US2725448A - Resistance apparatus - Google Patents

Description

Nov. 29, 1955 R. T. KINTZING 2,725,448

RESISTANCE APPARATUS Filed June 19, 1953 3 Sheets-Sheet l WITNESSES: W F 2 INVENTOR 5 X 5d 2d 5d Reese T. Kinizing u I u BY v ,2 f gjiw Id F|g.l3. ATTORNEY Nov. 29, 1955 R. T. KINTZING 2,725,448

RESISTANCE APPARATUS Filed June 19, 1953 3 Sheets-Sheet 2 Fig. IO.

Fig.6. Fig.5.

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WITNESSES: INVENTOR Reese T. Kinizing. BY

ATTORNEY United States Patent RESISTANCE APPARATUS Reese T. Kintzing, Buffalo, N. Y., assignor to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Application June 19, 1953, Serial No. 362,888

6 Claims. (Cl. 201-69) This invention relates to improved sheet metal electric resistance grids, and to improved electric resistance assemblies, or units, suitable for various purposes such as, for example, the control of electric motors.

In the application of the resistance units the available space is usually limited and it thus becomes a problem to provide a resistance unit having the maximum heating effect for the available space and the current carried by the grids. The several considerations involved in building a suitable grid must be compromised because the grid material must not be operated above a given temperature, if the grid is to have a long useful life. Generally, the attempt is made to provide the longest possible current conducting path per unit volume of the assembled resistance unit.

For reasons dictated primarily by manufacturing economies, it is customary to stamp these grid elements from sheet metal, using a metal having high unit resistivity. Such materials are relatively expensive. Heretofore, it has been the practice to obtain long current conducting paths by stamping out sections of the sheet material to form a somewhat sinuous path. The amount of metal removed by stamping to form the convolutions of the sinuous path and to provide means for mounting the grids in a unit assembly is determined largely by factors controlling the design of the stamping dies. In prior commercial grid designs, the material so removed as waste or scrap has amounted to approximately 20% to 40% of the total area of material needed to stamp the grid. Since the scrap value of this material is very low compared with its price in sheet form, this waste represents a considerable loss.

Accordingly, it is a general object of this invention to provide a resistance grid assembly which is small and compact and has improved heat dissipating properties.

More specifically, it is an object of this invention to provide a resistance grid assembly which has a high resistance per unit volume and in which the grid plates are of a configuration to have improved heat radiating properties.

Further to the preceding object, it is also an object of this invention to provide a resistance grid assembly having more heat radiating surface per unit volume than prior devices.

It is also an object of this invention to provide a resistance grid of the character referred to in which material waste in manufacture is minimized.

Another object of this invention is to provide a resistance grid in which more efficient use of the resistance material is realized.

A further object of this invention is to provide a resistance grid in which more heat radiation surface per unit area of the grid, based on its overall dimensions, is obtained.

Yet, another object of this invention is to provide a resistance grid, which for a given cross-sectional area of the conducting path and for a given material, may be operated at a higher current density than prior types, or

conversely has less cross-section area for a given current density.

Still another object of this invention is to provide a resistance grid having greater mechanical strength than prior devices.

The foregoing statements are merely illustrative of the various aims and objects of this invention. Other objects and advantages will become apparent upon a study of the following specification when considered in conjunction with the accompanying drawing, in which:

Figure l is a top view of a resistance grid assembly or unit embodying the principles of this invention;

Fig. 2 is a sectional view taken on the line II--II of Fig. 1;

Fig. 3 is a view looking at the right end of the resistance grid unit of Fig. 1;

Fig. 4- is a similar view of part of the left end of the resistance grid unit of Fig. 1;

Figs. 5 and 6 are views of the right and left ends of the resistance grid appearing in plan view in Fig. 2;

Figs. 7 and 8 are, respectively, fragmentary end and side views of another embodiment of this invention;

Fig. 9 shows a further modification of this invention;

Figs. 10 and 11 are enlarged, fragmentary, plan views of respective modifications of the resistance grid seen in Fig. 2; and

Figs. 12 and 13 are arbitrary, longitudinal sections of respective resistance grids illustrating further grid modifications.

