3 fusion. A metal collar @27 is also sealed by fusion to the oppo!;ite,end of -the glats ring 25 and another end wall plate 28 of metal conducting material is welded to metal collar 27. Element 29 represents a metal plate and resilient spring of conductive-material by means of which the electrod,_,esistor assembly are maintained by, pressure in,good electrical coiitact with end or terminal plates 26 :and 28. The free space within the element or unit 17 is filled with a dry or inert gas, such as nitrogen, at a pressure most suitable for the voltage class @for which the ,arrester unit is designed. The @sealed unit mai-,itains the .@gas density and hence the gap breakdown voltage practically constant, independent of variations of temperature and pressure. @In a conventional lightning arrester, gen@erally freely vcntilated@or at least capable of "breathing," the @gas,density@ at the;gaps inay vary by as much as 30% due to variations in the atmospheric temperature and pressure, @with corresponding changes in the breakdowii voltage of the gaps. The submersion of the arrester within the transformer liquid also prevents wide and rapid fluctuations of tompei-ature and the resulting physical sttains to which the conventional arrester insulations exposed to the -weather are subjected. Thus it will be -seen @ that the protective @@arrangement generally speakiilg involves a lightning arrester connected between the line rside of a winding and the other end or side thereof but preferably to ground:Ei-nd,comprises a plurality of series connected protector elements, each consistiing of a resistor connected in series with@ an @air gap and with the junction between each of the elements connected by relatively short leads to spaced points along the winding to be, protected. Iii conti'ast to prior@practice where shields have been employed:to reduce voltage concentration, it should be noted that in the present case, any excess local over-volt@age is discharged, 'not merely reduced or distributed. Ftirthcrmore, in the ' present arrangement there is, normally, no leakage of current tlirough the protective shunts aifd, @therefore, the resistance elements can be set for much @lower v6lues than in the older schemes involving rnerely resistan@e shunts between taps alon.- the winding. In this @ connection, I @have found that the overvoltages @permitted by the@older@schemes can be reduced in the ratio @s mucli as 5 to @ I by the novel @ means of the present invention. The:-arrangement;of the winding and the arrester with a plurality bf cross,coiinections between them makes the arrester highly 1 selective and @sensitive to those transient types of overvoltages,which tend to: produce voltage concentrations within the winding and discharges them at a lower terminal -voltage than other types of impressed overvoltages which@do not cause:similar voltage concentration and thus dependable overvoltage protection is provided for:each fportion of - a @ protected winding regardless of the type of ove'rvoltage to ivhich it may be subjected and regatdless of @what its individual voltage distribution el-aracter,istics@may be. This resul'L follows from the fact that @l,@xcessive -voltage coricentration across any portion of the winding, due; to@the omission of electrostatic shields, causes the% corresponding -arrester element to di8charge aind -as the total@ voltage -is then @impressed across a smaller number @ of gaps, ithe: remaining -gaps are also caused to discharge. That is, the discharging of one of the arrester elements acts@as a trig,,;er to cquse the entire arrester to discharge Thus,iioporticularauxiii.,@riesarerequiredfor the gaps to improve their discharge characteristics in this respect, as this function is effectively served by the high voltage winding,with -which the@ arrester is interconnected at a plurality of points. As the impulse voltages associated with appreciable @ time; lag in -the dischar-ae gaps are also those that tend to. produce a nonuniform voltage distribution Land local @voltage,coiteentratiotis in the:windings, tlierefore, v.,hen, the -winding and the arrester, are interconnected at a7plurality of corresponding p@oints, a voltage concentration across a portion of the winding appears - also, as, a voltage concentration across the corresponding portion of the@ arrester. As this -portion of the @arrester discharges, it throws the overvoltage, across the remainder of the@ arrester, which@ now is'overstressed,more than@ before,; and thus,, progre8sively (though very