Vm f) dem §24, i943» A. c. @CHW/«GER HIGH POTENTIAL CURRENT TRÀNSFORMER MEANS Filed Dec. 2l, 1942 »no9_5:ffaQ?.¿î“..MX 5% . $911. *_-Own .Año.. ` 2,413,195 Patented Dec. 24, 1946 2,413,195 UNITED STATES PATENT OFFICE HIGH POTENTIAL CURRENT TRANS FORMER MEANS lAugust C. Schwager, Miilbrae, Calif., assignor to Pacific Electric Manufacturing Corporation, San Francisco, Calif., a corporation of Cali-forni a ' ~ 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 ne. v 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 2 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 ings 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 45 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 '2,413,195 , 4 _ 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 A In the drawing: I ‘ ._ 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, 25 ' 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 of circuit breakers. v > - f y . , 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, 45 ' 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 v „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 _. is.one which might be connected directly to a high potential _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 2,413,195 5 . „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. I _ 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 toI have 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. l 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 2,413,195 8 7 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 therebetween. 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. 30 AuGUs'r c.v scHwAGER.