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Claims  |
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I claim:
1. A transfer switch assembly having:
(a) a body and a rotor means mounted for rotation about a rotor axis
relative to the body,
(b) first and second coupling means for operatively connecting first and
second switch toggles of first and second circuit breakers to move the
switch toggles to actuate the circuit breakers, the coupling means being
mounted for movement relative to the body,
(c) first and second link means connecting the rotor means to the first and
second coupling means respectively, the link means having outer ends
connected to the coupling means and inner ends hingedly connected to the
rotor means at positions spaced circumferentially apart relative to the
rotor axis,
so that the rotation of the rotor means in one direction moves the coupling
means to open one circuit breaker, and after a period of time, to close
the remaining circuit breaker, so that one circuit breaker opens prior to
closing the other circuit breaker to ensure that an electrical load is
momentarily isolated from first and second power sources associated with
the first and second circuit breakers respectively.
2. An assembly as claimed in claim 1 in which:
(a) the first and second coupling means are hingedly connected to the body
for rotation relative to the body about first and second hinge axes
respectively, which axes are disposed generally parallel to the rotor
axis,
(b) the inner ends of the link means are hingedly connected to the rotor
means at fixed positions, and the outer ends of the link means are
hingedly connected to the respective coupling means.
3. An assembly as claimed in claim 1 in which:
(a) an extension of the rotor axis passes between the first and second
coupling means.
4. An assembly as claimed in claim 2 in which:
(a) an extension of the rotor means passes between the first and second
coupling means.
5. An assembly as claimed in claim 1 in which:
(a) the inner ends of the link means are spaced circumferentially apart on
the rotor means at a sector angle of about 90 degrees relative to the
rotor axis.
6. An assembly as claimed in claim 1 further including:
(a) adjustment means for adjusting length of at least one of the first and
second link means.
7. An assembly as claimed in claim 2 in which:
(a) each coupling means has an arm and a toggle connector, the arm having
an inner portion hingedly connected to the body to permit rotation
relative to the body about a respective hinge axis, and an outer portion
carrying the toggle connector, the toggle connector having oppositely
disposed connector faces spaced apart to receive a respective switch
toggle therebetween.
8. An assembly as claimed in claim 7 in which:
(a) the toggle connector includes a toggle recess defined in part by the
two connector faces, the toggle recess facing toward the hinge axis so
that the connector faces operatively embrace the switch toggle,
(b) the outer ends of the link means are hingedly connected to the
respective arms of the coupling means at positions intermediate of the
toggle connector and the hinge axis.
9. An assembly as claimed in claim 2 in which:
(a) each coupling means has a pair of spaced parallel arms and a toggle
connector, the arms having inner portions hingedly connected to the body
to permit rotation relative to the body about the respective hinge axis,
and outer portions carrying the toggle connector extending therebetween so
as to define a U-shaped yoke, the toggle connector having oppositely
disposed connector faces spaced apart to receive a respective switch
toggle therebetween.
10. An assembly as claimed in claim 9 in which:
(a) the toggle connector includes a toggle recess defined in part by the
connector faces, the toggle recess facing towards the hinge axis so that
connector faces operatively embrace the switch toggle,
(b) the outer ends of the link means are hingedly connected to the
respective arms of the coupling means at positions intermediate of the
toggle connector and the hinge axis.
11. An assembly as claimed in claim 1 further including:
(a) a powered shaft which is powered for rotation relative to the body
about the rotor axis, the rotor means cooperating with the shaft,
(b) a manual lever operatively connected to the rotor means and having an
engagement means for releasably connecting and disconnecting the rotor
means and the powered shaft, so as to permit manual or powered rotation of
the rotor means as required.
12. An assembly as claimed in claim 1 in which:
(a) the rotor means is mounted on a powered shaft journalled for rotation
relative to the body.
and the assembly further includes:
(b) a motor connected to the shaft of the rotor means to rotate the rotor
means,
(c) limiting means for limiting rotation of the rotor to that necessary to
open one circuit breaker and to close the other circuit breaker, the
limiting means being responsive to movement of the coupling means.
13. An assembly as claimed in claim 12 further including:
(a) a manual lever cooperating with the rotor means and having an
engagement means for releasably connecting and disconnecting the rotor
means and the powered shaft so as to permit powered or manual rotation of
the rotor means as required.
