Note: Descriptions are shown in the official language in which they were submitted.
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HIGH SPEE~ CONTACT DRIVER
FOR CIRCUIT INTERRUPTION DEVICE
Backqround of the Invention
The advent of a practical solid state
current limiting interrupter such as described in
Canadian Application Serial No. 478,410, filed
April 4, 1985 in the name of E.K. Howell has provided
a synergistic relationship between the circuit
interrupter contacts and the contact operating
mechanism. By employing a solid state switch in
parallel with the contacts, the current is diverted
away Erom the contacts immediately upon contact
separation to substantially reduce the arcing energy
and hence essentially eliminate the deleterious arcing
effect on the contacts. This in turn allows the
contacts to be made much smaller and hence reduces
both their thermal and inertial mass. ~'he reduction
in the inertial mass in turn allows the contacts to be
more rapidly separated and hence allows circuit
interruption during the early stages of the current
waveform. The lower contact inertial mass allows the
use of a bridging contact between a pair of fixed
contacts such as described in U.S. Patent No.
4,598,1~7, issued July 1, 19~6, entitled "Current
Limiting Circuit Breaker" in the name of E.K. Howell.
The bridging contact arrangement provides for a
further reduction in the mass of the contacts such
that even more rapid contact separation can be
attained and allows the current interruption to occur
at the correspondingly earlier stages of the current
waveform.
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The aforementioned Canadian Application
Serial No. 478,410 and U.S. Patent No.
should be reviewed for a good description of the operation
of a solid state switch for circuit interruption as well
as for describing the configuration of a bridging electrode
arranyement.
The instant invention is directed toward a high
speed contact driver for rapidly separating bridging
contacts from a pair of fixed contacts such as described
in the aforementioned U.S. Patent No~ .
U.S. Patent No. 3,215,796, issued November 2,
1965 in the name of Bruno Leisi, discloses the idea of
utilizing line current to induce current in a current loop
including closely spaced parallel conduetors to drive the
conductors apart and to separate movable contacts from
associated Eixed contacts.
U.S. Patent No. 3,168,626, issued February 2,
1965 in the name of Richard Patrick, discloses a fuse
utilizing the repulsive forees developed by fault eurrents
flowing in opposite directions through closely spaced,
parallel fuse links to sever one or both links and thus
interrupt the faulted circuit.
U.S. Patent No. 3,002,065, issued September 26,
1961 in the name of John LaTour, Jr., discloses the
use of excessive line eurrents flowing in opposite
direetion through conductive columns to repulse one of
the columns and thus provide a shunt path to protect a
meter.
The purpose of the instant invention is to
provide a high speed contact driver arrangement wherein
a high current pulse is employed to electrodynamically
repulse a pair of conductors serving as a contact carrier
for a bridging contact arranged across a pair of contacts
within a protected circuit for extremely fast circuit
interruption upon eommand.
Summary of *he Invention
The invention eomprises a high speed eontaet
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driver wherein a bridging contact is resiliently
supported by means of a cantilever spring and is carried
by a pair of closely spaced electrical conductors. The
bridging contact is biased into electrical contact
relation with a pair of stationary contacts by means of
a contact spring. A pulse of current applied to the
conductors results in the electrodynamic repulsion of
the conductors and the lifting of the bridging contact
away from the stationary contacts against the bias of
the contact spring.
Brief De'scrip'tio'n'of the Drawings
Fig. 1 is a plan view in partial section
of the high speed contact driver according to the
invention;
Figs. 2A and 2B represent plan views in
partial section of the contact driver of Fig. 1 before
and after excitation;
Fig. 3 is a graphic representation of the
bridging contact separation force relative to the separa-
tion distance between the bridging contact and the
stationary contacts; and
Fig. 4 is a plan view in partial section of
an alternative embodiment of the high speed contact
driver shown in Fig. 1.
Description'of the Preferred Embodiment
An illustrative embodiment of the high speed
contact driver 10 of the invention is shown in Fig. 1
wherein a pair of rigid conductors 11 r 12 each carrying
a fixed contact 13, 14 are connected by means of a
bridging contact 15. The bridging contact is carriedby a pair of conductors 20, 21 which are attached to the
bridging contact at one end so that the bridging contact
electrically connects the two conductors in series.
The opposite ends of the two conductors are respectively
connected to a pair of terminal connectors 22, 23 by
means of ter~inal screws 24, 25. Electrical connection
is made to the two conductors by attaching a current
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source to the terminal screws. A block of insulating
material 16 of a predetermined mass Ml is attached to
one end oE a cantilever spring 18 by means of a screw
19 and the spring is attached to a support 17 at the
opposite end by means of a separate screw. The mass M2
of the bridging contact 15, is selected to be very small
with respect to the mass Ml of the insulating material.
