US3119087A - Electrical resistor - Google Patents

Description

Jan. 21, 1964 A. c. SCRIBN ER ELECTRICAL RESISTOR 3 Sheets-Sheet 1 Filed July 21, 1961 INVENTOR. AQT/IUQ cbqyrO/Y ting/ya zldrluplvsy Jan. 21, 1964 A. c. SCRIBNER 3,119,087

ELECTRICAL RESISTOR Filed July 21, 1961 3 Sheets-Sheet 2 INVENTOR. 144 mm Cmvrou pm Jan. 21, 1964 A. c. SCRIBNER ELECTRICAL RESISTOR Fil ed July 21, 1961 3 Sheets-Sheet 3 INVENTOR. APT/1Q Cmyro v SCQ/BNC'R W4 rrop Nay United States Patent 3,119,087 ELECTRICAL RESISTUR Arthur Clayton Scribner, Rowaytou, C0nn., assignor to Ward Leonard Electric Co., Mount Vernon, N.Y., a corporation of New York Filed July 21, 1951, S81. No. 125,845 6 Claims. (Cl. 33862) This invention relates to electrical resistors and is directed particularly to the mounting of the resistance wire to withstand repeated passage of high surge currents. The invention is particularly applied to non-inductive electrical resistors.

In previous non-inductive resistors the instantaneous wattage that could be applied without damage has limited their use in circuits Where transient or repetitive high surge currents occur.

An object of this invention is to provide an electrical resistor with a high normal rated Wattage and with the capacity to withstand repeated high surge currents.

Another object of the invention is to provide an electrical resistor with a high heat thermal stress capacity.

Another object of the invention is to provide an elec' trical resistor with a high heat dissipation and thermal stress capacity that is inexpensive to manufacture and assemble.

Other objects and advantages will be apparent from he following description taken in connection with the drawings in which .16. 1 is a side view of the resistor;

FIG. 2 is a top View of the resistor;

FIG. 3 is an end view of the resistor;

HO. 4 is a sectional view taken along lines 4--t of FIG. 5 is a fragmentary perspective View of a ceramic saddle and a mounting board;

FIG. 6 is an enlarged fragmentary side View of a saddle;

MG. 7 is a fragmentary sectional View of a terminal on a mounting board; and

Fit 8 is a diagrammatical perspective view of the two revcrsely wound windings.

Referring to FIGS. 1 and Z the resistor has two wind ings termed by the resistance wires Ztl 21. T he wires 26*, 2d are connected to the terminal 22 at one end and to the terminal 23 at the other end of the resistor. The

direction of winding of the wire it} is opposite to the direction of winding of the wire Zl, and the current in wire 21 flows in the opposite direction to the current in wire 2d. The resistance wires are supported on an open frame comprising three mounting boards 24, 25', 2c of heat resistant insulating material, four metal brackets 27, 28, 29, 35 secured to the ends of the boards and four saddles 31, 32, 33, 34 mounted on the boards to receive the resistance wires.

The insulating boards 24, 25, 26 are thin and straight and are rectangular in cross section. The brackets space the boards 24, 26 in a parallel, side by side relation with the board 25 positioned midway between and normal to the plane of the boards 24, 26. The boards are made of stiff asbestos cement and are heat resistant and dimensionally stable with changes in heat.

The brackets 27, 23, 29', 3dare identical in shape and each comprises flat portions 27a, 28a, 29a, 3th: and 27b, 2%, 291), 3% to which the boards are attached.

The

fiat portions are connected by the angle portions 270, 23c, 29c, Me to position the flat portions 2-71), 2%, 29b, 3% midway between the side boards 2%, 26 and centered on the plane through the side boards. The boards are secured to the brackets by the bolts and nuts 35a. The outer ends of the brackets have flanges 36, 37, 3h, 39 with holes for securing the resistor to a panel or the like. The flanges are at right angles to the iiat portions 270, 28a, 2 36a. Thus the brackets hold the boards in a given relation and also serve to attach the resistor to a panel.

The insulating boards and brackets form a rig-id open frame that is strong and rugged to firmly support the resistance Wires. The transverse mounting of the center board 2-5 to the side boards 24, 26 provides rigidity and strength to the frame. The center board reinforces the side boards in the planes normal to the side boards and the side boards reinforce the center board in the plane normal to the center board. Thus the boards mutually reinforce one another. Further the supporting flat portions 27a, 28a, 29a, 3% are perpendicular to the supporting flat portions 2-711, 2%, 1%, Stlb, and thus any force tending to distort the substantially rectangular form of the frame must bend the brackets in an edgewise direction rather than through the narrower thickness.