14. An assembly as claimed in claim 13 in which:
(a) the engagement means is mounted for rotational movement with the rotor
means, the engagement means having an inner end adapted to engage the
powered shaft, and an outer end to serve as the manual lever for gripping
by an operator to move the engagement means relative to the shaft so as to
engage or disengage the powered shaft as required.
15. An assembly as claimed in claim 1 in which:
(a) in a first operating position, the link means extending to the coupling
means cooperating with a circuit breaker that is presently closed is
disposed generally tangentially relative to a circle concentric with the
rotor axis,
(b) in the said first operating position, the remaining link means
extending to the coupling means cooperating with the circuit breaker that
is presently open is disposed generally radially relative to the rotor
axis.
16. An assembly as claimed in claim 1 further including:
(a) the first and second circuit breakers being disposed as mirror images
of each other about an extension of the rotor axis,
so that open and closed positions of the circuit breakers are disposed
symmetrically of the extension of the rotor axis.
17. An assembly as claimed in claim 16 in which:
(a) the closed position of each circuit breaker is closest to the extension
of the rotor axis, and the open position of each circuit breaker is
furthest from the extension of the rotor axis.
18. An assembly as claimed in claim 17 in which:
(a) in a first operating position, the link means extending to the coupling
means cooperating with the circuit breaker that is presently closed is
disposed generally tangentially relative to a circle concentric with the
rotor axis,
(b) in the said first operating position, the remaining link means
extending to the coupling means cooperating with the circuit breaker that
is presently open is disposed generally radially relative to the rotor
axis. |
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Claims |
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Description |
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BACKGROUND OF THE INVENTION
The invention relates to a transfer switch which transfers electrical loads
from one power source to another power source. This is usually performed
automatically by transferring power from a normal electrical power source
to an emergency electrical power source upon reduction or loss of voltage.
The invention also re-transfers the load to the normal power source when
the normal voltage has been restored within acceptable limits.
Automatic transfer switches have been used for many years in applications
where it is required to have an emergency power source that can be
automatically and quickly connected to a load should the normal power
supply to the load fail. Automatic transfer switches of this type are
generally characterized by complexity in view of the need to ensure that
the load is momentarily disconnected from both power sources. This
momentary interruption of power usually causes nothing more serious than a
flickering of lights, and is usually of no great consequence. The
automatic transfer switches of the type according to the invention
necessarily provide a clear "break-before-make" sequencing of switch
contacts, so that the load is momentarily isolated and the two power
sources are never connected together, which is an undesirable condition.
Several types of automatic transfer switches and/or associated circuitry
are disclosed in U.S. Pat. Nos. 4,157,461 to Wiktor; 4,189,649 issued to
Przywozny et al.; 4,398,097 issued to Schell et al. and 4,423,336 issued
to Iverson et al. Many types of automatic transfer switches are available
to actuate switch toggles of conventional molded-case circuit breakers,
but sometimes the circuit breakers are not easily adaptable to be actuated
by particular automatic transfer switches. Some of the automatic transfer
switches have complex cam mechanisms to provide fine adjustment for
opening the circuit breaker, and subsequent closing of the remaining
circuit breaker, so as to ensure the clear "break-before-make" sequence of
operation. The means to provide this adjustment results in complexity, and
requires some skill in setting up the transfer switch to ensure reliable
operation. The necessary adjustment to provide the correct sequence is
time consuming and is subject to human error.
In some automatic transfer switches, a motor is required to rotate the cam
mechanism which actuates the switch toggles. The motor rotates the cam
through a precise angle during the operation of the transfer switch, and
with some designs the cam is required to stop in a critical position after
complete actuation of the transfer switch. This often requires a brake on
the motor or an escapement means which allows for disconnection of the
motor from the cam mechanism so that "over-travel" of the motor is
isolated from the cam rotation. The brakes and/or escapement means of the
prior art transfer switches increase complexity and require additional
time for maintenance and checking, which must be performed periodically.
Furthermore, when servicing such transfer switches provided with
motor-driven cams, it is convenient to provide a manual operation mode
wherein the motor drive and the cam means can be disconnected to permit
manual rotation of the cam. Also, for servicing, it is necessary to
sometimes isolate the load from both power sources, and both of the
requirements above tend to increase complexity of prior art automatic
transfer switches.
