US2639346A

US2639346A - Transformer protective apparatus

Info

Publication number: US2639346A
Application number: US247442A
Authority: US
Inventors: Edward H Yonkers
Original assignee: Joslyn Manufacturing and Supply Co
Current assignee: Joslyn Manufacturing and Supply Co
Priority date: 1948-09-25
Filing date: 1951-09-20
Publication date: 1953-05-19
Anticipated expiration: 1970-05-19

Description

May 19, 1953 E. H. YONKERS 2,639,346

TRANSFORMER PROTECTIVE APPARATUS Original Filed Sept. 25. 1948 2 Sheets-Sheet l I IN V EN TOR.

Eda/a rdHYmz/zerq B Y KM m v r May 19, 1953 E. H. YONKERS TRANSFORMER PROTECTIVE APPARATUS Original Filed Sept. 25, 1948 2 Sheets-Sheet 2 VENTO a 0 6 mm m W; Z W fimm V. r m .w w

m MW Eda/adj? Patented May 19, 1953 TRANSFORMER PROTECTIVE APPARATUS Edward H. Yonkers, Glencoe, Ill., assignor to Joslyn Mfg. & Supply 00., Chicago, Ill., a corporation of Illinois Original application September 25, 1948, Serial No. 51,236, now Patent No. 2,572,901, dated October 30, 1951. Divided and this application September 20, 1951, Serial No. 247,442

4 Claims.

The present invention relates to protective apparatus and more particularly to improvements in apparatus for protecting a pole-supported electrical distribution transformer and for disconmeeting the transformer from its current supply line when a fault occurs therein. This application is a division of applicants copending application, Serial No. 51,236, filed September 25, 1948, now Patent No. 2,572,901, dated October 30, 1951, and assigned to the same assignee as the present invention.

. 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 arrester-cutout unit, an improved fused cutout of simple low cost construction which may be easily and quickly installed upon the available supporting facilities of a standard electrical distribution transformer.

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; V

Fig. 2 is a side perspective view of the transformer and protective apparatus illustrated in Fi 1; 'T

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 cutout 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 arrester and fused cutout unit supported by the existing supporting facilities of a standard electrical distribution transformer 10. Specifically, this transformer comprises two sets of supporting brackets H and [2 which are arranged in spaced-apart 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 terminals 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 of the drawings, the transformer is also equipped with the usual bushing insulator l3 which projects upwardly from the top of the transformer tank and serves insulatingly to support the usual terminal stud [8. This stud and the unused set of supporting brackets II and I2, are employed to support all parts of the present improved combination arrester-cutout unit.

In brief, this unit comprises a self-contained lightning arrester [4a, the parts of which are housed within a petticoated insulator [4, a fuse tube assembly [5, a terminal subassembly 16 for supporting the fuse tube assembly for pivotal swinging movement about the long axis of the stud I8 and a stationary terminal assembly H with which the contact provided at the swing end of the fuse tube assembly 15 is latchingly engageable. More specifically, the electrode structure of the lightning arrester I la shown in dash lines in Fig. 2 of the drawings is housed within a cavity extending upward from the lower end of the insulator I4. Preferably, this arrester is of the improved expulsion type disclosed and claimed in Patent No. 2,1643% granted July 4, 1939, to Ralph E. Pittman. Among other elements it comprises a pair of spaced electrodes. one of which is connected to a conductive rod i ioextending through the insulator i i to the upper end thereof to support the terminal assembly 27-, and the other of which is connected to a gap electrode Me.

For the purpose of adjustably supporting the insulator it and associated parts in a desired vertical and horizontal position upon either of the two sets of radially extending brackets l :l and 12, two cooperating brackets 59 and 19d are provided. More specifically, the two cooperating brackets is and We are constructed and arranged in the exact manner disclosed and claimed in applicants prior Patent No. 2,508,055; granted May 16, 1950. The construction is such that the insulator it may be supported upon either of the two transformer brackets H and S2 at any desired elevation, within limits, and any desired angular setting. The arrangement is also such that the electrode lie of the arrester assembly counts with the supporting bracket It to provide an isolating gap which is appropriately designed as to length to prevent system current leakage through the arrester.

