US2372150A - Resistor - Google Patents

Description

Patented Mar. 20, 1945 RESISTOR Charles C. Whittaker, Pittsburgh, Pa., assignor to Westinghouse Electric & Manufacturing Company, East Pittsburgh, Pa., a corporation of Pennsylvania.

Application May 20, 1942, Serial No. 443,697

(Ci. 20163i 16 Claims.

MyY invention relates, generally, to resistors, and it has reference in particular to' enclosed resistors.

Generally stated, it is an object of my invention to provide an enclosed resistor Awhich is simple and inexpensive to manufacture and is efficient and durable in operation.

More specifically, it is an object of my invention to provide an enclosed resistor having a resistance element supported within, and in spaced and insulated relation to a metal casing, and prevent the formation of moisture iilms between the terminals and the casing without requiring sealing of the casing.

It is also an object of my invention to provide for spacing a plurality of insulators supporting a resistance element in a casing.

Likewise, it is an important object of my invention to provide a resistor unit tha't is easy to assemble and is readily accessible for inspection.

An important object of my invention is to provile for supporting a resistance element within and in predetermined spaced relation to a metal casing having an integral cooling fin to dissipate the heat produced by the element.

Another object of my invention is to provide for integrating a metal resistor casing and members and cooling iin into a single unit by furnace brazing.

A further object of my invention is to provide for spacing a plurality of insulating supports which locate a resistance element within a casing without impeding the flow of heat from the element to the casing more than a minimum amount.

Yet another object of my invention is to provide a terminal construction for enclosed resistors wherein moisture traps are provided between the terminal and casing having ceramic creepage paths in series therewith.

Still another object of my invention is to provide a moistureproof terminal structure for an explosion-tested enclosed resistor.

It is an additional object of my invention to provide an improved explosion-tested enclosed resistor construction that is strong .andv durableand which is relatively. easy and inexpensive to repair in the event of a failure.

Other objects will in part be obvious. and will in part appear hereinafter.

In practicing my invention, a helical cooling iin and relatively heavy tubular end members are furnace brazed to arelatively thinmetal tubular casing. An elongated resistance element tained in such position by relatively thin elongated-insulating spacers positioned between adjacent supports onone side of the element. Terminal members secured to the ends of the element project through ceramic bushings having annular pockets adjacent the terminal members and the end members separated 'by suitable creepage surfaces. Asbestos washers placed in the pockets absorb moisture and keep the interior of the casing relatively dry. The bushings are secured in the end members by means of snap rings.

For a more complete understanding of the nature, scope and objects of my invention, reference may be had to the following detailed description which should be read in connection with the accompanying drawing, in which:

Figure 1 is a partly sectioned side elevational view, of an enclosed resistor embodying the principal features of the invention;

Fig. 2 is a partly sectioned side elevational view of a modied form of an enclosed resistor;

Fig. 3 is a cross-sectional view taken along the' line III-III 01' Fig. 1;

Fig. 4 is a reduced plan view of struction embodying the invention;

Fig. 5 is a left-hand end elevational view, broken out in part, of the resistor construction shown in Fig. 4;

Fig. 6 is a right-hand end elevational view of the resistor structure shown in' Fig. 4;

Fig. 7 is an end elevational view of the righthand or rear frame member of the resistor structure of Fig. 4; and

Fig. 8 is an end elevational view of the left' hand or front frame member of the resistor structure shown in Fig. 4.

Referring to Figs. 1 and 3, the reference numeral I0 may denote, generally, an explosiontested enclosed resistor such as is acceptable for use in gaseous atmospheres where the atmosphere may be ignited by a spark or overheated portion of the resistor, comprising a resistance element I2 provided with a casing I4 and projecting end terminals I5.