Also, some prior art transfer switches have a relatively short period or
"operating differential" betwee breaking contact with one power source,
and making contact with the remaining power source. Some prior art
transfer switches are not easily adjustable to increase the period during
which the load is isolated and this can present difficulties with the type
of electrical load which re-generates electricity immediately subsequent
to disconnection from the source. Electrical motors, when disconnected
from a first power source, immediately re-generate electricity, and when
the new or second power source is to be connected, an out-of-phase
connection to the second power source may cause damage to equipment.
Usually, the said re-generation is of a very short duration, and problems
associated with out-of-phase re-closing can be reduced if the load can be
de-energized for a substantial period of time, for example greater than
0.5 seconds. Transfer switches which would otherwise operate with
relatively short periods where the load is isolated or de-energized
consequently require either a pause in midtravel, or means to detect phase
of the two sources prior to connection, so that the load is transferred
only while the two sources are in phase. Both of these solutions to
out-of-phase reclosing problems increase complexity and reduce reliability
of the transfer switch due to introduction of additional control devices.
SUMMARY OF THE INVENTION
The invention reduces the difficulties and disadvantages of the prior art
by providing an automatic transfer switch assembly which is mechanically
relatively simple, and can be produced and maintained at relatively low
cost when compared with other automatic transfer switches. While the
device is simple, it is easily adjustable to accommodate the majority of
common circuit breakers. Furthermore, the design is easily adjustable to
provide a substantial period during which the load is de-energized, which
facilitates connection to types of loads that re-generate electricity
immediately subsequent to disconnection from a power source. Furthermore,
the invention has an actuating mechanism which can easily tolerate
over-travel of the electric motor resulting from inertia of the motor.
Thus, there is no requirement for a brake on the motor and/or for
escapement means which would allow for disconnection of the motor from the
actuating mechanism, so as to isolate the mechanism from the overtravel of
the motor. Most applications require automatic operation, but manual
operation can be easily substituted.
A transfer switch assembly according to the invention has a body, a rotor
means, first and second coupling means, and first and second link means.
The rotor means is mounted for rotation about a rotor axis relative to the
body. The first and second coupling means operatively connect first and
second switch toggles of first and second circuit breakers to actuate the
circuit breakers, the coupling means being mounted for mvoement relative
to the body. The first and second circuit breakers are associated with the
first and second power sources, for example a normal power source and an
emergency power source respectively. The first and second link means
connect the rotor means to the first and second coupling means
respectively. The link means have outer ends connected to the coupling
means, and inner ends hingedly connected to the rotor means at positions
spaced circumferentially apart relative to the rotor axis. In this way,
rotation of the rotor means in one direction moves the coupling means to
open one circuit breaker, and after a period of time, to close the
remaining circuit breaker. Thus, one circuit breaker opens prior to
closing the other circuit breaker to ensure that an electrical load is
momentarily isolated from both power sources.
In one embodiment, the first and second coupling means are hinged for
rotation about first and second hinge axes respectively, which axes are
disposed generally parallel to the rotor axis. The inner ends of the link
means are hinged to the rotor means at fixed positions, and the outer ends
of the link means are hinged to the respective coupling means. Preferably,
an extension of the rotor axis passes between the first and second
coupling means, and the inner ends of the link means are spaced
circumferentially apart on the rotor means at a sector angle of about 90
degrees relative to the rotor axis. Adjustment means for adjusting the
lengths of the link means is also provided.
A detailed disclosure following, related to drawings, describes a preferred
embodiment of the invention which is capable of expression in structure
other than that particularly described and illustrated.
DESCRIPTION OF THE DRAWINGS
FIG. 1 is a simplified perspective view of the apparatus shown cooperating
with a pair of circuit breakers, some details of the apparatus being
obscured by a control compartment box which encloses portions of the
invention,
FIG. 2 is a simplified front elevation of the invention, a door of the
control compartment being removed to show internal detail,
FIG. 3 is a simplified side elevation of a portion of the invention as seen
generally from line 3--3 of FIG. 2,
FIG. 4 is a fragmented, simplified section at enlarged scale showing
cooperation of the invention with a switch toggle,
FIG. 5 is a simplified diagram, similar to FIG. 3, showing an actuating
mechanism according to the invention in two positions,
FIG. 6 is a simplified graphical representation of switch toggle travel
with respect to rotor rotation, to illustrate operating differential of
switch contacts.
