US2292185A - Pile resistor - Google Patents

Description

1942. c. c, WHlTTAKER 2,292,185

PILE RESISTOR Filed Sept. 7, 1940 WITNESSES: INVENTOR as OW/zzzfakezr Patented Aug. 4, 1942 3 PILE RESISTOR Charles C. Whittaker, Pittsburgh, Pa., assignor to Westinghouse Electric & Manufacturing Company, East Pittsburgh, Pa., a corporation of Pennsylvania Application September 7, 1940, Serial No. 355,802

2 Claims.

This invention relates to resistors of the carbon pile type.

Carbon pile resistors are well known and have been utilized in regulator apparatus and systems for a number of years. The known carbon pile resistors, however, were formed of a plurality of discs of resistance material such as carbon or the like supported by insulated rods which touch the edge of the disc of high resistance material or the discs were supported by threading them on a central insulating rod or tube. With the known structures, it was impossible to obtain an even separation of the discs when pressure, which is applied to the assembled discs during their use as a resistor, was released. With the uneven separation of the carbon discs that is obtained in the known structures when the pressure is released, it is found that the voltage drop is not uniformly distributed throughout the assembly nor is the heat developed evenly therein, but instead a larger voltage drop is encountered at the end of the assembly where the pressure is applied and released. The known carbon pile resistors were, therefore, not satisfactory where a close control of resistance is necessary in order to closely control resultant conditions in a given electrical circuit.

An object of this invention is to provide for insuring a positive movement of an insulating member carrying the stacked discs of resistance material of a resistor of the pile type when pressure is removed from the pile for effecting an even separation of the discs throughout the stack.

A more specific object of this invention is to provide for obtaining a movement of an insulating member which supports the stacked discs of resistance material of a resistor of the pile type relative to the discs when pressure is applied and at least an equal but opposite positive movement ofthe insulating member relative to the discs when the pressure is removed to effect an even separation of the discs throughout the stack.

Other objects of this invention will become apparent from the following description when taken in conjunction with the accompanying drawing, in which:

Fig. 1 is an elevational view partly in section of a resistor embodying the teachings of this invention; and,

Fig. 2 is a diagrammatic view of a circuit in which the resistor of Fig. 1 is utilized.

Referring to Fig. 1, this invention is illustrated by reference to a resistor element formed of a plurality of discs [2 of resistance material such as carbon or the like. Any predetermined numher of disks l2 may be utilized, depending upon the resistance value which it is desired to secure in the assembly. In the particular embodiment illustrated, the discs l2 are of the circular type having a predetermined thickness and having openings centrally positioned therein so that when the discs are stacked as illustrated, the openings are aligned.

In order to support the discs in their aligned relation, an insulating supporting member is so disposed as to extend through the aligned openings of the discs l2. In the embodiment illustrated, the insulating supporting member comprises a metallic rod I4 having metal sleeves l6 disposed thereon and attached thereto as by means of the pins !8 and a tube of insulating material 2i] which extends between the sleeves Hi. The dics l2 are in direct contact with the tube 20 of insulating material such as porcelain, Micalex, Pyrex, glass or the like, the weight of the discs at least causing contact between the discs and tubular member 29 along the upper edge of the tube 20.

In order to retain the discs 12 in assembled position on the tube 20 of insulating material, a fixed stop or end plate 22 is disposed at one end of the stacked discs l2 and is secured in any well known manner to a panel, not shown. The fixed stop 22 has an opening 24 therein of a size suitable for permitting movement of the insulating rod or tube 2i) therethrough as will be explained more fully hereinafter. Adjacent the other end of the stacked discs [2 a pressure plate or disc 26 is positioned as to bear against the face of the end of the stacked discs [2 and has an outwardly projecting end cap 28. The end cap 28 is hollow to receive the end of the metal sleeve 16 attached to the metal rod I4 and the insulating tube 22 associated therewith. The metal sleeve I6 and its associated insulating tub 2% is secured to the hollow end cap 28 by any suitable means such as a threaded joint (not shown) or otherwise. This end of the assembly is held in position with respect to the fixed stop or end plate 22 by means of a fixed plate 30 which projects outwardly from a panel (not shown) to which it is attached, the plate 30 having an opening therein for receiving the projecting end cap 28 of the pressure disc. The opening in the fixed plate 30 is of suificient size to permit longitudinal movement of the end cap 28 therethrough when pres- 'sure is applied or released to the stacked assembly.

