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Патент USA US3078343

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Feb. 19, 1963
B. P. KANG
3,078,333
HIGH VOLTAGE POWER CABLE
Filed Dec. 24, 1959
2 Sheets-Sheet 1
FIG. 1
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8,000
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4,000
Legend___
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0 Paper- Polytetrafhoroethylene Laminate
D
:a
Q Paper- Polycarbonate Laminate
7 2,000
g
Paper
0
0
20
40
60
80
I00
I20
Temperature (°c)
INVENTOR
Bun P. Kong
ATTORNEYS
Feb. 19, 1963
B. P. KANG
'
3,078,333
HIGH VOLTAGE POWER CABLE
Filed Dec. 24, 1959
2 Sheets-Sheet 2
I.
‘..'.....""""
INVENTOR
29
29
29
29
Bun R Kong
3,078,333
United States Patent ()??ce
Patented Feb. 1%, i263
2
and
"l
-..
1:
Bun it). at
QAEELE
iulson, NY” assignor to Ana»
consla l"! e
Cable (Iompany, a corporation
Del
aware
Eco. as, was,
are. stasis
ll’. ?laims. (Si. lieu-120)
No matter what wrapping procedure is used, slight helical
?ssures exist between adjacent turns of the tape and pro
vide passages interconnecting successive layers of the
cellulosic paper laminae, thereby permitting easy penetra
tion of the dielectric cable oil throughout the wrapping.
A protective sheath advantageously surrounds the insula
tion.
The laminated dielectric tapes which are suitable for
use in the high voltage power cable of the invention are
This invention relates to electric power cables and,
more particularly, to power cables having a metallic con 10 formed by laminating or bonding a thin ?lm or sheet of
ductor surrounded by insulation which is impregnated
the polymer (polytetralluoroethylene, polypropylene,
with a dielectric cable oil.
polycarbonates, polyethylene, or an interpolymer or co
polymer thereof) over the full width of the tape to a thin
The invention provides an
improved oil-impregnated electric power cable which
may be operated at high voltages and over sustained
periods of time Without risk or danger of the oil-impreg
nated insulation failing due to electrical stress.
Although a large number of synthetic polymers possess
excellent chemical, physical, and electrical properties
which suggest their use as insulating materials for high
voltage power cables carrying relatively large currents,
their use for this purpose has been limited due to the dif
?culties which occur in impregnating sheets or tapes of
the polymer with a dielectric cable oil. Because tapes of
these polymers invariably are quite impervious to the
dielectric ?uid, it is impossible to impregnate a tightly
wound wrapping with cable oil without leaving numerous
small air gaps or cavities which become focal points for
ionization, the ultimate result of which is electrical fail
ure of the cable.
Using a dielectric tape consisting essentially of a thin,
porous sheet of cellulosic paper laminated to a thin, irn~
pervious ?lm or sheet of either polytetrailuoroethylene,
porous sheet of cellulosic paper; or, alternatively, the poly
mer is laminated to the paper over a substantially lOngi~
tudinal central portion of the tape, leaving at least one
narrow marginal edge portion of the paper projecting be
yond the edge of the polymer laminae. As indicated pre
viously, the polymer and paper layers in these laminated
dielectric tapes are either pre~laminated, as by being
chemically bonded together prior to wrapping about the
conductor, or are laminated in the course of forming
the body of insulation about the conductor by wrapping
separately alternate layers of paper and polymer about
the conductor, in which case these layers are held to
gether by mechanical force. The dielectric strength of
the paper-polymer laminated structures is substantially
the same in both cases. As a general rule, the insulating
quality of these laminated tapes is higher than that of
paper alone, so that the maximum working voltage at
which the cable may be operated is correspondingly higher
for a given thickness of insulation than that obtained With
oil impregnated paper-insulated cables of similar design.
