US3074041A

US3074041A - Fischer

Info

Publication number: US3074041A
Authority: US
Priority date: 1950-01-31
Filing date: 1955-05-23
Publication date: 1963-01-15
Anticipated expiration: 1980-01-15
Also published as: CH291642A; DE814624C; FR1097604A

Description

Jan. 15, 1963 Filed May 23, 1955 M. FISCHER ELECTRICAL RESISTORS AND STARTERS WITH SECONDARY COOLING SURFACES '7 Sheets-Sheet 1 MAX F/SC/fE/Q 4 TTOP/VEYS lNVfNToR Jan. 15, 1963 M. FISCHER ELECTRICAL RESISTORS AND STARTERS WITH SECONDARY COOLING SURFACES 7 Sheets-Sheet 2 Filed May 23, 1955 INVENTOR.

MAX FISCHER Jan. 15, 1963 Filed May 23, 1955 M. FISCHER ELECTRICAL RESISTORS AND STARTERS WITH SECONDARY COOLING SURFACES '7 Sheets-Sheet 3 INVENTOR MA X F/ S CHER ATTORNEYS M. FISCHER 3,074,041 ELECTRICAL REsIsToRs AND STARTERS WITH SECOND Y COOLING SURFACES 7 Sheets-Sheet 4 Jan. 15, 1963 Filed May 23, 1955 nvws/vroR M A X F/SCHER Jan. 15, 1963 M. FISCHER 3,074,041

ELECTRICAL RESISTORS AND STARTERS WITH SECONDARY COOLING SURFACES Filed May 23, 1955 7 Sheets-Sheet 5 llllllllllllll I ll IIIIIIIIIII ll wur-nnum INVENTOR MAX FISCHER v/flaswm /gofin Jan. 15, 1963 M. FISCHER 3,074,041

ELECTRICAL RESISTORS AND STARTERS WITH SECONDARY COOLING SURFACES 7 Sheets-Sheet 6 Filed May 23, 1955 IN vslvroR MA x F/s CHER 3 flfrak ffs Jan. 15, 1963 M. FISCHER ELECTRICAL RESISTORS AND STARTERS WITH SECONDARY COOLING SURFACES '7 Sheets-Sheet 7 Filed May- 23, 1955 INVENTOR Mnx Fl 5 CHER ATToIIvEYS United S ates Patent 3,074,041 ELECTRICAL RESISTORS AND STARTEIE WITH SECQNDARY COOLING SURFACES Max Fischer, Goethestr. 24, Neunkirchen (Saar), Germany Filed May 23, 1955, Ser. No. 510,350 In Germany Jan. 30, 1950 Public Law 619, Aug. 23, 3354 Patent expires Jan. 3t}, 1976 18 Claims. (Ci. 338-41) Previously known types of resistors and starters diife according to the service conditions to which the equipment is subject. In the case of equipment for continuous service, it has been usual to select a type in which less value is assigned to high heat storage capacity, the main emphasis being placed instead on the cooling situation, with large cooling surfaces of resistive material (strip and wire resistors). For this purpose, the wire or strip spirals are either suspended as open as possible in air or else wound on sheet-metal members, usually with the aid of ceramic insulators. In view of the linear expansion of the resistive material upon heating, the resistance ele ments are arranged vertically in this type. The insulators interfere with access of cooling air to the sheet-metal members and the sides of the resistive material facing the same.

Some types are also known in which heat is transferred from the actual resistive material to supplementary cooling surfaces. Thus in the case of fully enclosed resistors for continuous service on board ocean vessels, under dusty conditions or in installations subject to explosion hazard, a type is used in which the resistance wire is wound on porcelain cylinders and the-individual resistance elements closely surrounded by corresponding cooling surfaces of the casing. The casing may in addition he provided with pocket-shaped or tubular projections, forming supplementary air passages for cooling. In this type, the provision of supplementary cooling surfaces formed by the casing wall and/ or by tubular insertions permits more intensive utilization of resistive material. But since the resistance wire is wound on porcelain cylinders, there is only a unilateral cooling of the resistive material, cooling of the side of the wire in contact with the porcelain cylinder being very inadequate.

