High current capacitors

Details High current capacitors High current capacitors

2003-03-21

2004-11-16

Reichard, Dean A. (Department: 2831)

Electricity: electrical systems and devices

Electrolytic systems or devices

Solid electrolytic capacitor

C361S535000, C361S303000, C361S305000, C361S015000, C361S272000, C361S437000

Reexamination Certificate

active

06819545

ABSTRACT:

BACKGROUND
1. Field of the Invention
The present invention generally relates to capacitors and, more particularly, to high current capacitors.
2. Background of the Invention
Capacitors are widely used in electrical apparatus for different reasons. For example, capacitors can be used to store electrical charge and to generate a large electrical current and voltage, and the like.
Capacitors can be manufactured using different methods. More recently, capacitors, such as a metallized film capacitors, can be manufactured by wrapping two tightly wound sheets or sections around a core. Each sheet is composed of a dielectric film having a metallized layer disposed on one face of the film. The metallized layer extends to one edge of the face to provide an unmetallized edge. The unmetallized edges of the two sheets are placed opposite to each other when the sheets are stacked and wound together, such that only one metallized edge is available for connecting to a leas at each end of the rolled capacitor. Each end is sprayed with a conductive metal that bonds with the sheet having a metallized edge at that end. Leads are then attached to each sprayed end to form the capacitor electrode. The rolled capacitor is then placed in a housing and impregnated with a dielectric fluid. One example of the metallized film capacitors is disclosed in U.S. Pat. No. 4,897,761.
The metallized film capacitor can be used in an apparatus that provides a large electrical current or that is operated under a large electrical power. In a high current applications, a fault that occurs within the capacitor can cause a disaster. For example, the apparatus can catch a fire due to the fault. In addition, the fault in the capacitor can damage other electrical components of the apparatus. Accordingly, the ability to detect faults that occurs within the capacitor has become an important issue in the design of high current capacitors.
FIG. 1
shows a general structure of a typical metallized film capacitor
10
. As shown, capacitor
10
includes metal housing
11
, capacitor roll
12
mounted within metal housing
11
, and dielectric fluid
15
that is present between metal housing
11
and capacitor roll
12
. Inside of metal housing
11
, there are two leads
13
that connects the capacitor roll
12
to two external terminals
14
. Terminals
14
are used to connect to other electrical components of an electrical apparatus to form an electrical circuit (“apparatus circuit”). Metal housing
11
can be in a cylindrical, an oval, a circular or other desired shape. As known in the art, capacitor
10
can be used singly in the electrical apparatus. Several capacitors
10
can also be used together as an array of capacitors to provide a larger electrical current.
In high current applications, safety measures must be provided to detect a fault that could occur within the capacitor. The fault may include, for example, a excessive pressure or overheat condition within the capacitor housing, which is caused by an overload of the capacitor. The overload may cause a fire to an apparatus circuit which includes the capacitor or the array of capacitors. Conventionally, an internal fault interrupter is installed within metal housing
11
. The fault interrupter breaks when a fault occurs within capacitor
10
, thereby disconnecting the capacitor
10
from the apparatus circuit.
FIGS. 2A and 2B
show a conventional capacitor design that utilizes an internal fault interrupter. Such capacitor design is commonly used in the United States for AC capacitors.
With reference to
FIGS. 2A and 2B
, the internal fault interrupter is installed within metal housing
11
on the top of capacitor roll
12
. Capacitor
10
includes insulating barrier
21
on which leads
13
are extended from capacitor roll
12
are welded. Capacitor
10
further includes a contact plate
22
that is set on the top of insulating barrier
21
. The contact plate
22
is contacted with leads
13
on one side and with external terminals
14
on the other side. In this design, external terminals
14
are mounted on contact plate
22
by means of a rivet or a screw
23
. When capacitor
10
is operated normally, contact plate
22
rests on insulation barrier
21
so that the contact plate
22
is in contact with both leads
13
and external terminals
14
to provide a electrical circuit. When a fault occurs within capacitor
10
, the excessive pressure resulted from the fault forces contact plate
22
to expanded outwardly (or upwardly as depicted in
FIG. 2B
) to move away from leads
13
. When contact plate
22
is expanded, it is no longer in contact with leads
13
, resulting in a disconnection of the electrical circuit.
The capacitor shown in
FIGS. 2A and 2B
, however, is not suitable for providing greater than 15 amps RMS continuous duty. This is because a weak weld between insulation barrier
21
and leads
13
and the utilization of rivets
23
to mount terminals
14
on contact plate
22
are not capable of processing current greater than 15 amps.
FIGS. 3A and 3B
illustrate another capacitor having an internal fault interrupter. Capacitor
10
as shown in
FIG. 3A
includes a bellows
31
that is fabricated on a top side of housing
11
and at least one “notched” wire conductor
33
within housing
11
which replaces conventional leads
13
for connecting external terminals
14
with capacitor roll
12
. When capacitor
10
operates normally, bellows
31
maintains a non-expanded position as shown in FIG.
3
A and notched wired conductor
33
properly connects capacitor roll
12
with external terminals
14
. When an excessive pressure occurs resulted from a fault within capacitor
10
, bellows
31
expands in an axial direction of housing
11
. The expansion forces notched wire conductor
33
to be broken, as shown in FIG.
3
B.
Although capacitor
10
shown in
FIGS. 3A and 3B
provides more current duty than that shown in
FIGS. 2A and 2B
, the current is still limited by notched wire conductor
33
.
Capacitor
10
shown in
FIG. 4
includes a high current interrupter. In
FIG. 4
, capacitor
10
includes bellows
41
fabricated on a top side of housing
11
and plug-type conductors
42
within housing
11
. As shown, the top ends of plug-type conductors
42
connect to external terminals
14
. Connector
43
having a number of sockets
431
is attached to capacitor roll
12
which, when capacitor
10
operates normally (see dashed lines), receives the bottom ends of plug-type conductors
42
within sockets
431
. In this manner, capacitor roll
12
is electrically connected with an apparatus circuit by external terminal
14
. On the contrary, as shown by solid lines in
FIG. 4
, when a fault occurs within capacitor
10
resulting an excessive pressure inside capacitor
10
, plug-like conductors
42
disengage from sockets
431
of connector
43
due to an expansion of bellows
41
, thereby interrupting the electrical connection of
10
capacitor with the apparatus circuit.
The capacitor shown in
FIG. 4
can be utilized in applications for a larger current duty. However, the capacitor is much more costly than any of the other designs mentioned above. Furthermore, all of the capacitors described above includes an internal interrupter located within the metal housing, which in itself is a significant manufacturing cost.
SUMMARY OF THE INVENTION
Accordingly, one object of the present invention is to provide a capacitor housing that can be easily manufactured for use in a high current capacitor.
The present invention also provides a low-cost capacitor without internal weak links that is capable of operating under high RMS current conditions.
One embodiment of the present invention provides a capacitor which includes a housing and an expandable part. The housing has a first end and a second end. The expandable part is located on the housing between the first end and the second end and is configured to expand due to a fault that occurs within the housing. The expansion of the expandable part causes the housing to extend in length to make contact with an external int

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