Electricity: circuit makers and breakers – Multiple circuit control – Sequential operations
Reexamination Certificate
2002-07-24
2004-07-20
Enad, Elvin (Department: 2832)
Electricity: circuit makers and breakers
Multiple circuit control
Sequential operations
C200S00100B
Reexamination Certificate
active
06765157
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a transfer switch, and in particular to a transfer switch that includes an improved actuator.
BACKGROUND
A transfer switch is used to switch an electric load back and forth between a primary source, such as a utility, and a secondary source, such as a generator. Transferring power from the primary source to the secondary source is necessary when the utility experiences a blackout. The transfer switch is also used to switch the power source back to utility power when the power outage is over.
A typical transfer switch is composed of an actuator and a toggle mechanism. The actuator operates by supplying energy to the toggle mechanism to maneuver movable contacts that are within the toggle mechanism relative to stationary power input contacts. The movable contacts engage one set of stationary contacts when power is supplied from the primary source and engage another set of stationary contacts when power is supplied from the secondary source.
Actuators are activated either manually or automatically at a desired time to supply energy to the movable contacts on the toggle mechanism. Many transfer switches are able to disconnect the load from both sources for a desired period of time in order to allow residual electricity to discharge before the load is switched to an alternate power source.
FIGS. 1-4
illustrate an improved electric transfer switch
10
. Transfer switch
10
includes a toggle mechanism
12
(FIG.
2
). The toggle mechanism
12
includes a pair of crossbars
14
,
15
(
FIGS. 3 and 4
) that extend through the transfer switch
10
. The crossbars
14
,
15
in the toggle mechanism
12
are connected to an actuator
16
of the present invention that rotates the crossbars
14
,
15
about their respective longitudinal axes.
A first set of moveable contacts
20
is carried by crossbar
14
and a second set of movable contacts
25
is carried by crossbar
15
. Each moveable contact
20
,
25
is connected to an output contact
21
and is adapted to be intermittently connected to a respective primary input contact
22
or a secondary input contact
23
depending on which crossbar
14
,
15
the movable contacts
20
,
25
are mounted on. Cams
29
are mounted on the crossbars
14
,
15
to maneuver the movable contacts
20
,
25
into, and out of, engagement with the stationary input contacts
22
,
23
.
FIG. 3
shows the movable contacts
20
engaged with the primary input contacts
22
when power is being supplied from a primary power source, such as a utility. As shown in
FIG. 4
, when there is an interruption in the primary power supply, the cams
29
on crossbar
14
rotate to disengage the movable contacts
20
from the primary input contacts
22
, and the cams
29
on crossbar
15
rotate to allow the movable contacts
25
to engage secondary input contacts
23
so that power can be supplied from a secondary power source, such as a generator.
A similar operation is performed to transfer back to the primary source from the secondary source. The cams
29
on crossbar
15
rotate to disengage the movable contacts
25
from the secondary input contacts
23
and the cams
29
on crossbar
14
rotate to allow the movable contacts
20
to engage the primary input contacts
22
so that power can once again be supplied from the primary source.
Springs
28
are disposed between each of the moveable contacts
20
,
25
and another portion of the transfer switch
10
. The springs
28
apply a force to each movable contact
20
,
25
that directs each moveable contact
20
against a corresponding stationary input contact
22
,
23
.
During the operation of a typical transfer switch there may be extreme conditions where the movable contacts can become slightly tack welded to the stationary contacts. Known actuators are often unable to apply a large enough force to the contact-carrying members within the transfer switch to permit the contacts to open in a desired amount of time. In addition, existing actuators often times do not allow for different programmed transitions of the movable contacts within the transfer switch between the stationary input contacts of the alternative power sources. One example of a programmed transition could be where one set of moving contacts is disengaged from the primary input contacts followed by a predetermined delay before the another set of movable contacts is engaged with the secondary input contacts.
There is a need for actuator
16
which can be used with transfer switches that include two rotating crossbars. Actuator
16
is able to independently operate the two crossbars and generate enough operating force to separate any tack-welded contacts that need to be maneuvered by the crossbars. Actuator
16
is also be able to provide for a variety of programmed transitions between two separate power sources.
SUMMARY OF THE INVENTION
The present invention relates to a transfer switch that includes an actuator which is capable of independently operating two rotating crossbars within the transfer switch. Since the crossbars in the transfer switch are operated independently, the actuator may include two similar but interrelated mechanisms such that one mechanism maneuvers one crossbar and the other mechanism maneuvers the other crossbar.
Using two mechanisms within a single actuator facilitates operating the actuator with a variety of programmed transitions between two separate power sources. One such transition could involve including a predetermined delay before switching power sources. Another programmed transition could be a closed transition where both sets of movable contacts within the transfer switch are simultaneously engaged with the primary and secondary input contacts before one set of movable contacts is disengaged. The closed transition provides a no break transfer of power from one source to another. No break power transfers are likely to increase the service life of the contacts within the transfer switch, as well as providing the primary function of supplying loads that can not tolerate any kind of interruption, however brief.
In addition, it is easier to design each of the mechanisms so that they generate a larger operating force on the crossbars than could be generated by a single mechanism. The larger operating force on each crossbar helps separate the movable contacts when the contacts have become tack-welded together.
The transfer switch includes output contacts, primary input contacts, secondary input contacts and a toggle mechanism. The toggle mechanism includes moving contacts that alternately connect the output contacts with the primary and secondary input contacts. The transfer switch further includes an actuator that rotates the first crossbar to alternately engage a first set of moving contacts with the output contacts and the primary input contacts, and rotates the second crossbar to alternately engage a second set of moving contacts with the output contacts and the secondary input contacts.
The present invention also relates to a method of actuating a transfer switch to alternate the supply of power to an electric load. The method includes rotating a first crossbar within the transfer switch to engage a first set of switching contacts with a primary power source. The method further includes rotating a second crossbar within the transfer switch to engage a second set of switching contacts with a secondary power source.
The present invention also relates to a transfer switch that includes output contacts, primary input contacts, secondary input contacts and a toggle mechanism which has a first crossbar and a second crossbar. The transfer switch further includes means for rotating the first crossbar to engage a first set of switching contacts with a primary power source and rotating the second crossbar to engage a second set of switching contacts with a secondary power source.
In another aspect, the present invention is directed to an actuator for a transfer switch. The actuator includes a pair of couplings that are each adapted to be connected to a separate crossbar i
Hawkins Peter M.
Hokenson Larry D.
Morley John E.
Peterson Michael A.
Rademacher Loren L.
Enad Elvin
Klaus Lisa
Onan Corporation
Schwegman Lundberg Woessner & Kluth P.A.
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