High speed contact driver

A high speed contact driver for use in an electrical circuit interrupter includes a pair of series-connected, elongate and generally opposing electrical conductors bowed in predetermined, generally opposing contours. These conductors are connected to a bridging electrical contact which is normally biased into a bridging position between a pair of stationary contacts. Pulse generating means are provided for applying a current pulse of predetermined magnitude to the electrical conductors. In response to this current pulse, these electrical conductors electromagnetically repulse each other and drive the bridging contact out of bridging position between the stationary contacts.

RELATED APPLICATIONS 
This application is related to commonly assigned application Ser. No. 
684,307, filed Dec. 20, 1984, inventor E. K. Howell, the entirety of which 
is incorporated herein by reference. 
Application Ser. No. 684,307, is now abandoned and application Ser. No. 
814,865, filed Dec. 30, 1985 is a substitute. 
BACKGROUND OF THE INVENTION 
This invention relates in general to electrical circuit interrupters and in 
particular to a high speed contact driver for use in current limiting 
circuit interruption devices. 
In the past, typical alternating current circuit breakers required the 
creation of a large mechanical gap between two electrical conductors, and 
could only interrupt an alternating current at a zero-crossing. More 
recently developed current limiting circuit interrupters, for example of 
the type shown in U.S. Pat. No. 4,375,021 to Pardini et al. (assigned to 
the assignee of the present invention and incorporated herein by 
reference), provide the capability of substantially immediately 
interrupting alternating currents of high magnitude without waiting for a 
current zero-crossing. These current limiting interrupters are typically 
complex in construction, and thus somewhat expensive to fabricate. 
The above referenced application Ser. No. 684,307 (hereinafter referred to 
as "Howell") discloses a high speed contact driver for use in current 
limiting circuit interrupters. The contact driver of Howell, described in 
detail below, uses a pulse of current applied to a pair of closely spaced 
electrical conductors to cause these conductors to electromagnetically 
repulse one another and lift a bridging contact away from a pair of 
stationary contacts. 
While Howell provides fast and reliable separation of electrical contacts, 
the nature of current limiting interrupters is such that faster, more 
reliable interruption is always better. Thus, any improvement over Howell 
which provides for faster, more reliable circuit interruption provides a 
substantial benefit to the art. 
OBJECTS OF THE INVENTION 
Accordingly, a principal object of the present invention is to provide a 
high speed contact driver which is relatively faster and more reliable 
than those shown in the prior art. 
Another object of the present invention is to provide a high speed contact 
driver which is relatively simple in design and inexpensive to 
manufacture. 
A further object of the present invention is to provide a high speed 
contact driver which is particularly adapted for use in a current limiting 
circuit interrupter. 
SUMMARY OF THE INVENTION 
A new and improved high speed contact driver for electrical circuit 
interruption is provided wherein a pair of series-connected, elongate and 
generally opposing electrical conductors are bowed in predetermined, 
generally opposing contours to increase the speed with which the contact 
driver operates. In addition to the pair of bowed electrical conductors, 
the inventive contact driver further includes a wire for conducting a main 
current, means for interrupting the current flow through the wire, and 
circuit means connected to the pair of electrical conductors for applying 
a current pulse of predetermined magnitude thereto. The bowed electrical 
conductors are connected between the circuit means and the current 
interrupting means such that when a current pulse is applied to these 
conductors by the circuit means, these conductors electromagnetically 
repulse one-another and cause the current interrupting means to interrupt 
the flow of main current through the wire. 
In a preferred embodiment of the invention, the means for interrupting the 
current comprises a pair of stationary, spaced apart contacts disposed in 
the wire so as to interrupt the current flowing therethrough, and a 
bridging contact connected to the pair of electrical conductors and shaped 
to bridge said stationary contacts. The pair of electrical conductors 
comprises, alternatively, relatively stiff wire bowed in a predetermined 
contour, or relatively flexible wire bowed by an intermediately disposed 
wedge.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring now to FIG. 1, a high speed contact driver 10 is shown comprising 
a pair of spaced-apart, stationary contacts 12 and 14 connected by a 
bridging contact 16 shown situated in a bridging, or closed position 
therebetween. Stationary contacts 12 and 14 are disposed on the ends of 
spaced, rigid, and generally straight main current carrying wires 17 and 
18, the stationary contacts establishing an interruption 20 therebetween. 
