US 2572901 A
Description (OCR text may contain errors)
ct 3Q, 1951 E. H. YONKERS 2,572,901
FUSE LINK Original Filed April 26, 1947 2 SHEETSSHEET l INVENTOR.
BY flung KW My M Patented Oct. 30, 1951 FUSE LINK Edward H. Yonkers, Glencoe, Ill., assignor to Joslyn Manufacturing and Supply Corporation, Chicago, Ill., a corporation of Illinois- Original application April 26, 1947, Serial No.
744,061, now Patent No. 2,453,397, dated November 9, 1948. Divided and this application September 25, 1948, Serial No. 51,236
6 Claims. 1
The present invention relates to protective apparatus and more particularly to improvements in apparatus for protecting a pole-supported electrical distribution transformer and for disconnecting the transformer from its current supply line when a fault occurs therein. This application is a division of applicants copending application, Serial No. 744,061, filed April 26, 1947 and assigned to the same assignee as the present invention and which has resulted in Patent No. 2,453,397, dated November 9, 1948.
Apparatus for the purpose described is in certain installations mounted directly upon the housing or tank of the transformer which it is used to protect and conventionally includes entirely independent lightning arrester and fused cutout units for protecting the transformer primary winding against damage occasioned by lightning surges and overload conditions, respectively. In commercial practice few attempts have been made to provide a single unitary device for providing complete transformer protection against dangerous over-voltage and overloads while at the same time providing the usual feature of protecting the line against a short circuit caused by a fault in the transformer. As a result, the cost of providing and maintaining commercially available protective equipment is relatively high.
It is an object of the present invention, therefore, to provide an improved combination arrester-cutout unit of low cost construction which may be easily and quickly installed on any electrical distribution transformer of standard commercial construction, is easy to refuse and fully protects the transformer against damage by lightning surges and overload condition.
It is another object of the invention to provide for use in a combination arrestor-cutout unit, an improved fused cut out of simple low cost construction which may be easily and quickly installed upon the available supporting facilities of a standard electrical distribution transformer.
It is a further object of the invention to provide an improved fuse link, particularly adapted for use in the present improved cutout which is arranged to provide for are elongation incident to fuse rupture and yet is substantially weatherproof and does not require the use of the usual expulsion tube and associated fittings.
In accordance with a further object of the invention, improved and exceedingly simple facilities are provided in the link for protecting the link against burn-out or damage when subjected to lightning surges or the like.
According to still another object of the invention, improved facilities are provided in the link for weatherproofing the active components of the link against exposure to dirt and moisture without interfering with relative movement apart of the two are striking components of the link in response to rupture of the fusible element thereof. 1
It is a still further object of the invention to provide an improved fuse pigtail conductor which is flexible throughout the major portion of its length and is provided with a fixed configuration loop of exceedingly simple construction at one end thereof.
The present invention, both as to its organization and method of operation, together with further objects and advantages thereof, will best be understood by reference to the following specification taken in connection with the accompanying drawings in which:
Fig. 1 is a top perspective view of a conventional electrical distribution transformer equipped with the present improved protective apparatus;
Fig. 2 is a side perspective view of the transformer and protective apparatus illustrated in Fig. 1;
Fig. 3 is a shortened front perspective view of the spring arm forming a part of the cutout embodied in the protective apparatus;
Fig. 4 is a side edge view of the spring arm shown in Fig. 3;
Fig. 5 is a side view partially in section illustrating the structure of the fuse link assembly forming a part of the cut-out embodied in the protective apparatus; and
Fig. 6 is an enlarged view of a portion of Fig. 5 better illustrating certain of the components of the fuse link assembly.