polypropylene, polycarbonates, polyethylene, or an inter
To illustrate this rule, Table I sets forth the electrical
polymer or copolymer thereof, in which the cellulosic
paper is either chemically bonded or held by mechanical 35 properties of cellulosic paper as Well as that of several
paper-polymer laminates at various temperatures. In
force to the polymer ?lm, l have found that it is possible
each instance, the dielectric strength of the paper-poly
to completely and thoroughly impregnate a tightly wound
mer laminant is markedly higher than that of the paper
wrapping of this tape with a dielectric cable oil so that
alone. In addition, the dielectric constants of the laminat
no air or other gas bubbles or voids are formed or en
trapped in the wrapping. The cellulosic paper laminae 40 ed tapes are generally close to the dielectric constants of
the common liquid dielectric impregnants (hydrogen ca
apparently furnish capillary paths through which the oil
ble oils), so that the resultant impregnated insulation is
impregnant can penetrate into and ?ll all of the voids in
considerably more electrically homogeneous than oil
the wrapping. By applying the wrapping ta_ es with a
impregnated paper insulation.
negative butt lap, or even with the edges of the tapes
overlapping, so that slight helical ?ssures are created be 45
TABLE I
tween adjacent turns of the tape, each successive layer
Electrical
Properties
of
Cellulosic Paper and Paper-Poly
of the paper laminae will be interconnected by passages
mer Laminates at Various Temperatures
permitting easy penetration of the dielectric cable oil
throughout the wrapping.
Accordingly, a cable of the character contemplated 50
by this invention comprises a metallic conductor sur
Cellulosic
paper
Property
Polytetra?uoro- Polycarbonates
ethylene Iaminated to paper
laminated to
paper
rounded by insulation comprising an oil-permeable helical
Wrapping of a laminated dielectric tape and a dielectric
cable oil impregnated into and ?lling the pores and inter
stices of the wrapping. The dielectric tape consists essen
tially of a thin, porous sheet of cellulosic paper laminated
to an impervious ?lm of a normally solid polymer selected
from the group consisting of polytetra?ucroethylene,
polypropylene, polycarbonates, polyethylene, and inter 60
polymers and copolymers thereof. The dielectric tape
may be a pie-laminated tape formed by chemically bond
ing the polymer to the cellulosic paper prior to Wrapping
85° 0. 100° C. 85° 0. 100° 0. 85° 0. 100° C.
Dielectricconstant“
Power factor
(percent) _______ _.
2. 43
2. 42
2.00
1.99
2. 72
2.73
0.140
0.182
0.107
0.126
0.105
0.155
0.3l0
0. 440
0.214
0.251
0.286
0.422
Loss factor
(percent) _______ ..
Dielectric strength
(Volts/mil at
23° C.) ......... .-
1, 925
2, 608
2, 692
The insulation must be thoroughly impregnated with
the dielectric cable oil without entrapment of any air
about the conductor, or it may be laminated in the course
of forming the body of insulation about the conductor 65 bubbles in the wrapping, for air bubbles are focal points
for ionization and electrical failure of the cable. Vari
by wrapping alternate layers of paper and polymer about
ous types of dielectric cable oils may be employed in the
the conductor. The term “laminate” is used herein to de
power cables of this invention. In general, these di
?ne both types of structures. In either case, the wrapping
electric cable oils are either hydrocarbon oils isolated
tape is preferably applied with a negative butt lap at the
from petroleum distillates, one example of which is the
adjacent edges of polymer laminae, that is, the edges of 70 naphthenic-base mineral oils, or they are prepared from
the polymer are spaced slightly apart from, rather than
synthetic dielectric ?uids, such as the silicone oils or
overlapping, but it may be applied with edges overlapping.
organo~si1icon ?uids. When a hydrocarbon cable oil is
scrapes
used, it may be blended with a purified rosin or with a
nated dielectric tape 8 which forms a continuous con
high molecular weight polymer, such as polyisobutylene,
centric insulating layer about the conductor. Although
a single conductor cable is shown for the purpose of il
but for most purposes the unblended naphthenic-base
lustration in the accompanying drawing, it is undersoood
mineral oils are preferred, since in general they are more
resistant to decomposition and have better dielectric O1 that the invention is equally applicable to a cable having
two or more conductors, each of which may be separately
properties than the blended hydrocarbon oils.
insulated by individual layers of the laminated dielectric
In addition to the hydrocarbon cable oils, particularly
tape.
