TABLESS ROLL CAPACITOR AND CAPACITOR STACK
This application claims benefit of the 22 March 201 1 filing date of United States
provisional patent application number 61/466,265 which is incorporated by reference
herein.
FIELD OF THE INVENTION
The invention relates generally to roll capacitors and to capacitor stacks formed
of a plurality of roll capacitors, and more particularly, to roll capacitors connected in
parallel and/or series for capacitor voltage transformers, and to assembly thereof.
BACKGROUND OF THE INVENTION
Roll capacitors are formed by rolling two electrode strips separated by dielectric
strips. This forms a more compact capacitor than a flat plate capacitor with equivalent
capacitance. Capacitor chains can be made by stacking multiple roll capacitors, then
interconnecting them with conductive tabs that extend beyond the ends of the
capacitors between respective electrode strips in adjacent rolls. This is seen for
example in Figure 4 of United States patent 3,508,128 and in Figure 2 of United States
patent 4,623,953. Capacitor chains are used, for example, in capacitor voltage
transformers and other applications in the Medium to Ultra-High Voltage system
applications, such as: instrument transformers (protection, supervisory control, data
acquisition, metering and harmonics monitoring), power line carrier, system network
compensation, voltage dividers and tuned filter applications, for example.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention is explained in the following description in view of the drawings that
show:
FIG. 1 is a sectional end view of a roll capacitor in a first embodiment of the
invention.
FIG. 2 shows a stack of roll capacitors of the first embodiment.
FIG. 3 shows an electrical diagram of the stack of FIG 2.
FIG. 4 shows a stack of roll capacitors with shorter dielectric strips than in FIG 2.
FIG. 5 is a sectional end view of a roll capacitor of a second embodiment.
FIG. 6 shows a stack of capacitors of the second embodiment.
FIG. 7 shows an electrical diagram of the stack of FIG 6.
FIG. 8 is a sectional end view of a roll capacitor of a third embodiment.
FIG. 9 shows a stack of capacitors of the second and third embodiments.
FIG. 0 shows an electrical diagram of the stack of FIG 9.
FIG. 1 is a sectional end view of a roll capacitor of a fourth embodiment.
FIG. 2 shows a stack of capacitors of the fourth embodiment.
FIG. 13 shows an electrical diagram of the stack of FIG 1 .
FIG. 14 shows a stack of capacitors of the third and fourth embodiments.
FIG. 15 shows an electrical diagram of the stack of FIG 14.
FIG. 16 shows a stack of capacitors of the second and third embodiments.
FIG. 17 shows an electrical diagram of the stack of FIG 16.
FIG. 18 is a sectional end view of a roll capacitor of a fifth embodiment.
FIG. 19 shows a unit of two capacitors of the fifth embodiment.
FIG. 20 is a perspective view of a capacitor of the first embodiment.
FIG. 2 1 shows a bound stack of capacitors.
DETAILED DESCRIPTION OF THE INVENTION
The present inventors have recognized that assembling and interconnecting the
conductive tabs of roll capacitors to form capacitor chains is labor intensive, slow,
expensive, and subject to human error. The tabs are subject to mechanical stress and
cyclic thermal expansion that can fatigue and weaken the electrode strips and dielectric
strips. The tabs extend beyond the footprint of the capacitors, thus requiring additional
chamber width when enclosed within a porcelain insulator or other containment
housing, such as is common for capacitor voltage transformer applications. An
improved capacitor design useful for forming capacitor chains is disclosed herein.
FIG 1 shows a roll capacitor 20A with inner and outer electrode strips 2 , 23
separated by inner and outer dielectric strips 22, 24. The designations "inner" and
"outer" are best seen at the innermost lap 25 of the strips, since both electrodes 2 , 23
and both dielectrics 22, 24 are finally "outer" on different parts of the roll outer surface.