In order to apply pressure to the assembled discs, any suitable means can be employed such as the bell crank lever 32 formed of the short arm 34 and the long arm 36 which is disposed for movement about a pivot 38 in response to either the bias of a spring 40 which is secured between a fixed point 42 as on the panel (not shown) and a projecting lug 44 of the bell crank 32 or in response to a force applied to the end of the long arm 36 as will be hereinafter described. Since it is desired to provide for an even distribution of the discs I2 under all operating conditions of the resistor including the operation of the resistor when pressure is released, the short arm 34 of the bell crank lever 32 is mechanically coupled to the projecting end cap 28 to effect a positive movement of the insulating tube through the stack when the pressure is released. In the particular embodiment illustrated, the end of the end cap 28 is provided with a vertical slot 46 for receiving the end of the short arm'34 and is also provided with a slot 48 positioned at right angles to the slot 46 and intersecting therewith for receiving a pin 50 carried by the end of the short arm 34 of the bell crank lever 32. With this mechanical connection, any movement of the bell crank'32 is transmitted directly to the end cap 28 and its associated insulating member 28 to efiect a positive movement of the insulating tube 20 in a direction depending upon the applied force or release of force.

With the tubular member 20 of insulating material secured to the pressure disc 26, when pressure is applied to the end cap 28 as by reason of the spring 40, the discs are compressed, being forced to the right as illustrated, against the fixed stop or end plate 22 and simultaneously with th compression of the discs the tubular member 20 of insulating material is moved longitudinally through the central openings of the discs relative to the discs. Since the tubular member 20 is free to move through the fixed stop or end plate 22, and since the fixed stop 22 limits the movement of the discs I2 under pressure, a large movement between the discs I2 and the tubular mem ber 20 will be obtained adjacent the fixed stop 22, the relative movement between the discs I2 and the tubular member 20 progressively increasing from the end of the stack adjacent the pressure disc 26 until it reaches a maximum adjacent the fixed stOp 22.

With the discs I2 under pressureas described hereinbefore, when the pressure is removed from the projecting end cap 28 as by reason of a force being applied to the long arm 36 sufficient to overcome the pull of the spring 48, the movement of the bell crank 32 effects a positive movement of the tubular member 20 in a direction away from the fixed stop 22 simultaneously with the movement of the pressure disc 26. The positive movement of the tubular insulating member 20 through the stacked discs I2 when the pressure is released insures the cooperation of the frictional resistance between the discs I2 and the tubular member 2|] to effect a movement of the discs I2 adjacent the fixed stop 22 at the same time that the discs adjacent the pressure disc 28 move as a result of the release of the compressive force on the assembled discs. The movement of the tubular member 20 through the stacked discs when pressure is removed from the assembly is in an amount equal to at least the movement in the opposite direction when an equal amount of pressureis applied. The positive movement of the tubular member 20 thus insures an even separation of 'the'discs throughout the stack for any change in pressure as the pressure is released. This positive movement of the tubular member 26 relative to the discs when the pressure is removed also effectively breaks up any static friction between the discs and the tubular member. As will be understood, the frictional resistance between the discs I2 and the tubular member 20 of insulating material will be a maximum adjacent the fixed stop 22 and will be progressively decreased in the direction of the pressure disc 26, since the relative movement of the tubular member 20 with respect to the discs I2 when pressure is removed from the assembly progressively decreases from the fixed stop 22 in the direction of and to the pressure disc 26.

Referring to Fig. 2, the resistor element I0 of Fig. 1 is illustrated as employed in a regulating system for regulating the voltage generated from a generator 52. The armature 54 of the generator is illustrated as connected by conductors 56 and 58 to a load 60. A switch 62 is illustrated for closing the circuit from the armature through the load 60. A shunt field winding 64 for the armature 54 is illustrated as connected to the junction point 66 of conductor 56 through the resistor element I0, junction point 66, conductor III to the junction point I2 of the conductor 58, the resistor It] thus being in series circuit relation with the field winding 64 and in shunt with the armature 54. Since it is desired to control the voltage generated by the generator 52, an electromagnetic coil I4 is disposed to be connected between the junction point I6 and the junction point 68, which is connected by conductor H! to the junction point 12 of conductor 58. Thus the energization of the coil I4 is in direct response to the voltage drop ,acrossthe lines 56 and 58.

