Segmented metallized film

Details Segmented metallized film Segmented metallized film

2002-09-17

2003-10-07

Reichard, Dean A. (Department: 2831)

Electricity: electrical systems and devices

Electrostatic capacitors

With protection or compensating means

C361S303000

Reexamination Certificate

active

06631068

ABSTRACT:

BACKGROUND
1. Field of the Invention
The present invention relates generally to metallized film used in capacitors and, more particularly, to a segmented metallized film having fuses that protect a capacitor in the event of a short circuit.
2. Background of the Invention
Metallized film capacitors are typically made of two tightly wound sheets wrapped around a core. Each sheet is composed of a dielectric film having a metallized layer on one face of the film. The metallized layer extends to one edge of the face to provide a metallized edge. The metallized layer stops short of the opposing 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 lead 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 electrodes. The rolled capacitor is then placed in a housing and impregnated with a dielectric fluid or encapsulated in a resin.
FIG. 1
illustrates a conventional metallized film capacitor
100
. As shown, capacitor
100
includes two metallized films
102
placed on top of each other and wound around a core (not shown) to form a wound section
104
. Each metallized film
102
includes a dielectric film
106
that is coated on one side with a metallized layer
108
. The metallized layers
108
of the dielectric films
106
are separated by the unmetallized side of at least one of the dielectric films
106
.
Each metallized film
102
includes a metallized edge
110
and an unmetallized area
112
. The metallized edges I
10
of the metallized films
102
are oppositely positioned during winding of the metallized films
102
. Accordingly, the unmetallized areas
112
are also oppositely positioned. In this manner, after tightly winding metallized films
102
around the core, only one metallized edge
110
is available for connecting to a lead at each end of wound section
104
. The ends of wound section
104
are covered with a conductive metallic spray
114
. Leads
116
are connected to conductive metallic spray
114
to form electrodes
118
.
For purposes of defining the present invention, the direetion in which metallized films
102
are wound is referred to herein as the machine direction and is represented by arrow
120
.
Metallized film capacitors are non-polar and “self-clearing” (which is also referred to as “self-protected” or “self-healing”). Thus, when a metallized film capacitor is exposed to, for example, an excessive voltage, a short circuit develops through the dielectric film, between the metallized layers (i.e., plates) of the capacitor. The current from the short circuit vaporizes small areas of the metallized layer near the short circuit. The vaporization of the metallized layer opens the short circuit, after which the capacitor returns to normal function, usually with only a small reduction in microfarads. The typical “end of life” of these types of capacitors are “opens” caused by the accumulated, gradual loss of dielectric film metallized electrodes from repeated “self-clearing” or activation of protective devices (e.g., interrupters).
To minimize the loss in capacitance resulting from the loss of a portion of the metallization layer during a short circuit, manufacturers have developed “segmented” or “patterned” metallization films. These segmented metallization films include unmetallized margin areas that divide the metallization layer into multiple metal segments interlinked by small fuses. If a short circuit occurs within a segment, the fuses that interlink that segment to adjacent segments open and remove the segment from the capacitor, thereby avoiding a catastrophic failure of the capacitor and the circuit in which the capacitor is used.
FIGS. 2A-2C
and
3
A-
3
C illustrate two examples of conventional self-protected metallized film patterns.
FIGS. 2A-2C
illustrate the “13M” pattern used by Bollore of Ergue-Gaberic, France to make self-protected metallized polypropylene sections.
FIGS. 3A-3C
illustrate a segmented film pattern manufactured by Steinerfilm Inc. of Williamstown, Massachusetts.
FIG. 2A
shows a segmented metallized film
200
made of a dielectric film
202
coated with a metallized layer
204
. Metallized layer
204
covers most of dielectric film
202
, including a metallized edge
206
. Opposite the metallized edge
206
, metallized layer
204
stops short of an unmetallized edge
208
to provide an uncoated area
210
(which is approximately 2.50 mm wide). Metallized layer
204
includes a lattice pattern of margin areas
212
that divide metallized layer
204
into multiple segments
214
. Approximately 6.0 mm from metallized edge
206
, lattice pattern
212
includes an edge margin area
216
that contains edge fuses
218
. The width of edge margin area
216
is approximately 0.2 mm. The length of edge fuses
218
is approximately 0.6 mm.
FIG. 2B
illustrates an enlarged view of a segment
214
of metallized film
200
. As shown, the margin areas of lattice pattern
212
include a segment fuse
220
along each length of margin area that encloses segment
214
. Segment fuses
220
interconnect adjacent segments
214
. In this manner, when a faulting segment develops a short circuit, the segment fuses that interconnect the faulting segment to adjacent segments break, thereby isolating the faulting segment.
FIG. 2C
illustrates in greater detail a fuse
220
and the margin areas of lattice pattern
212
in the area of fuse
220
. As shown, the margin areas of lattice pattern
212
on either side of fuse
220
are squared. The width
224
of the margin areas of lattice pattern
212
is approximately 0.15 mm. The length of fuse
220
is approximately 0.30 mm.
FIG. 3A
shows another example of a segmented metallized film
300
made of a dielectric film
302
coated with a metallized layer
304
. Metallized layer
304
covers most of dielectric film
302
, including a metallized edge
306
. Opposite the metallized edge
306
, metallized layer
304
stops short of an unmetallized edge
308
to provide an uncoated area
310
(which is approximately 2.50 mm wide). Metallized layer
304
includes a lattice pattern of margin areas
312
that divide metallized layer
304
into multiple segments
314
. Approximately 4.7 mm from metallized edge
306
, lattice pattern
312
includes an edge margin area
316
that contains edge fuses
318
. The width of edge margin area
316
is approximately 0.33 mm. The length of edge fuses
318
is approximately 1.5 mm.
FIG. 3B
illustrates an enlarged view of a segment
314
of metallized film
300
. As shown, the margin areas of lattice pattern
312
include a segment fuse
320
along each length of margin area that encloses segment
314
. Segment fuses
320
interconnect adjacent segments
314
. In this manner, when a faulting segment develops a short circuit, the segment fuses that interconnect the faulting segment to adjacent segments break, thereby isolating the faulting segment.
FIG. 3C
illustrates in greater detail a fuse
320
and the margin areas of lattice pattern
312
in the area of fuse
320
. As shown, the margin areas of lattice pattern
312
on either side of fuse
320
are rounded. The width
324
of the margin areas of lattice pattern
312
is approximately 0.33 mm. The length of fuse
320
is approximately 0.24 mm.
Comparing film
200
of
FIGS. 2A-2C
to film
300
of
FIGS. 3A-3C
, film
300
has fewer and larger segments, with wider margin areas. That is, the width
322
of
FIG. 3B
(approximately 9.4 mm) is greater than width
222
of
FIG. 2B
(approximately 7 mm). In terms of the width of the margin areas that define the lattice pattern, segmented metallized film
300
has wider margin areas. That is, the width
324
of
FIG. 3C
(approximately 0.33 mm) is greater than the width
224
of
FIG. 2C
(approximately 0.15 mm). In either case, however

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