The tape 8, which is freely permeable to cable oil,
satisfactory results have also been obtained by using a
synthetic silicone fluid, such as the polysiloxanes, poly
silanes, and polysilicate esters, all of which have excel
is formed from a thin porous sheet of cellulosis paper
laminated over the full width of the tape to an impervi
ous sheet or ?lm of polypropylene, the cellulosic paper
lent dielectric properties and, moreover, have virtually no
solvating effect on the polymer layer of the laminated
laminae in this composite tape de?ning a multiplicity of
small oil-permeable channels disposed in the tape wrap
pings into and through which the cable oil may easily
penetrate. To illustrate the construction of the insulat
ing covering 7 in detail, a portion 9 of the exposed cross
dielectric tape. Of these silicone polymers, the ?uid poly
siloxanes in particular may be singled out for special
mention.
Since their dielectric constants are so nearly
identical to the dielectric constants of the polymers from
which the laminated tapes are formed, it is possible to
section of the wrapping is shown on a magni?ed scale.
obtain a polysiloxane-impregnated insulation which is
As shown in the magni?ed portion 9 of the wrapping,
considerably more electrically homogeneous than insu
lation impregnated with other ?uid dielectrics.
20 the tapes 8 are applied with their edges spaced apart so
that gaps or ?ssures 11 always exist ‘between adjacent
To illustrate the use of laminated dielectric tapes to
turns. These ?ssures, in cooperation with the paper
form the insulation of a high-voltage power cable in ac
laminae, permit the cable oil to penetrate from layer to
cordance with the invention, three preferred embodiments
layer through the entire body of the insulation. Since
‘are described below with reference to the accompany
ing drawings, in which:
25 the distance between adjacent paper laminae is small,
a ?lm of the cable oil also penetrates between the face
FIG. 1 shows the plotted curves for the initial insula
to-face surfaces of adjoining turn-s of the tape so that all
tion quality as a function of temperature for cellulosic
paper, laminates of cellulosic paper and a polycarbonate,
voids originally present become ?lled with the dielectric
and laminates of cellulosic paper and polytetra?uoro~
?uid. As a result, after the helical wrapping is thor
ethylene;
30 oughly impregnated with the cable oil, the insulation
FIG. 2 is an isometric view of a single-conductor
power cable in which the conductor is covered by a solid
layer comprising an oil-permeable wrapping of a tape
consisting essentially of cellulosic paper laminated to
surrounding the conductor becomes a mass of solid di
electric tape and impregnant which is substantially com
pletely free of voids.
The helically wrapped tape is impregnated through
polypropylene and a dielectric cable oil impregnated 35 out with a dimethylpolysiloxane liquid having a viscos
throughout the wrapping, a portion of the exposed cross
section of the wrapping being magni?ed to show its con
struction in detail;
FIG. 3 is a schematic view illustrating the manufac—
ture of a roll of tape comprising laminated layers of
cellulosic paper and polypropylene;
FIG. 4 is a cross-section showing schematically two
successive layers of a helical wrapping of tape formed
by laminating an impervious ?lm of polypropylene over
the full width of the tape to a thin, porous sheet of
cellulosic paper, the wrapping being applied with the 45
edges of the tapes overlapping each other; and
ity, at 25° C. in the range from 0.6 to 30,000 centi
stokes and a dielectric constant in the range from 2.2 to
2.8. The wrapped conductor is ?rst placed in an im
pregnating tank and dried under vacuum at a tempera
ture in the range between 100° C. and 130° C. After
the conductor has been thoroughly dried, the impregnat
ing liquid (polysiloxane or any other liquid dielectric
impregnant) is gradually introduced into the tank while
still under vacuum until the liquid level is at least 6
inches above the wrapped conductor, after which the
tank is alternatively subjected to vacuum and pressure
cycles until all residual air is completely removed and
FIG. 5 is a cross-section showing schematically two
the impregnating liquid saturates all voids and interstices
successive layers of a helical wrapping of tape applied
in the porous wrapping. Thereafter, a protective sheath
with a butt lap, the tape comprising an impervious ?lm 50 12 is applied about the polysiloxane-impregnated wrap
of polypropylene laminated to a thin, porous sheet of
ping throughout substantially the entire length of the
cellulosic paper over a substantially longitudinal central
cable.