The electrodes 2 1, 23 are designated with charges + or - for convenience only to show
relative charges in each embodiment. These designations are reversible. The
electrodes 23, 2 1 have exposed end portions 23E, 2 1E on opposite sides 26, 28 of the
roll 20A for electrical contact. The term "side" of a roll herein means a portion of the
outer surface of the roll facing in a given direction, such as first and second sides 26, 28
in the figures. The term "side" in this context is not intended to include the ends of the
roll. Pluralities of these capacitors 20A inherently interconnect by direct stacking
contact between the exposed ends 2 1E, 23E of the electrodes when they are stacked
as shown in FIG 2. No interconnection tabs are needed as are needed in the prior art.
Capacitor embodiment 20A may be described as a roll of four adjacent strips 21,
22, 23, 24 including, in a radially inward to outward sequence, an inner electrode 21, an
inner dielectric 22, an outer electrode 23, and an outer dielectric 24. In general, the roll
capacitors herein may be described as a roll of four adjacent strips 2 1, 22, 23, 24
including inner 2 1 and outer 23 electrode strips alternating with inner 22 and outer 24
dielectric strips, wherein the two electrode strips 2 1, 23 have respective exposed
radially outer ends 2 1E, 23E on a portion or side 26, 28 of an outer side surface of the
roll. A radially outer end of each dielectric strip 22, 24 is shorter than an inwardly
adjacent one of the electrode strips on the outer side surface of the roll, exposing the
outer end 2 E, 23E of the electrode strip. In some embodiments, one or both dielectric
strips 22, 24 may be short enough to expose one or both electrode strips 2 1, 23 on both
sides of the roll, as later shown.
FIG 2 shows a stack of three electrically interconnected capacitors 20A1 , 20A2,
and 20A3. FIG 3 shows an electrical diagram of the stack of FIG 2. Capacitors 20A1 ,
20A2, and 20A3 are connected in series. The inner electrode 2 1 of each roll contacts
the outer electrode 23 of the next roll in the stack. A gap G between adjacent contacts
2 1, 23 is illustrated in the stack 50 and others herein, but this gap is eliminated by
compressing the stack vertically in a chamber as later described. FIG 4 shows a stack
5 1 of two roll capacitors 20A1 and 20A2 with dielectric strips 22, 24 that are shorter
than in FIG 2, eliminating the gap G that is seen is FIG 2.
FIG 5 shows a roll capacitor 20B with inner and outer electrode strips 2 1, 23,
alternating with inner and outer dielectric strips 22, 24. The electrodes 2 , 23 have
respective exposed end portions 2 1E, 23E on opposite sides 26, 28 of the roll 20B for
electrical contact. This provides inherent electrical interconnection of the capacitors
20B when they are stacked. In addition, the outer electrode 23 is exposed on both
sides 26, 28 of the roll. This provides a serial connection of two adjacent rolls 20B in
one orientation, and a parallel connection in another orientation.
FIG 6 shows a stack 52 of four electrically interconnected roll capacitors 20B1 ,
20B2, 20B3 and 20B4. Each capacitor is inverted with respect to the previous capacitor
in the stack. The second sides 28 of capacitors 20B1 and 20B2 are in mutual contact,
such that electrodes 21, 23 of 20B1 contact both electrodes 23, 2 1 of 20B2 respectively
in a crossover as shown. This means the inner electrode 2 1 of capacitor 20B1 contacts
the outer electrode 23 of capacitor 20B2, and the outer electrode 23 of 20B1 contacts
the inner electrode 2 1 of 20B2, creating a parallel connection between them. Capacitor
20B3 is inverted with respect to 20B2 such that their respective first sides 26 are in
mutual contact. In this orientation, capacitors 20B2 and 20B3 are connected in series.
Capacitor 20B4 is inverted with respect to 20B3 such that they are connected in
parallel, as described above for the connection between 20B1 and 20B2. The circuit
resulting from the stack 52 of FIG 6 is illustrated in FIG 7. Capacitor embodiment 20B
allows connecting any two adjacent capacitors either in series or in parallel. If more
than two capacitors in a row are to be connected in series or parallel, this can be done
with other embodiments herein, either alone or in combination with embodiment 20B.