A contact spring 26 is attaehed to the bridging contact
at one end and the other end is fixedly attached to a
support 27. The tension supplied by contact spring 26
is adjusted to hold the bridging contact into good
electrical connection with the fixed contac-ts in opposition
to the force exerted by the cantilever spring 18 on the
bridging contact via the conductors 20, 21. When the
lS contact driver is used within a circuit interrupter, the
circuit current I2 transfers between the rigid conductors
11, 12 in the indicated direction, through the fixed
contacts 13, 14 and the bridging contact 15 in the
manner described in the aforementioned U.S.
~;; 20 Patent No. ~ of Howell. The length Il of
the conductors 20, 21 and the separation distance dl is
adjusted to ensure that a predetermined controlled
current pulse Il in the indicated directions, will
produce sufficient electrodynamic repulsion between the
two conductors to overcome the bias provided by the
contact spring 26 and to rapidly separate the bridging
contact from the fixed contacts within a time increment
of 10-100 microseconds from the initiation of the current
pulse I1.
The current loop provided between the terminal
screw 24, conductor 21, bridging contact 15, conductor
20 and terminal screw 25 is depicted at Fig. 2(a) with
no current flowing through the loop and with a permanent
magnetic field exerted across a central section of the
conductors as outlined by the dotted rectangle 30. The
substantial increase in the electrodynamic repulsion
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forces exerted upon the conductors by the addition of
the magnetic field will be descri.bed below with
reference to Fig. 3.
The effect of the electrodynamic forces
represented as Fl and Fl' in the indicated directions,
is shown in Fig. 2(b) for comparison to Fig. 2(a). It
is noted that the separation distance d2 between the two
conductors upon electrodynamic repulsion, is
substantially larger than -the inltial separation distance
dl and that the bridging contact 15 has separated from
the fixed contact 13 by an increment dl . The large
separation distance d2 is the effect of the repulsion
force Fl, which is proportional to the product of current
Il, times the magnetic field strength exerted by magnetic
field 30. The corce on the bridging contact is represented
by the force vector F2 which is exerted in the indicated
direction, wlth an equal magnitude force F2' exer-ted in
the opposite direction on block 16. Since the mass
M2 of contact 15 is much smaller than the mass Ml of
block 16, equal forces F2 and F2' will produce a much
larger acceleration of contact 15 than of block 16. Thus
in the 100 microsecond time frame, block 16 remains
essentially stationary.
The variation i.n the force F2 on the bridging
contact as a function of the separation distance between
the bridging and the fixed contacts in the absence of
permanent magnetic field 30, is shown at 28 in Fig. 3.
It is noted that the force F2 on -the bridging contact
is very high initially, in the order of one hundred
pounds, to provide a high acceleration when the current
pulse Il is first applied and decreases rapidly as the
bridging contact 15 becomes separated from the fixed
contacts 13, 14 and the separation distance increases
from zero to a few thousandths of an inch. The effect of
the permanent magnetic field 30 is shown at 29 to increase
the corce exerted on the bridging contact at larger
contact separation distances.
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A further embodiment of the high speed contact
driver 10 of Fig. 1 is shown in Fig. 4 and similar
reference nu~bers will be employed where possible. The
current loop is provided between conductor 20, bridging
contact 15 and conductor 21. A platform 35 of insulating
material, supported by a pair of support posts 17, 31 also
of insulating material, has an openiny 36 for the passage
of the two conductors and serves to support a helix
spring 33 which biases the bridging contact against the
bias of contact spring 26 in a manner similar to the
cantilever spring 18 described earlier with reference
to the arrangement depicted in Fig. 1. The platform
and the rigid conductors 11, 12 are attached to the
support posts 17, 31 by means of screws 19, as indicated.
The conductors 20, 21 are arranged as a single turn
secondary winding around a toroidal core 32, with the
multi-turn primary winding 34 connected to external
circuitry by means of terminal connectors 22, 23 and
terminal screws 24, 25. The toroidal core is secured
to insulative block 16 and adds to the mass of block
16 for the advantageous relation between this mass and
the mass which comprises the bridging contact as described
earlier. A current pulse applied to terminal connectors
22, 23 is amplified by transformer action through the
core and is induced within the conductors 20, 21 to
provide the predetermined current Il which flows in the
indicated directions to separate the conductors.
It has thus been shown that extremely fast
contact separation can be achieved against a large
contact holding force, such as exerted by the contact
spring 26 on a small contact mass such as Ml relative to
a lesser contact separating force, such as provided by
the cantilever spring 18 on a large mass such as M2. When
electrodynamic forces are provided to increase the
contact separation force, the large mass remains
virtually stationary resulting in a large acceleration
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during the initial contact separation which is highly
desired for limiting the amount o~ switching current.
It is understood that higher curren-t pulses such as
represented by Il can be employed along with stronger
magnetic fields to further increase the separation forces
and to provide even faster contact separation.