The resistance element I2 may be of any suitable construction, comprising, for example, an elongated helix of a plurality of turns of a relatively small resistance wire I6 such as shown in Figs. 1 and 3. The element may also comprise a resistor cona substantially straight rod l1 without depart-` t, ment.

ing from the invention, as shown in Fig. 2. Any of the well known materials may be used for the resistance element, such as, for example, one of the nickel-chromium alloys which has a relatively high resistance and a relatively high mechanical strength at high temperatures. Y

The casing I4 may not only serve to enclose and protect the resistor, but may serve also as a radiator therefor, and may, as shown in Figs. 1 and 3, comprise a suitable'length of metal tubing I8, of seamless steel or the like. In order to secure the maximum radiation from the resistance element with the minimum spacing, means such as the cooling iin 28 may be provided. The fin 28 may comprise a helix of soft steel ribbon wound on edge. positioned about the tubing I8 and stretched to the proper length.

Means such as the end members 22 may be connected to the tubing I8 adjacent the ends. The end members 22 may, tor example, comprise short lengths of a relatively heavy steel tubing having inner diameters slightly less than the outer diameter of the tubing I8, and recessed adjacent one end to provide peripheral shoulders 23, so that they may be fitted over the end portions of the tubing IB, which may abut the shoulders 2S. The inner surfaces of the end members may be suitably shaped at the other ends to provide peripheral shoulders 24 intermediate the ends and peripheral grooves 28 adjacent the outer ends.

The tubing I8, cooling nn 28 and the end mem bers 22 may be assembled in any suitable man ner, such as, by tack welding the cooling fln to the end members by welds 28, and tack welding the end portions of the iin to the tubing I8 by welds 21. The assembly of the tubing, end members and cooling iin may then be integrated by furnace brazing, through wrapping a suitable length of copper wire about the tubing between the turns of the cooling nn and heating the whole 'in a hydrogen atmosphere furnace to cause the copper to flow and form a fillet 28 completely integrating the end members, tubing and cooling iin.

In order to provide for positioning the resistance element I2 within the casing I4, suitable means such as the insulating supports 80 may be provided at spaced intervals along the ele- 'I'he supports 88 may comprise buttons, rings or relatively short refractory ceramic tubes having openings 8l therethrough and capable of withstanding heat shock. The outer diameter may be slightly less than the inner diameter of the tubing I8, and the diameter of the opening 8l may be slightly larger than the outer diameter of the resistance element. The su-pports 88 may be slipped onto the element I2 and spacing of the supports may be secured by'positioning elongated ceramic spacers 82 between the adjacent supports. The spacers 82 may comprise ceramic tubes of such an outside diameter that they may be relatively loosely positioned between the resistance element I2 and the tubing I8 on one side of the element, where'they are retained by the tubing, so as to impede the flow of heat thererom as little as possible.

The terminals may be of any construction I which provides a good electrical connection with tively high conductivity and may comprise a length of copper rod having ailange 84 adjecent the inner end with a longitudinal` opening 88 to receive a straightened portion of the wire I8.v The wire may be secured'to the terminal at the outer end by brazing 38, thus securing a good electrical connection with a minimum of heat conduction from the element to the terminal.

to receive the terminals I8 may be positionedI within the end members 22. These discs may be provided with peripheral recesses 4I and 42 adjacent the inner and outer edges. An additional ceramic member 43 may\be provided having a peripheral rib 44 adjacent one end, defining a peripheral end recess d5 corresponding to the outer peripheral recess $2 of the ceramic discs 38, and a peripheral shoulder 48 intermediate the ends. The ceramic discs and additional ceramic member are preferably of a ceramic material having a low moisture absorption factor, such as lava, or one ci the silicates, such as aluminum magnesium silicate.

By positioning the discs 38 within the end member 21 in opposed relation, with the inner one abutting the shoulder 2d of the end member 22, the two inner recesses 4I are juxtaposed, and cooperate to provide a substantially closed inner chamber about the terminal l5 for receiving a moisture absorbing material to prevent the passage of moisture along the terminal member I8 into the interior of the casing. The outer peripheral recesses 42 of the outer discs 39 and 48 of the insulating member 43 are likewise juxtaposed and cooperate to provide an outer annular chamber adjacent the inner surface 'of the end member. for receiving a moisture absorbent mate rial to prevent the passage of moisture along the inner surface of the end member. The chambers thus formed may be filled with any suitable moisture.absorbent material, such as,` for example, the asbestos discs 41 and 48. Moisture traps are thus provided at the inner and outer surface of the insulation supporting the terminal member I5, which are separated from each other, and have ceramic creepage surfaces 49 and 50 in series therewith between the terminal member and the end member. Moisture absorbed by the discs 41 and 48 cannot therefore bridge between the end member and the terminal to cause a breakdown.