FIG 8 shows a roll capacitor 20C with inner and outer electrode strips 2 1, 23,
alternating with inner and outer dielectric strips 22, 24. Both electrodes 2 , 23 have
exposed end portions 2 1E, 23E that extend to both opposite sides 26, 28 of the roll 20B
for electrical contact. Capacitors of this type 20C may be stacked by placing the
second side 28 of a first capacitor 20C1 against the first side 26 of a second capacitor
20C2, creating a parallel interconnection.
FIG 9 shows a stack 54 of four electrically interconnected roll capacitors 20B1 ,
20C1, 20C2 and 20B4. This stack has parallel connections between 20B1 and 20C1 ,
between 20C1 and 20C2, and between 20C2 and 20B2 as shown in FIG 10. Any
number of capacitors 20C may be interconnected in parallel by stacking them as per
20C1 and 20C2. Each end of a stack of capacitors of type 20C can be finished with a
capacitor 20B as shown by 20B1 and 20B2. This arrangement provides a single
respective + or - contact at each end of the stack 54 for circuit connections, which can
alternately be used for a series connection to additional capacitors as later shown.
Capacitor 20B2 is inverted with respect to capacitor 20B1 in this stack arrangement 54.
FIG 11 shows a roll capacitor 20D with inner and outer electrode strips 2 1, 23,
alternating with inner and outer dielectric strips 22, 24. Both electrodes 2 1, 23 have
exposed end portions 2 1E, 23E on a first side 26 of the roll 20D for electrical contact.
The end portion 2 1E of one of the electrodes 2 1 also is also exposed on the second
side 28 of the roll. Capacitors of this type 20D may be stacked in a parallel pair or a
sequential pair. Capacitor 20D of FIG 11 is similar to capacitor 20B of FIG 5 in that they
both expose both electrodes on one side and only one electrode on the other side.
However, they are different in that the one electrode exposed on the other side is the
outer electrode 23 in capacitor 20B whereas it is the inner electrode 2 1 in capacitor
20D.
FIG 12 shows a stack 56 of four electrically interconnected roll capacitors 20D1 ,
20D2, 20D3 and 20D4. Each capacitor is inverted with respect to the previous
capacitor in the stack. The first sides 26 of capacitors 20D1 and 20D2 are in mutual
contact, such that both electrodes 2 1, 23 of 20D1 contact both electrodes 23, 2 1 of
20D2 in a crossover. This means the inner electrode 2 1 of capacitor 20D1 contacts the
outer electrode 23 of capacitor 20D2, and the outer electrode 23 of 20D1 contacts the
inner electrode 2 1 of 20D2, creating a parallel connection between them as shown in
FIG 13. Capacitor 20D3 is inverted with respect to 20D2 such that their second sides
28 are in mutual contact. In this orientation, capacitors 20D2 and 20D3 are connected
in series. Capacitor embodiment 20D allows connecting any two adjacent capacitors
either in series or in parallel. If more than two capacitors in a row are to be connected
in series or parallel, other embodiments herein, either alone or in combination with
embodiment 20D may be used.
FIG 14 shows a stack 58 of four electrically interconnected roll capacitors 20D1 ,
20C1 , 20C2 and 20D4. This stack has parallel connections between 20B1 and 20C1 ,
and between 20C1 and 20C2, and between 20C2 and 20B2 as shown in FIG 15. Any
number of capacitors of type 20C may be interconnected in parallel by stacking them
per 20C1 and 20C2. Each end of a stack of capacitors of type 20C can be finished with
a capacitor 20D as shown by 20D1 and 20D2. This arrangement provides a single
respective + or - stack end contact for circuit connections at each end of the stack 56.
Either or both stack end contacts can alternately be used for a series connection to
additional capacitors as later shown. Capacitor 20D2 is inverted with respect to
capacitor 20D1 in this stack arrangement 58. Gaps G are eliminated by compression of
the stack 56 when installed in a chamber as later described.
FIG 16 shows a stack 60 of eight electrically interconnected capacitors 20B1,
20C1 , 20C2, 20B2, 20B3, 20C3, 20C4, 20B4, producing the circuit diagram of FIG 7.
This stack can be considered as two sequential stacks of type 54 of FIG 9. Similarly,
multiple stacks of type 58 of FIG 14 can be stacked, producing multiples of the circuit
diagrams of FIG 15 interconnected in sequence.
