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1266175 tesla lightning protector


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1266175 tesla lightning protector

  1. 1. UNITED STATES PATENT OFFICE. NIXOLA TESLA, OF NEW YORK, H. Y. LIGHTNIN'G-PROTECTOR. 1,266,175. specification of rotten Intent. Patented May 14, 1918. Application fled Xly 8, 1910. Serial No. 85,850. T 0 all whom. it may concern: Be it known that I, NIKOLA 'I‘asL. i, a citi- zen of the United States, residin at New York, in the county and State of ew York, have invented certain new and useful Im- pi-ovements - in Lightning-Protectors, of which the following is a full, clear, and ex- act description. , -. The , object of the present invention is to provide li htning protectors of-a novel and improved esign strictl in conformity with the true character of the phenomena, ‘more efficient in action, and far more dependable in safe-guarding life and property, than‘ those heretofore employed. To an understanding of the nature of my invention and its basic distinction from the lightning rods of common use, it is nec- ess'ai briefly to explain the principles upon. whic 1 my protector is designed as contrast- _ed with -those ‘underlying the now-prevail- ingtype of lightning _ _ . ince the introduction of the lightmng rod by Benjamin Franklin in the latter part of the eighteenth century, its adoption as a means of protection against destructive atmospheric discharges has been practically universal. Its efiiczicy, to a certain degr statistical records but there is genera prevalent, nevertheless, a singular theoreti- cal fallacy as to its operation, and. its con- struction is radically defective in one »fea-. turc, namely -its typical pointed terminal. In my lightning" rotector I avoid points, andnse an entire y diflerent type of ter- minal. . ‘ - According to th prevailin yirtue of the Franklin type o lig tning rod is largely based on the property of points or 'n‘llt| l'p e es to give oil’ electricity into the air. As 5 own by Coulomb, the quantiti-‘of electric-it_v per unit area, designated by ‘m “electrical density” increases as the radius of curvature of the surface is reduced. Sub- . ~a-quontly it was proved, by mathematical m‘ial_v. ~:is, that the accumulated char ' cre- ated an outward normatforce equa "to 21: limes the square‘-of the . densit , and experi- ment has demonstrated that w en the latter exceeds approximately 20 C. G. S. units, a streainor or cm-onafis formed. . From these 0hser'ul. ion. ~a and deductions it is obvious that such may happen at a comparatively low pressure if the conductor is of extremely 99: has been unquestionably established through ‘ 7 o inion, the- small radius, or pointed, and it is ursuant to a misapplication of these, an other, truths that the commercial lightning rod of today ismade very slender and ointed, My invention, on the contrary, w ' e ‘ cognizanceof these truths, correctly_appli them in the provision of a lightning pro- tector that distinctively afiords an ‘elevated terminal havi its outer conducting boun- daries arrang on surfaces of laége radii of curvature on two dimensions. . - e rin- ciples which underlie my invention an : co_r-' rect application of which dictate the form and manner of installation of my protector, I will now explain in contrast with-the con- " ventional pointed lightning rod. ‘ In perniittin leakage into the air the needle-shaped Iightning-rod is popularly believed to perform two functions: one to -drain the ground of its negative electricity, ' the other to neutralize the 'tive of the clouds. To some de ee it oes both. But a systematic study 0 electrical disturbances in the, earth has made it palpabl _evident that the action of Franklin’s con actor, as commonly interpreted, is chiefly illusionary. Actual measurement proves the quantity of electricity escaping even from many points, i to be entirely insignificant when com ared with that induced within a considerab e ter- restrial area, and of no moment whatever in the process of disipation. . But it is true that the negativelypcharged air in the vi- cinity of the r , rendered conductive through the influence of the same, facilitates the-passage of the bolt. Therefore it in- creases the probability of a lighting. dis- charge" in its vicinity. The fundamental facts underlying this type of lightning-rod are: First, it. attracts lightning, so that it will be struckoftener t n would be the building if it- were not present; second, it remit-. rs harmless most, but not all, of the discharges-which it receives; third, by ren- dering the air conductiv'e,4and for other reasons. it is" sometimes the cause of damage toneighboring objects; and fourth, on t e whole, its power of preventin injury re- dominates, more or less, over e hazar s it invites. My protector, by contrast, is founded on principles diametrically opposite. Its ter- minal has a large surface. It secures a very low density and preserves the insulating qualities of the ambient medium, thereby