portion of the tape so that narrow marginal edge por
To form a laminated dielectric tape suitable for use
tions of the paper project beyond the edge of the poly
in the high voltage power cable of the invention, an im
propylene laminae.
55 pervious sheet or ?lm of the polymer (polytetrafluorm
The curves depicted in FIG. 1 show the relationship
ethylene, polypropylene, polycarbonates, polyethylene,
of the service (or insulating) quality of cellulosic paper,
or any interpolymer or copolymer thereof) is laminated
laminates of cellulosic paper and a polycarbonate, and
or bonded over the full width of the tape or, alternative
laminates of cellulosic paper and polytetra?uoroethylene
ly, over a substantially longitudinal central portion of
as a function of temperature, the service quality of in
60 the tape to a thin, porous sheet of cellulosic paper. In
sulation being directly related to its dielectric strength
the latter instance, the laminated tape is left with at least
and inversely related to its loss factor. Analysis of these
one narrow marginal edge portion of the paper project
curves illustrates the general rule that the service quality
ing beyond the edge of the polymer laminae. As sche
of a paper~polymer laminated dielectric tape is invariably
matically illustrated in FIG. 3, the tape is formed by
higher than that of the paper alone. Thus, the service
bonding together two separate tapes 13 and 14- shown
quality of a laminate of polytetra?uoroethylene and
issuing from corresponding supply rolls 15 and 16. One
cellulosic paper is 2.46 times that of the paper alone,
of the tapes 13 is a thin, narrow, porous strip of cellu
while the service quality of a laminate of cellulosic paper
losic paper, while the other tape 14 is a sheet or ?lm of
and a polycarbonate is 1.46 times that of paper, demon
polypropylene Which is impervious to the dielectric cable
strating the unique advantages of using a paper-polymer 70 oil. The polypropylene tape 14 is drawn from roll 16
laminate in a high voltage electric power cable.
The cable shown in FIG. 2 is a single-conductor
cable having a central stranded conductor 6 surrounded
throughout its entire length by an oil-permeable cover
over a guide roller 17 and converges with the paper
tape 13, which is drawn over a corresponding guide roll
er 18, between a pair of rollers 19 and 20. Sufficient
heat and pressure are applied by these latter rollers to
ing '7 composed of many layers of helically wrapped lami 75 bond the two tapes 13 and 14 into a composite laminated
5
@
tape 21 without seriously impairing the permeability of
thin porous sheet of cellulosic paper laminated over the
full width of the tape to an impervious iilrn of a normally
the porous (paper) component 13. For convenience, the
composite laminated tape 21 is wound into a roll 22.
solid polymer of the group consisting of poiytetra?uoro
ethylene, polypropylene, polycarbonates, polyethylene, and
A multiplicity of layers of the laminated tape 21, the
manufacture of which is schematically illustrated in FIG.
interpolymers and copolymers thereof, the wrapping hav
ing slight helical ?ssures existing therein between ad
3, are hclically wrapped about a conductor to form an
insulating covering thereon of the character shown in
jacent turns of the tape providing passages between suc
cessive layers of the cellulosic paper laminae and thereby
permitting easy penetration of the cable oil throughout the
FIGS. 4 and 5, both of which show in schematic fashion
two successive layers of the helical wrapping. In FIG.
4, the composite tape, which consists of an impervious 10 wrapping.
