Note: Descriptions are shown in the official language in which they were submitted.
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MECHANICAL INTERLOCK WITH OVERTRAVEL COMPENSATION
FOR COORDINATING OPERATION OF CIRCUIT BREAKERS
BACKGROUND OF THE INVENTION
Field of the Invention
This invention relates to mechanisms for coordinating the operation of
circuit breakers so that only one of the circuit breakers can be closed at any
given time.
In particular, it relates to an interlock for circuit breakers each having a
state indicator
indicating the open/closed state of the main contacts of the breaker, and an
auxiliary trip
member which allows the circuit breaker to be tripped and held open. More
particularly,
it relates to such an interlock which incorporates a compliant member which
allows
overtravel of the components coupled to the state indicators without binding
of the
auxiliary trip members.
Background Information
There are a number of applications where the operation of a pair of
electrical switches be coordinated such that only one of the switches can be
in the on
position at a time. One such application is the transfer switch which is used
to provide
power to a load from two alternative sources. For instance, in many cases, an
auxiliary
power source is provided as an alternative to a utility source. As these two
sources are
independent, it is imperative that the one source be disconnected from the
load before the
other source is connected to prevent interconnection of two sources with a
random phase
relationship. Typically, circuit breakers are used as the switches in transfer
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switches so that overload protection is also provided. However, electrical
switches
without overcurrent protection are also used in transfer switches.
Another situation in which the operation of electrical switches must be
coordinated is in ac motor control circuits such as reversing controls where
one switch is
used to connect the motor to a source with one phase rotation for forward
operation and
another switch connects the motor with the opposite phase rotation for reverse
operation.
As in the case of the transfer switches, the switches for the motor control
may or may not
have overcurrent protection.
It is known to coordinate the operation of two such electrical switches by
the use of mechanical interlocks. One type of interlock couples the handles of
the two
switches. Another type of interlock used particularly when the switches are
circuit
breakers, utilizes a plunger mounted in the switch housing of each switch
which when
actuated engages the switch operating mechanism to prevent the switch from
closing. In
one such interlock, the plungers are coupled to opposite ends of a walking
beam so that
when one switch is closed it pushes down on its plunger thereby pivoting the
walking
beam and raising the other plunger to block closing of the other switch. The
circuit
breaker which is held open lacks sufficient force to override the interlock
and force the
closed switch open. A related type of interlock described in US Patent No.
5,436,415,
utilizes a pair of pivoted cam plates each coupled to the plunger of one of
the circuit
breakers and joined by a connecting rod for opposed action. With one of the
switches
closed, the cam plate associated with the other switch is rotated to an
overtoggle position
so that a force generated on the plunger of that open switch is directed
through the pivot
axis of the associated cam plate and therefore applies no force through the
connector
which would attempt to override the plunger on the closed switch.
Still another type of interlock for a pair of electrical switches is described
in US Patent No. 4,286,242. In this interlock, a plunger actuated by the
closing of the
contact arm on one switch rotates a connecting rod which acts through another
plunger to
hold the latch lever of the trip mechanism in the other circuit breaker in the
unlatched or
tripped position so that the second circuit breaker cannot be closed. A
similar
arrangement engaging the contact arm of the second breaker rotates a second
connecting
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rod which in turn holds the latch on the first circuit, breaker in the
unlatched or tripped
position when the second breaker is closed.
In a variation of the latter type of interlock, a pivoted arm which follows
the rotational position of the pole shaft on one power circuit breaker acts
through a
connecting rod to rotate another pivoted arm on the other end of the rod to
actuate a trip
lever on a second power circuit breaker. A similar mechanism holds the first
power
circuit breaker in the tripped condition when the second is in the closed
condition. The
connections between the rods and the pivot arms engaging the trip levers on
the
respective breakers allow these pivot arms to be rotated during alternative
actuations of
the trip lever without moving the associated rod. To this end, the rods extend
through a
swivel which slides relative to the rod during reverse rotation of the pivot
arm. This
mechanism, however, does not allow for overtravel of components.
While all of these interlock mechanisms prevent simultaneous closing of
the two switches, the latter two types especially do not accommodate well to
variations in
tolerances or wear or for overtravel of components..
There is a need therefore for an improved interlock for coordinating the
operation of a pair of electrical switches.
There is a particular need for such an improved interlock which can
accommodate for variations in tolerances and wear.
There is an additional need for such an improved interlock which will
accommodate overtravel of some of the components to assure reliable operation.