FIG 18 shows a capacitor embodiment 20E that can be combined with a second
such capacitor 20E as shown in FIG 9 to form a dual-roll unit capacitor 62. The dualroll
unit capacitor 62 has twice the capacitance of a single roll capacitor 20E within the
same chamber diameter D. FIG 19 shows two capacitors 20E1 , 20E2 assembled into a
dual-roll unit capacitor 62 by extending the exposed end 2 1E of the inner electrode 2 1
of each roll 20E1, 20E2 around the opposite side of the other roll to contact the exposed
outer electrode 23E of the other roll. This forms a parallel interconnection of the two
rolls 20E1 , 20E2. Multiple unit capacitors 62 can be stacked with other unit capacitors
62, which inherently forms sequential interconnections between them in the stack. The
unit capacitor 62 inherently interconnects sequentially with other unit capacitors 62
and/or with other types of capacitors 20A, 20B, 20D in various configurations in a stack
of capacitors by direct stacking contact between the exposed ends of the electrodes on
respective opposite sides of the unit capacitor 62 and/or the other types of capacitors
20A, 20B, 20D.
FIG 20 shows a perspective view of a capacitor of the first embodiment 20A.
The electrodes 2 1 and 23 are not exposed along ends 30 of the roll because they are
covered by overlapping edges 3 1 of the dielectric strips 22, 24. Advantageously,
pluralities of such capacitors can be interconnected in series or in parallel by simply
stacking them on top of each other, as described above, without conductive tabs
extending from and between the ends 30 (i.e. beyond the footprint) of the adjacent
capacitors. This provides a more compact stack than with prior art roll capacitor stacks
incorporating such tabs.
FIG 2 1 shows a stack 64 of capacitors 20, held together by a binding strap 34
(not an electrical connection strap) for shipping to a facility for installation into a
chamber of an insulator (not shown). Leads (not shown) may be provided on respective
plates for placement on the two ends 36, 38 of the stack 64. The stack 64 and leads
may be inserted into the chamber of the insulator, where the stack 64 may be held in
compression by a spring at an end of the stack (not shown) or by other means. The
capacitors 20 of the stack inherently interconnect with each other by direct contact
between the exposed ends of the electrodes shown in embodiments 20A-E. No
additional connection straps are needed.
Different combinations of series-connected and parallel-connected roll capacitors
provide different parameters of voltage, capacitance, resistance, and impedance that
can be selected for each application. Thus, it is useful to provide different embodiments
that inherently interconnect by direct stacking contact in series, parallel, and
combinations of series and parallel without a need for connection tabs extending from
an end of the rolls as in the prior art. The capacitors herein provide faster, less
expensive, and more reliable fabrication and assembly than prior stacked capacitors.
While various embodiments of the present invention have been shown and
described herein, it will be obvious that such embodiments are provided by way of
example only. Numerous variations, changes and substitutions may be made without
departing from the invention herein. Accordingly, it is intended that the invention be
limited only by the spirit and scope of the appended claims.

CLAIMS
The invention claimed is:
1. A capacitor, comprising:
a roll of four adjacent strips comprising first and second electrode strips
alternating with first and second dielectric strips;
wherein each of the dielectric strips is shorter at a radially outer end thereof than
an inwardly adjacent one of the electrode strips effective to expose a radially outer end
of each electrode strip on an outer side surface of the roll.
2. A capacitor according to claim , wherein the radially outer ends of the
first and second electrode strips are exposed on respective first and second opposite
sides of the roll.
3. A capacitor according to claim 2, wherein the radially outer end of at least
one of the electrode strips is exposed on both the first and second sides of the roll.
4. A capacitor according to claim , wherein the radially outer ends of the
first and second electrode strips are exposed only on respective first and second
opposite sides of the roll.
5. A capacitor according to claim 1, wherein:
the radially outer end of the first electrode strip is exposed on both a first side
and an opposed second side of the capacitor; and
the radially outer end of the second electrode strip is exposed only on the first
side of the capacitor.
6. First and second capacitors according to claim 5, wherein placing the first
sides of the two capacitors together creates a series interconnection of the two
capacitors, and placing the second sides of the two capacitors together creates a
parallel interconnection of the two capacitors.