3. A high voltage electric power cable comprising a
metallic conductor surrounded by insulation comprising
an oil-permeable helical wrapping of a composite lami
24, is applied with its edges overlapping so that slight
?lm of polypropylene 23 laminated over the full width
of the tape to a thin, porous sheet of cellulosic paper
nated dielectric tape and a dielectric cable oil impregnated
helical ?ssures or gaps 25 are created between adjacent
turns of the tape, thereby interconnecting each succes 15 into and ?lling the pores and interstices of the wrapping,
in which the composite dielectric tape is a thin impervious
sive layer of the paper laminae 24 by passages permit
layer or" polytetra?uoroethylene laminated to a thin porous
ting easy penetration of the dielectric cable oil through
the wrapping.
sheet of cellulosic paper over the full width of the tape,
the wrapping having slight helical ?ssures existing therein
FIG. 5 illustrates a helical wrapping in which the com
posite tape consists of a ?lm of polypropylene 26 lam 20 etween adjacent turns of the tape providing passages be
tween successive layers of the cellulosic paper laminae
inated or bonded to a thin, porous sheet of cellulosic
and thereby ermitting easy penetration of the cable oil
paper 27 leaving narrow marginal edge portions 28 of
the paper projecting beyond the edge of the polypropyl
ene laminae 26. This tape is helically applied to the
throughout the wrapping.
4. A high voltage electric power cable comprising a
conductor with a ‘butt lap (as shown) or with a nega 25 metallic conductor surrounded by insulation comprising
an oil-permeable helical wrapping of a composite lami~
tive butt lap so ‘that its edges abut or are spaced slightly
'nated dielectric tape and a dielectric cable oil impregnated
apart from the adjoining turns to form a gap between
into and ?lling the pores and interstices of the wrapping,
them. Gaps 29, which occur between adjacent edges of
in which the composite dielectric tape is a thin impervious
the polypropylene laminae in successive turns of the
layer of polypropylene laminated to a thin porous sheet of
wrapping, in cooperation with the porous paper laminae
cellulosic paper over the full width of the tape, the wrap
2-7, permit the dielectric cable oil to penetrate from lay
ping having slight helical ?ssures existing therein between
er to layer through the entire body of the insulation.
adjacent turns of the tapes providing passages between
in the foregoing embodiments of the invention par
successive layers of the cellulosic paper laminae and there
ticular reference has been made to the use of dimethyl
polysiloxane ?uid to impregnate the helical wrappings
35 by permitting easy penetration of the cable oil through
out the wrapping.
5. A high voltage electric power cable comprising a
metallic conductor surrounded by insulation comprising
of laminated tape surrounding the metallic conductor.
Various other dielectric cable oils, such as the hydrocar~
bon cable oils, or various other ?uid organosilicon poly
mers, such as the phenylmethylpolysiloxanes, the di~
an oil-permeable helical wrapping of a composite lami
phenylpolysiloxanes, the polysilanes, or even the poly 40 nated dielectric tape and a dielectric cable oil impregnated
into and ?lling the pores and interstices of the wrapping,
silicate esters, may also be employed as the ?uid impreg
in which the composite dielectric tape is a thin impervious
nant in place of (or, in some cases, in admixture with)
layer of a polycarbonate laminated to a thin porous sheet
these dimethylpolysiloxanes.
of cellulosic paper over the full width of the tape, the
Although a single conductor power cable has been
wrapping having siight helical ?ssures existing therein be
45
illustrated, the new cable of the invention may have
tween adjacent turns of the tape providing passages be
three, or any other desired number, conductors. More
tween successive layers of the cellulosic paper laminae
over, the cable structure may contain one or more elec
and thereby permitting easy penetration of the cable oil
trostatic shields as well as various other cable elements
which are neither shown nor described above, and may
be either a fluid-?lled, gas-?lled, or gas-pressure type of
throughout the wrapping.
6. A high voltage electric power cable comprising a
metallic conductor surrounded by insulation comprising
power cable rather than the relatively simple solid type
of power cable illustrated in the drawings.