SUMMARY OF THE INVENTION
These needs and others are satisfied by the invention which is directed to
an interlock for coordinating the operation of electric power switches, and
particularly to
such electric power switches which have a state indicator indicating the open
and closed
state of the switch, and an auxiliary trip member which can be moved from an
unactuated
to an actuated position to hold the associated switch in the open condition.
The novel
interlock includes indicator followers each following an associated state
indicator on an
associated electric power switch, and auxiliary trip member actuators each
positioned
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interlock further includes elongated connecting members, first couplers each
coupling one
end of an associated elongated connecting member to an associated indicator
follower on
a respective one of the electric power switches, and second couplers each
coupling the
other end of the associated elongated connecting member to an associated
auxiliary trip
member actuator on the respective other electric power switch to actuate the
auxiliary trip
member on the other electric power switch to the actuated position when the
state
indicator on the respective one electric power switch moves to the closed
position. Each
of the first couplers comprises a compliant member allowing initial movement
of the
associated state indicator on the one electric power switch before movement of
the
associated elongated connecting member and allowing overtravel of the state
indicator
when the associated auxiliary trip member actuator reaches its limit of
travel. In the
preferred form of the invention, the compliant member is a helical compression
spring.
Preferably, each of the indicator followers includes a follower member
biased by a biasing spring against the associated state indicator and the
first coupler
comprises a slip coupling mounted on the follower member with one end of the
elongated
connecting member slideably extending through this slip coupling. In this
arrangement
the helical compression spring is captured between the slip coupling and the
associated
end of the elongated connecting member. In the most preferred arrangement, the
state
indicator pivots on the associated electric power switch and the follower
member is also
pivoted. In this arrangement the slip coupling comprises a swivel mounted on
the
follower member with the elongated connecting member sliding through the
swivel. An
adjustment mechanism permits adjustment of both the length of the connecting
member
and the preload on the helical compression spring.
Preferably, the second couplers comprise one way connectors which
transmit motion of the elongated connecting member to the associated auxiliary
trip
member actuator but do not transmit movement of the auxiliary trip movement
actuator to
the elongated connecting member so that where the auxiliary trip member on the
switch
can be actuated by an alternate arrangement, this action is not transmitted
back through
the interlock.
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BRIEF DESCRIPTION OF THE DRAWINGS
A full understanding of the invention can be gained from the following
description of the preferred embodiments when read in conjunction with the
accompanying
drawings in which:
Figure 1 is an isometric view of two circuit breakers equipped with the
interlock of the invention.
Figure 2 is a fragmentary exploded isometric view of a portion of one of the
circuit breakers of Figure 1 with the cover removed.
Figure 3 is a front isometric view of one end of the interlock of the
invention.
Figure 4 is a front elevation view of the end of the interlock of Figure 3
showing coupling of the interlock with a circuit breaker and also showing in
phantom the
relationship between the one end of the interlock and its interface with a
cutout in a cassette
in which the associated circuit breaker is mounted.
Figure 5 is a fragmentary isometric view in enlarged scale of the upper end
of the interlock as shown in Figure 1.
Figure 6 is a fragmentary isometric view in enlarged scale of the lower end
of the interlock as shown in Figure 1; and
Figure 7 is a rear elevation view of the interlock of Figure 3.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The invention will be described as applied to a pair of power circuit
breakers, however, it has application to the coordination of the operation of
other types of
power switches with or without overcurrent protection.
Throughout this description, like parts are identified by like reference
characters. Many of the components are common to the two circuit breakers or
to the
ends of the interlock coupled to the respective circuit breakers. Where it
helps to identify
the circuit breaker with which a component is associated, the reference
character is
followed by the suffix "a" or "b". The identical elongated connecting members
and
couplings which interconnect opposing components on the two ends of the
interlock and
therefore, interconnect the two circuit breakers are distinguished by the
suffixes "1" and
"2".
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Referring to Figure 1, a pair of power circuit breakers la and lb are
mounted in vertical alignment in cassettes 3a,3b of a switchgear assembly 5.
These
circuit breakers la and 1b, which can be of the type described in US Patent
No.
5,929,405, have an operating mechanism which includes a pole shaft (see Figure
2). The
pole shaft 7 rotates during opening and closing of the circuit breaker so that
a drive arm 9
mounted on the end of the pole shaft outside the casing 11 of the respective
circuit
breaker serves as a state indicator to indicate the open and/or closed state
of the circuit
breaker. Each of the circuit breakers la and lb also has an auxiliary trip
member 13
extending outward from the casing 11 above the drive arm 9. This auxiliary
trip member
can be rotated between an unactuated position and an actuated position in
which it holds
the circuit breaker in the tripped or open condition.