Wires 17 and 18 and stationary contacts 12 and 14 comprise a conductive 
metal, such as copper. Bridging contact 16 is selected to have a 
predetermined mass M.sub.1, and preferably comprises a solid metal such as 
copper. Alternatively, bridging contact 16 need only comprise sufficient 
metal to bridge the gap between stationary contacts 12 and 14. 
Rigid wire 17 is fastened to an insulating frame 22 by a screw 24, the 
insulating frame preferably comprising a plastic. Rigid wire 18 is fixed 
relative to rigid wire 17, for example, by an insulating brace (not shown) 
to insulating frame 22. A block of insulating material 26, having a 
predetermined mass M.sub.2, is attached to one end of a cantilever spring 
28 by means of a screw 30, the opposite end of the cantilever spring in 
turn being attached to frame 22 by a screw 32. Mass M.sub.2 of block 26 is 
selected to be relatively much heavier than mass M.sub.1 of bridging 
contact 16. Bridging contact 16 is connected at one end of each of a pair 
of series-connected, parallel, elongate, and generally opposing electrical 
conductors 34 and 36, each of the electrical conductors being connected at 
an opposite end, via a screw 38, to a block 26. Electrical conductors 34, 
36 comprise flexible material, for example a thin copper wire. The series 
connection between conductors 34 and 36 is shown as established by bending 
a single conductor 34-36 in half at bridging contact 16. Alternatively, 
the series connection can be made between conductors 34 and 36 through the 
metal in bridging contact 16. A magnetic yoke 40, comprising a magnetic 
material such as iron, is supported by frame 34 and surrounds a portion of 
conductors 34 and 36 for establishing a magnetic field thereabout. 
A biasing means, for example a spring 42, is attached between bridging 
contact 16 and a fixed point, preferably frame 22, for biasing bridging 
contact 16 into the illustrated bridging position between stationary 
contacts 12 and 14. Spring 42 is selected to provide sufficient tension to 
hold bridging contact 16 in good electrical contact with stationary 
contacts 12 and 14, while working in opposition to the force exerted by 
cantilever spring 28 on the bridging contact via conductors 34 and 36. A 
current pulse generator 44, shown schematically in FIG. 1 and comprising 
one of many conventional generators known in the art, is connected to 
conductors 34 and 36 via a pair of leads 46 and 48, respectively, at 
screws 38. 
FIGS. 2 and 3 show the operation of contact driver 10 as it would occur 
when implemented in a current limiting circuit interrupter (not shown) of 
the type wherein a main current I.sub.1 is conducted in wires 17 and 18. 
FIG. 2 shows contact driver 10 with no current flowing in electrical 
conductors 34 and 36, and hence with bridging contact 16 biased by spring 
42 into the closed position to create a path for current I.sub.1 as 
indicated by dashed-line 50. For purposes of clarity, portions of contact 
driver 10 are omitted from FIGS. 2 and 3, and the magnetic field generated 
by yoke 40 is shown exerted across a central section of electrical 
conductors 34 and 36 as a dashed-line rectangle 52. 