The resistor may be assembled by stringing the insulating supports 30 on the resistance element I2 and inserting them in casing I4, placing the spacers 82 between adjacent supports in turn. The ceramic discs 89, additional ceramic members and asbestos discs may then be assembled on the .terminals I8, where they may be retained by means such as the turns of wire 58, which may be placed in grooves 54 about the terminals and secured by twisting the ends together as indicated. The terminal assembly may be dropped over the straightened end portions of the wire I6 into the end members and secured by means such as the snap rings 88, which may bel positioned in the grooves 28 adjacent the outer ends of the end members to engage the peripheral shoulder portions 48 of the insulating members 48. The

2,372,150 wire Il may then be cut oil' to the proper length' and secured to the terminals I8 by brazing Il.

The resistor 81 shown in Fig. 2 is substantially identical with the resistor shown in Fig. 1, so that, in general, details of the construction thereof need no further explanation. Since the resistance element I1 comprises a relatively heavy conductor, the insulating supports 80 of the re- .sistor 81 may be spaced further apart. Accordingly, the spacers 58 may be longer than the spacers 32 of the resistor I 0, Instead oi' providing an opening throughout the length ofthe terminal member 59 to accommodate the resistance element I1, only a relatively shallow recess 80 need be provided at the inner end of the terminal member 59 for securing the end portion of the resistance element I1 therein by brazing or the like, since a good connection may be effected therebetween which remains u'nail'ected by the heat developed in the resistance element I1. Since the contact between the element I1 and the terminal 59 is relatively limited, and little or no heat is developed in the terminal 59, it may be kept sufliciently cool for relatively high operating temperatures of the element. The terminal member 59 may be supported in the end member 21 by a terminal support structure 38 substantially the same as described in connection with the resistor of Fig. l.

Referring to Figs. 4 through 8, the reference numeral 64 may denote, generally, a resistor construction wherein a resistor unit 65 comprising a pair of resistors 86 of a type such as shown in Figs. 1 and 2, may be supported in spaced frame members 81 and 10 which may be connected by supports 1 I.

For the purpose of providing a resistor unit having readily accessible terminals, for application where one end of the unit is relatively inaccessible, such as, for example, in some applications on mining locomotives, the terminals at the rear end of the resistors may be connected by means of a conductor 12, so that both of the terminals to which exterior connections are to be made are at the other end of the unit. Means such as the yokes or connectors 13 and 14 may be provided adjacent the ends of the resistors tomaintain them in spaced relation and provide a substantially integral resistor unit. The connector 13 may, for example, comprise a substantially figure 8 shape having spaced openings 18 and 11 to receive the end members 22 of the resisters. The connector 1l may be of any suitable shape comprising, for example, a rectangular plate having spaced openings 18 and 19 to receive the opposite end members of the resistors,

In order to provide a substantially integral unit having relatively low replacement cost, the

- connectors 13 and 14 may be permanently connected to the end members 22 of one resistor by means of welds 80, and may be connected to the end members of the other resistor more or less temporarily by means of relatively frangible tack welds 8l which may be more or less easily broken inthe case it is found necessary to replace one or the other of the resistors. A relatively strong and rigid construction is thus provided, and yet in case of failure of either of the resistors, only one or the other need be replaced and not both, y

which would be the case if both resistors were permanently connected to the connectors.

