U.S. patent number 3,699,410 [Application Number 05/207,884] was granted by the patent office on 1972-10-17 for self-healing electrical condenser.
This patent grant is currently assigned to Robert Bosch GmbH. Invention is credited to Herbert Forster, Josef Juhasz, Helmut Maylandt.
United States Patent |
3,699,410 |
Maylandt , et al. |
October 17, 1972 |
SELF-HEALING ELECTRICAL CONDENSER
Abstract
A first and at least two second electrodes are provided, with
the latter flanking the former. First dielectric separating means
is provided between the first electrodes and one of the second
electrodes and has n paper strips and m synthetic plastic strips
with n being a whole number excluding zero and one, and m being a
whole number including zero and one, and with n being greater than
m. Second dielectric separating means is provided between the first
electrode and the other of the second electrodes and comprises N
plastic strips and M paper strips with N being a whole number
including one, M being a whole number including zero and N being
greater than M. The electrodes are each applied to one side of two
paper strips and the latter have uncovered sides facing one
another, with the first and second dielectric separating means
being electrically connected in parallel with each other.
Inventors: |
Maylandt; Helmut (Plochingen,
DT), Forster; Herbert (Grunbach, DT),
Juhasz; Josef (Stuttgart, DT) |
Assignee: |
Robert Bosch GmbH (Stuttgart,
DT)
|
Family
ID: |
22772382 |
Appl.
No.: |
05/207,884 |
Filed: |
December 14, 1971 |
Current U.S.
Class: |
361/273; 361/313;
361/304; 361/314 |
Current CPC
Class: |
H01G
4/015 (20130101) |
Current International
Class: |
H01g
003/215 () |
Field of
Search: |
;317/258,260 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Goldberg; E. A.
Claims
What is claimed as new and desired to be secured by Letters Patent
is set forth in the appended claims:
1. A self-healing electrical condenser, comprising at least one
first electrode; at least two second electrodes flanking said first
electrode; first dielectric separating means between said first
electrode and one of said second electrodes, said first separating
means comprising n paper strips and m synthetic plastic strips
wherein n is a whole number excluding zero and one, and m is a
whole number including zero and one, with n> m; and second
dielectric separating means between said first electrode and the
other of said second electrodes, said second separating means
comprising N plastic strips and M paper strips wherein N is a whole
number including one, M is a whole number including zero, with
N>M, said electrodes each being applied to one side of two paper
strips and the latter having uncovered sides which face each other,
and said first and second dielectric separating means being
electrically connected in parallel with each other.
2. A condenser as defined in claim 1, wherein said electrodes are
metallic coatings.
3. A condenser as defined in claim 1, wherein said first dielectric
separating means comprises two overlying paper strips having sides
facing away from each other, said electrodes being applied to said
sides, and an additional paper strip sandwiched between said two
paper strips; and wherein said second dielectric separating means
comprises a plastic strip sandwiched between said first and said
other of said second electrodes.
4. A condenser as defined in claim 1, wherein said first dielectric
separating means comprises two overlying paper strips having sides
facing away from each other, said electrodes being applied to said
sides; and wherein said second dielectric separating means
comprises a plastic strip sandwiched between said first and said
other of said second electrodes.
5. A condenser as defined in claim 1, wherein said first dielectric
separating means comprises two overlying paper strips having sides
facing away from each other, said electrodes being applied to said
sides, and a plastic strip sandwiched between said paper strips;
and wherein said second dielectric separating means comprises two
overlying plastic strips having sides facing away from each other
and respectively contacting said first electrode and said other
second electrode, and a paper strip sandwiched between said plastic
strips.
6. A condenser as defined in claim 1, wherein said plastic strips
are of polycarbonate.
7. A condenser as defined in claim 1, wherein said plastic strips
are of polypropylene.
8. A condenser as defined in claim 1, wherein said plastic strips
are of polysulfone.
Description
BACKGROUND OF THE INVENTION
The present invention relates generally to electrical condensers
and more particularly to self-healing electrical condensers.
Self-healing condensers are already well known in the art and are
not believed to require any detailed explanatory discussions. Among
these it is known to provide a construction having a paper strip
which carries a metallic coating as an electrode, with a synthetic
plastic layer being juxtaposed with the paper strip at the side
remote from the electrode and with another electrode being applied
to the exposed side of the synthetic plastic strip. Between two
electrodes of opposite sign there are thus interposed the paper
strip and the plastic strip.