Referring now to the drawings, and more particularly to Figs. 1 and 2 thereof, the present improved protective apparatus is there illustrated as comprising a combination lightning arrestor and fused cutout unit supported by the existing supporting facilities of a standard electrical distribution transformer I0. Specifically, this transformer comprises two sets of supporting brackets l l and I2 which are arranged in spacedapart relationship around the sides of the transformer tank to project radially therefrom, are fixedly mounted upon the transformer tank and are adapted for alternative use in supporting the tank upon a supporting pole or similar supporting structure. The purpose of providing two sets of brackets is to facilitate connection of secondary circuit conductors to the secondary terimpel minals of the transformer (not shown) which are brought out through a terminal block disposed along the hidden side of the transformer tank approximately midway between the brackets. As best shown in Figs. 1 and 2 ofthe draw ings, the transformer is also equipped with the usual bushing insulator [3 which projects up-v wardly from the top of the transformer tank and serves insulatingly to support the usual terminal stud I8. This stud and the unusedset of sup; porting brackets H and I2, 'are e rnplQyed to port all parts of the present improved combination arrestor-cutout unit. V 4 v In brief, this unit comprises a self-contained lightning arrestor Ma, the parts of which are housed within a petticoated insulatonlf l; a rus tube assembly I5, a terminal sub 'assmbly '16 for supporting the fuse tube assembly for pivotal swinging movement about the long axis of the tud .18. an a sta iona y te mina as embly. 1
wi h wh ch e eonta p ovided attne win e d oi hef e tube. asse bly ,5.is,. atc.h n 1y ne goab eo e. spe ifi a ly. h elec rod stru ureof. he tn ng r,... 4a shown in dash linesq n .Fier Zeithedrawims. is us d within a gavity extending upward from the lower end of the insulator I4. Preferably, this arrestor is of the improved expulsiontype disclosed and claimed in liatent No, 2,1 64,720 granted July, 4,1939, to
galph Pittman. Among other elements it comprises a, pair of spaced electrodes, one of whichi connected toa conductive rod Mb extending through the insulator l4 to .the.upper end thereof to support the terminal assembly H, and the other of which is connected to a gap electrode l4b;. e
Forthe purpose of adjustably supporting the insulator and associated parts in a desired vertical and horizontal position upon either of the two sets of radially extending brackets .ll and lZ, two cooperatingbrackets 'l9 and Mia are. .provided.,.More, specifically, the two coopcrating bracket 19 and lga are constructed and arranged. in. the exact manner disclosed and claimed in applicants copending application Sethe present invention. The construction is such that the insulator l4 may be supported upon either ofthe two transformer brackets i I and I2 at any desired elevation,.within limits, and any desired angular setting. The arrangement is also such that the electrode [40 of the arrestor assembly co-acts with the supporting bracket l9 to provide an isolating gap which is appropriately designed as to length to prevent system current leakage through the'arrestor.
"As'indicat'ed above, the cutout assembly comprises a bracket [6 mounted upon the terminal conductor Mb of the insulator [4 at the upper end of this insulator and a spring arm ll mounted upon the'bushi'n'g conductor or stud l8 of the transformer assembly. Preferably, the bracket 16 of 'arc'uate configuration and is fixedly mountedupon the terminal conductor [4b by means "of a nut Hlcthreaded onto this conductor. As will be evident, the 'angularsetting of the bracket l6 relative'to the insulator la'ma'y beadjuste'd as desired by rotating this bracket about the terminal conductor lqb. At its extended end, 'the bracket l6 provided with a pairfoffears "We aiidl bivhkh r spiifi dp ft to were a opening or 'slot'lfic for receivingoneof thepig- 4 tail ferrules of the fuse link assembly in the manner more fully explained below.
As best shown in Figs. 3 and 4 of the drawings, the spring arm I! is of laminated construction throughout the lower portion of its length. More specifically, this arm is comprised of a long lamination Ila and a short lamination llb having their lower ends received within a slot formed in the head 20a of a mounting piece 2!! which is arranged to extend into the eye of an eye bolt}! in mounting the arm [1 upon the transformer bushing stud I8. The lower end portions of the strin arm laminations lid and I'll) are anchored within the slotted head Zea of theypiece 20 by means of a rivet 22 extending, through registering opening in the two laminations and the head part 26a of the piece 20.. Idorder to increase the resiliency of the laminations, thereby to provide the desired tenpqn th i s link. '5 upp rte tw the extended o'f thearm I1 and the bracket [5, lamination [1d provided with elongated weakening slots '23 longitudinally spaced apart along upper part of this arm lamination and the lamination l is similarly provided with elongated weakening slots T24 throughout the lengthh thereof. The short lamination l l b acts as mp n nl nt M me u o i ah of he a e i i ixge e r l e the. a e? l'l from the deformed closed circuit position thereof illustrated in Fig, 2 of the drawings which w s ,i g nt f fi i o h f le elemen forming a part of the fuse link [5. Maximum effectiveness of theshort lamination lib to perq m t is ass ne un t o is ne bvtyin h u per. n or this l' i t i ec iq Qf .the e m ation "gi u h a meaeeregt erm r v i me e,- m t i i ei e ei. .T this @1 1. l rir .5 is extended. thr a pee in h lam n tio .1 a ill qu f the uppere in t e am nation [1b to receive awasherjfi which loosely h l e i tt le ipe n 1 12. b r fini over fli fi f the l lll lm n n .Thi a ra e e m re ei vesl dm m m n t 9? e. tween the, WQ. min i a d. 1 W l restraining the same against deformation in either direction independent of each other. Thus, a mechanical systern is provided which minimizes l' i g Olthe upper end iem in es ons m 'a' e o th in i l wme o ti n thereof. 'As extendedupper end, the spring a e eeieei en .1 l is prov d w h .be ve ears disposed at an angle of approximatelyseventy -five de'grees relative to the other pq l ons of the m. vhie spa e r t e nei n opening or slot 2 9 for receiving the contact ferrule of theother pigtailjcon ductor forming a part or the fuse unk assemmy l5. This open ing extend throughout the length of the ears 2] and 28 andjinto the upper end portion of the armjjin the manner best'illustr'ated in Fig. '3 of he.dfaW ,I r
