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§24, i943»
A. c. @CHW/«GER
Filed Dec. 2l, 1942
. $911.
.Año.. `
Patented Dec. 24, 1946
lAugust C. Schwager, Miilbrae, Calif., assignor to
Pacific Electric Manufacturing Corporation,
San Francisco, Calif., a corporation of Cali-forni
Application December 21, 1942, Serial Nia-469,613
5 Claims. (Cl. 175-358)
My present invention relates t0 high potential
current transformer means, and more particu
larly to an improved current transformer and
system for use in connection with the operation
of control apparatus responsive to current con
1tìitions upon a high potential power transmission
An object of the invention is to provide a cur
rent transformer of new and novel design for
high potential heavy current power transmissionl
lines which will be practical, efficient and more
economical to manufacture than would be a com
parable current
transformer for use under the
same conditions of operation.
Another object of the invention is to provide
a new and novel current transformer of small
size and simple construction in which an evac
uated spacing between the primary and secondary
windings is relied upon as a means to insulate the
to developments in the so-called “minimum oil”
circuit breakers and “air blast” circuit breakers
which have their operating and circuit interrupt
ing elements mounted and operating in the zone
of high potential, the aforementioned insulating
bushings have become unnecessary. Therefore, a
different form of current transformer must be
provided to meet this condition. Due to the
high voltages involved, the cost of an independent
transformer makes its use almost prohibitive, as
such a transformer must still be provided with
a large insulating bushing and an oil containing
' tank for its windings. For exampl
lthe primar-y
current of these transformers is generally some
where in the neighborhood of 600 amperes and,
therefore, heavy conductors of approximately one
square inch of cross-section must be used for the
primary winding. ` The secondary winding of
these transformers is usually designed for ap
operates at a substantially lower 20 proximately five amperes and, consequently, av
very small wire can be used for this winding.
and safe voltage at ground potential.
However, in order to prevent electrical break
Another object of the invention is to provide
down between Vthe primary winding and the core
a current transformer that is particularly well
and the secondary winding of -such a transformer,
adapted for use in connection with the so-called
“minimum oil" and "air blast” types of high 25 a large insulating space must be provided, and
while this spacing is somewhat reduced when
voltage circuit interrupter which operate in a
an oil or other insulating medium is used, the
zone of high potential and consequently do not
distance between theprimary winding and the
require the conventional insulating ` bushings
core >must still remain relatively large in order to
within which the current transformers of former
high potential primary winding from a secondary
design were customarily mounted.
30 insure sufficient safety. This distance must be
somewhere in the neighborhood of ten inches on
Another object of the invention is to provide a
a 115,000 volt circuit.
transformer system for effecting an insulated
It has also been recognized that air under
current responsive control connection between a
high pressure breaks down under electrical stress
high potential power transmission line and a con
trol circuit in which a current condition respon~ 35 less easily than air at atmospheric pressure, and
recently, as a solution to the above problem, it
sive to current conditions upon the high poten
has been proposed to insulate the core and wind
tial transmission line is inductively transmitted
ings of a transformer by placing them in a, suit~
through an insulating vacuum to a control circuit
able container under high air pressure. 'I'his
operating at a. safe grounded potential.
-In the art to which the invention relates, cur 40 will reduce the required spacing or clearance dis
tance between the primary and secondary wind
rent transformers are relied upon to provide a
and the core of the transformer. While
measure of the current flowing in a. high voltage
these transformers have the advantage that they
alternating current system and/or to provide a
avoid the fire hazard inherent in the use of an
source of current for a system of control having
inflammable insulating oil, they still have the dis
relays and other instruments operating at a con
advantage that extra precautions must be taken
siderably lower potential.. In the past, where
to insure that the high air pressure surrounding
these current transformers have been associated
the windings of the transformer is maintained
at all times.
with extremely high voltage circuits, it has been
the custom to mount the current transformer in
In accordance with the present invention and
the insulating bushingsy generally provided with 50 as distinguished from the above prior art prac
the terminals of circuit breakers and like appa
ratus to insulate the apparatus operating at
ground potential from the high potential circuit.