DETAILED DISCLOSURE
FIG. 1
An automatic transfer switch assembly 10 according to the invention has a
body 13 and is shown cooperating with first and second circuit breakers 11
and 12 which are connected to a normal electrical supply and an emergency
electrical supply respectively. The circuit breakers 11 and 12 have
respective switch toggles 15 and 16 which are shown engaged by first and
second yokes 19 and 20 of the invention. Three electrical terminals
severally 22, are shown disposed between the circuit breakers 11 and 12
and are connected by wires, not shown, to a load as well as to appropriate
portions of the circuit breakers, as is well known. The circuit breakers
are conventional moulded case types and are disposed so that the switch
toggle of a particular breaker is inclined towards the terminals 22 when
that particular circuit breaker is closed, and consequently the switch
toggle is inclined away from the terminals 22 when that particular circuit
breaker is opened. Consequently the circuit breakers are "reversed"
relative to each other.
The first and second yokes 19 and 20 are mounted for rotation relative to
the assembly about first and second hinge axes 25 and 26 respectively, so
as to engage and swing the respective switch toggles between respective
open and closed positions as will be described. The first yoke 19 has a
pair of spaced parallel yoke arms 35 and 36 and a toggle connector 37
extending therebetween and cooperating directly with the switch toggle 15.
It can be seen that the yoke arms straddle the circuit breaker 11 and have
inner portions hinged for rotation about the first hinge axis 25. The arms
have outer portions carrying the toggle connector which extends
therebetween to define the U-shaped yoke. The second yoke 20 is generally
similar and is mounted for similar hinging movement relative to the second
circuit breaker 12 to actuate the switch toggle 16.
The assembly 10 includes a control compartment 29 which is disposed to one
side of, and extends between, the circuit breakers 11 and 12. The
compartment 29 encloses an actuating mechanism of the invention, not shown
in FIG. 1, which swings the yokes about the respective hinge axes in a
generally parallel manner so that one circuit breaker is opened and the
remaining circuit breaker is closed in sequence. This is to provide a
momentary delay during which the load is isolated or disconnected from
both of the electrical power sources. The compartment 29 has a hinged door
30, and an inner wall 31 which has first and second clearance openings 33
and 34 which provide clearance for connections between the first and
second yokes 19 and 20 and the actuating mechanism within the compartment
29 as will be described.
FIG. 2-5
Referring to FIG. 2, the actuating mechanism 41 within the compartment 29
includes an electrical motor 43 having a right-angled output gear box 44
which has an output shaft 46. A rotor means 49 is an arm mounted radially
on the output shaft 46 for rotation about a rotor axis 50. It can be seen
that the first and second circuit breakers 11 and 12 are disposed as
"mirror images" of each other about an extension of the rotor axis 46 so
that open and closed positions of the circuit breakers are disposed
symmetrically of the extension of the rotor axis. Similarly, the extension
of the rotor axis passes symmetrically between the first and second
coupling means, and thus serves as a general horizontal axis of symmetry
of the assembly.
A control means 52 supplies power to the electrical motor 43 from a power
source that is about to be connected, and is controlled by known means,
including electrical switches, not shown, which are activated when either
the normal power source generates a voltage less than a minimum threshold,
so as to cause transfer to the emergency power source, or alternatively
the electrical switches are activated to cause re-transfer to the normal
power source, when the normal power source has recovered. A controlling
device having voltage detecting and switching capabilities to actuate the
electric motor 43 from either power source is well known in the trade, and
forms no portion of the present invention. The control means 52 provides a
limiting means for limiting rotation of the rotor to that necessary to
open one circuit breaker and to close the other circuit breaker, the
limiting means being responsive to movement of the yokes. Prior art
limiting means can be used, for example simple limit switches which are
actuated by means responsive to movement of the yokes, or equivalent
means. As will be described, over-travel of the motor can be accommodated
by the invention, which contrasts with some prior art devices.