As indicated above, the cutout assembly conipris es a bracket l6 mounted upon the terminal conductor Mb of the insulator H3 at the upper end'oi this insulator and a spring arm I? mounted upon the bushing conductor or stud iii of the transformer assembly. Preferably, the bracket It is of arcuate configuration and is fixedly mounted upon the terminal conductor Mb by means of a nut Hid threaded onto this conductor. As will be evident, the angular setting of the bracket IS relative to the insulator Ill may be adjusted as desired by rotating thisbracket about the terminal conductor l ib. At its extended end, the bracket 1 6 is provided with a pair of cars IGct and lob which are spaced apart to define an opening or slot I80 for receiving one of the pig'- tail ferrules of the fuse link assemblyin the manner more fully explained below.

As best shown in Figs. 3 and 4 of the drawings,

21 in mounting the arm i1 upon the transformer bushing stud 18. The lower end portions of the spring arm laminations Ha and Eli) are anchor'ed within the slotted head We of the "piece Ebbymeans'oi a rivet 22 extending through registering openings in the two laminations and the head part 2601. of the piece 2i]. In order to increase theresiliency of the laminations, thereby to provide the desired tension upon the fuse link l -supported between the extended end of the arm ll and the bracket "l8, lamination Ha is provided with elongated weakening slots 23 longitudinall'y spaced apart along the upper part of this arm lamination and the lamination I-1b is similarly provided with elongated weakening slots 2 4'throu'ghout the length thereof. The'short lamination i'lb acts as "a damping element to damp out oscillation of the arm 11 in response t'o'rele'ase of the'arm it from thedeform'ed-closed circuit position thereof illustrated in Fig. 2 "of the drawings whichoccurs incident to rupture-of i the fusible element forming a part of the fuse link 15. Maximum effectiveness of the short lamination ill) to. perform this assigned function is obtained by tying the upper end of this lamination to the adjacent section of the long lamination llc in such manner as to permit relative sliding movement therebetween. To this end, a rivet 25 is extended through an opening in the lamination Ila and through the upper slot 24 in the lamination Hb to receive a washer 26 which is loosely held against the lamination I'Ib bypeen ing over the rivet in the usual manner. This arrangement permits relative sliding movement to occur between the two laminations Ila J and l'lb while restraining the same against deformation in either direction independent of each other. Thus, a mechanical system is provided which minimizes oscillation of the upper end of arm H in response to release of the arm following deformationthereof. At its extended upper end, the spring arm lamination Ha is provided with bent over ears: disposed at. an angle of approximately s'eventy-five degrees relative to the other portions of the arm which are spaced apart to define an opening or slot 29 for receiving the contact ferrule of the other pigtail conductor forming apart of the fuse link assembly I5. This opening extends throughout the length of the ears 2? and 28 and into the upper end portion of the arm in the manner best illustrated in Fig. 8 of the drawings.

As indicated above, the mounting piece 20 is arranged to coact with an. eye bolt 2| in mounting the arm ll upon the trans-former bushing stud it. As best shown in Fig. 2 of the draw ings, the eye of this bolt is arranged to enter an eye receiving slot provided at the upper end of the stud l8 and is threaded to receive a nut .2111

which is used in pulling the eye into the slot to clamp the shank 20b of the mounting piece '20 against one side of the stud It. Preferably the shank 20b of the mounting :piece 211 is of round cross sectional configuration in order to permit the arm H to be singularly adj ustedabout its iongitudi'nal axis so that it is readily deformable flatw-ise toward the bracket '26. Protection against birds falling upon the arm I! or the bushing stud l8 and producing a short circuit to the transformer tank It is obtained by enclosing this stud and the major 'p'or'tion of themounting piece Iii-within an inverted cup-shaped insulator -30. Th'e'top wall 30a of this insulator is slotted to receive the head toe of the mounting piece 20 so that it may be telescoped upward along the arm 1-! while the arm assembly is being mounted upon the stud i8 and then dropped down after the mounting o 'aera'tion is completed to enclose the stud 1'3 and the ico extending part of the mounting piece 20. s

Referring now more particularly tolligs. :5 and 6 of the drawings, the fuse link i5 is there illustrated as "comprising a tubular :metal casing :3l having an open lower end and a flanged upper end which isclosed by the 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 LEllQtEJl-l conductor extends away, from the end'cap 32 and is provided "at its extended end with a ferrule-35 The ferrule 35 isand a manipulating loop 36. provided with a conical part 3 5a adapted for wedging engagement with the ears 2"! and 280i the springarm l1 in the manner more fully explained below. :Preferably, the ferrule v:33 em ployed in electrically and mechanically connect ing 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 a flange 33a seated against the under side of the cap and solder-connected thereto,

A second pigtail conductor 31 projecting from the lower end of the link l functions as the opposite terminal thereof. This conduptor is provided at its extended end with a contact ferfule 38 and a manipulating loop 39 of different configuration from the loop 36 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 33 is provided with a conical ortion 33a adapted for wedging engagement with the ears Ito and |6b of the bracket I6 within the slot |6c between these ears.