fast) the entire arrester discharges. It may @be seen @'that, in this .arrangement, the more nonlinear the initial voltage distribution in the @vinding,-the lower will be the terminal value! of the dvervoltage which the arrester will discliarge. ,That is, in this @,itrangement,- the arrester is highly respon@sive@to@the@8peciflc-"needs@of@any l-given'wiiiding to@be@pro2,703,852 4 tected, and provides equivalent protection to all, without being designed for the peculiarities of any particular winding with respect to impulse voltages. Because of this action the auxiliary structures provided in conventional arresters for control of their voltage distribution is dispensed with, thus resulting in the greatly simplified arrester structure illustrated. In addition, various other auxiliaries provided in conventional arresters to causeionization and thereby render th6ir discharge characteristics more 10 prompt, positive and dependable, have also been dispensed 'with, Althotigh the@dis6harging of an arrester element is theoretically preceded 'by an overvoltage in - the corresponding poi-tion of the winding, this is nothing to be concerned about bccause it is onll, an attempted overvoltage 16 and cannot rise above wliat the gap involved will permit. It actually represents a smaller strain in the winding than what@can exist in those shielded designs in @vhich the voltage distribution within the winding may have cu,sps or other sharp local irregularities not under direct control 20 or,protection by an arrester element in shunt for that portion of the winding. A further important beneficial effect of the present arrangement on the performance of the arrester. is that in the conventional practice, in which the arrester is 25 mounted external to the transformer, the arrester is some distance from the.protected winding, and the standard rules of:the American Institute of Electrical Engineers permits a separation-of as much as 75 feet. However, based,on some recent experiences and tests, I am.con30 vinced that,even a 25 foot -separation maY Tesult in as much as 20% difference @between the tenninal impulse @overvoltages of the:arrester@and the winding. In view of the close, proximity of the arrester to the winding and the relatively @ shott@ cross connections, such difference is 35 obviously impossible in the --present arrangement. While @l @have, in accordance with the patent statutes, shown @and, described@ a particular @ embodiment of my invention, it will @be obvious that changes and modifications can be made without departing from the inven40 tion in its broa:der,aspects and, 1, therefore, aim in the appended claims to-cover all such changes and modifications as i fall within the true spirit and scope of the invention. What.l.claim@as new and desire to secure by Letters 45 Patent@: of the United.-States -is: 1. Electromagnetic,induction apparatus comprising@a -container, insulating.fluid in said container, a.magnetic core having a pair of spaced winding legs submerged in Said flui I d, said winding legs having their axes in sub50 stantially-par@llel relationship, a winding disposedlongitiidin@lly along each of said s@bmerged winding le s, said %win'dings being @lectrically connect6d in parallel! an in sulating tube in said fluid@mounted closely adjacent @each of said windings with ihe longitudinal axis of said tube 1.@ 5 substantially. parallel to the axes 6f said windings, a @lur@lity of likhtning arrester elements mounted end to,end in, said tube and electricqlly connected in series,,each element comprising a ;non-linear resistance and structure forming a series connected gap hermetically sealed -within 60 an: enclosure, said plurality of eleme having an overall length s6bstantially equal,to the p on of said winding.legs albng v@hich said windings are disposed and -so position'd in said tube that the end elements are respectiv6ly,located adjacent opposite. ends of said windings, and 65 electrical conductors extending through openings in-said tube and connecting the end elements to the winding.ends adjacent thereto and the junction between a pair of said elements to -points on each of - said windings, adjacent thereto, @said tiibe being located. in, such.-a.. position:. that 7o each of, sdid coiiductors - is 6f substantiany equal, length. .2. @The - apparatus . 6f claim @ I in *hich the seat@d - elements of said'lighthing arrester are further.characterized by said enclosure being:formed 6f a hollow vitreous member;and a pair of flanged metallic end walls,.said 75 flanges being sealed to said vitreous member by fusion. References,Cited in the'.file, 6f this. patent ;UNITED @STATES 80 745,379 Pearson-et @l - ---------- June 13, 1902 11 @@00,127 Creighton -------------- Apr., 8, 1919 11,809,895 Gay ------------------ June 16, 1931 Y,220,61@5 Pittman et al ------ Nov.@ 5, 1940 @2 242@838 'SOmes 1941 85 @@2' ;276,'855 ,Meador -------------- Mar. 17, 1942