  2. 2. trical. iiiveau”~—such stored ‘over and under it are e ual. In neg ‘that _the onefibuilding 3 . re minimizin leakage, and in thus acting as a quasi-rep ant to increase enormously the safety factor. , ‘. . - For the best-and most economical installa- 'tion, _of protective devices according to‘my invention, those factors and phenomena that dictate size, number of protectors and 'ph ical qualities’ of the Aapparatus‘ must rasped by the install‘ . engines_r, and _minarily, _for erstandini of the principles of_ m invention, these s OJ-11d be briefly exp 2 ~ ' - Economical installation, . _ maiids that the protective capabihty given equipment be not needlessl than is meet the -maximum ex-- tancies under the conditions surrouiidin t e*particular build’ to be rotected‘ an - these depend, ~ pai-ti y as shall dicw, upon the character of the landscape proxi- mate‘to the bujl ' site. _» _ V In the drawings, igures 1 to 4 inclusive, are diagrams requisite to illustration of the facts and conditions" relevant to the deter. - mination of s ' installations of my in- ventic and 6 to. Srillustrate construc- of any igs; an application of the protectors. ‘ Spe- cifically: . V Fig. 1 is_a'. lsndscape suited for urpose $1’ e§1plana'. tion° Figs. 2, 3 and.4.aJ: e eoreti- s; » igs. 5 and 6 illustrate forms . of ‘improved protectors; and Fi 7 and 8 show biiildings equipped with t e same. _ . In Fig. 1, 1 reprwents-Lord Kelvin’s “re- duced” area_ of the region, which is virtually. part of the extended unrufiled ocean-surface. (See “Pa’ an an Elect: -ostqticc and Magnet- i’a_m” by. ir William Thomson). Under or- dinary weather conditions, when the sky is clear, the total amount of electricity‘ dis- tributed _over the land is nearly the same as -that which would _ _ _ _be"contai'iied'within. its horizontal «projection. But. in times of storm, owing to the inductive action of the clouds, -an immense, char e may be-, 'accu- inulated. inthe locality '_t e density be" fiffifitefit It the’ most evi. “ ortionsufi t _e_ _ Assumiiigfliis, un er the'con- dit1on_s existm at any moment, -let another 3Ph°D081 0e 2, . coi; _centric7 with the‘ earth, be di-awn. ——'which maybe called “elec-_' words, theirvalgebraic sum‘, , en relativel to the imaginary surface, ‘in-the positive an ~ ative, sense, is mil. Objects above the “iiiveau” _t_ire exposed toever so'mu'ch more -' risk than those below. '_Thus, a building at- _ 3"'on a sitc. of excessive density, is apt td_‘bei hit sooner" or later, while one in a depression‘ 4, where the charge per unit area is very small, is almost entirely safe; It "follows _ . _ quires . more . ex- tensive equipment than does the other. In both instances, . however, the prcbability_; of. greater- that the quantities , other-. 1,386,175 being struck is decreased by the presence of my -- rotector, whereas it would be increased by ' e presence of the Franklin rod, for rea- sons that I will now-ex lain. . An understanding 0 but part of the relative to electrical discharges, and their niisapplication due to the want of '-fuller appreciation -has doubtless been re- ranklin. ' tning rod taking its conventioiial poin form, but - theoretical considerations and the important discovei-is that have een « made in the. course of investigations with a wireless transmitter of 1: activity by which arcs of a volume an tension comparable to those ogcur ' in. nature were obtained ‘(“APi'ol)‘-' lems of crcasin , Human Energy” Oenmry Magasim June 900 and Patents 645,576, 649,621, 787 412 and 1,119,732) at once estab- lish the fallacy of the hitherto prevailing notion on which the Franklin t ‘of _1'0’l is based, show the distinctive nov ty of my lightning protector, and guide the construc- tor in theuse of my invention. In Fi . 