The understanding of this invention will be facilitated by first considering the details of the resistance grids and thereafter considering their assembly in the resistance unit.

An important aspect of this invention resides in the provision of a resistance grid assembly including resistance grids of sheet material having substantially parallel slits disposed laterally of the grid sheet, and alternately extending through opposite sides of the grid sheet, to define integral adjacent sections forming part of a sinuous current path between the ends of the grid, in which, at least portions of the aforesaid adjacent sections are displaced from the plane of the sheet of material to physically separate the adjacent slit edges of the sections.

Although this invention is illustrated by means of grids in which the slits are parallel and are positioned at an angle of with respect to the side margins of the grid plate, it will be appreciated that the essential aspects of this invention may be achieved with different slit geometry. That is the slits need not be parallel nor need they occupy positions at 90 with the side margins of the sheet.

The aforesaid features are clearly illustrated in Figs. 1 and 2 wherein the resistance grid is formed of a sheet of resistance material generally designated 1. This sheet is provided with slits 2 extending laterally of the sheet t and which alternately pass through the edges at opposite sides of the sheet. Flanges or louvers 3 are displaced outwardly from the plane of the sheet, as viewed in Fig. 1, along respective lines 4 (see Fig. 2) paralleling or substantially paralleling an associated slit 2. The angular displacement of each flange is sufficient to completely clear the slit edge thereof from the adjacent slit edge so that no electrical connection exists between the respective relatively displaced slit edges.

This arrangement defines a current path between the ends of the sheet 1 which comprises the integral end-toend connected, substantially parallel disposed sections 5 which are defined by the spaced slits. By this expedient, a relatively long current conducting path between the ends of the resistance sheet 1 is obtained in a relatively short length of resistance sheet.

In this illustration, the flanges or louvers 3 are displaced or bent from the plane of the sheet in an operation which draws the metal at the inner ends of respective slits 2 forming a tapering flange or louver portion flowing into the plane of the sheet at the inner ends of the respective slits. With this construction, all of the grid material is used to carry current; that is, all that grid material in the sections 5 between each slit 2, including the flanges or louvers in each case, forms part of the current conducting path between the ends of the grids.

Because the grid according to this invention uses that part of the material formerly scrapped, for instance, the material in the louvers or flanges which forms part of the useful, current carrying, cross-sectional area, the same cross-section of material, in a grid of given length, is obtained with a material several gage sizes thinner. The weight of the material required is reduced by an amount which averages better than 28% per grid, which in a high production activity results in very substantial material savings.

Because the cross-sectional area of each section in a grid of given length is relatively wider and thinner, the material may be worked at higher current density, the heat being dissipated by radiation across a larger surface area. Thus, in a grid assembly of given volume, the present invention in addition to providing a substantial saving in relatively high cost material, provides a unit having a higher rating than those constructed according to prior art principles. Hence, for a given rating, further material savings are achievable through reduction in volume of the assembled unit.

For assembly purposes (see Fig. 2), suitable mounting holes 6 are provided at opposite ends of the resistance sheet and on the same side thereof, and a third mounting hole 7, located substantially centrally of the length of the resistance sheet and on the opposite side thereof from the mounting holes 6, may also be provided, if needed.

As seen in Figs. 1 through 4, respective grids 1 are stacked in spaced side by side relation over electrical insulating tubes 8 which pass through the holes 6 and over an electrical insulating tube 9 which passes through the hole 7 in each grid. Threaded support rods 10 pass through the tubes 8 and a threaded support rod 11 passes through the tube 9. These rods are carried between channel-shaped end plates 12 which are spaced by spacing rods 13 which secure the end plates 12 in spaced relation between nuts 14.

Spacers 15 and 15a, which latter are of shorter axial dimension than spacers 15, are of electrical insulating material and slide over tubes 8. These spacers are disposed between respective plates 1. Spacers 16, also of electrical insulating material are disposed between the plates 1 about tube 9 to correspondingly support and space the grid plates 1 intermediate their ends. The axial dimension of a spacer 1511 plus the thickness of a terminal plate 17 or 17a with which it is employed, equals the axial dimension or length of a spacer 15.