The pigtail 34 is formed from a short length of'b'raided conductive strands, and in the construction thereof is threaded through the ferrule 35 until the length remaining at the upper end thereof is just sufficient to form a loop 36 of the desired diameter. The upper end of the conductor is 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. Thepigtail 31 is formed in an identical manner, except that it 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 prior Patent No.. 2,453,396, granted November 9, 1948, with the important exceptions pointed out below. This casing 3| houses three fusible elements 40, 4| and 42 which. are connected in series circuit relationship between the, casing 3| and the pigtai],

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-cur-v rent fusing characteristics. The fusible element 41 is substantially straight throughout the maj or 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 31 being telescoped within a metal assembly sleeve 44. This sleeve is crimped adjacent the lower end thereof, as indicated at 44a, and the lower-end of the fusible element 4| is brought out through the strands of the conductor 3'! and wrapped around the conductor 37 as indicated at 4|b. After the three elements 4|, 31, and 44 have been assembled to occupy the relative positions illustratedin Fig. 6 of the drawings, the crimp 44a 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 40 and 4| and also acts to heat the fusible element 40 to a fusing temperature 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 underside of the contact head 32 by crimping the same between the flange 3|a 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 Portland cement or any ceramic material which is chemically inert, has high specific heat, and is possessed of good electrical insulating proper ties. In order to increase the inductance of the element 42, thereby to enhance the surge current blocking function thereof, particles of magnetic material, such, for example, as iron owder 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 45 serves rigidly to position or support the turns of the element 42 Within the tube 3|, and to this end entirely fills the upper portion of the tube. It also serves to support a tubular conductor 46 centrally of the tube 3|, this element being utilized in the connection of the fusible element 4| with the lower end portion of the combination heating and inductance element 42. More specifically, the upper tubular portion of the connecting element 46 is projected well within the turns of the element 42 in spaced apart relationship therefrom, and is embedded in the body 45. ment 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 tubu lar portion of the element 46 is substantially concentrically disposed within the turns of the element 42. This lower turn of the element 42 is electrically and. mechanically connected to the flanged portion 46a of the element 46 by means of a high melting point solder 41, or the like. The

upper end of the connecting element 46 is elec-- trically and mechanically connected to the upper serpentine end Ma of the fusible element 4| through the fusible element 40, the latter element being in the form of a body of alloy solder having a melting point of approximately 365 F. It is to be noted that the fusible element 40, as thus formed Within the tubular portion of the connecting element 46, is disposed well within the turns of the element 42 so that heat generated by current conduction through the latter element,

may be transferred to the fusible element 40 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 3! may be utilized to rapidly withdraw the end 4la of the fusible element from the At its lower end this connecting eleconnecting element 45 when the named fusible element is heated to a melting temperature, and to widen a break in the fusible element 41 coca sioned 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 40 and the heating element 42. This element is in the .form of a copper or brass rod disposed centrally of the tubular cas ing 31 and having its lower end contacting the exposed upper surface of the fusible element 4%. 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 40 may many times be heated to a fluid state without actual rupture of the element due to lack of persistence of the current overload responsible for the excessive heat energy, Also repeated heating and cooling of the body 45 may result in the formation of small interstices therein through which the fluid metal could be dispersed to short-circuit the lower convolutions of the coiled conductor 4:2. This would result in undesired modification of the time-overload characteristic of the link. In order to obviate this possibility, a ceramic insulating tube 49 is provided to act as a barrier between the parts .411, -45., and :48 and the turns of the coiled conductor element it. Specifically, this tube is telescoped over the tubular cnductor 46 to rest upon the'fiange 43c and is embedded in the body 45 in the manner illustrated. Being of heat resistant ceramic material, the tube to is not subject to cracking and hence acts .as a leak-proof barrier between the fusible element 40 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 46 and 48 and the element 42 does not seriously complicate the problem of producing links having substantially the same time-overload characteristics in production quantities. Further, provision of the tube 49 in the structure facilitates assembly of the component elements of the structure in the manner explained below.