2, 5 is a small sphere in contact with a uric one, 6, partly shown. It. can be proved the theory of ‘elect: -icimages that when e two bodies are charged the mean density on the small one‘ will be "only T, . . 6,-1.64499 times" greater than that on the other, See “Electricity and Illagnctisna, ” __by - erk Maxwell); In Fig. 3, the two spheres 7 and .8 are placed some distance apart and con- nected through a thin wire 9. This system having been excited as-before, the density on- the'smal1 sphere is likely to be many times that-on the large-one. Since both are at the same potential it follows directly that the densities on them will be inversely as their radii_, of curvature. If the density of 7 be designated as 21 and the radius r, then the charge q=4a: r‘d, the potential p=4m'd and the outward force normal to the sur- face, r-=21"; -. As before stated, when d 20 C. G. S. units, the force I be- comes sufiicicntly intense to break down the -dielectric and _a sti-eainer'or corona appeais. In this case p=801:r. Hence, with a sphere of onecentimeter radius disru tion_ would_' take‘ place at -a potential--p= _=251.328 E. S. units, or 75,398.-1 volts. In reality, the- discharge occurs at a lower‘ pressui'e, as ii consequence of, uneven distribution on‘ the all sphere, the densiliy being greatest on the side turned awayehrom the large one. In this respect the avior of "a pointed ' conductor is 'ust the reverse. Theoretically. it mi ht erroneously be inferred from" the‘ pi_ 'ng, that sharp projections would per- mit. _electricity _to escape-nt the lowest po- tentials’, but-this does not follow. The‘ rea- son WillCb, e3cl,6Il“fl'OIn an inspecticnof Fig.
  3. 3. 1,2ec,1-79 4, in which such a needle-shaped. conductor 10, is_ illustrated, a minute rtion of its tapering end being "marked 1:» Were this portion removed from the large part-10.and electrically connected with the same throu h an infinitely thin wire, the charge would 'ven oil‘ readily. ‘ ‘But the resence of 10 as the effect of reducing" e [capacity of 11,_ so that a much -higher» pressure «is re- quired to rsisethe densi to~tlie= critical values The larger the y, th_e_morejpro- nounced is this influence, which is also dc-i pendent on tion, and. is maximum’ for a sphere. en the same is of con- siderable size it’tak'es a much greater elec- tromotive force than under ordinary circum- stances to produce streamers from the point. To explain this apparent anomaly attention‘ is called to Fig. 3. ‘If the radii of the two’ spheres, 7 and 8,’ be designated rand ,' spectively, their charges gand Q and the distance between their centers‘ D, the po- tential at_ 7, due to Q is ‘But-7, owing to the metallic‘ connection 9, is at the potential at When D is comparable to R, 'the medium ' surrounding the small sphere will ordinarily -be at a potential not much difierent from", t that of e latter and millions of volts may have to be applied before streamers issue, _even from shai'p_protruding edges. 7It is important to bear this in min , earth is but a vast conducting globe. It follows that a pointed lightning-rod must be run far above‘ ound in order to o crate at all, and from t e foregoing it will e ap- parent that the pointing of the end, for sup- ? . and the larger t e rod, for reduction of elec- trode resistance, the more renounced is this’ counter-influence. ' For ese reasons it is important to. bear in mind that suilicient thickness ‘of the'r0d, for very low electrode- resistance is rather incompatible with the high emissive capability sought in the nee- dle-like Franklin-rod, but, as hereinafter set forth, it is wholly desirable in the use of'my invention, wherein the terminal con-' struction is intended for ' suppremion of charge-emission rather than to fosterlit. The notion that Franklin's device would be effective in dissipating terrestrial charges may be traced to early experiments with static frictional machines, when a_needle was found capable of quickly draining an insulated electrified body. But the inappli- _ cahility of this fact. the conditions, of ‘lightning protection will be evident from examination of the simple theoretical prin- ciples involvetl, which at the same time sub-. for the _ posed emissive effect, is in part neutralized, the increasin‘ size below the extreme end, " B stantiate the dmirability of establishing protection b avoidin such drainage. 