indicatedabove,the mo'unting piece'ZD is arranged to co-act with aneyebolt 2| in mountingfthe arm i1 uponthe 'tran'sformer bushing stiid'lt. A 'b'est'shojwn in'Fig. 2 of the drawings, tlie'eye of thisjboltls arrangedto enter an eye receiving slotjprovided 'atj'the upper end of the studylB andfifs"threadedfto receive a nut 2m which is use'df'in pulling the'eye into theslot' to clamp the shank 2 Ubof the mounting piece 2 0 "ag instone'side of th emu I8. Breferablythe shankzflbof the I unting jpiece 2ll'is'ofround cross sectional configuration in'order'to permit 5. the arm H to be angularly adjusted about its longitudinal axis so that it is readily deformable flatwise toward the bracket l3. Protection against birds falling upon the arm IT or the bushing stud I8 and producing a short circuit to the transformer tank In is obtained by enclosing this stud and the major portion of the mounting piece 20 within an inverted cup-shaped insulator 33. The top wall 33a of this insulator i slotted to receive the head 20a of the mountin piece 25 so that it may be telescoped upward along the arm I! while are arm assembly is being mounted upon the stud 8 and then dropped down after the mounting operation is completed to, enclose the stud l8 and the co-extending part of the mounting piece 20. r a r Referring now more particularly to Figs. and 6 of the drawings, the present improved fuse link I5 is there illustrated as comprising a tubular metal casing 3| having an open lower end and a flanged upper end which is closed by a terminal cap 32. This cap rigidly mounts a small metallic ferrule 33 within which is solder-connected one end of a pigtail conductor 34. This flexible pigtail conductor extends away, from the end cap 32 and is provided at its extended end with a ferrule 35 and a manipulating loop 36. The ferrule 35 is provided with a conical part 35a adapted for wedging engagement with the ears 2'! and 28 of the spring arm I! in the manner more fully explained below. Preferably, the ferrule 33 employed in electrically and mechanically connecting the pigtail conductor 34 to the end cap 32 is inserted through an opening in this cap and \is provided at its lower end with aflange 33a seated against the under side of the cap andsolderconnected thereto.
A second pigtail conductor 3'! projecting from the lower end of the link l5 functions as the opposite terminal thereof. This conductor is provided at its extended end with a contact ferrule 38 and a manipulating loop 39 of different configuration from the loop 35 in order to permit the two ends of the link to be readily distinguished for the purpose stated below. Preferably, the configuration of the loop 39 is as shown in Fig. 5 of the drawings. The ferrule 38 is provided with a conical portion 38a adapted for wedging engagement with the ears I61: and IB'b of the bracket l6 within the slot |6c between these ears.
In accordance with one feature of the present invention, the pigtails 34 and 35 are constructed in an entirely novel manner. Specifically, and considering the pigtail 34 by way of example, this element is formed from a short length of braided conductive strands, and in the construction thereof is threaded through the ferrule 35 until the length remaining at the upper end thereof is just sufiicient to form a loop 35 of the desired diameter. The upper end of the conductor i now inserted back into the upper portion of the ferrule, following which the loop and ferrule are submerged in a solder bath to impregnate the loop portion of the cable with solder. When this solder is permitted to cool, the loop is stiffened, the end part of the conductor is fixedly anchored within the ferrule 35 and the ferrule is rigidly anchored to the intermediate portion of the conductor adjacent the loop part thereof. The pigtail 37 is formed in an identical manner, except that a differently shaped forming mandrel is employed in the loop forming operation. The construction and mode of operation of the fuse link components provided within the metallic casing 3| are substantially the same as disclosed and claimed in applicants co-pending application Serial No. 637,528, filed December 28, 1946, which has resulted in Patent No. 2,453,396, dated Nov. 9, 1948,. and assigned to the same assignee as the present invention, with the important exceptions pointed out below. This casing 3| houses three fusible elements 4|], 4| and 42 which are connected in series circuit relationship between the casing 3| and the pigtail conductor 31. The two elements 4| and 42 are both formed of Nichrome wire or another metal wire or ribbon of the desired resistivity, and are both of the same cross sectional area, such that they possess substantially identical time-current fusing characteristics. The fusible element 4| is substantially straight throughout the major portion of its length and the lower end portion thereof is centrally disposed within the upper end portion of the stranded pigtail conductor 31, the overlapping portions of the two elements 4| and 3'| being telescoped within a metal assembly sleeve 44. This sleeve is crimped adjacent the lower end thereof, as indicated at 44c, and the lower end of the fusible element 4| is brought out through the strands of the conductor 31 and wrapped around the conductor 31 as indicated at 4|b. After the three elements 4|, 31, and 44 have been assembled to occupy the relative positions illustrated in Fig. 6 of the drawings, the crimp 44c may be formed around the lower portion of the sleeve 44 for the purpose of providing a rigid mechanical connection between the three named parts. Thereafter, the lower end portion of the sleeve 44, the adjacent portion of the pigtail conductor 31 and the wrapped end portion 4|b of the fusible element 4| may be soldered to provide a rigid connection therebetween.