In order to maintain the turns of the element 42 out of contact with the metal casing ii, to maintain the element 41 out of contact with the tubular casing 31 and to provide a support for the surge ga facilities described below, the en-' tire assembly within the casing 3i and .a part ofthe sleeve 14 are surrounded by a tube 50 formed of Bakelite or other suitable insulating material. At its upper end, this tube is provided with a flange 50a pressed against the metal cas ing flange am when the cap 32 is fastened to the flange 31a. This tube 59 fits snugly within and is adhesiv'ely bonded to the tubular mem--- ber 31, and the lower end portion 56b thereof projects outwardly from the open lower end of the casing 3 i. It is counterbored from the upper end to provide a first portion 50o of large internal diameter for receiving the

parts

42, 45, 11 6, .418, and 49, and a second portion 50b of smaller internal diameter for receiving the fusible element 41. The flange 45a of the tubular conductor 45 is seated upon the step 5% between these two portions of the tube 50.

In order to assist in producing arc extinction within the tube 5.0 when the link is ruptured either through fusing of the element form-sing of the element 41, that part of the tube portion b through which the fusible element .41 extends may be lined with a gas evolving material 54. Preferably, this lining is in the form of a layer of long fiber cellulose adhesively secured to the inner surface of the tube portion 50b between the flange 50d and the upper end of the sleeve 44 to surround the fusible element 4:1. 7

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 tube150 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 4l-to insure good sealing action. It has been found that the use of such material in the space between the liner 5i and the fusible ele ment 4! does not interfere with are interruption and does not impede the separation of the parts of the fuse link unon interruption thereof.

As indicated above, in order to prevent light ning surges from rupturing the fusible heatinz element 42, a surge gap having relatively immov able electrodes is connected in shunt with this element. Specifically, and in accordance with one feature of the present invention, the heat storage element 43 having its lower end in electrical and mechanical contact with the upper end of the fusiblebody 40, is provided with upper end which is spaced apart from a member 54 associated with the .cap assembly :32 in a. manner so as to define a small air gap 52 be tween the member .54 and the adjacent end of the heat storage member 48. This gap in eombination with the storage element 48 and the fusible body at provides a surge path in shunt with the heating element 42 for lay-passing surges around this element.

In order to assist in weatherprooflng the above described active components of the l5 and more important to assist in producing arc extinction in response to rupture of the by heavy overloads, a weatherproof tube 153 is provided which is wholly supported by the cue ing 3L More specifically, the upper portion of this tube as viewed in Fig. 5 of the drawings is press fitted onto the casing 31 to bring the'upper end thereof into abutting engagement with the ends of the cap The lower end or the tube 53 extends outwardly beyond the lower end .0; the insulating tube 50 to house an appreciable portion of the Pigtail conductor 3.1. In order toaid in the are extinguishing action the portion of the tube 53 below the end of the tube '58 is lined with a short length 01 2 tube $55 preferably formed of a gas evolving insulating material which is pinned into position within the expul s-ion tube 53 by means of a small pin '56. should be understood that the tubes '50 and :58 could comprise a single tube in which case the casing 3:: would be dispensed with. Withksuch 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 93 when a single tube is used.

Whenthe fuse link I 5 to :tuse 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 H. In this regard it Will be understood that the line connection is brought into the terminal conductor Nb of the arrester Me so that with the apparatus unfused, a connection is first made with the dead spring arm I! during the fusing operation. This connection may conveniently be made by using the hook of a "hot-stick to position the contact ferrule 35 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 hot-stick hook may be shifted to the loop 39 and the link l5 pulled toward the bracket 16 to insert the contact ferrule 38 into the slot lie between the ears [6a and [6b of this bracket. As this operation is performed, the spring arm I! is de-formed toward the bracket I6 in the manner illustrated in Fig. 2 of the drawings. After the contact ferrule 38 is positioned between the bracket ears "5a and [6b, the pulling force exercised on the loop 39 through the hot-stick may be relieved permitting the ferrule 38 to move into the channel "5a to bring the conical part 38a thereof into Wedging engagement with the sides of the ears I60. and 16b. Thus the fusing operation 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 [5 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 and 38 are wedgingly engaged with the ears provided at the extended ends of the spring arm I? and the bracket [5 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 arrester unit 14a so that current is normally fed to the transformer primary winding over a path which includes the bracket Hi, the contact ferrule 38, the pigtail conductor 31, the fusible elements 4|, 40 and 42 in series, the casing terminal cap 32, the pigtail conductor 34, the contact ferrule 35, the spring arm 11, mounting piece 20 and the transformer bushing stud [8. The tank of the transformer it! provides the usual ground connection. With the circuit thus arranged, the arrester Ma provides a lightning surge path between the high voltage side of the line and ground which serves to icy-pass the link 15 and the primary winding of the transformer when li htning 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 arrester 14a is such that these two elements are not susceptible of being ruptured.