Another known construction utilizes two electrodes of opposite sign
between which there are dielectric of polyethylene-terephthalate,
or of a laminate of such material with paper. In addition, there is
a further undefined laminate of paper and
polyethylene-terephthalate provided, and the construction may vary
depending on whether the electrodes are applied to the exposed
surfaces of papers or polyethylene-terephthalate strips.
Other constructions are also known but they share with the
aforementioned ones the characteristic that the sequence and
arrangement of paper and plastic strips is selected irrespective of
the strongly different dielectric characteristics of these
materials. Evidently, this is not satisfactory and further
improvements are therefore desirable and have been sought in the
art.
SUMMARY OF THE INVENTION
It is, accordingly, a general object of the invention to provide
such improvements.
More particularly it is an object of the present invention to
provide an improved self-healing electrical condenser which has
incorporated the aforementioned desirable improvements.
In pursuance of these and other objects which will become apparent
hereafter, one feature of the invention resides in a self-healing
electrical condenser which, briefly stated, comprises at least one
first electrode, at least two second electrodes flanking the first
electrode, and first and second dielectric separating means.
According to the invention the first separating means is between
the first electrode and one of the second electrodes and comprises
n paper strips and m synthetic plastic strips wherein n is a whole
number excluding zero and one, and m is a whole number including
zero and one, with n being greater than m. Furthermore, the second
dielectric separating means is located between the first electrode
and the other of the second electrodes and comprises N plastic
strips and M paper strips wherein N is a whole number including
one, M is a whole number including zero, with N>M, said
electrodes being each applied to one side of two of said paper
strips and the latter having uncovered sides which face one
another, and said first and second dielectric separating means
being electrically connected in parallel with each other.
An electrical condenser constructed in accordance with the present
invention provides for a fuller and more effective utilization of
the advantages to be obtained from a composite use of paper strips
and synthetic plastic strips as the dielectric of the condenser. In
such a construction the number of paper strips between the
electrodes is always greater at one side than the number of
synthetic plastic strips, whereas at the other side the number of
synthetic plastic strips is always greater than the number of paper
strips, meaning that at the one side there is predominantly paper
and that at the other side there is predominantly synthetic plastic
material. The advantage obtained in this manner resides in the fact
that the novel self-healing electrical condenser has the electrodes
provided exclusively on paper strips, with no electrodes being
provided on the synthetic plastic strips and in that the exposed
sides of the electrodes are under all circumstances contacted by
the plastic strips.
In this connection it is important to take into consideration that
it is considerably less expensive to deposit the electrodes--as by
vapor deposition-- on paper strips than on synthetic plastic
strips. The vapor deposition of the metallic material of the
electrodes on the paper strips can be carried out more rapidly than
would be possible on synthetic plastic, the metallic material will
adhere better. There is further a lesser incidence of rejects. In
fact, the deposition of metallic material (to form electrodes) on
synthetic plastic strips is considerably more difficult than on
paper strips and in some instances cannot even be carried out to
the necessary thickness required for the electrodes.
A further advantage of the construction according to the present
invention is inherent in the contact of the plastic strips to the
metal-coated paper strips, because the gap width between the strips
is very small so that after self healing breakdowns a high
potential can be reached before the danger of corona discharge
occurs.
It should be recalled here that the gap widths are determined by
the roughness of the surfaces which contact one another. When paper
strips surfaces contact one another the gap width is equal to twice
the so-called "rough depth" of the contacting surfaces, with the
term "rough depth" referring to the distance between the highest
and lowest points of the paper strip surface. On the other hand,
the gap width between contacting paper and synthetic plastic
surfaces (in the condenser according to the present invention) is
smaller than the single "rough depth" of the paper surface because
the synthetic plastic material has a very smooth surface and
additionally has a tendency to swell under the influence of
impregnating media so that it at least partially fills any
depressions in the surface of the paper strip which it
contacts.
The invention also provides for optimum utilization of paper and
synthetic plastic material in accordance with their voltage
resistance and/or provides for optimum permissible operating field
strength by correct choice of the strip thicknesses. If, for
instance, in a specific application one side of a condenser is
composed of two metallized paper strips having a thickness of 12
microns, with between them a polycarbonate strip having a thickness
of 15 microns, and if the other side of the condenser is composed
of two polycarbonate strips having a thickness of 8 microns and
between them a paper strip having a thickness of also eight
microns, then a condenser or capacitor so constructed and
subsequently impregnated with mineral oil will have in its
rolled-up dielectric components a specific volume of 28 cm.sup.3
/.mu.F. Of course, this exemplary condenser according to the
present invention is constructed asymmetrically with respect to its
dielectrics, as are all ones according to the present invention.
