and 21, is also fitted with similarly 
circular-shaped sections 34 and 35. As is well known, the design can 
ensure, by a locking assembly (not shown), that contact lever 5 is held 
fast in its eletrodynamically opened position until release of the latch. 
Housing 1 is subdivided in the area of the contact assembly shown by 
partitions so that a first arcing compartment 23 and a second arcing 
compartment 24 as well as a middle pocket 25 are formed. The usual 
extinguishing plate assemblies 25 and 26 are located in the arcing 
compartments. The middle pocket 25 is designed to accommodate the 
switching shaft 22 and the biasing springs, as will be explained further 
below. The partitions of pocket 25 limit slots 27 and 28 designed to 
permit passage of arms 8 and 9 of contact lever 5. Circular-shaped 
components 30 and 31 of the unit are positioned near the center of contact 
lever 5 at a slight distance facing edges 32 and 33, which limit slots 27 
and 28. The points are located on the side of contact lever 5 with arms 8 
or 9 which are on the side of contact pieces 10 and 11. Thus at each angle 
setting of contact lever 5 a good sealing of the switching arc formation 
area relative to pocket 25 is attained. Thereby no switching gases can 
penetrate into pocket 25. 
Referring to FIG. 2, the housing 1 is equipped with adjoining areas to 
install three parallel current paths in accordance with FIG. 1. Bearing 
pin 13 extends over all current paths as does switching shaft 22 which is 
swivel-mounted on bearing pin 13. In the area of partitions 40 and 41 
between the adjoining current paths 42, 43 and 44 the switching shaft is 
designed so that it encloses the partitions forming a labyrinth gap. One 
does not, however, have to tightly dimension this gap since the load on 
pockets 25 by arcing gases is relatively low, as has already been noted. 
In this connection, FIG. 2 shows that slots 27 and 28 between the 
partioning of pockets 25 are sized so that the contact lever can rotate 
without impediment. The slots are wide enought so that arms 45 and 46 of 
biasing springs 47 and 48 which are designed as torsion springs also find 
space beside arms 8 and 9 of contact lever 5. Arms 45 and 46 can, however, 
be shortened, in contrast to the example shown, to the extent that they 
contact arms 8 and 9 still within pocket 25 in order to facilitate 
adjusting the slot width to the thickness of arms 8 and 9. This is shown 
in the section indicating the middle current path 43 where the narrower 
slots are designated 57 and 58. 
Torsion springs 47 and 48 always have another arm 50 or 51 supported by 
switching shaft 22. By the symmetrical arrangement of two biasing springs 
for each contact lever, the design avoids any one-sided load and the 
balance of the contact forces is assured. 
FIG. 2 schematically shows that switching shaft 22 is connected at one end 
to a drive device which has a latch 52 and a manual actuation link 53 
(FIG. 1). In addition, latch 52 is connected to release switches which in 
this embodiment are shown as an overload switch 54, a short-circuit 
release switch 55 and an undervoltage release switch 56. 
The above-described low-voltage circuit breaker operates with high current 
limitation. This characteristic is based upon the looping current leads to 
the fixed-mounted contact pieces 4 and 6. This arrangement means that arms 
8 and 9 and contact lever 5 face the bus bars supporting contact pieces 4 
and 5 at a small distance only so that high currents exert a torque on 
contact lever 5 moving it in the opening direction. Under the impact of 
this torque, contact lever 5 is moved to the position shown in broken 
lines in FIG. 1. This design thereby limits the short-circuit current. 
Immediately following the dynamic contact opening, the latch 52 is 
released (FIG. 2) since the short-circuit current also activates release 
switch 55. 
It should be noted that the described low-voltage circuit breaker also has 
a current-limiting characteristic if the power feed is not designed in the 
loop pattern shown since even between the contact pieces themselves 
current-dependent contact separating forces arise which have a greater 
impact due to the dual-contact assembly than they would in single-contact 
assemblies. An example in this regard is shown in a simplified fashion in 
FIG. 3. The connecting bars shortened in contrast to FIG. 1 are herein 
designated as 60 and 61. By the design of the power feed to the 
fixed-mounted contact pieces 4 and 6 the desired amount of current 
limitation can thus be influenced. 