As will be seen by reference to Fig. 2, terminal plates 17 and 17a are provided with faces 17c and 17d, respectively, which are respectively displaced laterally of the grid plates. These faces in conjunction with suitable clamps or connectors (not shown) provide means for making electrical connections to the terminal plates.

The grids 1 are connected in series by tabs 18, at each end of each grid, which are displaced from the grid plane in an amount sufiicient to engage the adjacent tab. Proceeding from top to bottom of the assembly as seen in Figs. l and 4, these tabs electrically connect the first and second, the third and fourth grids, etc., at the left end or" the assembly. And in the same sense with regard to Figs. 1 and 4, tabs 8 connect the second and third, the fourth and fifth grids, etc., at the right end of the assembly.

Terminal plates 17 and 17a, as will be seen by reference to Fig. 4, have the same surface configuration as the tabs.

'These terminal plates are alternately disposed against 4 the first, third, fifth, etc., grids at their right ends, proceeding from top to bottom in thefigure, and, hence, provide terminal connections on faces 17c and 17d, respectively, which are laterally displaced of the grids, between each pair of series connected grids.

Nuts 20 on threaded support rods if) clamp the grid assembly between insulatorsZl, and nuts 22 on rod 11 clamp the grids'at this intermediate point between insulators 22a, and the respective rods are, in turn, secured across insulator bushings 23, in the end plates 12, by nuts 24 threading over the rods.

Certain simplifications and improvements'are apparent in the embodiment of this invention shown in Figs. 7 and 8. In these figures parts corresponding to those of Figs. 1 through 4 carry like reference characters but in each instance the reference characters are primed.

As in Fig. 7 this assembly comprises the resistance grids i mounted between channels 12 on insulated rods 1b and 11' and spaced by spacers 15, 15a and 16. In this embodiment the grid resistor configuration is simpler, being provided with straight sides rather than the sawtoothed shape seen in Fig. 2. This materially simplifies the stamping dies.

This construction also features a two point suspension for the terminal plates 17 and 17a. These plates are again clamped between spacers 15 and 15a in contact with selected grid resistors but in this instance each terminal is provided with a forked extension 172 which straddles a rod 13a of electrical insulating material which is carried between the channels 12. This materially improves the stability of the terminals, that is, it reduces the tendency of the terminals to turn about insulated rod 10. As a consequence no load is applied to the electrical connection between the respective terminals and the tabs 18 of the grid resistors when the terminals 17' and 17a are bolted to system bus bars or cable terminals.

In Fig. 9 the spacing between the slits which define the current path sections 5' has been reduced. For a given thickness of grid material this results in less crossseetional area of the current path and reduces the current rating. If the grid material is relatively thin, two adjacent sections or loops of the current path may be spanned by using a larger diameter spacer 16 over the insulated bar 11 between the respective grids 1; as seen in Fig. 9. In order that washers having flat faces may be used, the flanges or louvers 3' are cut off above spacers 16 and the louver 3c is shortened sufficiently to maintain the needed current path dimension around its inner end. Otherwise this assembly corresponds to the two embodiments hereinbefore described.

A variety of obvious modifications of the structures disclosed may be made within the spirit and scope of this invention. Four such modifications are fragmentarily shown in Figs. 10, ll, 12 and 13.

In Fig. 10, the inner ends of slits 2a in grid 1a terminate in rectangular (or circular) holes 25. These rectangular holes span the width of the respective flanges or louvers 3a and thereby provide a clean edge at the inner end which facilitates bending. However, some loss in cross-sectional, current carrying area results from this expedient, but the advantages of better heat radiation and mechanical stiffness due to the projecting louver 3a are retained.