2 9 7 0 3 @ 8 5 2 Un'lted States Paten't@ Office :,.,ented Mar. 8, 1955 2,703, 852 OVE RVOLTAGE PROTFCTED INDUCTION APP ARATUS 5 lack R. Meador, Pittsfield, Mass., assignor to G@iieral Electr ic Company, a corporation of New York .Appli cation August 31, 1951, Serial No. 244,541 10 2 Claims. (Cl. 317-15) This invention relates to electromagnetic induction appar atus, such,as high voltage power transformers, and more partictilarly to overvoltage protection thereof. 15 Heret ofore, the better grades of high voltage transforme rs have been provided with two kinds of overvoltage protec tion, simultaneously. That is, internal electrostatic shields to avoid voltage concentrations and resonance pheno fnena and external lightning arresters to avoid ex- 20 cessiv e voltages at the terminals of the winding@ Al-@ thoug h well protected Iiigh voltagd tratisformers can "d have been made by this method, tl-ie method is not free from various limitations and disadvantages, which the prese nt invention aims to overcome. For instance, con- 25 siderin g the factor of shielding, adequate electrostatic shieldi ng has been found applicable so far only to limited types of windings, and o-@ily,in a limited class of oircuit ' conne ctions, so that certain winding arrangements desirable for other purposes have either had to be dis- 30 pense d with or used with in@idequate shielding. Furthermore, the successful perform@ince of a shield depends on the siiccessful adaptation of the shield design to the char.acteri stics of- the winding itself, requiring great design skill, and not all of the so-called "shielded" windings 35 ;have necessarily the hoped-for impulse voltage distribution. It follows that no standardized shield may be applied to any and all high voltage windings and be expecte d to do well what it is iptended to do, regardless of the type of design of the,winding. The nature of the 40 overv oltages and the protection problems involved in such cases are explained in my United States Patent No. 2,276, 955, which explains also the liinitations of electrostatic shields as applied to them. That patent discloses a protective arrangement, the main feature of which is 45 the application of a plurality of nonlinear resistance shunts between, taps along the winding. That arrangement represents the best in the prior art that I know of and it has been used effectively and successfully in a numb er of siieh cases. However, I find that it bas cer- 50 tain limitations in that the shunt resistors are a constant drain on the rurrent and eliergy of the circuits. In order to reduce this wastage to tolerance values, the resistance values must be increased, and this tends to lower the pr,otectio n which they afford. 55 Conce rning the lightning arrester, although good arrester s are available as such, yet by virtue of their design as an indep&ndent piece of apparatus, they cannot discriinin ate bet@Aeen the different kinds of overvoltages and the differeiit classes and types of equipinent for which 60 they are to provide Drotection. Neither can they take substa ntial advantage of possible help from the protected appar atus. For exai-nple, when a ligh@ning arrester made up 6f several elements, each comprising a gap in series a current limiting resistor, is connected to a 65 with high voltage circuit, the voltage distribution among the elements; in the absence of a dis6barge curreni, is determined by their capacitances to each other and to,ground. This generally tends to be some undesired.function, and, therefore, alixitiary means have to be provided to lm 70 prove this distribution. Even with such auxiliary means, some of the standard arresters are sensitive to changes in the' ir exposure to ground and their prot@ctive value may be lowered by Linapproriated iiiifavorable electro- 75 static exposures in varioug installations. Under impulse conditions, it is expeoted cif an arrester that it - discharge an excessive overvoltage without time lag. However, for very steep in-ipulses, arrester gaps do have a time lag, and various types of auxil.iaries,are utilized in the 80 :a;rre ter art t6 redu6e' this time