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Description  |
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FIELD OF THE INVENTION
The present invention relates generally to transfer switches for
transferring electrical loads from one power source to another, and more
particularly to an actuating mechanism for use with transfer switches.
BACKGROUND OF THE INVENTION
The interruption of normal power supply can be caused by a variety of
reasons, for example, earthquake, flood damage, adverse weather
conditions, or utility unreliability. In the event that a normal power
source, such as an electric utility, experiences an outage and fails, it
is often necessary to supply critical and essential electrical needs by
means of a standby electrical power system.
Often, the standby power supply system is an on-site electrical power
source suitable to the needs of the applicable legal requirements and user
criteria. The standby or emergency power supply system functions to
provide a source of electrical power of required capacity, reliability and
quality within a specified time after loss or failure of the normal power
supply. The emergency power supply system varies depending upon the
particular situation, for example, there may be a specified maximum time
for which the load terminals of the transfer switch are permitted to be
without acceptable electrical power. Quick transfer is especially
important where critical equipment is involved, as in hospitals, airports
and computer installations.
With conventional transfer switches, it is possible for the load to be
transferred to the standby power source before the standby power source
has built up enough energy to sufficiently handle the load. To address
this problem, a suitable timer mechanism must be employed to delay the
transfer, or a capacitor must be employed to supply the necessary power at
the outset after transfer.
One type of conventional transfer switch utilizes a linear actuator
mechanism which has a single central solenoid with a plunger which can be
ejected from either end. On each side of the solenoid are two separate
contact blocks. With this design, a bidirectional linear induction motor
is utilized. As mentioned above, one or more boosters or motor-starting
capacitors are required. In order to prevent the application of power to
the load from both sources at the same time, this linear actuator
mechanism also has a mechanical interlocking beam.
However, conventional actuator mechanisms such as the one described require
a substantial amount of space, thereby making the unit unsuitable for some
applications and more costly. Further, the linear motor utilized with the
conventional transfer switch is relatively expensive and requires
additional space.
In addition, it is possible for the interlocking beam to become displaced,
for example, if a screw becomes loose. In that event, power could be
applied from both the primary power source and the standby power source,
which could result in dangerous short circuits and destruction of the
standby system.
The present invention addresses these and many other problems associated
with currently available transfer switches.
SUMMARY OF THE INVENTION
The present invention comprises an actuating mechanism for moving an
electrical transfer switch between two power sources. The actuator
mechanism is used in conjunction with an electrical transfer switch of the
type having a plurality of contacts mounted upon a rotatable cross bar and
movable between first and second stationary contact bars corresponding to
two different power sources, for example, a normal power source and an
emergency power source. The transfer switch is movable by the actuator
between the contact block corresponding to the normal power source and a
contact block corresponding to the standby or emergency power source. The
actuator comprises first and second rotatable drive disks in parallel
relationship which are interconnected by a pin which extends through a
slot in the rotatable drive disks, the pin also being connected to a
third, parallel driven disk. The driven disk is interconnected to the
cross bar which supports the movable contacts, so that rotation of the
driven disk causes rotation of the cross bar, thereby accomplishing the
power transfer. There are also linear actuating means which are suitably
interconnected to the pins so as to cause rotational movement of the pin.
In the preferred embodiment, the actuating means comprises electromagnetic
means such as a pair of solenoids, each solenoid being interconnected to
one of the drive disks. Preferably, the solenoid plungers and drive disks
are interconnected by suitable linkage means having a pivotal connector on
each end thereof.
A particular advantage of the present invention is its "load shedding"
capability; that is, the actuating mechanism is able to move into a
neutral position wherein power is transmitted from neither source. This
feature is useful, for example, in the event the standby power source does
not immediately have sufficient voltage to supply the necessary power. In
this situation, the actuator of the present invention can be placed in the
neutral position for the number of seconds required until the proper
voltage is achieved, which may range from a fraction of a second to twenty
seconds or more.
Another feature of the actuator of the present invention is that it does
not draw as much current at the outset when the transfer operation takes
place. The actuating mechanism requires less energy to operate, because of
the reduction in the number of necessary parts and the simplicity of
construction, so that the actuator has less mass to move. Because less
energy is required, a capacitor is not necessary.
Another feature of the present invention is that it requires less space
than conventional transfer switch actuators, thus enabling the actuator to
be positioned even where there are tight space constraints. This feature
results in an actuator which is more cost-effective.