Since the resistive material assumes a higher temperature than the supplementary cooling surfaces, heats more rapidly than they, and moreover has a larger coefficient of heat expansion of the resistive alloy material than that of the surrounding sheet-metal, heating and hence the capacity of the resistive material are sharply limited if the wire spirals are not to touch the surrounding sheetmetal Walls and establish contact with the casing.

In another type, a resistance winding consisting of wire is wound on a metal tube with lengthwise grooves. To insulate the resistance wire from the metal tube, insulator bars are inserted in the lengthwise grooves of the metal tube at suitable intervals. The lengthwise grooves impart radial spring to the metal tube, with the intended result that the resistance wire resting on the insulator bars will be kept firmly on the insulation even when heated in service. The metal tube also serves as supplementary cooling surface, to which a portion of the heat of the resistance wire is transferred by radiation.

According to the invention, eat capacity is transferred to the secondary cooling surfaces to be described, whose time constant is substantially greater than that of the actual resistive material. The resulting devices are of substantially smaller weight than conventional types. Moreover, they are more economical of space, especially in Water-cooled equipment.

In particular, resistors and starters according to the Patented Jan. 15, 1953 ice invention may be further characterized by the following features.

The actual resistance material is freely suspended, with the aid of metal clips, in the form of looped spiral strips. The resistance strip has no connection with the secondary cooling surfaces, the two engaging in radiant exchange only. This eliminates difliculties resulting from unlike linear expansions of the actual resistance material and the secondary cooling surfaces. Differences in linear expansion due to heating are fairly great, the resistance alloy having a substantialiy larger coeflicient of heat expansion than the iron or copper cooling sheets, and the temperature of the primary heating surfaces, i.e. of the resistance strip, being higher than that of the secondary cooling surfaces, in addition to which the time constant of the resistance strips is smaller than that of the cooling sheets, with the result that the situation continues to deteriorate until tl: equilibrium condition is reached. Here the idea of the invention again intervenes to eliminate this ditliculty.

The arrangement of the spiral strips is so devised that the resistance strip is held taut in all operating conditions, so that there can be no conductive connection with the coolin sheets or frame.

The resistance strips are fixedly attached to the frame at one end with the aid of wedge-shaped metal clips and interposed insulation. At the other end, each spiral singly, insulated with another clip, is hooked to a tension spring and the latter so attached to the frame that it can be prestressed. The extent to which the spring is prestressed is so adjusted that its travel is equal to or somewhat greater than the elongation of the spiral strip upon maximum heating of the resistor. As a result of this, the strip is made to stay taut at all operating temperatures. The residual spring tension upon maximum heating of the strip may either be zero or be kept so small that the tension exerted on the tape at maximum service temperature is far below the strength of the strip. To relieve the strip of its own weight and that of the clip, the latter is slidably mounted on a support so that the tension springs need only equilibrate frictional forces and strip tension.

Since each loop of spiral has its own tension spring, temperature differences among the spirals can have no adverse effect. it is likewise indifferent whether individual ones of the spirals comprising a resistor battery are connected or disconnected. With easonably precise manufacture of the spirals, it is also unnecessary to provide a separate adjusting screw for each individual tension spring, since even at maximum service temperature, only a smail tension can be exerted on the spiral strips. Hence small di'lferences in the length of individual spirals can be compensated even if the springs of a resistor battery are all prestressed together.

- In the case of resistors with cooling lates, t.e tern perature of the latter may reach the scale limit of about 520 C. for iron and about 400 C. for copper. To avoid the ill effects of buckling of the plates at these temperatures, the cooling sheets are subdivided and so suspended in the frame as to be free to expand in all directions.

