US2276808A - Resistor - Google Patents

Description

. March 1942- J. F. TRITLE ETAL RESISTOR Filed July 25, 1940 Invehtorvs:

John FTritle, Charles A.Fecersen by Theiv- Attorney- Patented Mar. 17, 1942 RESISTOR John F. Tritle and Charles A. Petersen, Erie, Pa.,

assignors to General Electric Company, a corporation of New York Application July 23, 1940, Serial No. 347,048

7 Claims.

This invention relatesto resistors, more particularly to dynamic braking resistors for the driving motors of locomotives or other vehicles, and has for its object a simple and reliable resistor having provision for the rapid dissipation of heat therefrom.

In carrying out our invention in one form, we provide a braking resistor in the form of a duct through which a cooling fluid may be circulated, to dissipate energy when the resistor is being used. The resistor is formed in two sections which are connected in parallel with each other for'the circulation of cooling fluid therethrough, but electrically in series with each other in a dynamic braking circuit. Also the diameter of the resistor is increased toward the cooling fluid outlet end to maintain the fluid pressure in the resistor within a predetermined value, and the wall thickness of the resistor is increased to provide for a reduced generation of heat per unit area of resistor surface and therefore less heat transfer per unit area of resistor surface as the temperature of the cooling medium increases toward the outlet end.

For a more complete understanding of our invention reference should be had to the accompanying drawing, the single figure of which is a diagrammatic representation of a dynamic braking resistor embodying our invention.

Referring to the drawing, for purposes of clarity and completeness we have shown in addition to the resistor the elementary electrical connections utilized during the dynamic braking of a plurality of motors. This dynamic braking system is described and claimed in a copending application of John F. Tritle, Jacob W. McNairy,

and Charles A. Petersen, Serial No. 288,372, filed August 4, 1939, and assigned to the same assignee as this application.

In the form shown, the resistor comprises a plurality of lengths of tubing made of electrical resistor material such as stainless steel, the lengths being mechanically connected together at their ends to form two duct sections I and H which are however mechanically and electrically connected together. The various lengths of the resistor may be suitably arranged if desired in layers to provide the most compact assembly and one most conveniently fitting into the space available for it on the Vehicle.

A suitable cooling fluid preferably water at a, suitable low pressure, such as 75 pounds per square inch, is fed through a pipe I2, a normally closed valve I3, and a check valve M to the two steam operated water injectors l and It, constituting a positive fluid feed device. A by-pass pipe I! around the valve l3 provides for the continuous flow of a small amount of water through the resistor, even when it is not being used, for the purpose of maintaining the resistor at a suitable high temperature during coolweather to, prevent freezing.

High pressure steam is supplied from a pipe l8 through a steam valve I9, biased closed as by a I spring, and pipe 20 to the water injectors l5'and l6. This assures a positive or pressure feed of the cooling water at a predeterminedrate. It will be understood that for the purposes of space economy the resistor is made as small as possible and may be heated in a very short interval such as a few seconds after the beginning of dynamic braking to a high temperature such that steam is formed rapidly in the resistor with cons:quent considerable back pressure by the steam against th entrance of cooling water.

From the resistor sections [0 and II through which it will be noted the cooling water flows in separate parallel streams, the two sections 10 and It being connected in parallel with each other for the circulation of cooling water, the heated water and steam passes through a manually-operated shut-off valve 2| and the pip 22 to the separator 23 in which the water is separated from the steam. The steam then goes on to a condenser 24.

The resistor sections l0 and II are electrically insulated from the cooling water supply pipes by means of sections of pipe 25 and 26 made of a suitable electrically insulating material such as a molded compound. At their opposite ends no insulating pipe sections are provided between the sections and the pipe 22 which therefore consti- Lutes a ground connection.

Furthermore the tubes forming the resistor gradually increase in cross-sectional area in steps by increasing the diameters from the left-hand end toward the right-hand end of each section, i. e., in the direction of the flow of water through the resistor sections. The purpose of thus increasing the tube diameters is to reduce the water pressure required of the steam injectors to force the water and steam through the tubes. As the water passes through the tubes, an increasing and substantial amount of it is converted into steam and, as a result, the velocity pressure drop per unit length of the tube wouldv increasegreatly if the tube diameters were not increased to accommodate the greater volume of steam. The resistor is maintained at a substantially uniform temperature.