1 claim:
1. A high voltage electric power cable comprising a ,
metaliic conductor surrounded by insulation comprising
an oil-permeable heiical wrapping of a composite lami
nated dielectric tape and a dielectric cable oil impregnated
into and biting the pores and interstices of the Wrapping,
the composite dielectric tape consisting essentially of a
thin porous sheet of cellulosic paper laminated to an im
an oil-permeable heiical wrapping of a composite lami
nated dielectric tape and a dielectric cabie oil impregnated
into and ?llinr7 the pores and interstices of the wrapping,
in which the composite dielectric tape is a thin impervious
layer of polyethyiene laminated to a thin porous sheet of
cellulosic paper over the full width of the tape, the wrap
ping having slight helical iissures existing therein between
adjacent turns of the tape providing passages between
60 successive layers of the cellulosic paper laminae and there
pervious film of a normally solid polymer of the group
consisting of polytetra?uoroethylene, polypropylene, poly~
carbonates, polyethylene, and intcrpolymers and copoiy
mers thereof, the wrapping having slight heiical ?ssures
existing therein between adjacent turns of the tape pro
viding passages between successive layers of the cellulosic
paper laminae and thereby permitting easy penetration of
the cable oil throughout the Wrapping.
2. A high voltage electric power cable comprising a
metallic conductor surrounded by insulation comprising
an oil-permeable helical wrapping of a composite lami
nated dielectric tape and a dielectric cable oil impregnated
into and ?lling the pores and interstices of the wrapping,
the composite dielectric tape consisting essentially of a 75
by permitting easy penetration of the cable oil through
out the wrapping.
7. A high voltage electric power cable comprising a
metallic conductor surrounded by insulation comprising
an oil-permeable helical Wrapping of a composite lami
nated dielectric tape and a dielectric cable oil impregnated
into and filling the pores and interstices of the wrapping,
the composite dieiectric tape consisting essentially of an
impervious film of a normally soiid polymer of the group
consisting of polytetraiiuoroethylene, polypropylene, poly
carbonates, polyethylene, and interpoiymers and copoly~
mers thereof, laminated over a substantially longitudinal
central portion of the tape to a thin porous layer of colic
losic paper, at least one marginal edge portion of the
paper layer projecting beyond the edge of the polymer
8,078,383
7
8
lamina, whereby the wrapping is formed with slight helical
wrapping, the composite dielectric tape consisting essen
?ssures existing therein between adjacent turns of the
polymer laminae providing passages between successive
layers of the cellulosic paper laminae and thereby per
over a substantially longitudinal central portion of the
tape to a thin porous layer of cellulosic paper, at least
mitting easy penetration of the cable oil throughout the
wrapping.
tially of an impervious ?lm of a polycarbonate laminated
one marginal edge portion of the paper layer projecting
beyond the edge of the polycarbonate laminae, whereby
the wrapping is formed with slight helical ?ssures existing
8. A high voltage electric power cable comprising a
therein between adjacent turns of the polycarbonate
metallic conductor surrounded by insulation comprising
laminae providing passages between successive layers of
an oil-permeable helical wrapping of a composite lami
nated dielectric tape and a dielectric cable oil impregnated 10 the cellulosic paper laminae and thereby permitting easy
penetration of the cable oil throughout the wrapping.