'In considering the mode of operation of the fuse link IE, 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 trans former 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 Hi.- 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 with-'- standing 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 in crease in the voltage applied thereto. I '1 The fuse link operates to protect thetransformer against damage occasioned by overload currents caused by any one of the mentioned factors. At the same time, the fuselink permits the transformer to be operated under sus= tained 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 cur.- rents which are produced incident to motor start;- ing, or the like. In this regard it will be understood that since the three serially related elements 4! 4i and 42 of the link it are traversed by the current flowing through the primary winding of the transformer, they are all heated by current conduction andrthe temperatureof each element varies with changes in the magnitude of this current. The fusible element 40 is also heated by the heat conducted thereto from the element 42 through the walls of theconnecting element 46. Heat energy is also trans.- ferred from the turns of the element 42 to the fusible element 4a through that portion of the refractory body 45 and the tube 4% which are disposed between the tubular portion of the connecting element -48 and the surrounding turns of the element 42, and also from the thermal storage element 48. Under constant load current conditions and with a constant voltage so long as the load current through the secondary winding of the transformer does not substantially exceed the full load capacity of this transformer, the fusible element 48 is operated at a temperature well below that required to produce fusion thereof. When, however, the secondary load current of the transformer gradually rises and is sustained for a period approaching 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 4!), 4| and 42 is correspondingly increased so that more heat is produced in the fusible element 48 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 l-ll through the refractory body 45-, and the tube id is increased. A portion of the heat energy accumulating in the element 40 is transferred to the storage element 48 by conduction. After av predetermined time interval, required for the accumulation of heat. within the fusible element 2 3, 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 4!] 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 56 under the influence of the spring arm [1, thereby rapidly to: break the circuit for energizing the primary winding of the transformers.

During the described separation of the element 4| from the tubular conductor 45 upon fusl ng; ofv the element 40,, an arc is drawnv within the portion 50b of the tube 50. This: are insta-ntly heats the coating 51 to gas evolving temperature, with the result that gases are evolved therefrom which accelerate extinction of the arc. It has been found that provision. of the gas evolving coating 5| permits the link itself to eftectively extinguish heavy current arcs of the; order of several hundred ampers even when the link is: used in high voltage circuits of several thousand volts.

To consider the action of the fuse link it further, it may he pointed out. that the refractory body 45 and: the tube 419 prevent the. fusible ele- Moreover, those portions of the refractory body 45 and the tube E9 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' dissipatea largev portion of" the heat resulting from the current surge through the element 42 away from the element 4|. They also delay the transmission of the increased increment of heat produced by the element 4? to the storage element it and the ad j'acent 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 48 from the element 42 as a result of the momentary high current, effectsan insufiicient increasein the temperature of the fusible element 49' to cause this element to melt. In other words, the total heat accumulated in the fusible element 40 as a resultof 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 element 40 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 12 fusible element 4|]v to a point such that it will provide no protection for sustained overload currents.

The thermal impedance of the refractory bod-y the tube 59 also prevents the fusible element- 40 from immediately rupturing when the transformer is subjected to a highcurrent, such, for example, as that; which isv produced when the secondary winding of the transformer is shortcircuitesl- In the absence of an additional protective clement, therefore, the transformer could easily be darn-aged by an overload current of: this character during. the period required: to transfer snihcient heat from the heating element t2 to the fusible element W to cause the latter element to melt-- The second fusible element 41. functions to guard the transformer against damage when suhiected to an overload current of this type. immediately the element ll is' subjected to transientcurrent' of particular character just referred tor, a portion thereof lying: between the: upper end of the sleeve and the lower end the fusible element ift is heated to a fusing temperature, permi ing this element to rupture.