Alternatively, as seen in Fig. 11, the inner end 26 of flanges 3b in. grid 1b may be defined by plate shearing when the flange is formed, or, may be cut prior to forming of the flange. In this case as in the construction of Fig. 10, there is a slight loss in cross-sectional area. But, in each case, this loss can be minimized by keeping the lateral dimension of the flange as small as practical, that is, just sufficient in width to separate the slit edges 2b in bending. Again due to flange projection,

"the advantages of better heat radiation and stiffness are inherent.

A further expedient is shown in grid 1c in Fig. 12, wherein the entire sections 50 intermediate the slits 2c are angularly displaced across their lateral dimension. This view is a fragmentary showing to an enlarged scale, of an arbitrary, longitudinal section along the grid. This construction retains all the advantages of the type shown in the assembly of Figs. 1 through 4 and in end detail in Figs. 5 and 6.

A variation of this latter principle is shown in the grid id in Fig. 13 in a corresponding cross-sectional view. Here, the sections 50! intermediate slits 2d are displaced from the plane of the grid to positions paralleling the grid plane, instead of being angularly tilted as in Fig. 9. By displacing adjacent sections in opposite directions from the plane of the grid, some foreshortening of the lateral dimension of the grid takes place which minimizes drawing or stretching of the grid material at any point and tends to maintain a more uniform crosssectional area in the material.

The assembly of any of the above-described grids, or their equivalents, in a unit as shown in connection with Figs. 1 through 4, provides a sturdy, compact grid unit.

Compactness inheres from the unique grid configuration with its longer current path for a given length of grid plate and given width of the path sections and with its improved heat radiating property. The ability to radiate more heat means that for a given ampere rating more ohms of resistance may be placed in a given space, or, more ohms per grid may be used.

Sturdiness inheres from supporting the grids at points on the grid plate removed from the connectors or tabs 18. These points are designed as to support area to adequately carry normally imposed loads, rather than supporting the grids on the electrical connecting tabs, such as 18, as is practiced in some prior art devices.

These and other features including the terminal plate assemblies, contribute to a low-cost unit assembly oifering marked operational and manufacturing advantages over existing structures.

However, this invention both in its details and in the organization of such details is susceptible of various modifications, in addition to those noted, within its spirit and scope. Accordingly, it is intended that the foregoing disclosure and the showings made in the drawings shall be considered only as illustrative of the principles of this invention and are not to be interpreted in a limiting sense.

I claim as my invention:

1. A resistance grid assembly comprising, a plurality of grid plates of electrical resistance material, each grid plate having a plurality of spaced slits therein alternately extending through opposite side edges of the respective grid plates, said slits defining a series current path between the ends of each grid plate, said respective paths including adjacent sections formed by said slits; at least portions of adjacent sections in each grid plate being relatively displaced from the plane of said grid plate to separate adjacent slit edges, terminal plates, support means insulatedly supporting said grid plates in spaced, substantially parallel relation; alternate grid plates having a terminal plate supported by said support means in contact therewith adjacent an end thereof, said ends of adjacent pairs of grid plates being displaced from the grid plate plane into contacting relation to form electrical connections therebetween, each terminal plate being shaped to conform to the shape of the end of the associated grid plate for mechanically supporting and electrically contacting said end.

2. A resistance grid assembly comprising, a plurality of grid plates of electrical resistance material, each grid plate having a plurality of spaced slits therein alternately extending through opposite side edges of the respective grid plates, said slits defining a series current path between the ends of each grid plate, said respective paths including adjacent sections formed by said slits; at least portions of adjacent sections in each grid plate being relatively displaced from the plane of said grid plate to separate adjacent slit edges, each grid plate having spaced mounting holes therein, terminal plates having respective mounting holes support rods, electrical insulating means in said holes in said grid plates and said terminal plates mounting said grid plates and terminal plates along said rods with said grid plates in spaced relation and with a terminal plate arranged in side by side contacting relation with alternate grid plates, end plates, means securing the ends of said rods in said end plates, the ends of respective pairs of adjacent grid plates being displaced to engage and form electrical contact, and each associated terminal plate being of a configuration to contact and support the associated end of the associated grid plate.