However, due to recent trends, and particularly
tices, I propose to seal the entire transformer unit
Within a glass or other form of envelope from
which the air is completely exhausted and use a
high vacuum as the insulating medium between
the primary and secondary windings and the core
since it is appreciated that there may be limita
so that an evacuated space will be interposed be
tions in the size or character of the lead in con
tween'the two windings and/orbetween atleast
ductors I4 and I_5 that would preclude or make
one of the windings of the transformer and the
core. In this manner the spacing between the
transformer windings and the core and the spac
ing between the two windings can be reduced to
difficult the sealing of such conductors in the wall
of anïevacuated-container, it is contemplated that
resort may be had to the use of la conventional
current transformer for the purpose of providing
a, minimum and, at the same time, a maximum
a. current of- reduced value that can be accom
modated by lead in conductors of a size suitable
factor of insulating safety will be provided.
In accordance with another aspect of the in-'f
for sealing in the wall of an evacuated container.
vention, I may employ a transformer of the above
In Figure 2v of the drawing there is shown an
design in series with one or,V more transformers ^. » ¿ >embodimentof the invention inwhich both the
of conventional design that may be connectedto
operate in a zone ofhigh vpotential and from
'primarywinding and lthe secondary winding of
which a relatively lowerv current may be taken
are each spaced from the magnetic core and in
my high potential insulating current transformer
into my improved insulating transformer by rel
atively smaller lead wires that can be more con
veniently sealed inthe wall of a glass or other
sulated from `the core and from each other by a
high vacuum. vAs here shown, the transformer is
„enclosed within an elongated and evacuated bulb
type of evacuated envelope. ,
.'22 having an extending neck 23 at one end in
For a better understanding of the invention y
which primary current leads 24 and 25 are sealed.
.These vcurrent leads 24 and 25 form the input
conductors of a primary winding 26 that is suit
reference should'be had to the accompanying
drawing, wherein there Yis shown byrway of illus
tration and not of limitation preferred embodi
» ments thereof.
ablyrnountedv within the bulb 22 by means of a
reentrant stem `21 formed within the bulb 22. At
In the drawing:
its other end_»the bulb 22 has -an oppositely ex
tending neck 28 in which 'lead out conductors 23
and 30 are sealed. These latter conductors 23
and 30 form the output conductors of a secondary
, Figure 1 is a diagrammatic sectional view show
ing one form of my invention,
Figure 2 is a similar view illustrating another '
form of‘my invention as connected inr series with
winding'âl which, like the primary winding 26, is
suitably supported within the bulb 22 by means
a current transformer of conventional design, andV
Figure 3 is a vertical sectional vview showing 'an
adaptation of my invention "suitable _for use in
connection with minimum oil and air blast types
circuit breakers.
of a second reentrant stem 32.
With this ar
rangement it lwill be seen that the primary wind
ing 2li> and ' the secondary winding 3| will be
spaced and insulated from each other. To com
plete an inductive coupling between the primary
In Figure 1 of the drawing the invention is
shown in simplified form as employing a suitable -
lwinding 26 >and the secondary winding- 3I the
evacuated glass bulb or rece'ptacieill in which the
transformer is enclosed and sealed as a unit. ',I‘he
bulb 22 is shown as vhaving a substantially cen
trally disposed magnetic core 33 ’that is posi
glass bulb Ill has an-enlarged central body >portion
II from which reduced end portions I2 and/I3
tioned by'means of supports 34'with its opposite
Álegs disposed’ in spaced and substantially central
extend in' -opposite directions. , Sealed in and 40
with respect to the convolutions ofthe
passing through the extending end v»portion I2 ' relation
primary andfsecondary windings. In this trans
of the bulb I0 there are two, relatively largecon
I ductors I4> and I5 whichprovide lead in lconnec
tions for a lrelatively small number >of ampere
turn forming convolutions _I6 of .the same con
ductor which form> the primary windingvof a
transformer. Positioned within the enlarged por
former it is contemplated that the ratio of turns
ofthe primary winding 26 -and the secondary
winding 3| will be substantially 1:1. However,
' it is conceivable that this ‘ratio of transformation
, may'v be of any desired value,’either'in a step-up
or step-down sense. In practice, it is customary
tion Il of the bulb I0 by means Aof suitable sup
ports I'I and with one of its legs extendingcen
to provide transformers >for this service which
have a secondary current output of approximately
_five amp'eres‘., as this value of current' is very' sat
trally through the convolutions I6 of the lprimary
winding, there is a magnetic core >I8 of suitable
construction. This magnetic core I8 is shown as
isfactory for'meters and relay control circuits.