The invention includes first and second link means 55 and 56 which extend
between the rotor means 49 and first and second yokes 19 and 20
respectively. The link means are essentially similar and thus the first
link means only will be described in detail. The first link means has an
outer end 58 connected to the first yoke means 19 by a bolt/swivel
connector 60. The outer end 58 of the link means is hinged to the arm 36
of the yoke 19 at a position intermediate of inner and outer portions of
the arm, that is intermediate of the toggle connector 37 and the hinge
axis 25. Clearly, a wide degree of adjustment is possible to select an
appropriate yoke movement in response to rotation of the rotor means as
will be described. The first link means has an inner end 62 which is
similarly connected by a bolt/swivel connector 64 to the rotor means 49.
The swivel connectors are partially spherical hinge connectors which are
preferably threaded onto respective ends of the link means, and provided
with undesignated lock nuts to permit adjustment of length of the link
means. Thus, the link means is hingedly connected at opposite ends thereof
to the rotor means and to the yoke.
The second link means 56 has an inner end 66 similarly hingedly connected
to the rotor means, and an outer end 67 similarly hingedly connected to
the yoke 20. It can be seen that the threaded connection between the
swivel connectors and the link means provides adjustment means for
adjusting the lengths of the link means. As best seen in FIGS. 3 and 5,
the inner ends 62 and 66 of the first and second link means are spaced
circumferentially apart on the rotor means at a sector angle 68 of about
90 degrees relative to the rotor axis 50. This provides a particular
sequencing of actuation of the circuit breakers as will be described.
As seen only in FIG. 4, the first toggle connector 37 of the yoke 19
includes a toggle recess 70 defined in part by connector faces 72 and 73
respectively which are spaced apart sufficiently to accept the switch
toggle 15 therebetween. There is a variation in maximum dimensions of
switch toggles of the major manufacturers, and the recess 70 is
sufficiently large to accommodate the largest switch toggle of the most
common manufacturers. The recess 70 is adapted to face inwardly towards
the hinge axis 25, (not shown in FIG. 4) so that as the yoke member 19
swings about the hinge axis, the toggle is actuated between closed and
open positions and vice versa. Because axes of rotation of the switch
toggle and the toggle connector 37 may not be coincident sufficient
clearance is required between the recess and the switch toggle to prevent
interference or binding therebetween. Clearly, for the smaller toggles
additional clearance or lost motion will inevitably exist between the
toggle and the toggle recess than for the larger toggles. This additional
clearance is of no significance in the present invention which can
accommodate several types of moulded case circuit breakers, which
contrasts with some prior art transfer switches.
From the above it can be seen that the yoke is a coupling means adapted for
cooperation with the switch toggle of a circuit breaker to actuate the
circuit breaker associated with a particular power source. Also, it can be
seen that the coupling means are hinged for rotation about respective
hinge axes which are disposed generally parallel to the rotor axis.
Referring to FIG. 3, a manual lever 80 is provided within the control
compartment 29 and is releasably connectable to the rotor means 49 so as
to permit manual rotation of the rotor means as required, without use of
the electrical motor 43. The manual lever 80 is a straight rod which is
mounted for radial movement relative to the rotor axis and is carried
within an opening of a rotor guide 79 which extends from an outer portion
of the rotor means and guides the lever for a longitudinal movement
relative to the rotor means. The lever 80 has an inner end 85 adapted to
engage an undesignated radially disposed opening in a shaft sleeve 84
secured to the shaft 46 so as to lock the rotor means 49 to the shaft 46.
A compression coil spring 82 encloses a portion of the lever 80 and is
interposed between a spring stop 83 carried on the lever and the guide 79.
The spring 82 forces the end 85 of the lever into the undesignated opening
in the shaft sleeve so as to engage the rotor means with the motor. This
engagement represents a normal mode of operation and permits the rotor
means to be rotated by actuating the motor 43.
The lever has an outer end 88 adapted for gripping by an operator to move
the lever radially outwardly against the spring force so as to withdraw
the end 85 out of engagement with the shaft sleeve. When the end 85 is
disengaged from the shaft sleeve, the lever 80 and the rotor means 49 can
be rotated on the motor shaft without corresponding rotation of the motor
shaft. Thus the rotor means can be easily disengaged from the motor. It
can be seen that the manual lever 80 is adapted to releasably connect and
disconnect the rotor means and the powered shaft so as to permit powered
or manual rotation of the rotor means as required. It can be seen that the
end 85 of the lever serves as an engagement means mounted for movement
with the manual lever, and is adapted to engage the powered shaft. The
engagement means is adapted for movement by an operator to move the
engagement means to engage or disengage the powered shaft as required. The
manual lever 80 is particularly required for servicing of the apparatus
when power to the motor is disconnected, or the motor is inoperative.