3. A resistance grid assembly comprising, a plurality of grid plates of electrical resistance material, each grid plate having a plurality of spaced slits therein alternately extending through opposite side edges of the respective grid plates, said slits defining a series current path between the ends of each grid plate, said respective paths including adjacent sections formed by said slits, at least portions of adjacent sections in each grid plate being relatively displaced from the plane of said grid plate to separate adjacent slit edges, each grid plate having spaced mounting holes therein, support rods, electrical insulating means in said holes mounting said grid plates along said rods in spaced relation; support plates, means securing the ends of said rods in said support plates, tabs on each grid plate at the ends thereof, said tabs being displaced from the plane of each grid plate in a position to engage an adjacent tab of an adjacent grid plate to provide an electrical path therebetween, said tabs connecting said plates in series with each other, and terminal plates insulatedly mounted on said rods adjacent to and contacting corresponding ends of alternate grid plates and being of a configuration to engage and support the associated grid end and tab in electrical contacting relation.

4. A resistance grid assembly comprising, a plurality of grid plates of electrical resistance material, each grid plate having a plurality of spaced slits therein alternately extending through opposite side edges of the respective grid plates, said slits defining a series current path between the ends of each grid plate, said respective paths including adjacent sections formed by said slits, at least portions of adjacent sections in each grid plate being relatively displaced from the plane of said grid plate to separate adjacent slit edges, each grid plate having spaced mounting holes therein, support rods, electrical insulating means in said holes mounting said grid plates along said rods in spaced relation; support plates, means securing the ends of said rods in said support plates, and tabs on each grid plate at the ends thereof, said tabs being displaced from the plane of each grid plate in a position to engage an adjacent tab of an adjacent grid plate to provide an electrical path therebetween, said tabs connecting said plates in series with each other, and terminal plates insulatedly mounted on said support rods in positions adjacent and contacting the ends of some of said grid plates for providing electrical connections and support for said ends of said grid plates.

5. A resistance grid assembly comprising, a plurality of grid plates of electrical resistance material, each grid plate having a plurality of spaced slits therein alternately extending through opposite side edges of the respective grid plates, said slits defining a series current path between the ends of each grid plate, said respective paths including adjacent sections formed by said slits; at least portions of adjacent sections in each grid plate being relatively displaced from the plane of said grid plate to separate adjacent slit edges, angle shaped terminal plates having one leg adapted to receive electrical connections and a second leg for supporting the terminal plate, support means insulatedly clamping said grid plates in spaced side by side relation with respective terminal plates engaging an end of intermediate grid plates, electrical insulating means securing said-second leg against movement, adjacent grid plates having the ends thereof displaced into contacting relation to form anelectrical connection therebetween, and each terminalvplate associated with a displaced grid plate end being displaced correspondingly to support said end and have electrical contact thereover.

6. A resistance grid assembly comprising, insulated support rods, a plurality of grid plates of electrical resistance material and having holes thereinfitted over said rods, terminal plates, each terminal plate having a hole therein and being fitted over said-support rods in a position adjacent to and contacting a respective grid plate, spacer means on said support rods spacing said grid plates in side by side relation and maintaining the respective grid plates and terminal plates incontacting relation, each grid plate having slits therein alternately extending through opposite side edges, thereof, the marginal edges of the respective grid plates adjacent the respective slits being displaced from the plane of the-grid plate to separate the slit edges, support means insulatedly mounting said support rods, an extension on each terminal plate, electrical insulating means mounted on said support means and engaging said extensions to secure said terminal plates against movement, the ends ofadjacent grid plates being displaced into contacting relation to form an electrical connection therebetween and each terminal plate associated with a displaced grid plate end being displaced correspondingly to support said end and have electrical contact thereover.

References Cited in the file of this patent UNITED STATES PATENTS 1,088,003 Wilkinson Feb. 24, 1914 1,233,183 Carter et a1 July 10, 1917 1,233,191 Collins July 10, 1917 1,455,903 Clark May 22, 1923 1,794,310 McCauley Feb. 24, 1931 1,928,142 Trent et al Sept. 26, 1933 2,665,358 DuBois Jan. 5, 1954

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