The right-hand or front frame member 10 may be provided with a pair of spaced openings 82'connected by a restricted opening 83 sutilciently large to permit the resistors and the connector 19 to pass therethrough, as shown in Fig. 8. The left-hand or rear frame member I1 may be provided with a pair of spaced openings 8l, connected by a restricted opening 85 sumciently large to permit the terminal conductor 12 to pass' therethrough and to receive the end members 22. To assist in inserting the resistor unit 85 in the frame openings, means such as the rod 81 may be provided. extending between the front and rear frame members 10 and 61, and positioned in openings 88 and 89 therein intermediate and slightly below the spaced frame openings 82 and 8l therein. The rod 81 may be so positioned relative.to the frame openings that the connector 18 may rest thereon as the resistor unit is being inserted in the openings whereby the rear end members 22 will be guided into the spaced opening 84 in the rear frame member. Suitable means may be provided for securing the resistor unit relative to the frame members, such as, for example, the nut 90, which may be positioned on the front end of the rod 81.

From the above description and the accompanying drawing, it will be apparent that I have provided in a simple and inexpensive manner for supporting a resistance element within a metal casing. Eflicient radiation of heat generated by the resistance element is eifected by providing a relatively unobstructed path between th'e resistance element and the metal casing, and providing the maximum cooling arrangement for the casing by means of a helical iin integrally connected to the casing throughout its length. The entrance of moisture Within the casing, when the resistor is voperating in relatively damp locations, through the breathing action thereof as the air in the casing expands and contracts, is effectively prevented by means ofthe improved terminal structure I have provided. Resistors embodying the features of my invention have been successfully operated and tested by heating the resistors to a' maximum operating temperature and draping the terminal ends with wet rags and rapidly cooling the whole resistor. Subsequently, while in a wet condition the resistors withstood from 3,800 to 4,400 volts before breaking down between the resistance element and the casing. After slight- 1y heating the resistors they withstood 5.000 volts safely, thus indicating a satisfactory control of moisture leakage which heretofore caused failure in other designs of resistors used in locations where a relatively high moisture content is found.

Since certain changes may be made in the above description. and different embodiments of the invention may be made without departing from the spirit thereof, it is intended that all the matter contained in the above description and shown in the accompanying drawing shall be considered as illustrative, and not in a limiting sense.

I claim as my invention:

l. A resistor comprising, an elongated resistance element, a plurality of relatively thin `insulatine supports positioned substantially symmetricaily about the element at spaced intervals at least four times the thickness of the supports, a relatively narrow insulating spacer loosely positioned between adjacent supports, and a metal casing symmetrically positioned about the element supports and spacers.

2. The combination in an enclosed resistor, of an elongated resistance element, a metallic casing positioned about the element, insulating supports positoned between the element and casing at spaced intervals, and an elongated insulat- Aing spacer positioned between adjacent supports to one side of the element and in engagement with the inner surface of the casing so as to be retained between said supports and on one side only of the resistance element by the casing.

3. A resistor comprising, an elongated resistance element, insulating supports positioned about the element at spaced intervals. a relativelythin-walled metal tube positioned about the element and supportshaving relatively thickwalled metallic tubular end members secured elongated refractory spacer freely positioned be-f tween adjacent supports and located only on one side of the element, and a casing enclosing the element, supports and spacers.

5. The combination in a resistor, of an elongated resistance element, a plurality of rings of refractory material positioned about the element at spaced intervals, and substantially concentrically therewith, an elongated tubular refractory spacer loosely positioned eccentrically of the element so as to oat between adjacent rings and Y to one side of the element, a metal tube positioned about the element, rings and spacers: and terminal members connected to the element projecting from the ends of the tube.

6. A resistor comprising, an elongated resistance element, a tubular casing positioned about the element, insulating means supporting the element in spaced relation within the tube, a terminal member connected to one end of the resistance element, and means insulating the terminal member from the tube including a plurality of ceramic discs having central openings to receive the terminal member and spaced recesses adjacent the inner and outer edges contiguous with the terminal member and tube, respectively, con- .taining a moisture absorbent material.

7. An enclosed resistor comprising, an elongated resistance element, a plurality of refractory supports positioned along the element, an elongated spacer positioned between adjacent supports on one side of the element, a metal tube positioned about the element, supports and spacers, and means including a plurality of refractory discs having central recesses on one side and projecting central bosses on the other positioned in opposed relation to define inner and outer peripheral recesses in spaced relation to receive a moisture absorbent material.