'The ' ensity at V e 130' end fshould be in- zversely as ‘the radiusof curvature of the surface, abut such -acondition’ is unrealizable. " Fig. 4 to represent. a ‘conductor of 'ns'100§times' ‘ "that of the needle; then, altho‘u'gh'_ its-‘ surface ' unit length greater in the same- r , only, do1_ibl'e. Thus, while'. twice t tity of ; electi-iéity , _ -the rod is but '_one-fiftieth of on the nee-_ dle, ‘£ro_m, wliichit follows that the‘ latter is far more e'fiicient. " But the eniissive power of any such conductor is circumscribed. Imagine that the “pointed” (_in reality bluI_1t or rounded) end-be continuously reduced in size so as to‘ approximate the ideal more and ‘more. Durin the process of reduction, the density will, ‘ increasing as ‘the rad1us_of curvature smaller, but in a proportion distinctly ess than hnear; ‘ on -the other hand, the area of the extreme end, ‘ that . 'is, the section through which the‘ charge passes e quan- ‘out into the air; will, "-be diminishing as the. square of the radius. This relation alone -imposes a definite limit to the perforinance of amgointed-conductor and it should ‘be noti that the electrodvresistance would be augmented at ‘the same time. ‘Further- -more, -the eflicacy of the rod is much ‘im- paired througdh potential due to_ the char of the groun , as has been indicated fwit ' reference to Fig. ‘ 3. Practical estimates of the electrical uantities concerned in natural” disturbances s ow, moreover, how absolutely impossible. are the functions attributed to‘ the ’ ointed lightning conductor. A single clou ‘ma contain 2X10" C. G. S. units, or more‘, in ucing in the earth an equivalent amount, which a number of lightning rods could "not" neutralize in many ‘years. Par- ticularly to ‘instance conditions that may "have to be met, reference is inadeto the Electrical "World of March 5, 1904, wherein it . ap ears that upon one occasion approxi- mate y 12,000 Istrok occurred within two hours within a radius ‘of, ;.less than 50 kilo-~ meters from the placeof observation. , But although the pointed 1ig‘htni_ng-rod is" quite iIiefi_eétive'in the one respect noted, it has the sroperty of attracting lightning _to a high egree iirstly ‘on account of its shape and'secon y because it ionizes and ren ers ‘conductive the surroundin air. This has been unquestionablyestabli ed in long continued testswith the wireless trans; mitter above-mentioned, and in this feature lies the chief disadvantage ofthe Franklin type of apparatus. ' Allpf» the foregoing serves to show that since it is utterly impracticable to effect an equalization of char es emissively through pointed lightning-r s‘ under. the conditions ‘ presented by the vast forces of nature. great, io, the capacity is" is stored, the density our‘
  4. 4. surface of lai- 4', i, aec, i-uh improvement lies in the attainment of—a protectors if equipped with suitable devices minimized . probabi1it, y'-of lightning stro or designed in conformity with this inven-‘ ke to the areawto be prote'cted_co'up ed with tion; Still another modificationisillustrated adequate conductivity to render hariiiles in Fi . 8 in which, --instead of one, four those strokes that may, notwithstanding, groun ed bars. are ‘fil: V1ded with as many occur. ., _ spun_ shells, or attac _ ents 1§, with the ob- Furthermore, ‘a cerrectiipplication oflthe vious object of reducing the risk. truths that have thus been explained with i From the foregoing it will be clear that in reference to the familiar pointed type of all casesthe terminal prevents of lightning-rod not onlfy substantiates the electricity ‘and attendant ionization o the theoretical 'proprie‘tyo the formin whichI air. It is immaterial t. his; _end whether it develo my improved lightning protector, is insulatedor not. ould it be the but w’ lead the installing engineer properly current will pass to the ‘und either to take cognizance of those -conditions due directly or, as in F1 . 