The contemplated construction avoids the difficulties arising from poor heat conductivity of insulators and their sensitivity to high temperatures in that the resistance strip does not come into direct but only into indirect contact, via the clips, with the dielectric. The clips consist of two metal parts so arranged that the resistance strip is clamped between two wedged surfaces. The result is a high compression between strip and clip; for carrying current, the entire cross ection of the clips, considerably greater than that of the strip, is available. In the first place, therefore, the loss heat is kept very small in the clips, and in the second place their best storage capacity is increased. The clips are open to the air current, and may additionally be provided with cooling fins. Their temperature remains low enough as not to constitute any hazard to the screw connection for the current leads, while at the same time the dielectric insulating the clips from the frame is under only a very small thermal load. In one type, the insulation of the clips consists merely of two insulating washers insulating the bolt head and nut of a screw fastening from the clip, and an insulating bushing electrically isolating the shank of the bolt from the two parts of the clip. Temperatures at the points of insulation do not call for high-grade ceramic high-temperature-resistant insulating materials. Ordinary insulating materials of ample mechanical strength may be used, so that it becomes a simple matter to build resistors in concussion-proof construction.

The insulation of the resistance material may alternatively be placed at points where the clips are attached to the frame, and/or the tension springs may be hooked into parts of insulating material. The temperature at such points is substantially lower still than at the clips.

The resistors are constructed within each battery without any clamped, screwed or welded connection of the actual resistive material, being wound with one uninterrupted endless resistance strip. Arcing at junctions of individual resistor elements is therefore prevented. The several resistor batteries are interconnected beyond the clips in the range of lower temperatures, the cross section of communicating lines being chosen such that no excessive heating can occur.

Contact connections for leads are located at points where the temperature is perfectly safe for the screw connection.

Since the permissible service temperature of the actual resistive material is not limited by considerations involving contact connections or insulators, but depends entirely on the physical properties of the resistance strips, and is therefore higher than in conventional types, the resulting linear elongations of the spiral strips are considerable. The wound strip is therefore provided at suitable intervals with fixed points by the arrangement of the clips, the total length variation of the strip being subdivided according to the number of spirals. Each tension spring need compensate only the length variation of spiral strip that occurs between two clips.

As resistance material, use is made of thin strips of high specific resistance, preferably of austenitic chromenickel alloys, which are far more resistant to deformation at high temperatures as compared to resistance material of ferritic structure.

In equipment for intermittent service, the less heat generated in service may further be carried off through the secondary cooling plates into bodies of Water or metal, and the latent heat of evaporation of the water or the heat of fusion or evaporation of the metals utilized for purposes of heat storage. During the off-duty periods, upon transition from the gaseous to the liquid and/or from the liquid to the solid state of aggregation, the heats of evaporation and/ or fusion are liberated and returned to the surrounding air.

In the case of equipment with water-cooled secondary cooling surfaces, hazards involved in evolution of steam are avoided by maintenance of water circulation through an electric lock, or installation of electromagnet valves.

FIG. 1 is a plan view of a pair of resistor units according to the invention,

FIG. 2 is a section on line IIII of FIG. 1,

FIG. 3 is a section taken on line,IIIIII of FIG. 1,

FIG. 4 illustrates a clamping piece with securing means and the manner of securing same,

FIG. 5 is a view in elevation of a spring suspension,

FIG. 6 is a side elevation of the spring suspension of FIG. 5,

FIG. 7 is a plan view of a pair of resistance units,

similar in construction to FIG. 1, but with water-cooling means added,

FIG. 8 is a section taken on line VIIIVIII of FIG. 7,

FIG. 9 illustrates an airand water-cooled resistor construction with tilted resistor strips.

In the figures, resistance bands 1 are attached at one end by means of clips 2 and clevises 3 as well as bolts 15 to the members of the device (not shown). On the sides lying oppositely, the clevises 3 and bolts 15 are attached to coil springs 4. Coil springs 4 are secured to flats of metal or insulating material 5 which are so attached to the frame that the coil springs 4 may be secured adjustably to carriers 16. The load of the spiral bands 1 and the clips 2 is carried by carriers 9 on which the clevises 3 are superimposed. The slot of the clevis 3 extends in the direction of tension of coil spring 4. In FIGS. 1, 2, 5 and 6, is shown the position of the spring when in a cold state. When the resistance bands 1 are heated, clevises 3 and clamps 2 move to the flats 5 and maintain the resistance bands tight in each operative position. In FIGS. 1, 2 and 3, the resistance bands are arranged substantially transversely to flats 5. The secondary cooling surfaces consist of sheet metal pieces 6 which are arranged parallel to and over the upper surfaces of resistance bands 1.