The fusible element 42 may be more properly designated a combination impedance element and heating element in that it functions in conjunction with the improved surge gap facilities described below to prevent surge currents of large magnitude from traversing the fusible elements 45 and 4| and also acts to heat the fusible element 4!] to a fusingtemperature when the link is subjected to an overload current for a sustained time interval. In order to perform these two functions the element 42 is constructed in the form of a helically coiled conductor, and the upper end portion 42a. thereof is electrically and mechanically connected to the under side of the contact head 32 by crimping the same between the flange 3 la and the cap 32.
The convolutions of the element 42 are spaced apart axially of the tube 3|, and the spaced apart relationship between the turns is maintained by embedding the same in a body of dielectric refractory material 45. This body is preferably formed of a refractory cement and serves several functions which are pointed out with particularity below. It may, for example, be formed of Port land cement or any ceramic material which is chemically inert, has high specific heat, and is possessed of good electrical insulating properties. In order to increase the inductance of the element 42, thereby to enhance the surge current blocking function thereof, particles of magnetic ma-- terial, such, for example, as iron power or magnetite, may be dispersed throughout the body 45, but in no case should the density of the magnetic particles be such as to provide conductive paths capable of short-circuiting the convolutions of the element 42. Among other functions, the body of the element 42 in spaced apart relationship therefrom, and is embedded in the body 45-. At its lower end this connecting element is provided with an outwardly extending flange 46a which serves to seat the lower turn of the element '42 in a manner such that the tubular portion "of the element 46 is substantially concentrically disposed within the turns of the element 42. This lower turn ofthe element 42 is electrically and mechanically connected to the flanged portion 46a; of the element 46 by means of a high meltin point solder '41, or the like. The upper end of ,the connecting element -45 is electrically and mechanically connected to the upper serpentine end 4|a of the fusible element 4| through the fusible element 40, the latter element being inthe form of a body of alloy solder having a melting point of approximately 365 F. It is to be noted that, the fusible element 4|), as thus formed within the tubular portion of the connecting element 46, is disposed well within the turns of the ole-- .ment 42 so that heat generated by current conduction through the latterelement may be transzferred to the fusible element 463 through that portion of the refractory body 45 which separates the fusible element 40 from the adjacent turns of the element 42. Spring tension imposed upon the free lower end of the pigtail conductor 31 may be utilized to rapidly withdraw the end 4|a of the fusible telement 4| from the connecting element 46 when the named fusible element is heated to a melting temperature, and to widen a break in the fusible element 4| occasioned by heating this element to a fusing temperature;
For the purpose of increasing the heat storage "capacity of the structure including the fusible element 40, a thermal storage element 48 is provided which is arranged in heat transfer relationship with the element 48 and the heating element 42. This element is in the form of a copper or brass rod disposed centrally of the tubular casing 3| and having its lower end contacting the exposed upper surface of the fusible element 40. It is held in an upright position in axial alignment with the tubular conductor 46 by virtue of its being embedded in the body 45.
During prolonged use of the link, the upper. portion-of the fusible element 43 may many timeslower convolutions of the coiled conductor 42-,- This would result in undesired modification of ,the time-overload characteristic of the link. In order to obviate this possibility, a ceramic 'insu' llating tube 49 is provided to act as a barrier between the parts. 43, 46, and 48 and the turns; of the coiled conductor element 42-. thistube is telescoped over the tubular conductor 46 to rest upon the flange: 46aand is embedded in 'the body 451 inthemanner illustrated. Being Specifically,
8 of heat resistant ceramic material, the tube 49 is not subject to cracking and hence actsas a leak-proof barrier between the fusible element and the convolutions of the coiled conductor, element 42. Also, since the tube 49 has approximately the same heat transfer characteristics as the body 45, its presence in the zone of heat "transfer between the elements to and as and the" element 42v does not seriously complicate the problem of producing links having substantially the same time-overload characteristics in pro-- duction quantities. Further, provision of the tube 49 in the structure facilitates assembly of the component elements of the structure the manner explained below.