7. A capacitor according to claim , wherein:
the radially outer end of the first electrode strip is exposed on both a first side
and an opposed second side of the capacitor; and
the radially outer end of the second electrode strip is exposed on both the first
side and on the opposed second side of the capacitor.
8. First and second capacitors according to claim 7, wherein placing the
second side of the first capacitor against the first side of the second capacitor creates a
parallel interconnection of the two capacitors.
9. A stack of capacitors comprising the first and second capacitors according
to claim 8, and further comprising third and fourth roll capacitors on respective opposite
ends of the stack, wherein each of the third and fourth roll capacitors comprises:
a radially outer end of a first electrode strip exposed on both first and
second opposite sides of the roll capacitor; and
a radially outer end of a second electrode strip exposed on only the
second side of the roll capacitor;
wherein the capacitors in the stack are all interconnected in parallel by direct
stacking contact between the exposed ends of the respective electrodes of each of the
adjacent capacitors.
10. A capacitor, comprising:
a roll of four adjacent strips comprising inner and outer electrode strips
alternating with inner and outer dielectric strips;
wherein each of the dielectric strips is shorter at a radially outer end thereof than
an inwardly adjacent one of the electrode strips effective to expose a radially outer end
of each electrode strip on respectively different portions of an outer side surface of the
roll;
wherein "inner" and "outer" mean radially inward and outward in a sequence of
the four adjacent strips in an innermost lap of the four adjacent strips.
11. A capacitor according to claim 10, wherein the radially outer ends of the
inner and outer electrode strips are exposed on respective first and second opposite
sides of the roll.
12. A capacitor according to claim 11, wherein the radially outer end of at
least one of the electrode strips is exposed on both the first and second sides of the roll.
13. A capacitor according to claim 10, wherein the radially outer ends of the
inner and outer electrode strips are exposed only on respective first and second
opposite sides of the roll.
14. A capacitor according to claim 10, wherein:
the radially outer end of one of the electrode strips is exposed on both a first side
and an opposed second side of the capacitor; and
the radially outer end of the other one of the electrode strips is exposed only on
the first side of the capacitor.
15. First and second capacitors according to claim 14, wherein placing the
first sides of the two capacitors together creates a series interconnection of the two
capacitors, and placing the second sides of the two capacitors together creates a
parallel interconnection of the two capacitors.
6. A capacitor according to claim 10, wherein:
the radially outer end of the inner dielectric strip is exposed on both a first side
and an opposed second side of the capacitor; and
the radially outer end of the outer dielectric strip is exposed on both the first side
and on the opposed second side of the capacitor.
17. First and second capacitors according to claim 16, wherein placing the
second side of the first capacitor against the first side of the second capacitor creates a
parallel interconnection of the two capacitors.
18. A stack of capacitors comprising the first and second capacitors according
to claim 17, and further comprising third and fourth roll capacitors on respective
opposite ends of the stack, wherein each of the third and fourth roll capacitors
comprises:
a radially outer end of a first electrode strip exposed on both first and
second opposite sides of the roll capacitor; and
a radially outer end of a second electrode strip exposed on only the
second side of the roll capacitor;
wherein the capacitors in the stack are all interconnected in parallel by direct
stacking contact between the exposed ends of the respective electrode strips of each of
the capacitors.
19. A capacitor, comprising:
at least one roll of four adjacent strips comprising first and second electrode
strips alternating with first and second dielectric strips;
wherein each of the dielectric strips is shorter at a radially outer end thereof than
an inwardly adjacent one of the electrode strips effective to expose a radially outer end
of each electrode strip; and
wherein the capacitor is configured to interconnect with other capacitors in a
stack of capacitors by direct contact between the exposed ends of the electrode strips
without need for any conductive tab to extend beyond a footprint of the capacitor.
20. A capacitor according to claim 19, comprising two rolls of the four adjacent
strips;
wherein the two rolls are interconnected in parallel by extending one of the
exposed ends of one of the electrode strips from each of the rolls around the other roll
to an opposite side of the other roll.