The clamping piece 2 consists of two parts with inclined surfaces a. The resistance band 1 is clamped be tween these inclined surfaces by means of bolt 15 and the clevis 3.

When resistors and starters which are cooled by air and water, as shown in FIGS. 7 and 8, are used, cooling boxes 7 are arranged in place of cooling plates 6 with water flowing through them.

The wedge effect produces very high compression on the inclined surfaces with only very low tension on the bolt, thus ensuring favorable conduction of heat and current. The two-part clip 2 is of substantially larger crosssection and size than the resistor band. The loss heat generated in it is negligible, and the heat storage capacity large. The clips are freely exposed to the flow of air, and may be provided with supplementary cooling fins, as illustrated in FIGS. 4, 5 and 6. V

The insulation consists of two insulating washers 18 and an insulating bushing 12, the latter electrically isolating the shank of the bolt 15 from the clip 2. To protect the insulating washers 18, guard washers 11 are interposed between them and the bolt head 15 and clevis. The clips are bolted firml to flat frame members 14 through the bolts 13. If the flats 14 are replaced by a bar of insulating material, the insulators 18 and 12 may be dispensed with and the insulation transferred to a point where the temperatures are even lower than at the clips.

As shown in FIG. 6 and FIG. 7, the spring suspension of the bands, the tension springs 4 are suspended in fiat steel members or insulator bars 5 movably arranged. The adjustment screws 8, abutting on the attachment members It serve to adjust the flat members or insulator bars 5 in such manner that when the resistor band is cold, the tension springs 4 are prestressed to an extent equaling or somewhat exceeding the expansion of the resistance bands at maximum service temperature.

Connections for current leads are made at terminals 17.

As shown in FIG. 9, the cooling plates are immersed in troughs 19 through which flows the cooling water. The clips '2 are slightly turned, as compared to the position in FIGS. l-8, so that hypothetical planes through the resistors are bent at an angle to the vertical.

The chief advantage of devices according to the present invention consists in the great saving of weight over About 18% of the weight of a comparable resistor for like load with 40% duty cycle.

About 45% of the weight of a comparable resistor designed for like load but only 12.5% duty cycle.

I claim:

1, An electrical resistor and a cooling system for the resistor, in particular for a starter, comprising at least one thin flat strip resistor having two faces, and at least one cooling unit having two faces and spaced apart from the strip resistor opposite and parallel thereto, said unit being of a material having a high heat conductivity, said two cooling unit faces being arranged opposite and substantially parallel to said resistor faces, respectively.

2. An electrical resistor and a cooling system for the resistor, in particular for a starter, as claimed in claim 1, in which said cooling unit is cooled by air.

3. An electrical resistor and a cooling system for the resistor, in particular for a starter, as claimed in claim 1, in which said cooling unit is cooled by water.

4. An electrical resistor and a cooling system for the resistor, in particular for a starter, as claimed in claim 1, in which said cooling unit comprises two parallel plates made of copper.

5. An electrical resistor and a cooling system for the resistor, in particular for a starter, as claimed in claim 1, in which said cooling unit comprises two parallel plates made of iron.

6. An electrical resistor and a cooling system for the resistor, in particular for a starter, as claimed in claim 1, in which said cooling unit comprises two copper ducts cooled by water passing the-rethrough.

7. An electrical resistor and a cooling system for the resistor, in particular for a starter, as claimed in claim 1, further comprising means for resiliently suspending said strip resistor, whereby the variation in length of said resistor with temperature will be substantially compensated and the resistor will be straight at all operating temperatures.

8. An electrical resistor and a cooling system for the resistor, in particular for a starter, as claimed in claim 1, in which said cooling unit comprises subdivided plates and means for mounting said plates, said means being adapted to permit expansion of said plates when heated.