Since it is desired to control the amount of resistance in circuit with the field winding 64 and the bell crank lever 32 is utilized for controlling the pressure applied to the stacked discs I2 of the element II], the free end of the arm 36 of the bell crank has an arm 18 pivotally connected thereto by any suitable means, the arm I6 carrying an iron or magnetic portion disposed to be actuated when the coil I4 is energized. When energized, the coil I4 tends to lift the iron or magnetic core portion 88, thereby rotating the bell crank 32 in a counterclockwise direction against the bias of the spring 40 to decrease the pressure applied to the stacked discs, thereby increasing the resistance in circuit with the field winding 64.

In operation, with the switch 62 closed, the tension of the spring 40 is so adjusted by any suitable means (not shown) that with a normal or predetermined voltage generated, a predetermined pressure is applied to the stacked discs of the resistor element I0 and the pull of the spring 40 balances the pull of the coil 14 on the magnetic core portion 86 of the arm I8. If for any reason, the voltage generated fiuctuates'from this predetermined normal value or generated voltage as, for example, if the voltage generated increases above the predetermined value, the coil 54 will become sufiiciently energized to overcome the pull of the spring 40 to cause the bell crank 32 to rotate in a counterclockwise direction about its pivot point 38 to remove some of the pressure from the end cap 28 thereby removing the pressure from the stacked discs I2. Simultaneously with the counterclockwise movement of the bell crank 32, there is a positive movement of the tubular member 20' longitudinally through the stacked discs away from the fixed stop 22. The frictional resistance of the discs l2 carried by the tubular member 20 cooperates with the positive movement of the tubular member as the pressure is released to effect an even separation of the discs 12, giving a substantially uniform voltage drop across the stacked discs. The release of the pressure on the assembly increases the resistance introduced in circuit with the field winding 64 thereby reducing the excitation of the winding 54 so that the resulting generator voltage is decreased.

On the other hand, if the voltage generated is decreased from the normal generated value, the pull of the spring 48 overcomes the pull of the winding 15 to effect a movement of the bell crank 32 in a clockwise direction about its pivot point 38, whereby a larger pressure is applied to the disc assembly thereby decreasing the resistance in circuit with the shunt field winding 64 to increase the generator voltage.

By means of the resistor element described hereinbefore and particularly by reason of the positive movement of the insulating member carrying the discs when the pressure is removed, a very close control of the generated voltage is obtained, and a uniform voltage drop throughout the resistor element is secured since even separation of the carbon disc is secured as pressure is removed therefrom. This even separation of the carbon disc can only be obtained when a positive movement of the supporting insulating member is provided for cooperating with the frictional resistance of the discs mounted thereon. By utilizing a resistor element of the type described, it is found that the desired regulation can be obtained with a smaller element since fewer discs of the high resistance material are necessary for retaining the desired voltage drop in the assembly, the construction described effectively breaking up the static friction in a uniform manner between all the discs in the assembly and providing for a uniform heating of the assembled discs.

Although this invention has been described with reference to a particular embodiment thereof, it is, of course, understood that the invention as described is illustrative only and is not to be interpreted in a limiting sense.

I claim as my invention:

1. A pile resistor comprising, a plurality of discs of resistance material having central openings therein, an insulating member extending through the central openings in frictional engagement with the discs to support the discs in stacked alignment, a fixed stop disposed at one end of the aligned discs, a pressure applying disc disposed on the insulating member at the other end of the aligned discs, actuating means disposed for movement in response to predetermined conditions to simultaneously apply a force to the pressure applying disc and move the insulating member longitudinally through the stack in the direction towards the fixed stop, and means independent of the stack of discs for effecting a positive movement of the insulating member longitudinally through the stack in the direction away from the fixed stop as the actuating means is moved to decrease the force applied to the pressure disc, the positive movement of the insulating member away from the fixed stop being equal to the movement of the insulating member towards the fixed stop for all equal but opposite movements of the actuating means.

2. A pile resistor comprising, a plurality of discs of resistance material having central openings therein, an insulating member extending through the central openings in frictional engagement with the discs to support the discs in stacked alignment, a fixed stop disposed at one end of the aligned discs, a pressure applying disc disposed on the insulating member at the other end of the aligned discs, actuating means disposed for movement in response to predetermined conditions to simultaneously apply a force to the pressure applying disc and move the insulating member longitudinall through the stack in the direction towards the fixed stop, and means for securing the insulating member to the actuating means for insuring a positive movement of the insulating member longitudinally through the stack in the direction away from the fixed stop as the actuating means is moved to decrease the force applied to the pressure disc, the positive movement of the insulating member away from the fixed stop being equal to the movement of the insulating member towards the fixed stop for all equal but opposite movements of the actuating means.

CHARLES C. WHITTAKER.

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