lag: 4nd resulting overvoltage. Nevertheless, in the -leading types of the present day arresters with such auxiliaries, the impulse dis charge voltage for the standard AIEE irnpulse wave is about twice as high as the nornial frequency spark over N,oltage of the arrester, It is therefore, an object of the present invention, to provide' a protective arrangement in which electrostatic shields can be dispensed with altogether, thereby eliminating all such Iiinitations in winding design or circuit connection, as well as expense of shielding. It is also an object of the present invention to provide a protective arrangement in which the lightning arrester can be assisted by the protected apparatus to make the response of tlie arrester more selectiv-e and positive, improve the protection, aiid simplify the arrester structure. The invention will be better ..understood from the following description when taken in connection with the accompanying drawing and the @cope of the invention will be pointed out in the appended claims. In the drawing, Fig. I ilIListrates a side elevation view partly in section of an induction apparatus and anarrangement for the protection thereof in accordance with the invention; Fig. 2 is a schematic diagram illustrating the circuit layout in ttie arrang-,ment illustrated in Fig. I and Fig. 3 is aii enlarged crosssectionat view of a protective elemeiit sliown in Fig. 1. Referring now more specifically to the details of the figlres, a representative twolegged core-type high-voltage transformer in combination with the overvoltage protective means of the present invention is shown mounted in a tailk or container 10 filled with an insulating oil or liquid 11. Transformer windings 12 and 13 are arranged in two stack's resi)ectively on the two legs of a ma- etic ,n core and are connected. in parallel and submerged along with the core in the insulating fluid 11. The numeral 14 identifies the line terminal of the windings while the other terminal 15 is shown as grounded althougli it may be connected to a line circuit. A plurality of protector elements 17 comprising an arrester protective device are stacked end to end in electrical contact with each other in a tube 16 of instilating material and positioned closely adjacent to windings 12 and 13 with the longitudinal axis of the tube and the common axis of the stack of elements 17 substantially parallel to the axis of the winding. A 1)ortion 6f tube 16 h6s be6n shown cut away to expose t@ view the lightning arrester protector elements which have aii over-all length substantially equal to the portion of the winding leg along which the winding is disposed aiid ,ire so positioned in the tube that the end element at one end of the stacklis disposed opposite and closely adjacent one end of the winding and the end elenient at the other end of the stack is disposed opposite -,tnd closely adjacent the other or opposite end of the winding. Relatively short electrical conductors extending throtigh openiiigs in tube 16 electrically connect the end elements of the stack respectively to the winditi.ends adjacent and opposite thereto while a plurality of similarly short conductors or cross connections 30, also extending through openings in the tube, electrically interconnect the junction between each pair of elements 17, intermediate the ends of the stack, to a correspondin@, point of each winding located, intermediate the ends of the windine;, at approximately the same distance as t@-e, junction to vvhich it is connected is located from an eiid of the winding. CorresDonding points here means poipts that are intended to have the same potential Linder operatirig conditions and the shortness of'these cross coiinections ,.issures that the pair of poihts so interconnected shall have their potential alike under impulse conditioTt.9 also. The tube 16 is located in such a position that each of the short conductors 30 is of substantially equal length. As better illustrated by Fig. 3, each of the arrestor elements comprise an are gap IS connected electrically in series @vith a resistor disk 19, preferably of the non-lineat type. Gap 18 is defined by a pair of electrodes 20 ahd 21, respectively part of metal disks 22 and 23, maintain@d spaced or separated by a spacor of insulating material such as porcelaiii ring 24. The resistance and gap iii series therewith are hermetically sealed within a chamber or enclosuie comprising a glass riag 25 with an end wall .,Plate 26 of metal conducting rn Aterial @ sealed thereto by