In order to maintain the turns of the element 42 out of contact with the metal casing 3| to maintain the element 4| out of contact with the tubular casing 3| and to provide a support for the surge gap facilities described below, the entire assembly within the casing 3| and a part of the sleeve 44 are surrounded by a tube formed of Bakelite or other suitable insulating material. At its upper end, this tube is pro vided with a flange 50a. pressed against the metal casing flange 3|a when the cap 32 is fastened to the flange am. This tube 50 fits snug- 1y within and is adhesively bonded to the tubular member 3|, and the lower end portion 58b: thereof projects outwardly from the open lower endof the casing 3|. It is counterbored from the upper end to provide a first portion 500 of large internal diameter for receiving the parts 42, 45, 46., 48, and 49, and a second portion 56b of smaller internal diameter for receiving the fusible element 4|. The flange 46a. of the tubular conductor 46 is seated upon the step 5011 between these two portions of the tube 50.
In order to assist in producing arc extinction within the tube 50 when the link is ruptured either through fusing of the element 43 or fusing of the element 4|, that part of the tube portion 5% through which the fusible element 4| extends may be lined with a gas evolving material 5|. Preferably, this lining is in the form of a layer of long fiber cellulose adhesively secured to the. inner surface of the tube portion 5% between the flange 56d, and the upper end of the sleeve 44 to surround the fusible element 4|.
For the purpose of preventing moisture, dirt and the like from coming into contact with the active components of the fuse link there is provided in accordance with the present invention a viscous sealing material, preferably comprising one of the recently developed silicones, which .is inserted in the space between the tube 50 and the sleeve 44. If desired this viscous sealing material may also fill a substantial portion 'of the space between the liner 5| and the fusible element 4| to insure good sealing action. It has been found that the use of such material in the space between the liner 5| and the fusible element 4| does not interfere with are interruption and does not impede the separation of the parts of the fuse link upon interruption thereof.
" end which spaced apart from a member 54 associated with the cap assembly 32 in a manner so as to define a small air gap 52 between the member 54 and the adjacent end of the heat storage member 48. This gap in combination with the storage element 48 and the fusible body 40 provides a surge path in shunt with the heating element 42 for by-passing surges around this element.
In order to assist in weather proofing the above described active components of the link and more important to assist in producing arc extinction in response to rupture of the link by heavy overloads, a weather proof tube 53 is provided which is wholly supported by the casing 3|. More specifically, the upper portion of this tube as viewed in Fig. 5 of the drawings is press fitted onto the casing 3| to bring the upper end thereof into abutting engagement with the ends of the cap 32. The lower end of the tube 53 extends outwardly beyond the lower end of the insulating tube 50 to house an appreciable portion of the pigtail conductor 31. In order to aid in the arc extinguishing action the portion of the tube 53 below the end of the tube 50 is lined with a short length of a tube 55 preferably formed of a gas evolving insulating material which is pinned into position within the expulsion tube 53 by means of a small pin 56. It should be understood that the tubes 53 and 53 could comprise a single tube in which case the casing 3| would -be dispensed with. With such an arrangement a much longer are extinguishing section is provided without the requirement of a separate expulsion tube. In the illustrated embodiment the two separate tubes 50 and 53 are provided so that a standard fuse link may be employed while affording the same operation as when a single tube is used.
When using the fuse link I 5 to fuse the cutout embodied in the protective apparatus shown in Figs. 1 and 2 of the drawings, the round configuration of the loop 36 provides an indication to the lineman that this end of the link should be connected to the upper end of the spring arm ii. In this regard it will be understood that the line connection is brought into the terminal conductor Nb of the arrestor Ma so that with the apparatus unfused, a connection is first made with the dead spring arm [1 during the fusing operation. This connection may conveniently be made by using the hook of a hot-stick to position the contact ferrule in the channel 29 between the ears 2! and 28 with the conical part of this ferrule engaging the edges of the two ears. After this connection is made, the hotstick hook may be shifted to the loop 39 and the link I5 pulled toward the bracket IE to insert the contact ferrule 38 into the slot I between the ears Mia and I512 of this bracket. As this operation is performed, the spring arm I! is de-formed toward the bracket [6 in the mannerillustrated in Fig. 2 of the drawings. After the contact ferrule 38 is positioned between the bracket ears 18a and lBb, the pulling force exercised on the loop 39 through the hot-stick may be relieved permitting the ferrule 38 to move into the channel 16a to bring the conical part 38a thereof into wedging engagement with the sides of the ears [6a and I 6b. Thus the fusing op- .eration is completed through the performance of a relatively few simple steps.
As best shown in Fig. 2 of the drawings, with .the cutout of the unit fused, the fuse link I5 is angularly disposed with respect to the horizontal with its open end disposed in the lowermost portion. This positioning of the link, insures against rain entering the expulsion tube 53 and assists the viscous sealing material in preventing moisture, dirt and the like from coming into contact with the active components of the link. Thus there is no necessity for housing the link to protect the same.