For a better understanding of the invention, and of the advantages obtained
by its use, reference should be made to the Drawing and accompanying
descriptive matter, in which there is an illustrated and described a
preferred embodiment of the invention.
BRIEF DESCRIPTION OF THE DRAWING
Referring particularly to the Drawing, wherein like reference numerals
indicate like parts throughout the several views:
FIG. 1 is perspective view of the actuating mechanism of the present
invention;
FIG. 2 is a perspective view of the actuating mechanism and transfer
switch, as viewed from the opposite side as FIG. 1;
FIG. 3 is a plan view of the actuating mechanism;
FIG. 4 is a side elevational view, partially cutaway, of the actuating
mechanism taken along line 4--4 of FIG. 3;
FIGS. 5a-5c are schematic views of three positions of the disks of the
actuating mechanism, as viewed from the side of the transfer switch; and
FIGS. 6a-6c side views of the contact arms in the three positions
corresponding to the positions shown in FIG. 5.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring to FIGS. 1-2, the actuating mechanism of the present invention is
illustrated generally at 10, in conjunction with a transfer switch 11. The
transfer switch 11 moves between a pair of stationary contact blocks 13,
14 which correspond to the normal power source and standby or emergency
power source respectively. There are one or more stationary contacts 9
within each of the contact blocks 13, 14. Although there is only one set
of contacts 9 illustrated in FIG. 1, it is to be understood that the
number of contacts would depend upon the number of phases. Thus, if the
particular application required a transfer switch which could accommodate
multiple phases, then multiple sets of main contacts 15, 18 would be
positioned along the contact crossbar 16, and multiple corresponding
stationary contacts would be positioned along the contact blocks 13, 14.
The transfer switch 11 transfers the electrical load from one power source
to the other and prevents the two power sources from being interconnected
to the load at the same time. The actuating mechanism 10 transfers the
power automatically by activating and moving suitable main contacts 15, 18
to perform transfers of power from either source. The contacts 15, 18 are
arranged such that they cannot both be in contact with a power source at
the same time.
In the preferred embodiment, the transfer switch 11 has a contact crossbar
16 upon which are mounted the contacts 15, 18. The contacts 15, 18 are
positioned on the distal end of extension fingers 17 which extend
outwardly in a perpendicular relationship from the crossbar 16. The first
contact 15 corresponds to the normal or primary power source, whereas the
second contact 18 corresponds to the standby or emergency power source.
Electrical wires 19 extend from the contact arms 17 and are interconnected
to the load terminals (not shown). The actuating mechanism 10 serves to
rotate the crossbar or shaft 16 in order to accomplish the transfer
procedure, as will be more fully described below.
The actuating mechanism 10 is a three-position mechanism operated by two
solenoids 20, 21. The disk assembly or actuator 10 is mounted upon a
suitable support or bracket assembly 37. Energization of suitable linear
actuating means causes rotation of the disk assembly 10 and causes the
transfer of power between the two sources. The actuator 10 has three
positions: 1. a first position, as illustrated in FIG. 5c, in which the
contact 15 is electrically connected to the primary or normal power
source; 2. a central, neutral position in which neither contact 15, 18 is
connected to a power source; and 3. a third position, as illustrated in
FIG. 5a, in which the contact 18 is connected to the standby or emergency
power source.
The actuator 10 has two disk drives 22, 23. The first disk drive 22 is
proximate the crossbar 16, whereas the second disk drive 23 is in a
parallel relationship to the first disk drive 22. In the preferred
embodiment, the disk drives 22, 23 are approximately 21/2 inches in
diameter. Each disk drive 22, 23 is identical in construction, and a shaft
25 extends through central apertures in each disk drive, the shaft 25 (see
FIG. 3) being in alignment with the crossbar 16. The shaft 25 is
interconnected to the crossbar by suitable means. For example, the shaft
25 may be a screw with one end extending into a central aperture in the
cross bar 16, with suitable tightening means (not shown) interconnecting
the shaft end within the cross bar 16. One end of the shaft 25 terminates
in a screw head 27. Thus, rotation of the shaft 25 causes rotation of the
crossbar 16 and contacts 15, 18.
The actuator 10 also includes an end disk or driven disk 26 (shown in FIGS.
1 and 3) which is preferably of the same size as the disk drives 22, 23
and in parallel relationship thereto. The shaft 25 is interconnected to
the end disk 26, so that rotation of the end disk 26 causes rotation of
the shaft 25.