into and ?lling the pores and interstices of the wrapping,
11. A high voltage electric power cable comprising
the composite dielectric tape consisting essentially of an
a metallic conductor surrounded by insulation compris
impervious ?lm of polytetra?uoroethylene laminated over
ing an oil-permeable helical wrapping of a composite
a substantially longitudinal central portion of the tape
to a thin porous layer of cellulosic paper, at least one 15 laminated dielectric tape and a dielectric cable oil ini
pregnated into and ?lling the pores and interstices of the
marginal portion of the paper layer projecting beyond the
wrapping, the composite dielectric tape consisting essen
edge of the polytetra?uoroethylene lamina, whereby the
tially of an impervious ?lm of polyetheylene laminated
wrapping is formed with slight helical ?ssures existing
over a substantially longitudinal central portion of the
therein between adjacent turns of the polytetra?uoro
tape to a thin porous layer of cellulosic paper, at least
ethylene laminae providing passages between successive
one marginal edge portion of the paper layer projecting
layers of the cellulosic paper laminae and thereby per
beyond the edge of the polyethylene laminae, whereby
mitting easy penetration of the cable oil throughout the
the wrapping is formed with slight helical ?ssures exist~
wrapping.
9. A high Voltage electric power cable comprising a
ing therein between adjacent turns of the polyethylene
metallic conductor surrounded by insulation comprising
laminae providing passages between successive layers of
an oil-permeable helical wrapping of a composite lam
the cellulosic paper laminae and thereby permitting easy
inated dielectric tape and a dielectric cable oil impreg
penetration of the cable oil throughout the wrapping.
nated into and ?lling the pores and interstices of the
References Cited in the ?le of this patent
wrapping, the composite dielectric tape consisting essen
tially of an impervious ?lm of polypropylene laminated 30
UNITED STATES PATENTS
over a substantially longitudinal central portion of the
tape to a thin porous layer of cellulosic paper, at least
one marginal edge portion of the paper layer projecting
beyond the edge of the polypropylene lamina, whereby
the Wrapping is formed with slight helical ?ssures exist 35
ing therein between adjacent turns of the polypropylene
lamina providing passages between successive layers of
the cellulosic paper laminae and thereby permitting easy
penetration of the cable oil throughout the wrapping.
10. A high voltage electric power cable comprising
a metallic conductor surrounded by insulation compris
ing an oil-permeable helical wrapping of a composite
laminated dielectric tape and a dielectric cable oil im
pregnated into and ?lling the pores and interstices of the
2,135,315
2,309,992
Walters et al ___________ __ Nov. 1, 1938
Scott et a1 _____________ __ Feb. 2, 1943
2,314,694
2,320,922
2,454,625
Dodds ______________ __ Mar. 23, 1943
Ford ________________ __ June 1, 1943
Bondon ____________ __ Nov. 23, 1948
2,650,261
Davey ______________ __ Aug. 25, 1953
355,291
Great Britain _________ __ Aug. 21, 1931
439,345
456,139
553,596
Great Britain __________ __ Dec. 4, 1935
Canada ______________ __ Apr. 26, 1949
FOREIGN PATENTS
773,563
Italy ________________ __ Dec. 28, 1956
Great Britain ________ __ Apr. 24, 1957
UNITED STATES PATENT OFFICE
CERTIFICATE OF CORRECTION
Patent No, 3,078,333
February 19, 1963
Bun Pu Kang
It is hereby certified that error appears in the above numbered pat
ent requiring correction and that the said Letters Patent should read as
corrected below.
1 _
Column 4,
line 3,
for "purpose" read -—— purposes ——;
True 10, for "cellulosis" read —— cellulosic ~—; column 6,
llne 33,
for "tapes" read H tape ——n
Signed and sealed this 8th day of October 1963:,
(SEAL)
Attcst:
ERNEST W. SWIDER
Attesting Officer
Ac Ling
‘Conunissioner of .‘?uéente
UNITED STATES PATENT OFFICE
CERTIFICATE OF CORRECTION
Patent N00 3,078,333
February 19, 1963
Bun PD Kang
that error appears in the above numbered pat
It is hereby certified
Patent should read as
ent requiring correction and that the said ‘Letters
corrected below.
I
Column 4,
‘
line 3,
for "purpose" read —— purposes --;
line 10, for "cellulosis" read —— cellulosic —-; column 6,
line 33,
for "tapes" read »* tape ——n
Signed and sealed this 8th day of October 1963a
(SEAL)
Attest:
ERNEST W. SWIDER
Attesting Officer
Ac L i ‘m;
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