Therefore, as illustrated'in this ñgure of the
of rectangular shape` and upon the .other ofits
legs and, _wound in a suitably insulated manner,
drawing; my improved transformer is shown as
connected in series with Va transformer of con
ventional design which has a heavy current car
rying primary windingv 35 and a secondary wind
ing 36 >that will' provide a control current of sub
there lis a secondary winding I9 having lead out
-.wires 20 and 2 IthatV are sealed in and extend out
wardly through the end of the extending >neck
III. >With thlsar
rI3 of the evacuated glass bulb
„rangement it will' be seen that _the turns orncon- i
Y stantially ñve amperes~ whenV the normal line cut
upon the bulb Ill'outwardly a vsafe distance, de
, potential insulating bushings such as are now’re
rent is iiowing through its primary winding.
volutions AI 6 of the primary w'nding willbe'spaced so v'In Figure 3 of theÄdrawingthere is shown 'an
from the core .I Bof the transformer ‘.ati'id'thus> pro
of the invention'which it is believed
videan evacuated space between this windingand ,A¿embodiment
may find considerable useinvr connection with the
.the core I8v that will effectively insulate> the 'turns
controler hignpotennarcircuit breakers of the
I6 of the primary winding from the corel I8.A ¿it` 65 Yminimum oil or air blasttypeY whichbasv pre
the same time, by extending the n'eclrsk l2 and I3
>`viously suggested; may ’not employ the usual high
pending uponthe voltage involved, the terminal
ends of the conductors I4', l5'and 2.0,r 2lvmay be ` .
spaced apart suiiìcíentlyf'to avoid any external
arc-over. around the `vacuum insulated gap be
tween the primary and secondarywindings of the
power transmission line with its primary ,Y
winding carrying the full line current. However,V
As here shoWrrthe insulating transformer
70. iis enclosed within an evacuated glass >bulb oren
transformer'.` The transformer described above
_. which might be connected directly to a high
_quired on circuit breakersfof the oil insulated
, type.
velope 31. The insulating transformer in this in
_stancelcomprises a magnetic core 38 that is >posi
, ftion'ed within the bulb 31'bys`uitable'supports 39
' and 40. The core._38"carries a secondary winding
4I having leads 42 and 43 that extend through and
. „l“
are sealed in the wall of the bul'bg31 nearits ¿bot
to`m. At Vits upper end >the bulb 31 yis ‘provided
with a neck of reduced vdiameter having a _'re
entrant stem 44 upon which there` is suitably
m'ounted‘a primary winding 45. yThis primary
winding 45 has >relatively large'convoluti'on's 45
that surround'and are disposed in spacedre'lat'ion
with the upper legoi tlieïmagnetic coref38. iEx
tending adjacent the reentrant vstern 44 'there-'are
two lea'dsin Aconductors '41 `‘and '48- vthat extend
may `be lomitted altogether.`
groundingv con
nection may be 'purely 'a >‘safety measure so Ytl'ia’t
in the event of a flash-over, Íthe high jpotential
*current will -no't damage associated instruments
and `apparatus »or 'injure ’an attendant. I AIn the
>case `of extremely high potentialefit may also `be
desirable to employ and connect two or `more of;
these ‘insulating 'transformers `in series soies to ,l y
establish any numberfo'f ¿stages of l trans formation
‘and insulation.
through andare sealed‘in the end of the'upwa'rdly
extending 'neck of'tlie bulb 31. VIn this arrange
ment, like that illustratedin connection with Fig
ure 2, Ythe insulating transformer isfadap'te'd'to‘be
yexplained in `detail in-conlunction'with aspeci?lc
"application-*andas a current transformery forvhigh
support and insulation of 'this conventional trans
former, the bulb 31 is shown as disposed‘cen'trally
within a bushing-type insulator 4,9 o'f'porcelain
î‘for inductivelycoupling and insulating two cir
Vcuitsïthat operate at >greatly'.dllïerent potentials.