' As indicated above, the conical portions of the two ferrules 35 and 38 are wedgingly engaged with the ears provided at the extended ends of the spring arm I! and the bracket [6 respectively. This wedging engagement insures good electrical conductivity between the contact ferrules and the spring arm and bracket without the necessity of imposing an excessive pull upon the fusible element 40 of the link which might destroy the current-time characteristics thereof.
As pointed out above, the live or high voltage side of the line feeding the transformer I0 is connected to the terminal conductor Nb of the ar restor unit [4a so that current is normally fed to the transformer primary winding over a path which includes the bracket IS, the contact ferrule 38, the pigtail conductor 31, the fusible elements 4|, 4!] and 42 in series, the casing terminal cap 32, the pigtail conductor 34, the contact ferrule 35, the spring arm I1, mounting piece 20 and the transformer bushing stud I8. The tank of the transformer 10 provides the usual ground connection. With the circuit thus arranged, the arrestor Ma provides a lightning surge path between the high voltage side of the line and ground which serves to by-pass the link l5 and the primary winding of the transformer when lightning surges are impressed upon this side of the line. Such surges are prevented from burning out or damaging the heating element 42 of the fuse link through the action of the facilities including the gap 52 for by-passing this element. In this regard, it is noted that the character of the surges which may be permitted to act upon the fusible elements 4| and 42 by the arrestor Hat is such that these two elements are not susceptible of being ruptured.
' In considering the mode of operation of the fuse link l5, it may be assumed that the transformer I0 is provided with a low voltage secondary load which under normal conditions approximates the full load'capacity of the transformer l0, and that this secondary load includes motors and other devices which, during the starting periods thereof, are capable of producing heavy transient currents of relatively short duration in both the primary and secondary windings of the transformer I0. In this regard, it will be understood that due to the heat radiating capabilities of the transformer parts, the transformer I!) may be capable of withstanding an overload current'of reasonable magnitude, such, for example, as 200 to 300 per cent, for a relatively long time interval; whereas it can withstand current of the order of 500 per cent of normal for only a short time interval. It will also be understood that the transformer is capable of being damaged by a sustained increase in the voltage applied thereto.
The fuse link I5 operates to protect the transformer against damage occasioned by overload currents caused by any one of the mentioned factors. At the same time, the fuse link permits the transformer to be operated under sustained overload current conditions for a period less than that required to damage the transformer, and will not rupture when subjected to the normal and non-injurious high currents which are pro- "thethermal storage element 48. load current conditions and with a constant voltage so long as the load current. through the duced incident to motor starting, or the like. In this regard it will be understood that since. the
three serially related elements 40, 4| and 42 of the link 15 are traversed by the current flowing through the primary winding of the transformer,
"they are all heated by current conduction and the temperature of each element varies with changes in the magnitudeof this current. The
fusible element 4|) is also heated by the heat Heat rounding turns of the element 42, and also from Under constant secondary winding of the transformer does. not substantially exceed the full load capacity of this transformer, the fusible element 4|] is operated at'a temperature well below that required to produce fusion thereof. When, however, the secproaching that at which the transformer will be damaged, the temperature of the fusible element '40 is raised accordingly. Thus, as the load current increases, the current traversing the three elements 40, 4| and 42 is correspondingly increased so that more heat is produced in the fusible element 40 by current conduction. Concurrently the amount of heat conducted to this fusible element from the fusible elements 4| and 42 is increased. Also concurrently, the amount of heat transferred from the turns of the element 42 to the fusible element 4|) through the refractory body 45 and the tube 49 is. increased. A portion of the heat energy accumulating the element 4|] is transferred to the storage element '48 by conduction. After a predetermined time interval, required for the accumulation of heat within the fusible element '23, this element is heated to its fusing temperature and melts.
Provision of the storage element 48 materially increases this time interval over that which would obtain in the absence of this element in the combination. When the element 40 is thus ruptured, the fusible element 4|, the sleeve 44, and the upper end of the pigtail conductor 31, are
quickly expelled from the lower ends of the tubes 3| and 50 under the influence of the spring arm I I, thereby rapidly to break the circuit for energizing the primary winding of the transformer.