In FIG. 3, contact driver 10 is shown with a current pulse I.sub.2, for 
example a pulse in the range of from 800-1,000 amperes, flowing through 
conductors 34 and 36 in the indicated direction. Current pulse I.sub.2 is 
selected to be of sufficient magnitude to establish respective, opposing 
electromagnetic forces F.sub.1 and F.sub.1 ' on conductors 34 and 36, 
respectively, these forces operating to move bridging contact 16 to the 
illustrated open position (i.e., spaced apart from stationary contacts 12 
and 14). With bridging contact 16 spaced from stationary contacts 12 and 
14 by an incremental distance d1.sub.1, the separation distance d.sub.2 
between conductors 34 and 36 is substantially larger than the initial 
separation distance d.sub.1 (FIG. 2). The length of distances d1.sub.1 and 
d.sub.2 are determined by the power of repulsive forces F.sub.1 and 
F.sub.1 ', these forces being proportional in magnitude to the product of 
the magnitude of current pulse I.sub.2 and the strength exerted by 
magnetic field 52. The force on bridging contact 16 is represented by the 
force vector F.sub.2 and is exerted in the indicated direction towards 
block 26, an equal magnitude force F.sub.2 ' being exerted in the opposite 
direction on the mass. The dynamics of the operation of contact 
interrupter 10, in part determined by the relative masses of block 26 and 
bridging contact 16 and the strength of spring 42, insures the rapid 
motion of bridging contact 16. In a typical implementation of contact 
driver 10, bridging contact 16 is capable of moving from the closed to the 
open position in the range of from 10-100 microseconds. 
In constructing contact driver 10, the length l.sub.1 of conductors 34 and 
36 and the separation distance d.sub.1 therebetween is selected to ensure 
that when current pulse generator 44 is used to generate a current pulse 
of a predetermined magnitude, sufficient electromagnetic repulsion is 
produced between the two conductors to overcome the bias provided by 
spring 42 and thus to rapidly separate bridging contact 16 from stationary 
contacts 12 and 14. These length, separation distance, and pulse magnitude 
parameters are preferably further selected to insure that this separation 
occurs within a time increment in the range of 10-100 microseconds from 
the initiation of current pulse I.sub.2. 
Referring now to FIGS. 4 and 5, a high speed contact driver 110 is shown 
constructed in accordance with one embodiment of the present invention. 
Features similar to those of contact driver 10 (FIGS. 1-3) are indicated 
by like reference numerals incremented by 100. 
In contact driver 110, conductors 134 and 136 are each connected directly 
to the base end 122a of a generally U-shaped insulating frame 122 (i.e., 
without intervening mass 26 and cantilever spring 28 of FIGS. 1-3), and 
are each bowed in a generally opposing, predetermined contour X,Y when 
bridging contact 116 is in the closed position (FIG. 4). Main current 
conducting wires 117 and 118 are supported by legs 122b and 122c of frame 
122, respectively, via screws 124. The predetermined contour X,Y 
establishes an angle .theta. between each end of conductors 134 and 136 
and that ends' respective connection to frame 122 or bridging contact 116. 
In this embodiment of the invention, predetermined contour X,Y is 
established through the use of relatively stiff wire for conductors 134 
and 136. This wire is selected to be stiff enough to maintain contour X,Y 
when bridging contact 116 is in the closed position, and flexible enough 
to yield to the previously described electromagnetic forces which act on 
conductors 134 and 136 when a current pulse is applied thereto. This wire 
is also preferably selected to be resilient enough such that no spring 
(i.e., spring 42 of FIGS. 1-3) is required to bias bridging contact 116 
into the normally closed position, making a spring optional in this 
embodiment of the invention. Such wire comprises, for example, 
phosphor-bronze spring wire of 0.025 inch thickness bowed by compression 
to a predetermined contour X,Y defining a 6 inch radius. The remaining 
features of contact driver 110 are substantially identical to the 
analogously numbered features of contact driver 10 (FIGS. 1-3). 
In operation, described with respect to FIG. 6, when a current pulse 
I.sub.2 ' is generated by pulse generator 144 through conductors 134 and 
136, the bowed configuration of the conductors causes bridging contact 116 
of contact driver 110 to open substantially faster than contact driver 10 
(FIGS. 1-3). This is theorized as being due to two synergistic causes. 
First, the initial angle .theta. at the ends of conductors 134 and 136 
increases considerably, with respect to the Howell embodiment of FIGS. 1-3 
above, the rate of change of contact displacement d1.sub.1 ' with respect 
to wire displacement d.sub.2 '. This is believed to have a particularly 
large effect in the early stages of the opening of bridging contact 116. 