If, however, the dielectric were arranged in accordance with the
prior art as a symmetric mixed dielectric, meaning that at each
side of the electrodes there were provided two paper strips having
a thickness of 12 microns and intermediate them a synthetic plastic
strip having a thickness of 15 microns and for instance consisting
of polycarbonate, then a corresponding volume of 41 cm.sup.3 /.mu.F
would be obtained. It is readily evident therefore that the volume
of the condenser constructed according to the present invention is
approximately 32 percent smaller than that of a similar condenser
constructed in accordance with the prior art. In addition, the
condenser according to the present invention has lower dielectric
losses because on the side in which the dielectric is predominantly
composed of synthetic plastic strips are smaller than the losses at
the other side.
The novel features which are considered as characteristic for the
invention are set forth in particular in the appended claims.
The invention itself, however, both as to its construction and its
method of operation, together with additional objects and
advantages thereof, will best be understood from the following
description of specific embodiments when read in connection with
the accompanying drawing.
BRIEF DESCRIPTION OF THE DRAWING
FIG. 1 is an axial section through a rolled self-healing condenser
according to one embodiment of the invention;
FIG. 2 is a view similar to FIG. 1 but of a further embodiment of
the invention; and
FIG. 3 is a view similar to FIG. 1 but of still another embodiment
of the invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Discussing now the drawing in detail, and firstly the embodiment
illustrated in FIG. 1, it will be seen that this Figure illustrates
a self-sealing condenser according to the present invention having
three dielectric strips, a synthetic plastic strip and two paper
strips each of which latter carries on one exposed side a electrode
which is provided by metallic vapor deposition and whose uncoated
sides contact one another. As pointed out earlier, this condenser
thus has the electrodes provided exclusively on paper strips.
FIG. 1 shows that there is provided one first electrode 15 and a
second electrode 14 which, when the assembled strips are rolled up
to the configuration of FIG. 1, actually constitutes with its
different portions two second electrodes 14 which flank (are
located at opposite sides of) the electrode 15 as illustrated. The
electrodes 14 and 15 are provided on one side each of two paper
strips 16 and 17, as by vapor deposition. The non-coated or
metallized sides of the paper strips 16 and 17 contact one another,
a construction which is particularly advantageous if the condenser
is to be used for higher winding potential and to be particularly
resistant.
Located between the exposed side of the electrode 15 and that
portion of the electrode 14 which will face the exposed side of the
electrode 15 when the assembly is rolled up to the configuration of
FIG. 1, is a strip of synthetic plastic material, identified with
reference numeral 18. In this embodiment, as in the others to be
discussed, it should be understood that various different synthetic
plastics well known to those skilled in the art are suitable. This
includes in particular low-loss synthetic plastic foils which may
be made of polycarbonate, polypropylene, polyphenylene oxide,
polytetrafluoroethylene, polysulfone and other plastics.
It is quite evident that at one side of the condenser of FIG. 1,
that is at one side of the electrode 15, the number n of paper
strips 16 and 17 is greater than the number m of plastic strips 18,
namely in the illustrated embodiment there are at this side no
synthetic plastic strips at all. On the other hand, on the other
side of the electrode 15, between it and the facing portion of the
electrode 14, the number N of plastic strips 18 is greater than the
number M of paper strips, namely in the illustrated embodiment
there are at the side no paper strips at all.
If the condenser according to the present invention is constructed
with a synthetic plastic material having particularly high
potential resistance, then it may be advantageous to so construct
the condenser that the paper component of the dielectric is not in
form of two layers or strips but is in the form of three layers.
FIG. 2 shows such an embodiment in which there are provided two
paper strips 21 and 22 analogous to the strips 16 and 17 of FIG. 2
and each carrying at an exposed side one of the vapor-deposited
electrodes 19 and 20. Located between the juxtaposed non-coated
surfaces of the paper strips 21 and 22 is a further non-coated
paper strip 23. This assembly is then rolled up to the
configuration of FIG. 2, with again a synthetic plastic strip 24
being provided which is located between the exposed side of the
electrode 20 and that portion of the electrode 19 which on rolling
up will become juxtaposed with the exposed side of the electrode
20.