In order to coordinate the operation of the two circuit breakers la, 1 b, so
that only one may be in the closed condition at any one time, an interlock 15
couples the
state indicator on each circuit breaker with the auxiliary trip member on the
other circuit
breaker. The interlock 15 includes a pair of brackets, 17a and 17b, secured to
the outer
surface of the side wall 19 of the cassettes 3a, 3b, associated with each of
the circuit
breakers by standoffs 21. Pivotally mounted on each bracket 17a, l7b is an
indicator
follower 23a, 23b. As best seen in Figures 3, 4 and 7, each indicator follower
25
comprises a follower member 25 which includes a follower shaft 27 rotatably
mounted in
the bracket by a bearing 29.
The follower shaft 27 extends through the cassette wall 19 and supports a
follower finger 31 adjacent the associated state indicator. A follower arm 33
is secured to
the outer end of the respective follower shaft 27. A biasing spring in the
form of helical
tension spring 37 biases the follower member 25 in the counterclockwise
direction as
viewed in Figure 3 (clockwise in Figure 7).
Returning to Figure 1, the interlock 1 `_i also includes a pair of auxiliary
trip
member actuators 39a, 39b. Again, as shown in Figures 3, 4 and 7, these
auxiliary trip
member actuators 39 each comprise an actuator member which includes a first
actuator
member 41 pivotally mounted on the outside of the associated bracket 17 on
pivot shaft
42 and a second actuator member 43 pivotally mounted on the opposite side of
the
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member 41 on shaft 42 has a drive pin 47 which engages the second actuator
member 43
so that rotation of the first actuator member in one direction results in
rotation of the
second actuator member in the opposite direction. The second actuator member
43 has a
lateral projection or paddle 49 which extends through an opening 51 (see
Figure 4) in the
cassette sidewall 19 and is positioned adjacent the auxiliary trip member 13
on the
associated circuit breaker la or lb. The auxiliary trip member actuator 39
includes a
second biasing spring in the form of helical tension spring 53 connected to
the first
actuator member 41 which biases the projection 49 on the second actuator
member 43
clockwise as viewed in Figures 3 and 4 against the upper edge of the opening
51 and
away from the auxiliary trip member 13.
As seen in Figures 1, 5 and 6, the interlock 15 also includes a pair of
elongated connecting members 55. A pair of first couplers 571, 572 connect one
end 591
592 of each of the elongated connecting members to an associated indicator
follower 23b,
23a on a respective one of the circuit breakers lb, la. These first couplers
57 include a
slip connection 611, 612 formed by a swivel 63a, 63b pivotally mounted on an
end of the
associated follower arm 33a, 33b and having a through aperture 65a, 65b
through which
the one end 591, 592 of the elongated connecting member slides. These first
couplers
further include a compliant member in the form of a helical compression spring
671, 672.
The helical compression spring 671, 672 is captured between the associated
swivel 631, 632 and a stop formed by an adjusting nut 691, 692 threaded onto
the end 591,
592 of the elongated connecting member 551, 552. This nut 691, 692 forms part
of an
adjustment mechanism 711, 712 included in each of the first couplers 57a, 57b.
Threading
of the nut 691, 692 along the one end 591, 592 of the elongated connecting
member 551,
552 adjusts the preload on the helical compression spring 671, 672. The
adjusting
mechanism 71 also includes another threaded member 731, 732 engaging threads
on the
elongated connecting member and bearing against the opposite side of the
swivel 631, 632
from the helical compression spring 671, 672. Adjustment of this threaded
member 731,
732 along the elongated connecting member 551, 552 adjusts the effective
length of the
elongated connecting member 55. A lock nut 751,7'2 can be provided to fix the
position
of the threaded member 731, 732.
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The interlock 15 also includes a pair of second couplers 771, 772 which
connect the other ends 791, 792 of the elongated connecting members 551, 552
to the
associated auxiliary trip member actuator 39a, 39b. Each second coupler 771,
772
comprises a one way connector 811, 812 which transmits motion from the
associated
elongated connecting member 551, 552 to the auxiliary trip member actuator
39a, 39b, but
does not transmit movement of the auxiliary trip member actuator 39a, 39b back
to the
elongated connecting member 551, 552. Each one way connector 811, 812 includes
additional swivels 831, 832 pivotally mounted to the associated first actuator
member 41 a,
41b and having through holes 851, 852, though which the opposite ends 791, 792
of the
elongated connecting members extend. Stops in the form of nuts 871, 872 are
provided on
the ends 791, 792 of the elongated connecting members. These stops are larger
than the
holes 851, 852.