During the described separation of the element 4| from the tubular conductor 46 upon fusing of the element 40, an arc is drawn within the portion 50b of the tube 50. This are instantly heats the coating 5| to gas evolving ternperature, with the result that gases are evolved therefrom which accelerate extinction of the are. It has been found that provision of the gas evolving coating 5| permits the link itself to effectively extinguish heavy current arcs of the order of several hundred amperes even when the link is used in high voltage circuits of several thousuit of motor starting or the like. Such surge currents are of short duration, being of the order of only a few seconds. The resulting momentary increase in heat generation Within the fusible element 48 is wholly insufficient tov raise the temperature of the element to its melting point. Moreover, those portions of the refractory body 45 and the tube 49 which are disposed between the tubular portion of the connecting element 46: and the storage element 48 and the turns of the heating element 42 dissipate. a large portion of the heat resulting from the current surge through the element 42 away from the element 4|. The also delay the transmission of the increased increment of heat produced by the element: 42 to the storage element 48 and the adjacent walls of the connecting element 46 for an interval which will normally exceed the duration of the current transient. Accordingly, the increased increment of heat energy arriving at the surfaces of the connecting element 46 and storage element 43 from the element 42 as a result. of the momentary high current, effects an insufficient increase in the temperature of the fusible element 49 to cause this element to melt. In other words, the total heat accumulated in the fusible element 4|! as a result of the transient high current is insufficient to heat this element to its fusing temperature. Thus it will be understood that the refractory body 45 and the tube 49, or more exactly the thermal impedance of this composite structure, protects the fusible eieinent 44 against outages occasioned by transient currents of the character which frequently occur in the load pattern of any transformer secondary load. This is accomplished, moreover, without increasing the thermal capacity of the fusible element 40 to a point such that it will provide no protection for sustained overload currents.
The thermal impedance of the refractory body 45 and the tube 49 also prevents the fusible element 45! from immediately rupturing when the transformer is subjected to a high current, such, for example, as that which is produced when the secondary winding of the transformer is short-circuited. In the absence of an additional protective element, therefore, the transformer could easily be damaged by an overload current of this character during the period required to transfer sufiicient heat from the heating element 42 to the fusible element 41] to cause the latter element to melt. The second fusible element 4| functions to guard the transformer against damage when subjected to an overload current of this type. Thus, immediately the element 4| is subjected to a transient current of the particular character just referred to, a portion thereof lying between the upper end of the sleeve 44 and the lower end of the fusible ele-- ment 40 is heated to a fusing temperature, permitting this element to rupture.
When the fuse link I5 is ruptured in response to an overload condition of any one of the types mentioned above, i. e., through melting of the fusible body 4!] or melting of the fusible element 4|, the holding forces imposed upon the deforming spring arm IT are instantly released permitting this arm to swing to the left from its closed circuit position illustrated in Fig. 2 of the drawings. Incident to this operation the link I5 is pulled away from the pigtail 31 to produce arc elongation within the tube 50. As the arm I! swings away from the bracket l6, thetubes 3! and 0 are pulled away from the pigtail '31 and describe an are above the extended end of the arm IT. The elements of the link being pulled away from the element l6 obviously gather momentum as the movement of the arm I! proceeds with the result that when this arm stops at a position to the left of its unrestrained position as shown in Fig. 2 of the drawings the contact 35 is pulled out of the channel 29 and drops to the ground. In this regard, it will be noted that all of the components within the tube 3| which may become heated to a high temperature incident to rupture of the fuse and extinction of the are are contained within the tube 3|, the outside of which remains at a low temperature. Hence there is no possibility of the production of grass fires when the parts of the link 15 fall to the ground. When the pigtail 31 becomes disengaged from the remaining components of the link through the action of the spring arm I! in the manner just explained, it falls down. over the bracket is and remains in this position until such time as the cutout is re-fused. In this regard it is pointed out that the length of the pigtail 3'! is substantially less than the distance between the upper end of the insulator I4 and the grounded brackets supporting this insulator so that there is no possibility of this conductor short-circuiting the high voltage side of the line to ground. The manner in which the cutout may be re-fused will be clearly apparent from the foregoing explanation.
' From the preceding explanation it will be understood that the disclosed protective apparatus is exceedingly simple in arrangement, may be easily and cheaply manufactured, and yet provides positive protection against damage to an associated transformer or the like when the transformer is subjected to all types of overloads and lightning surges of the character normally encountered in operating practice. Thus the cutout portion of the apparatus requires only three elements in addition to those normally provided in transformer protective equipment, namely, the small bracket I B, the simple spring arm assembly l1, and the fuse link l5. .All of these elements are of very simple construction and may be easily manufactured at low cost. Further, the operations required in re-fusing the assembly may easily be performed by relatively unskilled linemen without danger and in a very short time.
While there has been described what is at present considered to be the preferred embodiment of the invention, it will be understood that various modifications may be made therein which are within the true spirit and scope of the invention as defined in the appended claims.
1. A fuse link adapted for support between a pair of supporting elements which are biased for relative movement away from each other, comprising a tubular metal casing having an open end and a closed end, a terminal conductor electrically and mechanically connected to said casing and extending away from the closed end thereof, for connection to one of said supporting elements, an expulsion tube closely embracing said casing and extending away from the open end of said casing, said expulsion tube forming a unitary part of said fuse link, a second terminal conductor adapted for connection to the other of said supporting elements and extending into said expulsion tube, and fusible means disposed within said casing and serially connected between the inner end of said second terminal conductor and said casing.