FIG. 3 shows an embodiment of a condenser which is suitable if
still higher voltages are to be utilized than are permissible in
the embodiments of FIGS. 1 and 2. In this case there are provided
two paper strips 27 and 28 analogous to the strips 21 and 22 of
FIG. 2 and each provided on an exposed side with one of the
electrodes 25 and 26 which is vapor-deposited thereon. The
non-coated surfaces of the paper strips 28 and 27 face one another
and juxtaposed with them and sandwiched between them is a synthetic
plastic strip 29. When this assembly is rolled up so that again a
portion of the electrode 25 will face the exposed side of the
electrode 26, there will be located between this exposed side of
the electrode 26 and the aforementioned portion of the electrode 25
a dielectric component composed of two synthetic plastic strips 30
and 31 one of which is in contact with the exposed side of the
electrode 26 and the other of which is in contact with the exposed
side of the portion of the electrode 25 which is juxtaposed with
the electrode 26. Located between these plastic strips 30 and 31
and sandwiched between them is a paper strip 32.
If the novel condensers are to be used with alternating potential,
they are saturated with an auxiliary liquid dielectric, for
instance mineral oil. In such an embodiment the lowest increase of
the loss factor and the highest potential resistance before the
beginning of corona discharge and breakdown is obtained when the
gap for the saturating liquid (adjacent one of the electrodes) has
intermediate the electrode and the adjacent strip contacting the
electrode the smallest possible extension in the direction of the
electric field. This inhibits the movement of charge carriers and
prevents the formation of damaging gas bubbles at the electrodes.
The requirements for affording these characteristics exist in the
novel condensers to an almost ideal extent, because the electrodes
are always firmly adhered to two different paper strips so that the
formation of gas bubbles between the electrodes and the paper
strips carrying them is reliably precluded.
It will also be evident that the exposed surfaces of the electrodes
which are deposited on the respective paper strips will under all
circumstances bound one side of a gap which is filled with the
liquid saturation dielectric and whose width or depth is dependent
upon the roughness of the paper strip surface, with the other side
of the gap being delimited and bounded by a synthetic plastic
strip, that is the strip 18, 24, 30 or 31. Because of this the
width of this gap is narrower than a gap which would exist between
two juxtaposed paper strip surfaces, for the reasons discussed
earlier.
The width of this gap can be still further reduced, and any
depressions or roughnesses in the surface of the paper strip be at
least partly filled, if synthetic plastic material is used for the
plastic strips which swells during saturation with the liquid
dielectric and thus at least in part fills these depressions. Such
synthetic plastics may be given the swelling characteristic by
preliminary heat treatment which in each case will depend upon the
synthetic plastic material utilized. For instance if an electrical
condenser according to the present invention utilizes synthetic
plastic strip or strips of low-swelling polycarbonate, it is
advantageous to impregnate them (after the usual vacuum-drying
process) with mineral oil at temperatures of between 90.degree. and
130.degree.C, and of course it is understood that dielectric other
than mineral oil can be utilized for this purpose in accordance
with the teachings of the prior art. Subsequently, the thus
impregnated condenser is maintained at the above temperature range
for several hours before it is cooled off. On the other hand, if
the condenser utilizes plastic strips of for instance
polypropylene, which has a higher swelling tendency, then the
condenser may for instance be dried in vacuum at temperatures of
90.degree.- 130.degree.C, and may subsequently be cooled down to
temperatures of between 60.degree. and 90.degree.C to be
impregnated with a liquid dielectric whose temperature may be below
the temperature of the condenser itself. Only when the dielectric
has entered into the condenser winding or roll, will the condenser
then be maintained at the temperature of impregnation or at a
higher temperature for some hours before it is subjected to cooling
or is permitted to cool.
It will be understood that each of the elements described above, or
two or more together may also find a useful application in other
types of constructions differing from the types described
above.
While the invention has been illustrated and described as embodied
in a self-healing electrical condenser, it is not intended to be
limited to the details shown, since various modifications and
structural changes may be made without departing in any way from
the spirit of the present invention.
Without further analysis, the foregoing will so fully reveal the
gist of the present invention that others can by applying current
knowledge readily adapt it for various applications without
omitting features that from the standpoint of prior art fairly
constitute essential characteristics of the generic or specific
aspects of this invention and, therefore, such adaptations should
and are intended to be comprehended within the meaning and range of
equivalence of the following claims.
* * * * *