Furthermore, the thickness of the wall of the resistor tube is varied for the purpose of varying the rate of generation of heat per unit inside surface area of the resistor by the current pass ing through the resistor. In general the sections of the resistor which remain in the braking circuit for the longest period of time have increased thicknesses for the purpose of reducing the rate of heat generation per unit area. In a typical resistor the sections short circuited by the switches 59a and 60a were constructed from tubes having the same wall thickness, while the two sections short circuited by the switch 56, i. e., between the switch 56 and the switch 600, had much greater wall thicknesses to reduce the rate of heat .generation between these sections. The resistor sections 53, 54, and 55, on the other hand, had wall thicknesses thinner than any other portions of the resistor for the reason that these sections each carry the current of one motor only. The resistor section 51 had a wall thickness substantially the same as the wall thickness of the sections between the switches 56 and 60a for the reason that the section 51 carries the combined current for all three pairs or motors In other words, the diameter of the resistor tube is increased toward the right-hand end or water outlet end to maintain the fluid pressure in the resistor not greater than a predetermined maximum value, and then the wall thickness is varied so as to adjust the rate of heat generation per unit area in conformity with the capacity of the fluid to absorb heat from the resistor so as to maintain the resistor at a substantially uniform maximum limiting temperature through out its length. Substantially one half of the cooling water is converted into steam under maximum operating conditions.

As shown, the motors to be dynamically braked are connected to the resistor in three series connected pairs 21, 28 and 29 which are connected in parallel with each other. A suitable controller 30 is provided for controlling the connections of the motors to the resistor, this controller being preferably a rotatable drum or cam switch controller having an operating handle 3|. To establish dynamic braking connections, the controller is turned to a first position from its off -position in which one side of a suitable source of control voltage supply, the other side of which is grounded, is connected to a control conductor 32. The circuit leads through the conductor 32, the normally clo'sed switches 33 and. 34, the conductor 35, and the coil 35 to ground. This coil 36 opens a water drain valve 36a on the separator and closes an interlock switch 31 which closes a circuit through the conductor 38 and the coil 39 to ground. Energization of the coil 39 opens the cooling water valve l3.

Admission of cooling water by the opening of the valve |3 closes a cooling water pressure responsive switch 4|, this switch being biased to the open position, as by a spring not shown, and operated to its closed position by a piston in a cylinder 42 connected to the cooling water supply pipe or conduit means 43. The switch 4| closes a circuit from the conductor 35 through the switch 4| and the coil 44 to ground. This coil 44 opens the steam valve l9 admitting steam to the injectors l and I6 and closes an interlock switch 44a which closes a circuit from the conductor 35 through the switch 4| for the coils 45, 46, 41 and 48 to ground. The coil 45 closes one side of the dynamic braking circuit, thereby connecting one side of the parallel motor circuit to a point 45a on the braking resistor. The coils 45, 41 and 45 operate switches on contactors in the respective circuits of the pairs of motors whereby the other sides of the motors are connected to selected points 49, 50 and 5| oi the resistor.

The points 50 and 5| are electrically insulated from each other by a section of electrically insulating tubing 5|q. This arrangement together with the conductor 52 provides for the connection of short sections of the resistor permanently in circuit with the pairs of motors. Thus the pairs 21, 28 and 29 have the resistor sections 53, 54 and 55 permanently connected respectively in series with them for stabilization purposes, these sections not being short circuited later on by the closure of the last short circuiting contactor 55. Also the section 51 on the left-hand end of the section II is not short-circuited and it is always included in circuit with the motors.

It will be noted that the sections l0 and it are connected in series with each other electrically in the dynamic braking circuit.

In the event of failure of the cooling water supply, the switch 4| opens in accordance with its bias, and thereby opens the circuits of the coils 44, 45, 46, 41 and 48 thereby to interrupt both the supply of steam to the injectors and the dynamic braking circuit.

The switches 33 and 34 are operated by pistons in cylinders connected to the resistors adjacent the injectors l5 and i5 respectively. in the event that the back steam pressure in the resistor becomes excessive,- these switches 33 and 34 are opened whereby the motors are disconnected from the braking resistor and the supply of steam and cooling water is shut off. This interruption of the braking by the opening of the switches 33 and 34 and also by the opening oi the switch 4i may be only temporary. Dynamic braking will be resumed by the closing of these switches in accordance with their spring or other biases when the steam pressure drops to a suitable low value or when the cooling water supply is resumed, as the case may be.

Continued movementof the controller 30 oper- I ates to energize the operating coils 59, and 6| in the order named which close their switches 59a, 50a and 56 to short circuit sections of the braking resistor.

While we have shown a particular embodiment 'of our invention, it will be understood, of course,

that we do not wish to be limited thereto, since many modifications may be made and we, therefore, contemplate by the appended claims to cover any such modifications as fall within the true spirit and scope of our invention.

What we claim as new and desire to secure by Letters Patent of the United States, is:

1. A resistor comprising a duct made of re-- sistor material, positive supply means for forcing cooling fluid into said duct at a predetermined rate, conduit means for supplying cooling fiuid under pressure to said positive supply means, a valve in said conduit means, manually operated means for opening andclosing said valve to control the supply of cooling fiuid to said positive supply means, means responsive to the pressure of the fluid in said conduit means for controlling the operation of said positive supply means so as to start said supply means when said manually operated means is operated to open said valve and the pressure in said conduit means is above a predetermined value and stop said supply means when the pressure in said conduit means is below a predetermined value, and a bypass pipe around said valve providing for a limited flow of cooling fluid through said duct when said valve is closed.