The saddles 3d, 33 are mounted on the outer edges of the side boards 24 2 6 and the saddles 32, 34 are mounted on the opposite edges of the center board 25. The saddies are made of ceramic and have transverse notches 4t '41, d2, d3 uniformly spaced longitudinally along the respective saddles. The saddles are wider than the boards and have longitudinally extending grooves 24, 46, 37 generally rectangular in cross section and having. a depth to provide substantial supporting walls 4%, 49, 5 th, 51 engaging the boards. Flanges 52, 53, 5d, 55 extend along he inner edges normal to the boards to reinforce the saddles. Along the sides extending from the flanges are uniformly spaced bosses $7, 58, 5*? to further reinforce the saddles. The saddles are secured to the edges of the boards by a heat refractory adhesive applied between the edges and the grooves. The notches are formed by partitions '68, 61, d2, 63 extending outwardly from and laterally to the frame. The notches all, 413 ct the saddles on the center board are offset one-half the pitch from the notches ill, 42" of the saddles on the side hoards. The notches as, 42 of the side saddles are aligned and the notches, 4'1, 4? or" the center saddles are aligned. The centers of the notches of the saddles on the center board are laterally midway between the centers of the saddles on the side boards.

The terminals 2-2, 23 a e L-shaped metallic pieces with bolts 66 and nuts or fastening the terminals to the center strip. Openings 22a, 23a are provided on the perpendicular extending portions for attaching leads to the terminals. On the other end of the terminals are projections 22b, 23b for fastening the ends of the resistance wires 2%,

As illustrated in the drawing, the wire 2G threads through every other notch in the side saddles El, 33 and similarly the wire 2 threads through every other notch in the side saddles 3d, in the center notches 4d, 43 the wires 23, 21 cross in the same notch so that every other notch is empty. The wire is circular in cross section and the bottom walls are convex laterally to conform to the bend in the wire.

Starting with terminal 22 the wire 29 is wound from the terminal 22 through the notch 32a in the side saddle and the wire 2"; is wound from the terminal 22 through the opposite notch 447a in the side saddle. The wires cross in the notch 43a of the lower center saddle and wire 25} extends through notch 4d!) adjacent to notch 49a passing wire 2i, and wire 23 passes through notch 42]) adjacent to the notch 62o passing wire Ztl The wires aga'm cross in the notch 41b of the upper center saddle. This notch is aligned with the empty notch 43b of the lower center saddle. In the manufacture of the resistor the frame is assembles and mounted in winding machine to rotate about the central longitudinal axis extending through the center board 25. The frame is rotated to move the lower side board away from the operator by a suitable motor. The wire 21 is fastened to terminal 22 and the wire wound in the manner previously de "ribed. The wire 21 is fast-e to terminal and the f ame is rotated in the same direction. The wire 29 is wound from terminal 23 to terminal 22 and fa .e ed thereto. The wire overlies the wire in the cross notches. At the terminals 223, the wire is silver soldered or welded to the terminals to provide good current transfer characteristics and to maintain a good electrical connection under heat and stress.

Each turn of one winding is closely associated with a conresponding turn of the other winding and the lengths of the turns are of equal length and are in electrical contact at the crossover point in the notches ll, 43 to pro duce equal current distribution and. mutual cancellation of the inductive proper ies of the two windings. The flat or oval form of the turns assists in reducing the selfinductance of each winding.

The wires 2d and 21 are free to move relative to the walls or" the notches to permit expansion and contraction of the wires without applying any stress on the ceramic eddies. The high surges rapidly heat the wires causing the turns to enlarge. Since the surge is only momentary the wire cools and contracts. This easy adjustment permits the wire to carry the maximum current for which the wire is designed. The frame places no limitations on the surge current carried.

Another feature or re winding is separation of the winding from the metallic supports. This eliminates any increase in inductance of the windings due to the proximity of ferromagnetic. metal and permits high voltages to be applied to the winding. The winding is particularly suitable for high frequency alternating currents due to the low inductance of each turn produced by the crossover of the wire, the spacing from the metallic brackets and the oval shape of the turns.

Due to the open support of the wire and the spaces provided through the frame, the resistor is easily air cooled by circulating currents. The resistor is normally supported with the longitudinal center axis horizontal. .Air circulates up through the turns of the winding and 335833 over the ceramic saddles which are heated by direct contact wi h the wires and in turn dissipate heat rapi ly .to the air because of the large exposed surface area.

As illustrated the resistor has an oval shape. The outer edges of the boards d, 26 are spaced further apart than the width of the center board 25. This oval shape reduces the inductance of the winding. However other configurations may be used such as square, circle, etc. Further, a single winding may be wound on the frame with the wire in each notch. The turns will not be non-inductive, however, the oval shape of the turns will reduce the inductance from that of a winding with circular turns.

The boards 2d, 2:5, 2d may be identical in size and shape. The ceramic saddles may also be identical. The sameness of the parts reduces the cost of manufacture of the individual parts and the cost of assembly of the frame. The parts cannot be misassembled since they can fit togetner in only one way.