-Although'thefinvention has been .illustratedand
Ypotential `>alternating l cu-rrent systems, .it is »not
connectedvin series with a vtransformer ‘of icon- ï" ¿necessarily limited to such afield of-application.
ventional design, and in order to provide for'the
The inventionquitegenerally shows a novel means
or other suitable material. This will 'i orm 'aïme- .
chanical and insulating -support'for the conven
tional current transformer. Theinsulatingbush
ing 49 has a plate 50 upon which 'a 'core 45| of the
conventional transformer is supported. The ’core
5i of this latter transformer has a,V primary wind
ing 52 ’anda secondary vwinding 53 that may be
designed to provide -a control current of ?any Ide
v»sired value, as will «be determined by'the normal
4It will also -be understood that the systems dc
scrlbed ‘canbe used to transmit direct current im
pulses from the. primary'tc the-secondary or vice
-versa, fand in this manner y.the-transformer here
disclosed could be usedvas the insulated inductive
c'oupling-meanssh’own and‘described in U. S. Pat- ,
ent No. 2,301,765, issued November 10, 1942, to
»Roy Wilkins.
While I have, for the sake of clearness and in
order to disclose the invention so that the same
current of the lineconductor in Vwhichthe pri-mary
can be readily understood, described and illusvwinding~52_ of this transformer‘may be connected. l30 trate'd
speciñc devices and arrangements, I desire
Terminals 54 and 55 carried by the primary'wind
it understoodthat this invention is not
-ing 52 are here shown as insulated, froml and :pro
limited'to the specific meansdisclosed, but may be
Jecting through' an enclosing cover 56 that'is like
embodied in other‘ways ythat will suggestthem
wise insulated and supported in ythe zone vof high
4selves to persons skilled in the art. It is believed
`potential at the upper end of-the‘bushing 49. In
that this invention is new and it is desired to claim
connection with vthis latter arrangement, it »will
it so >thatfall such changes as come within the
be noted that the first stage or conventionall trans
Yscope of the appended claims are to be considered
former, together with its enclosing'housing 56 and
Las partof this invention.
the power line conductorsl connected to’ theïter
Having thus described my invention, what I
minals 54 and 55 of ïthe primary Windingf52, will 40 claim
Vand desire to secure by Letters Patent is:
be eiTectively insulated from ground by meansof
1. A current transformer for use on high po
the supporting insulator bushing 49. fNow, in
î-tentlal circuits, comprising an evacuated en
order to further insulate the high potentiaicir
“velop-e having armagneticcore mounted therein
cuit and reduce thepossibility- of any creepage
current or arc-over'within the bushing 49 and ex 45 andsurrounded rbye. vacuum, a primary‘wind
>ing mounted inloose coupled magnetic relation
ternally of the tube 31, itis contemplatedy that the
vïuporiîsaid. magnetic-core within said evacuated
leads 42 and 43 of the secondary windingf4| of
fßenvelo‘peßand 'adapted' to be >excited by vthe line
the insulating transformer may be passed‘through
fcurrentwof avhigh potential circuit, anda secandfsealed in _the wall of the insulating vbushing
î'ondary ï'win'din‘g 'mounted' upon said Acore in close
49 to thus 'provide an oil tight receptacle thatmay
vcoupled inductive y»relation with Hsaid magnetic
be filled with an insulating 'oil or `other medium:
= core, characterized. by theV fact that said primary
51. In'this figure of the drawing'thev primary
ï-win'ding will be' electrically ` insulated ïfrom said
windingf45 is shown as provided with’an‘ï'electro'
v'magnetic core andk from said’V secondary winding-Y
static shield 60. This shield maybe Aof‘fan'x'r'ac
cepted form and will functiony to prevent-any elec ss‘fsole'ly by .the levacuated »space therebetween
within said-evacuatedenvelope.