Also, by use of the manual lever the rotor can be set in a neutral
position i.e. in an intermediate position in which both circuit breakers
are open, so that the load is isolated from both power sources for ease of
servicing. This neutral position is attainable for a relatively short
period during automatic operation of the transfer switch as will be
described.
Referring to FIG. 5, the rotor means 49 is shown simplified as a disk
mounted for rotation about the shaft 46 and axis 50. The yokes 19 and 20
and the link means 55 and 56 are shown in full outline in initial
positions representing normal power supply to the load, that is the yokes
are shown inclined downwardly, which reflects the position also shown in
FIGS. 2 and 3. Thus, switch contacts controlled by the yoke 19 are closed,
and those controlled by the yoke 20 are open. In the initial positions,
the first link means 55 is disposed generally tangentially to the axis 50
of the rotor, and the second link means 56 is disposed generally radially
of the axis 50. The terms "generally tangentially" and "generally
radially" are terms that refer to approximate geometrical relative
positions between the link means and a circle 89 (broken outline)
concentric with the axis 50 and containing inner ends 62 and 66 of the
link means. In practice, the second link means is not "disposed radially"
with respect to the axis 50 until the rotor has rotated a few degrees in
direction of an arrow 74, which occurs during initial movement of the
rotor means.
When the rotor means 49 rotates through 90 degrees from the initial
position as shown, the first link means assumes a broken outline final
position 55.1, which is generally equivalent to the initial position of
the second link means 56 prior to the rotation, and is now disposed
"generally radially" of the axis 50. In this position, the yoke 19 has
swung to a broken outline final position 19.1 about the first hinge axis
25. Likewise, when the rotor means has rotated through 90 degrees from the
initial position as shown in full outline, the second link means,assumes a
broken outline final position 56.1 and is now disposed "generally
tangentially" of the axis 50 and is generally similar to the initial
position of the first link means 55 prior to rotation. Similarly, the
second yoke means has assumed a broken outline position 20.1 after
rotating about the second hinge axis 26. In the final position, the
circuit breaker 11 is open, and the breaker 12 is closed.
Since the motor 43 rotates at an essentially uniform speed as the output
shaft 46 of the gear box rotates through 90 degrees, the rotor 49
similarly rotates uniformly from the initial position to the final
position. In this mode of operation, the rotor passes uniformly through
the intermediate or neutral position in which both circuit breakers are
open, and the load is isolated from both power sources, which are also
isolated from each other. When both circuit breakers are open together the
apparatus is in the neutral position during which electrical regeneration
of the load can decay rapidly to avoid problems of out-of-phase
re-connection of the load to the new electrical source. If necessary, the
duration of the time interval in the neutral position can be increased by
decreasing the speed of rotation of the motor, or the gear box ratio, as
may be appropriate. Alternatively, the motor can pause momentarily as the
rotor enters the neutral position, and can then resume the complete
rotation through the remaining portion of the 90 degrees. This deliberate
pause in the neutral position is termed a neutral position time delay and
it can be controlled electronically by known means provided in the control
means 52 which controls current to the motor 43. Stopping and restarting
of the motor is adjustable for selecting the exact time period after one
circuit breaker opens, and the remaining circuit breaker closes.
FIG. 6
FIG. 6 shows a graphical representation of the angle of separation between
opening and closing of switch contacts of the circuit breakers 11 and 12
with respect to rotation of the rotor means through 90 degrees. Vertical
axes 93 and 94 show complete travel of the switch toggle of the circuit
breakers 11 and 12 respectively, in which 0 percent represents the toggle
switch outermost position when the circuit breaker contacts are open, and
100 percent represents the toggle switch innermost position when the
circuit breaker contacts are closed. A horizontal axis 96 represents rotor
rotation over a range of 90 degrees in either direction. Curve 98 shows
the switch toggle travel with reference to rotor rotation for the switch
contacts of the circuit breaker 11, and curve 99 shows the similar
relationship for switch contacts of the circuit breaker 12. Horizontal
broken line 100 shows a position at which switch contacts close for either
switch, typically at about a 78 per | | |