2. A fuse link adapted for support between a pair of supporting elements which are biased for relative movement away from each other, comprising a tubular metal casing having an open end and a flanged end, an end cap closing the flanged end of said casing, an open-ended insulating tube projecting from the open end of said casing, a terminal conductor projecting from the open end of said insulating tube for connection to one of said supporting elements, means including a fusible element disposed within said casing for providing a conductive path of limited current capacity between said conductor and said casing, an expulsion tube embracing and press fitted onto said casing and provided with an end abutting the flanged end of said casing, said expulsion tube projecting beyond the open end of said insulating tube to enclose a substantial portion of said terminal conductor, and a second terminal conductor electrically and mechanically connected to said end cap and extending away from said end cap for connection to the other of said supporting elements.
3. A fuse link adapted for support between a pair of supporting elements which are biased for relative movement away from each other, comprising a tubular metal casing having an open end and a closed end, an open ended insulating tube projecting from the open end of said casing, a terminal conductor projecting from the open end of said insulating tube for connection to one of said supporting elements, means including a fusible element disposed within said insulating tube for providing a current conductive path between said conductor and said casing, an
expulsion tube mounted upon said casing and projecting beyond th open end of said insulating tube to house a substantial portion of said terminal conductor, and a second terminal conductor electrically and mechanically connected to said casing and extending away from the closed end thereof for connection to the other of said supporting elements.
4. A fuse link adapted for support between a pair of supporting elements which are biased for relative movement away from each other and are provided with openings for receiving the terminal conductors of said fuse, comprising a tubular metal casing having an open end and a closed end, a flexible pigtail conductor electrically and mechanically connected to said casing and extending away from the closed end thereof, an expulsion tube mounted upon said casing and extending away from the open end of said casing, a second flexible pigtail conductor extending into said expulsion tube, means including a fusible element disposed within said expulsion tube for providing a conductive path of limited current capacity between the inner end of said second pigtail conductor and said casing, said second pigtail conductor being withdrawable from said expulsion tube to effect are elongation within said tube in response to rupture of said fusible element, and conductive ferrules fixedly embracing said pigtail conductors adjacent the extended ends thereof and provided with portions adapted for engagement with the openings in said supporting elements.
5. A fuse link adapted for support between a pair of supporting elements which are biased for relative movement away from each other and are provided with openings for receivingthe terminal conductors of said fuse, comprising a tubular metal casing having an open end and a closed end, an open ended insulating tube projecting from the open nd o said insulatin 'tube, means i .li d ns -.a.fnsib e e ement dispos d within sai nsulatin tube f prov din a onductive path 5Q: limited semie capa ity b we sa d c n uctor an said casin an expulsi n tu e unted in n seidea ine a dpr i tins ey nd the open e doi s id i sul ti e to u e a s b a tial portion of said pigtail conductor, said pigtail conductor being withdrawable fromsaid tubes to effect are elongation therewithin in response to rupture of said fusible element, and conductive rrules fixedly embracing said pig-tail conductors ac ent the extended ends thereof and provided "with eonica l portions adapted for wedging encas ment w th ope n s in sa supportin nts. fuse link adapted for support between a pair ei s pp in el ments which a e' esed for r lativerne e n n awa fr m h th r a d 3E nre ided th openin for e ing the erminal condu o o a fuse pri ng a tu ula zneta eesi e havin a p d and a a g d end, an end cap closing the flanged end of said leasin an p ended in ulat n t e projecting iron; the open end of said tube, a-ilexible pigtai] onductor projecting from the open end of said insulating tube and provided with a solder connested end ferrule fitting snug y Within the bore of said insulating tube to weather seal the interior of said tube, means including a fusible element disposed within said insulating tube for providing a conductive path of limited current capacity hetween the inner end of said flexible pigtail eonductor and said-casing, an expulsion tube clampingly enclosing said casing and having an end abutting the flanged end of said casing, said expulsion tube projecting beyond the open end of said insulating tube to enclose a substantial portion of said conductor and said conductor being withdrawable from said tubes to effect are elongation in response to rupture of said fusible element, a second flexible pigtail conductor connected to and extending away from said end cap, and conductive ferrules fixedly embracing said pigtail conductors adjacent the extended ends thereof and provided with conical portions P adapted for wedging engagement with the openings in said supporting elements.
EDWARD H. YO-NKERSl REFERENCES CITED The following references are of record in the file of this patent:
UNITED STATES PATENTS Number Name Date 1,944,762 Sandin Jan. 23, 1934 1,952,635 Steinmayer Mar. 27, 1934 2,256,360 Steinmayer et a1. Sept. 16, 1941 2,281,795 Pittman et al. May 5, 1942 2,315,311 Brown Mar. 30, 1943 2,333,345 Steinmayer Nov. 2, 1943 2,485,076 Timerman Oct. 18, 1949