9. An electrical resistor and a cooling system for the resistor, in particular for a starter, comprising a supporting frame, a plurality of holders, said holders being mounted on said frame in two opposing parallel rows, along fiat strip resistor having two faces, said strip resistor being held by said two rows of holders in alternate succession, means to insulate said strip resistor from said frame, and a. cooling unit spaced apart from the faces of the strip resister, said cooling unit being of a material having a high heat conductivity and arranged to extend opposite both said faces of said strip resistor.

10. An electrical resistor and a cooling system for the resistor, in particular for a starter, as claimed in claim 9, in which the sections of said strip resistor between said two rows of holders extend substantially in two planes which are parallel to the longitudinal direction of the said rows and said cooling unit comprises three sections positioned parallel to said planes, one of said sections being centrally positioned between said planes and the other two sections to either side of said planes, respectively, and spaced therefrom.

11. An electrical resistor and a cooling system for the resistor, in particular for a starter, as claimed in claim 10, in which said cooling unit sections are copper plates, further comprising three spacedly arranged troughs, each of said copper plates extending into one of said troughs, and means for passing water through said troughs.

12. An electrical resistor and a cooling system for the resistor, in particular for a starter, as claimed in claim 10, some of said strip resistors being slightly tilted with respect to said planes, whereby the cooling air is rendered more effective.

13. An electrical resistor and a cooling system for the resistor, in particular for a starter, as claimed in claim 9, in which at least one of said two parallel rows of holders is resiliently mounted on said frame, further comprising means to support the weight of said strip resistors and said resiliently mounted holders near said clamps, said means being secured to said frame.

14. An electrical resistor and a cooling system for the resistor, in particular for a starter, as claimed in claim 13, in which said resilient mounting is effected by tension springs, further comprising means for collectively pretensioning said springs.

15. An electrical resistor and a cooling system for the resistor, in particular for a starter, as claimed in claim 10 in which said holders are two-ended clamps, said strip resistor extending through said clamps and being clamped at both ends thereof.

16. An electrical resistor and a cooling system for the resistor, in particular for a starter, as claimed in claim 15, in which each clamp is insulated from said supporting frame, further comprising at least two terminals, said terminals being secured to the clamps.

17. An electrical resistor and a cooling system for the resistor, in particular for a starter, as claimed in claim 15, in which each of said clamps is provided with cooling fins.

18. An electric resistor and a cooling system for the resistor, in particular for a starter, according to claim 7, wherein said means for the resilient suspension of the strip resistor are characterized by straight-lined tension springs, said springs being prestressed and exerting a decreasing tensile stress upon said resistor strip at increasing temperatures of same, said springs being so dimensioned that the tensile stresses upon said resistor strips at maximum temperature are smaller than the creep strain of the bands.

References Cited in the file of this patent UNITED STATES PATENTS 614,275 Porter Nov. 15, 1898 2,104,886 Rohn Jan. 11, 1938 2,156,832 Ayers May 2, 1939 2,206,734 Stassinet July 2, 1940 2,367,170 Fahrenwald Jan. 9, 1945 FOREIGN PATENTS 814,624 Germany Sept. 24, 1951 291,642 Switzerland Sept. 16, 1953

Claims

1. AN ELECTRICAL RESISTOR AND A COOLING SYSTEM FOR THE RESISTOR, IN PARTICULAR FOR A STARTER, COMPRISING AT LEAST ONE THIN FLAT STRIP RESISTOR HAVING TWO FACES, AND AT LEAST ONE COOLING UNIT HAVING TWO FACES AND SPACED APART FROM THE STRIP RESISTOR OPPOSITE AND PARALLEL THERETO, SAID UNIT BEING OF A MATERIAL HAVING A HIGH HEAT CONDUCTIVITY, SAID TWO COOLING UNIT FACES BEING ARRANGED OPPOSITE AND SUBSTANTIALLY PARALLEL TO SAID RESISTOR FACES, RESPECTIVELY.