8. The combination with a resistance element positioned within a casing and having an end terminal, of a plurality of ceramic discs positioned in opposed relation having central recesses and bosses on opposite sides defining inner and outer peripheral recesses adjacent the terminal and casing separated by ceramic leakage surfaces, and a plurality of asbestos discs positioned in the recesses against the terminal and tube.

9. lAn enclosed resistor comprising, an elongated metal casing, a resistance element positioned within the casing, spaced supports separating the element from the casing, a terminal member connected to the element, and a terminal lil support positioned about the terminal member within the end of the tube including a, plurality of ceramic discs having central openings to receive the terminal member and inner and outer peripheral recesses filled with a moisture absorbent' material, said inner and outer recesses being separated from each other by continuous rib portions on the discs. Y

10. A terminal support for mounting a terminal member in a tubular container comprising, a plurality of ceramic discs having central openings for the terminal member and central recesses and projections on opposite sides positioned in opposed relation to dei-lne inner and outer peripheral recesses separated by ceramic creepage surfaces, plurality of asbestos discs positioned in the recesses to engage the terminal member and the container, and means to secure the ceramic discs in the container.

11. A resistor unit for mounting in a frame comprising, a pair of elongated resistance units having metallic casings, means comprising a pair of connectors secured to the casings adjacent the ends to mechanically connect the casings and position them in spaced relation, a pair of spaced frame members having openings to receive the units and at least one or the connectors, and means securing one of the connecting means to one of the frame members to. secure the resistor unit relative to the frame.

12. A resistor structure comprising, a pair of elongated resistor units having metallic casings with terminals projecting from the ends, separate connecting members having openings to receive the ends of the casings positioned adjacent the ends thereof and welded thereto for mechanically connecting the casings to position them in spaced relation, and a terminal connector bridging the terminals at one end of the units.

13. A unit resistor comprising, a pair of elongated resistance elements positioned in metal casings with en d terminals projecting therefrom, connectors rigidly attached to only one of the casings adjacent each end and having an opening spaced from said one casing to receive the other casing, -frangible means mechanically connecting the other casing to the connectors so as to provide for readily separating the casings in the event of failure of one element, and a terminal connector connecting the terminals at one end. ,A

14. A resistor structure comprising, a pair of 'resistor units having resistance elements supported within metal casings with end terminals projecting therefrom, connectors positioned adjacent each of the ends of the casings mechanically secured to the casings to maintain them in spaced relation, front and rear frame members positioned in spaced relation having openings to receive the casings and at least one of the connectors, andmeans including a tie rod extending between the frame members positioned to engage the connectors at the leading end of the units when the leading end is inserted through the opening in the front frame member to guide the leading end of the units into the opening in the rear frame member.

15. An enclosed resistor comprising, an elongated resistance element, a tubular metal casing positioned about the element, insulating supports spaced within the casing to support the element, a tubular end member secured about an end of thefcasing, a terminal connected to the element projecting through the end member, means including a plurality of refractory discs having vcentral openings to receive the terminal and inner andv outer annular recesses adjacent the terasunto B minal and end member, moisture absorbent means positioned in the recesses, and retaining means attached to the terminal and end member to engage one of the refractory discs.

16. A resistor comprising, a pair of resistor4 units having resistance elements enclosed in tubular metal casings with terminals projecting from each of the ends, a. pair of connectors mechanically connecting the casings adjacent each of the ends to secure the casings in fixed relation to each other, a terminal conductor connecting the terminals of the units at one end, spaced iront and rear frame members having aligned openings to receive the casings, the opening in one of the frame members being so shaped as to receive one of the connectors, and a tie rod for connecting the front connector relative to the frame members extending between the frame members intermediate the casings positioned to engage the connector at the leading end of the units so as to support said end of the units when said end is inserted in the opening in the front frame member to guide it into the opening in the rear frame member.

CHARLES C. WHIITAKER..

Images