In the exemplary embodiment of the invention, the elongated connecting
members 551, 552 are tension members. While cables could be used for these
tension
members, the exemplary tension members are threaded rods. Where the two
circuit
breakers are mounted side-by-side rather than being vertically aligned, cables
would be
used for the tension members.
With both circuit breakers 1 a, 1 b in the open position, the respective drive
arms 9, are in the vertical position shown in Figure 4. The biasing springs 37
bias the
associated follower fingers 31 against the associated drive pin 9. Under these
conditions,
the biasing springs 53 bias the projections 49 of the auxiliary trip member
actuators 39
away from the associated auxiliary trip member 13. When one of the circuit
breakers is
closed, the associated pole shaft rotates to rotate the drive arm in a
counterclockwise
rotation as viewed in Figure 2. Assuming for purposes of illustration, that
the circuit
breaker la is closed, the drive arm 9a engages the follower finger 31a
rotating it
clockwise as viewed in Figure 3. This results in rotation of the arm 33a of
the associated
follower member 25a in the counterclockwise direction, as viewed in Figure 5.
Thus, the
swivel 632 lifts up on the helical compression spring 672 compressing it
during initial
rotation of the follower member. The force generated is then applied through
the spring
672 to the connecting rod 552 to raise the rod upward. Upward movement of the
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of the auxiliary trip member actuator 39b. This rotation is reversed by the
reversing cam
45 so that the second actuator member 47 is rotated counterclockwise as viewed
in Figure
3. With this motion, the projection 49 on the second actuator member 43
engages the
auxiliary trip member 13 on the circuit breaker lb to rotate it
counterclockwise as viewed
in Figure 2 and thereby hold the circuit breaker lb in the tripped condition
so that it
cannot be closed. As discussed, the projection 49 extends through the opening
51 in the
sidewall 19 of the cassette 3b in which the circuit breaker lb is mounted.
When the
projection 49b comes to rest against the edge of this opening 51, the follower
member 25a
permits overtravel of the drive arm 9 on the circuit breaker 1 a through
compression of the
spring 672.
In a similar manner, when the circuit breaker lb is closed, the follower
member 25b is rotated counterclockwise as viewed in Figures 1 and 6. This
results in
initial compression of the spring 671, followed by lowering of the connecting
rod 551 to
rotate the auxiliary trip member actuator 39a counterclockwise (see Figure 5).
As this
occurs, the paddle 49 engages and rotates the auxiliary trip member 13
counterclockwise
as viewed in Figure 2 to hold the circuit breaker la in. the tripped
condition.
Although not shown, each of the circuit breakers 1 a, lb is tripped by a
device as the circuit breaker is withdrawn from the cassette. The mechanism
(not shown)
which provides this function also rotates the auxiliary trip member actuators
39a, 39b.
The one way connectors 811, 812 formed by the swivels 831, 832 allow this
motion to
occur without applying force to the connecting rods 591, 592.
In an alternate configuration, the elongated connecting members 551, 552
can be compression members (not shown) rather than tension members. In such an
arrangement, additional swivels, 631, 632', are provided on the opposite end
of the
pivoted follower arms 33a, 33b so that when the associated circuit breaker
closes, the
follower arm 33a, 33b pushes on the associated elongated connecting member.
The rods
then push against additional swivels 831', 832' provided on the opposite ends
of the first
actuator members 41 a, 41b to actuate the associated auxiliary trip member 13.
The interlock 15 does not draw significant energy from the closing circuit
breaker. In addition, incorporation of the compliant member in the form of the
helical
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cables. This eliminates faulty operation and or jamming of the interlock. The
interlock
of the invention also provides for overtravel of the drive arm on the circuit
breakers to
compensate for tolerance errors, variation in customer mounting locations,
wear and
slight misalignment. It also decouples alternate actuation of the auxiliary
trip member on
one circuit breaker from the other circuit breaker.
While specific embodiments of the invention have been described in
detail, it will be appreciated by those skilled in the art that various
modifications and
alternatives to those details could be developed in light of the overall
teachings of the
disclosure. Accordingly, the particular arrangements disclosed are meant to be
illustrative only and not limiting as to the scope of the invention which is
to be given the
full breadth of the claims appended and any and all equivalents thereof.