When the fuse it it is. ruptured in response to an overload condition of any one of the types mentioned above, i. e., through melting of the fusible body kill or melting of the fusible element the hol'ding forces imposediupon. the deforming' spring arm it! are instantly released permittin-g this arm to swing to: the: left from it closed circuit position illustrated in Fig. 2 0i the drawings. Incident to this operation the link 15 is pulled away from the pigtail 33' toproduce arc elongation within the tube 58. As the arm l- 'l swings away from the. bracket It, the tubes 31 and Ell are pulled away from the pigtail 3'5 and de scribe an are above the extended end of the: arm Eff. The elements of the link being pulled away from the element H5 obviously gather momentum as the movement of the arm it proceeds with the result that when this arm stops at a position to the left of its unrestrained position as shown in 2 of the drawings the con-tact 35' is pulled out of the channel 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 extinction of the are are contained with-in the tube ill, the outside of which remains at a low temperature. "Hence tlii'ere 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 tln'ougl i the action of the spring arm 81 in the manner just explained, it falls down over the bracket l6 and. remains in this position until such time as the cutout is refused. In this regard it ispointed out that the length of the pig,- tail 3 7 is substantially less than the distance between the upper end ofthe insulator l4 and the grounded brackets supporting this insulator so that there is no possibility of this conductor short-oircuiting the high voltage side of the line to ground. Ihe manner in which the cutout may be refused will be clearly apparent from the foregoing explanation.

From the 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 subject 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 16, the simple spring arm assembly l1, and the fuse link I5. All of these elements are of very simple construction and may be easily manufactured at low cost. Further, the operations required in refusing 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.

What is claimed as new and is desired to be secured by Letters Patent of the United States is:

1. Protective apparatus for a transformer provided with a terminal conductor extending upward from the transformer tank, comprising an elongated lightning arrestor supported at one side of said tank in a substantially vertical position and provided with a terminal conductor at its upper end, a conductive bracket mounted upon one of said terminal conductors, and a spring arm mounted upon and extending upwardly from the other of said terminal conductors, said bracket and arm being provided with means at the extended ends thereof for mechanically holding the opposed terminal conductors of a fuse link and said arm being deformable toward said bracket to permit connection of the terminal conductor of the link to said holding means and to bias the link for are elongation in response to rupture of the fusible element of the link, said bracket and arm being so supported and arranged that the inner portions of the holding means thereof form a pair of acute angles with respect to the tensioned fuse link.

2. Protective apparatus for a transformer provided with a terminal conductor extending upward from the transformer tank, comprising an elongated lightning arrestor supported to one side of said tank in a substantially vertical posi-- tion and provided with a terminal conductor at its upper end, a conductive bracket mounted upon one of said terminal conductors, and a spring arm mounted upon and extending upwardly from the other of said terminal conductors, said bracket and arm having slots at their extended ends for receiving the terminal conductors of a fuse link and said arm being deformable toward said bracket to permit connection of the terminal conductors of the link to said arm and bracket and to bias the link for are elongation in response to rupture of the fusible element of the link, said bracket and arm being so supported and arranged that the closed end of the slotted portions thereof form a pair of acute angles with respect to the tensioned fuse link.

3. Protective apparatus for a transformer provided with a terminal conductor extending upward from the transformer tank, comprising an elongated lightning arrestor supported to one side of said tank in a substantially vertical position and provided with a terminal conductor at its upper end, a conductive bracket mounted upon one of said terminal conductors, a spring arm mounted upon and extending upwardly from the other of said terminal conductors, and a fuse link provided with oppositely extending pigtail conductors each provided with a ferrule having a conical part embracing the conductor, said bracket and said arm having slots at their extended ends for wedgingly receiving the conical parts of said ferrules and said arm being deformable toward said bracket to permit insertion of the conical parts of said ferrules in said slots and to bias the link for are elongation in response to rupture of the fusible element of the link, said ferrules being so supported by the slots that said slotted ends form a pair of acute angles with the tensioned pigtail conductors whereby the wedging of the ferrules with respect to the slots is increased.

l. Protective apparatus for a transformer provided with a terminal conductor extending upward from the transformer tank, comprising an elongated lightning arrestor supported to one side of said tank in a substantially vertical position and provided with a terminal conductor at its upper end, a conductive bracket mounted upon one of said terminal conductors and extending away from said one terminal conductor, a partially laminated spring arm mounted upon and extending upwardly from the other of said terminal conductors, the laminated portion of said arm extending from a point intermediate the ends of said arm to said other terminal conductor, and a fuse link provided with oppositely extending pigtail conductors each provided with a ferrule having a conical part embracing the conductor, said bracket and said arm having slots at their extended ends for wedgingly receiving the conical parts of said ferrules and said arm being deformable toward said bracket to permit insertion of the conical parts of said ferrules in said slots and to bias the link for arc elongation in response to rupture of the fusible element of the link.

EDWARD H. YONKERS.

References Cited in the file of this patent UNI'IED STATES PATENTS Number Name Date 2,325,555 Steinmayer July 27, 1943 2,327,865 Brown et al. Aug. 24, 1943