Each of the disk drives 22, 23 has a cut out slot 28, 29 respectively. As
illustrated, the slots 28, 29 are configured so as to be circumferential
and proximate the outside edge of the disk drives 22, 23. Preferably, the
slots 28, 29 are of the same size and extend the length of approximately a
45 degree arc. Extending through the slots 28, 29 is a pin 30. The pin 30
is sized and configured so as to have a diameter which is slightly less
than the width of the slots 28, 29 so as to be slideably movable within
the slots 28, 29. The pin 30 is interconnected to the end disk 26 by
welding or other suitable means.
In the preferred embodiment, there is a spring 38, one end of which is
interconnected to the pin 30, and the opposite, lower end being
interconnected to the stationary bracket 37. The spring 38 serves to
accelerate movement of the disk drives 22, 23 during the transfer process
and also maintains the contacts 15, 18 against the appropriate stationary
contact 9.
Each disk drive 22, 23 is operatively linked to linear actuating means,
which preferably consists of electromagnetic means and an energizing
circuit therefor. In the preferred embodiment, the electromagnetic means
comprises two solenoids 20, 21. As illustrated in FIGS. 1, 2 and 3, the
first solenoid 20 is interconnected to the first disk drive 22, whereas
the second solenoid 21 is interconnected to the second disk drive 23. In
the preferred embodiment, the solenoids 20, 21 are of the type sold by
Trombetta Corporation of Milwaukee, Wis., Part No. P-514 or Q-514. It is
also within the scope of the present invention to construct the actuator
10 with a single solenoid.
Each solenoid 20, 21 has a plunger 31, 32 respectively. The disk drives 22,
23 and solenoid plungers 31, 32 are interconnected by suitable linkage
means, there being a pair of linkages 33, 34 respectively in the preferred
embodiment. Preferably, each disk drive 22, 23 consists of two circular
plates 40 in parallel relationship, each plate having a central aperture.
The disks or plates 40 for the disk drives 22, 23 are spaced a relatively
small distance from each other and are interconnected proximate their
central portion. In the preferred embodiment, the linkages 33, 34 are
elongated, relatively flat members, with the inner end of each linkage 33,
34 fitting within the space between the two disks 40 which comprise each
of the disk drives 22, 23. The linkages 33 and 34 each carry a coupling
pin at their connection to the drive disk. Each linkage 33, 34 has a
connector on both ends thereof: an inner connector 35 which is attached to
the disk drives 22, 23, and an outer connector 36 which is attached to
guide members or levers 40, 41, which are in turn interconnected to the
inner ends of the solenoid plungers 31, 32. In the preferred embodiment,
the outer connectors 36 are roll pins, whereas the inner connectors 35 are
clevis pins. It is also within the scope of the present invention for the
linkages 35, 36 to be directly interconnected to the pin 30. Each guide
member 40, 41 is held slidably in corresponding guide slots 42, 43 in the
framework 37. The ends of the slots 42, 43 serve to limit movement of the
members 40, 41.
When one of the solenoids 20 or 21 is energized, its plunger 31 or 32
becomes magnetized and causes the plunger 31 or 32 to move within the
solenoid body 20 or 21. Upon deenergization, a plunger spring or other
biasing means within the solenoid (not shown) biases the plunger 30 or 31
to push it outside of the solenoid 20 or 21. Thus, deenergization of the
solenoid causes the plunger 30 or 31 to move into a position outside the
solenoid housing, as illustrated in FIGS. 1-4. This deenergization
position is referred to as the solenoid plunger's inward position with
respect to the disk assembly 10 or unretracted position. FIGS. 1-4
illustrate a situation in which neither of the solenoids 20 nor 21 is
actuated.
In the preferred embodiment, energization of the solenoid 20 or 21 exerts
approximately a 70-80 pound force on the corresponding solenoid plunger 31
or 32. When the plunger 31 or 32 is in the energized position, the spring
within the solenoid exerts approximately a 20 pound force in the opposite
direction. The solenoid 20 or 21 is engaged momentarily and operates
rapidly, on the order of two to three seconds. The solenoids 20, 21 are
activated by suitable control means (not shown).
During the transfer operation from one of the power sources to the neutral
position, one solenoid is energized and activates the linkage connected to
it. If it is then desired to transfer from the neutral position to the
opposite power source, the other solenoid is subsequently energized to
activate its corresponding linkage. If, on the other hand, it is desired
to return to the original power source from the neutral position, the
first solenoid is energized for a second time. When activated, the
linkages 33, 34 apply inertial torque to the drive disk and generate
rotational speed. Activation of the solenoid(s) causes rotation of the
drive disk's axis 25 and the contact cross bar 16, thereby allowing
appropriate electrical contact to be made.