It will now be understood that there has been disclosed an improved contact 
assembly which improves the mounting, drive and contactor force generation 
of a rotary contact system. The contact lever mount incorporates a bearing 
pin and a slot enclosing the bearing pin, whose longitudinal axis is 
positioned at approximately a right angle to the longitudinal axis of the 
contact lever. The the contact lever incorporates at least one stop 
aligned at approximately a right angle to its longitudinal axis to 
accommodate a catch which is movable around the rotary axis and actuates 
the contact lever for switch-off. The slot permits an alignment of the 
contact lever so that the same forces always act upon the contact pieces, 
regardless of the unavoidable and possibly varying material burn-off 
during operation. This positioning cannot be impeded by a drive assembly 
of the contact lever, since the position of the stop on the contact lever 
also permits its alignment to the catch. 
In principle it does not matter whether the bearing pin is 
fixedly-connected to the switch lever or fixedly-mounted separately from 
the latter, since in both cases the contact lever can be properly aligned. 
For multi-pole switchgear in which the contact levers are installed in 
parallel-mounted switching compartments, it is, however, advantageous to 
design the unit with a common fixed-mounted bearing pin and to install the 
slot at the contact levers. 
The contact lever can be equipped with two stops aligned symmetrically to 
its center, and there can also be two catches. The assembly thereby 
attains symmetrical points of application of force. 
Effective power limitation can be attained by having the catch or catches 
installed relative to the contact lever with adequate play so that the 
contact lever can move to its opening position given unchanged setting of 
the catch or catches. The opening position can correspond to the normal 
switch-off setting or even a larger opening angle if a high current 
limitation is desired. In this context it is advantageous if the rotation 
of the contact lever can take place only against the action of the biasing 
spring, independently of the drive parts. 
The catches can be integral to a switching shaft which rotates around the 
bearing pin. Onto said switching shaft a drive force can be introduced 
from a compartment or section positioned next to the switching compartment 
and well separated from it. In addition, the switching shaft is best 
suited to provide the common drive of the contactor levers of a multi-pole 
switch. The contact springs can be preferably designed as torsion springs 
enclosing the bearing pin, whose one arm is supported by a facing surface 
of the switching shaft and whose other arm is supported by the contact 
lever. The contact springs in this assembly are relatively far away from 
the contact points, thereby reducing the danger that the characteristics 
of the contact springs would be adversely affected by the switching arcs. 
It is preferable to install the biasing springs designed as torsion springs 
on both sides of the contact lever in such a fashion that each is slid 
into a pocket of a housing supporting the contact assembly, with the wall 
sections of the pocket defining certain slots for passage of the arms of 
the contact lever. The wall sections thereby form an additional protection 
of the contact springs against any impairment by switching arcs. 
The best protection of the contact springs from this perspective can be 
attained by having the torsion springs mesh at one end with sections of 
the contact lever positioned inside the pockets. 
It is of further advantage if the contact lever is designed in the shape of 
an arc circle in its center on the side facing the contact pieces. Thus 
the space between the contact lever and the wall sections at this point 
remains the same, regardless of the angle setting during switching, so 
that the arcing gases arising during switching face a high resistance to 
flow. This not only provides additional protection to the biasing springs, 
but also reduces any load on the bearing gap of the switching shaft due to 
the arcing gases and the gas passage to the adjoining phase. At the 
bearings of the switching shaft between adjoining current paths of a 
switch, one can thus permit a relatively coarse tolerance which simplifies 
the fabrication of a single-unit switching shaft for multi-pole switches. 
As will be evident from the foregoing description, certain aspects of the 
invention are not limited to the particular details of the examples 
illustrated, and it is therefore contemplated that other modifications or 
applications will occur to those skilled in the art. It is accordingly 
intended that the claims shall cover all such modifications and 
applications as do not depart from the true spirit and script of the 
invention.