trostatic discharge to the primary coil. y'The bot
>.2. ¿In-a ‘current transformer for4 tappi-ng va »high
tom ofthe insulating bushing 49 is ‘shown'as
.a potential'v circuit, `lthe combination». of :an evacu
closed by a plate 58, but it will be understood that
»ated fseala‘blet container 1.» ofv Vnon-conducting ' ma
»this closure may be provided by any 'suitable
laprimary! coil havingv relatively large turn
means and -may constitute a part of otherfappara-~vv60 "terial,
forming'convblutionsfdisposed within said con
tus with which the insulating transformeris' used.
tainer *andfhaving f'extending .terminal ends
In this instance the evacuated glas's- bulb `or en~
adaptedffor’connection to 1a. high potential cir
velope 31 is supported upon insulating blocks -'59,.
fcuit, atclosed> magnetiecoi-ehaving one-leg ex
However, it will be understood that the`-bulb`31
may be supported in many other ways. v"For ex 65 ` tendingfcentrally' through andl in" loose coupled
.-lrnagnetic >relation with the; large turn . forming
ample, it may be carried by shelf formingfbosses
‘convolutionst-of saidifprimary> coilfand a second-formed integrally upon the inside wallfof the
¿aryrcöil >mounted >in closecoupled magnetic re
bushing 49, or it may besuspended from 'the-plate
50 which supports the core 5I of the conventional
transformer. As an additional safety measure,Y it
will be understood that yif desired, the cores of
the insulating transformers described'above lmay
-be grounded, as indicated in Figure 3. yIn 'the Acase
of high frequencies, or other conditions'permit
lation-.upon 'another' leg "of said l'magnetic core,
lwhereby* said‘primary coillwill be electrically in
sulated».ffrom'said'closed magnetic core and said
- -secondary coil by a vacuum.
*3; In a current transformer of the character
cdesc’ribed, the combination voi' an evacuated con
ting, itis also conceivable that the'magnetic core 75, tainer, an electromagnetic core mounted within
and supported by said container, afprimary wind
ing having large turn forming convolutions sup
said secondary windings by the evacuated space
ported from a wall of said container and dis
posed in loose coupled inductive relation with a
portion of said electromagnetic core, and a sec
ondary winding vdisposed inV close coupled in
ductive relation with another portion of said
magnetic ‘core and in spaced relation with said
primary winding, whereby 'said primary winding
will be insulated from said electromagnetic core
and from said secondary winding by an evacu
' ing large. turn forming convolutions adapted to
be excited by a current at high potential, a close/d
magnetic. core having a portion thereof extend~
ing through and in loosely coupled magnetic re
lation with the large turn forming convolutions
of said primary winding, a secondary winding
ated space therebetween'.
4. A current transformer'for Obtainmgmeter
disposed inspaced relation with said primary
ing and control current values of low ratio er
v winding and wound 'in closecoupled magnetic re
. ror from high potential power transmission‘cir
cuits', the combination of a primary winding hav
ing large turn formingconvolutions adapted to be
5. A current transformer for obtaining meter
ing and control current values of 'low `ratio er
ror fi‘om high potential power transmission cir
cuits, the combination of a primary winding hav
V.lation upon another portion of said closed mag
netic core, an evacuated enclosure forming means
having terminal leads for said windings extend
connected toa high potential circuit, a closed
magnetic core having a portion extending
through the large turn forming convolutions of
I ing through opposite walls thereof and completely
, surrounding and supporting said primary Wind
said primary winding and y, in spaced loosely 20 ing and said-magnetic core in spaced relation to
each other, whereby said high potential primary
coupled magnetic relation therewith, a second
ary winding disposed in spaced relation with said „ winding will lbe eiîectively insulated from said
_ magnetic core and said secondary winding by
primary winding and wound in close coupled re
, an evacuated 'space therebetween, and a bushing
lationk about another portion of said closed mag
‘ netic core, and a sealed' and evacuated enclosure 25 like support containing a fluid insulating medium
forming‘means completely surrounding and sup
within which-said evacuated enclosure forming
" portingsaid primary winding and said magnetic
-"core 'in spaced relation to each other, whereby
means is vsubmerged to prevent current creepage
between the terminals of said prímaryand said
said highV potential primary winding will be ef
fectively _insulated from said magnetic Vcore and
, secondary windings.
AuGUs'r c.v scHwAGER.
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