6, throng a small air- to location of the ‘building, with respect to gap between 12 an 14. But such an acci- sun-ounding_ earth . formati/ ons and other ‘_ ent is rendered extremely improbable ow- buildings, probabilities of maximum oten- mg to the fact that there are everywhere tial-difierences and charge-densities to ex- ‘points and pl'0]t_5Gt10nB_ on which the terres- pected under the prevailing atinospheric trial charge . ttains a high density and where conditions of the site, and desirable electrode the air is ionized. -_ Thus the action of the im-- resistance and capacities of the protectors proved rotecto_r is equivalent to a repellant -installed. - - ' force. his being so, it ianot “i{. cessary to The improved protector, as above stated, support_ it at 2‘ eat lieight, .bii the ground behaves in axmanner just opposite to the- connection sho d be made_ wit _the usual Franklin type and is incomparably safer for care and the conductor l_eadin to tmust be thisreason. The result is secured by the use of as small a self-induction an resistance as of a terminal or conducting surfaceof large practicable. ‘ I ' radius of curvature and suflicient area to _ I claiin as my invention: _ _ make the density ve ~ sina. ll and thereby 1. A lightning protector consistingof an prevent the leakage o _ ionization of the air. The device may be in boundaries arr-an on surfaces of large greatl varied in size and shape but it is es- ra ii of curvature in .031 dimensions, and a sentia that all its outer conducting elements grounded conductor of small self-induction, should be disposed along an ideal enveloping as set forth. _ ge radius and that they should 2. A li htnm . protector" com of a have a considerable total area. . metallic all 0 lar radius o curvature, In Fi . 5, Fig. 6, Fig. 7 and_Fi . 8, difi'er-. and _a grounded -_con uctor of small self-in- ent ‘kinds of such terminals‘ and arrange- vduction, as described. ' - '_ . ments of-‘same are illustrated. In Fig. 5,12 3. Apparatus for protection against at- is a cast or spun metal shell of ellipsoidal mospheric dischar comprising an earth ' ‘ts under side 'a sleeve connection of sins resistance, a conductor outlines, having on i . _ _ . with a bushiiig_13 of rcelain or other in- of small self-induction and a terminal car- sulating material, apted to be ‘Slipped ried by the same and having‘ a large radius tightl on a rod 14, which may be an ord; i- of curvature ‘in two dimensions as. and for nary ightning conductor. Fig. 6' shows a the purpose set forth. < , terminal 15- made up. of rounded or flat 4. "In apparatus for pmtectioir inst at- metal bars radiating; from a central hub ‘mos hericdischarges an ind axed metallic which is supported irectlyon a similar rod she of lar radius of curvature supponed und in electrical contact with the same. The I gtofilln ed conductor and separa from special object of this type is to reduce the e same through a small air-gapas, d for wind resistance but it is essential that the the purpose described. - _ ‘ bars. have a an cient area to insure small 5. A ' dgnsity, and also that they arelclose enough combination an elevated terminal of large to make the aggregate capacity nearly equal area and r ius of curvature in two dimen- to that of a continuous shell of the same out- . sions, and a grounded conductor of small side dimensions. Fig.7 a cupoln. -shaped self—induction, as set forth. ; and_eart_hed roof is carried by a chimney, _ 6. In apparatus for protection against serving in this way‘ the two old practical . lightning discharges, the combination of an purpose of ‘hood and protector. An_y, kind elevated metallic roof of large area and of metal may be used in its construction but radius of curvature in two dimensions, and it is indispensable that its outer surface ll grounded conductor. of small . self-induc- should be free of sharp edges and projec- tion and i'esista'iice, as described. tions from which streamers mi ht emanate. 7. As an article of manufacture a me- In like mannoi: ‘iiiufilers, funne s uiul -‘cuts tullic shell of large radius of curvature pro- inuy be transfoi-med into eflcctive lightning vided with asleeve adapted for attachment the ‘charge and the elevated terminal, having its outer conduct-a ‘lightning protector - comprising, " ‘in.
  5. 5. 1,2oo,17s to a lightning rod as, and for the purpose set forth. ' 8. A H litnin protector comprising an ellipsoids. met "c shell and a grounded conductor of "small self-induction, as ‘set forth. 9. In apparatus for protection against ate mospheric ‘discharges a cupola-shaped "me- tallic terminal of smooth outer surface, in combination with a scribed. In testimony whereof I afix my NIKOLA T B1 grounded conductor of small self-induction and resistance, as de- g%‘i: i‘. ’°*
  6. 6. N. TESLA. LIGHTNING PROTECTOR. Armenian min an 5. um. 1,266,175. Patented Mn‘y14,1918. . _ _ . _ p ‘I A Md ‘I Iwtiiyrok. -' ’ . ' BY " ' : _ . it at. W - Wt -L ATTOA; Ajirs