2. A resistor comprising a duct made of resistor material, positive supply means for forcing cooling fluid into said duct, conduit means connected to supply a cooling fluid under pressure to said positive supply means, a normally closed valve in said conduit means, a controller operable to cause opening of said valve to supply fluid to said positive supply means, means responsive to the pressure of the fluid supplied to said positive supply means for causing operation of said supply means to force cooling fluid into said duct, and a by-pass pipe around said valve providing for a limited flow of cooling fluid through said duc when said valve is closed.

3. A resistor comprising a duct made of resistor material, connections for connecting said duct in an electric circuit whereby said duct is heated, a positive fluid feed device for forcing cooling fluid at a predetermined rate into one end of said duct, an outlet for said fluid at the other end of said duct, said duct increasing in diameter from the inlet end to the other end to limit the fluid pressure therein to a value not greater than a predetermined value and said duct having walls varying in thickness to vary the rate of heat generation in said walls per unit area in conformity with the capacity of the fluid in said duct to absorb heat asits tem-' perature increases from the inlet end of said duct to the other end whereby said duct is maintained at a substantially uniform temperature throughout its length, conduit means for supplying cooling fluid to said feed device at a predetermined pressure, a manually controlled valve in said conduit means and fluid pressure operating means connected to said conduit means between said valve and said feed device for controlling said feed device to cause said device to force cooling fluid into said duct when said valve is opened to supply cooling fluid to said feed device at said predetermined temperature.

4. A resistor comprising a duct made of resistor material, connections for connecting said duct in an electric circuit whereby said duct means is heated to a temperature above the boiling point of water, a positive water feed device for forcing cooling water at a predetermined rate said'ma'nually operated means is operated to open said valve and supply water at said predetermined pressure to said injector.

6. A resistor comprising a tubular member made of resistor material, connections for connecting said tubular member in an electric circuit whereby said tubular member is heated to a temperature above the boiling point of water. a pressure water feed device for supplying a cooling water at a predetermined rate to one end of said tubular member against the steam pressure therein, an outlet for the steam and water at the other end of said tubular member.

a said tubular member increasing in diameter from the water inlet end to the other end to limit the steam and water pressure therein to a predetermined value and said tubular member having walls varying in thickness to vary the rate .of heat generation in said walls per unit area and fluid pressure operating means connected into one end of said duct against the steam pressure therein, an outlet for the steam and water at the other end of said duct, a pipe for supplying water to said feed device at a predetermined pressure, a valve in said pipe, manually operated means for actuating said valve to control the supply of water to said feed device, and fluid pressure operating means connected to said pipe between said valve and said feed device for controlling said feed device to cause said device to force water into said duct when said manually operated means is operated to open said valve and supply water at said predetermined pressure to said device.

5. A resistor comprising a duct made of resistor material, connections for connecting said duct man electric circuit whereby said duct is heated to a temperature above the boiling point of water, a steam injector for forcing cooling water at a predetermined rate into one end of said duct against the steam pressure therein, an outlet for the steam and water at the other end of said duct, a pipe for supplying water to said injector at a predetermined pressure, a valve in said pipe, manually operated means for actuating said valve to control the supply of water to said injector, means for supplying operating steam to said injector, and fluid pres- .to said pipe between said -valve and said feed device for controlling said device to cause said device to feed water to said tubular member when said manually operated means is operated to open said valve and supply water at said predetermined pressure to said device.

'7. A resistor comprising a duct made of resistor material, connections for connecting said duct in an electric circuit whereby said duct is heated to a temperature above the boiling point of water, a steam injector for supplying cooling water at a predetermined rate to one end of said duct aga nst the steam pressure therein, an outlet for the steam and water at the other end of said duct, said duct increasing in diameter from the water inlet end to the other end to limit the steam and water pressure therein to a predetermined value, said duct having walls varying in thickness to vary the rate of heat generation in said walls per unit area in conformity with the capacity of the steam and water mixture in said duct to absorb heat as its temperature increases in flowing from the water inlet end of said duct to the other end whereby said duct is maintained at a substantially uniform temperature throughout its length, a pipe for supplying water to said injector at a predetermined pressure, a valve in said pipe, manually operated means for actuating said valve to control the supply of water to said feed device,- means for supplying operating steam to said injector, and fluid pressure operating means connected to said pipe between said valve and said injector for controlling said steam supply means to cause said injector tofeed water to said duct when said manually sure responsive operating means connected to said pipe between said valve and said injector for controlling said steam supply means to cause said injector to force water into said duct when operated means is operated to open said valve and supply water at said predetermined pressur to said injector.

JOHN F. TRITLE. CHARLES A. PETERSEN.

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