More specifically, the transfer operation from the normal power source to
the emergency power source will now be described. One of the two solenoids
is actuated (in this case, the second solenoid 21), as by passing a
current therethrough. The second solenoid plunger 31 moves to its outer or
retracted position within the solenoid body, thereby causing the second
disk drive 23 to move in a clockwise direction, as viewed in FIGS. 2-5 or
in a counterclockwise direction, as viewed in FIG. 1. Before activation of
the second solenoid 21, the pin 30 is at the right end of the slot 29 in
the second disk 23, and the pin 30 is at the left end of the slot 28 in
the first disk, as illustrated in FIGS. 4, 5c and 6a. Referring to FIG. 4,
movement to the left of solenoid plunger 31 causes the linkage 34 to be
pulled into a substantially horizontal position, and causes the second
disk drive 23 to move in a clockwise direction. After the plunger 31 has
reached the outermost point and begins to return toward the right, the
linkage 34 does not return to its original position but instead rotates so
that the right end (as viewed in FIG. 4) of the linkage 34 is above its
left end. Consequently, inward movement of the plunger 31 causes clockwise
movement of the disk 23, which in turn causes clockwise movement of the
drive disk 22, the end disk 26, the central shaft 25, and the crossbar 16.
When the solenoid plunger 31 comes to a rest in its retracted position,
the assembly 10 is in the neutral position illustrated in FIG. 6b, in
which neither contact is in electrical connection with either power
source. That is, the contacts 15 and 18 are not in contact with either
contact block 13 and 14. The neutral position can be maintained for a
predetermined amount of time by means of a suitable timer mechanism.
In order to then complete the transfer procedure by moving from the neutral
position to the emergency power source, the first solenoid 20 is then
actuated. As viewed in FIG. 4, the solenoid plunger 32 moves in the right
direction, thereby causing the linkage 33 to assume a horizontal position,
and causing the disk 22 to rotate in the clockwise direction. When the
plunger 32 moves to the left to its unretracted position, the left end of
the linkage 33 moves below the right end of the linkage 33. As a result,
inward movement of the plunger 32 causes rotation of the drive disk 22,
the driven disk 23, the end disk 26, and the crossbar 16. After this
transfer operation, the pin 30 is at the left end of the slot 28 in the
first disk 22 and at the right end of the slot 29 in the second disk 23,
as viewed from the side opposite the contacts and as illustrated in FIG.
5a. The end result is that electrical contact is made with the emergency
power source, and the position of FIG. 6c is achieved.
The linkages 33 or 34, during the energization process, apply inertial
torque to the disk drives 22 or 23 to generate rotational speed which
causes movement of the crossbar 16 and causes transfer to the other
contact block 14. The rotational inertia overcomes the force of the spring
38. When the contact 15 or 18 comes to rest on the appropriate power
source contact block 13 or 14, the transfer operation is complete.
Transfer of the contacts from the emergency source to the normal source
proceeds along the same basis outlined above, except that the first
solenoid 20 is initially activated to begin the transfer process, and the
corresponding first disk 22 acts as the drive disk. The disk 23 acts as
the drive disk during transfer from normal mode to emergency mode, whereas
the disk 22 acts as the drive disk during transfer from emergency mode to
normal mode.
FIGS. 5a-5c illustrate the three positions of the disk drives 22, 23 with
respect to the pin 30. FIGS. 5a, 5b and 5c correspond to the emerging
power source mode, the neutral mode, and the normal power source mode
respectively. The slot 29 on the second disk drive 22 is illustrated with
a solid line, whereas the slot 28 on the first disk drive 22 is
illustrated with the dashed, hidden lines. FIG. 5c illustrates the same
configuration as is shown in FIG. 3.
FIG. 6 illustrates the three positions corresponding to the three modes
illustrated in FIG. 5. That is, FIGS. 5a, 5b, and 5a correspond to FIGS.
6a, 6b, and 6c, and correspond to the normal power source mode, the
neutral mode, and the emergency power source mode respectively.
Even though numerous characteristics and advantages of the invention have
been set forth in the foregoing description, together with details of the
structure and function of the invention, the disclosure is illustrative
only, and changes can be made in detail, especially in matters of shape,
size and arrangement of parts, within the principles of the invention, to
the full extent indicated by the broad general meaning of the appended
claims.
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