Second, the pre-bowed contour X,Y of conductors 134 and 136 eliminates the 
time required to establish angle .theta., the angle being required before 
any movement of bridging contact 116 can occur. In addition to the 
substantial advantage of increased opening speed, the predetermined 
contour X,Y in conductors 134 and 136 eliminates the requirement for a 
dynamically moving mass (i.e., block 26 and cantilever spring 28 of FIGS. 
1-3) between the conductors and frame 134. This combined elimination of 
spring 42, cantilever spring 28 and mass 26 (FIGS. 1-3) makes contact 
driver 110 more economical to construct, and more reliable in operation 
than contact driver 10 (FIGS. 1-3). Further, the elimination of this mass 
and spring reduces the affect of gravity on the dynamics of the operation 
of contact driver 110, and thus permits the contact driver to operate 
reliably through a broader range of orientations than contact driver 10. 
Referring now to FIGS. 7 and 8, an alternate embodiment of the invention is 
shown wherein features similar to those of FIGS. 4-6 are indicated by 
like, primed reference numerals. 
Contact driver 110' is substantially identical in construction to contact 
driver 110 of FIGS. 4-6, with the exception of the construction of 
electrical conductors 134' and 136', the inclusion of an insulated wedge 
162' situated therebetween, and the inclusion of a spring 142' disposed 
between bridging contact 116' and frame 122'. In accordance with this 
embodiment of the invention, conductors 134' and 136' each comprise wire 
having a low bending stiffness and which thus can easily conform to the 
shape of wedge 162'. Such a flexible wire comprises, for example, metal 
coated graphite bundles of 26 mil total diameter. Insulated wedge 162', 
has a selected, predetermined contour X',Y', and is disposed within yoke 
140' between conductors 134' and 136' for establishing a substantially 
identical contour X',Y' in the conductors. 
The operation of contact driver 110' is similar to that of contact driver 
110 (FIGS. 4-6), with the exception that the bowed shape of conductors 
134' and 136' is established by wedge 162'. Further, spring 142' is no 
longer optional, some biasing means being required to situate bridging 
contact 116' in the closed position illustrated in FIG. 7. The use of 
flexible wire for electrical conductors 134' and 136', in combination with 
wedge 162' for establishing the predetermined contour X',Y', permits the 
operation of contact driver 110' to be tailored to specific operating 
requirements by simply changing the wedge, and hence the contour. By 
substituting wedges of various contours in contact driver 110', the 
contours of conductors 134' and 142' are changed, thereby altering the 
operating characteristics of the contact driver. 
In this embodiment of the invention, wedge 162' is shown constructed of 
plastic. However, it will be appreciated by those skilled in the art that 
wedge 162' need not comprise plastic, but need only be insulated to 
prevent electrical short-circuiting between conductors 134' and 136'. 
Further, while a magnetic yoke has been illustrated in both embodiments of 
the invention (i.e., 140 and 140' in FIGS. 4-6 and 7-8, respectively), it 
will be appreciated by those skilled in the art that this yoke operates 
only to enhance the repulsive forces F.sub.1 and F.sub.1 ' established 
between the parallel conductors in response to a current pulse, and may be 
optionally eliminated from the contact drivers. 
There are thus provided multiple embodiments of a high speed contact 
driver, each of which is relatively faster, simpler, more reliable, and 
more easily adaptable to different operational requirements than those in 
the prior art. 
While preferred embodiments of the invention have been illustrated and 
described, it will be clear that the invention is not so limited. Numerous 
modifications, changes, variations, substitutions and equivalents will 
occur to those skilled in the art without departing from the spirit and 
scope of the present invention. For example, while exemplary materials 
have been described and illustrated throughout, they are characterized by 
their relevant properties, and materials of similar properties may be 
substituted therefor. Accordingly, it is intended that the invention 
herein be limited only by the scope of the appended claims.