The ability of the resistor to adjust to wide ranges of currents, particularly surge currents, and temperature and dimensional changes increases its wattage rating by permitting high rated currents to pass. The resistor replaces a large number of the present type resistors thereby saving space even though the described resistor has open spaces.

it is thus seen from the foregoing description that a new high surge current resistor has been developed. The frame is dimensionally stable and is rigid so that it maintains its shape under wide change in heat and external forces. In the foregoing embodiment the supporting boards are of the same size. However the size and spacing of the boards may be changed to alter the shape of t the turns of the windings. The oval or elliptical shape is preferred to reduce the inductance of the turn". The spacing of the outer edges of tr e boards 24, 26 may be increased to further flatten the oval shape or the center board increased in width to impart other shapes. The saddles are preferably formed of one piece. In order to adapt the manufacture of the resistor to different lengths the saddles may be made in se mcn ts. The number of segments used depends on the length of the winding and the desired wattage. The saddles have round surfaces at the bottom of the slots or notches to conform to the bends in the wires.

The dimensionally stable frame securely and firmly supports the winding to be dimensionally independent of the frame on expansion and contraction of the wire. Thus the physical variations of the wire are accommodated without stress being applied to the frame. A particular embodiment of the invention has been set forth in the foregoing description. Other and different embodiments may be developed from the teachings herein without departing from the scope of the invention as set forth in the appended claims.

I claim:

1. An electrical resistor for passing high surge currents com-prising a resistance wire wound in a plurality of spaced turns along a longitudinal axis and encompassing an interior space for a winding support and passing cooling circulating currents, an interior winding support of outer brackets and of solely non-magnetizable material extending longitudinally of said winding formed of at least two rigid non-magnetizable insulating means extending generally transversely to one another in intersecting transverse planes and longitudinally to a longitudinal axis in said space to longitudinally and circumferentially support said winding at spaced locations, said means having a narrow thickness normal to a respective transverse plane and a width substantially greater than the thickness to impart rigidity and strength to said means, brackets outside of said winding to firmly and rigidly support said means on said interior winding support in a rigid nonmagnetizable supporting relation with said winding.

2. An electrical resistor as set forth in claim 1 Wherein said non-magnetizable insulating means are the see members said space and one of said means comprises a first and third spaced insulating non-magnetiza'ble supporting members on opposite portions of said space and said other means is a second insulating non-magnetizable supporting member centered between said first and third members.

3. An electrical resistor as set forth in claim 2 wherein four ceramic saddles are provided on the outer edges of said members with each saddle having lateral slots opening outwardly for receiving wire.

4. An electrical resistor as set forth in claim 2 wherein said brackets comprise four identical members each having two flat attaching portions for securing said sup porting members together to form a frame, said attaching portions being at right angles to support the second member at right angles to the first and third supporting members.

5.' An electrical resistor as set forth in claim 3 where- References Cited in the file of this patent UNITED STATES PATENTS Harthan June 9, 190 3 Dunlop Dec. 10, 1929 Mucher Jan. 5, 1932 FOREIGN PATENTS France Aug. 25, 1926

Claims (1)

1. AN ELECTRICAL RESISTOR FOR PASSING HIGH SURGE CURRENTS COMPRISING A RESISTANCE WIRE WOUND IN A PLURALITY OF SPACED TURNS ALONG A LONGITUDINAL AXIS AND ENCOMPASSING AN INTERIOR SPACE FOR A WINDING SUPPORT AND PASSING COOLING CIRCULATING CURRENTS, AN INTERIOR WINDING SUPPORT OF OUTER BRACKETS AND OF SOLELY NON-MAGNETIZABLE MATERIAL EXTENDING LONGITUDINALLY OF SAID WINDING FORMED OF AT LEAST TWO RIGID NON-MAGNETIZABLE INSULATING MEANS EXTENDING GENERALLY TRANSVERSELY TO ONE ANOTHER IN INTERSECTING TRANSVERSE PLANES AND LONGITUDINALLY TO A LONGITUDINAL AXIS IN SAID SPACE TO LONGITUDINALLY AND CIRCUMFERENTIALLY SUPPORT SAID WINDING AT SPACED LOCATIONS, SAID MEANS HAVING A NARROW THICKNESS NORMAL TO A RESPECTIVE TRANSVERSE PLANE AND A WIDTH SUBSTANTIALLY GREATER THAN THE THICKNESS TO IMPART RIGIDITY AND STRENGTH TO SAID MEANS, BRACKETS OUTSIDE OF SAID WINDING TO FIRMLY AND RIGIDLY SUPPORT SAID MEANS ON SAID INTERIOR WINDING SUPPORT IN A RIGID NONMAGNETIZABLE SUPPORTING RELATION WITH SAID WINDING.

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