US2325815A - Electrical system - Google Patents

Description

g- 1943. L.-H. VON OHLSEN ET AL 7 2,325,815

ELECTRICAL SYSTEM Filed May 14, 1941. 2 Sheets-Sheet 2 o INVENTORS Zoo/.5 l a/v div/.55

domv J Kevwvcoy ATTORNE S Patented Aug. 3, 1943 ELECTRICAL SYSTEM Louis H. Von Ohlsen and John J. Kennedy, New Haven, Conn., asslgnors to The Safety Car Heating and Lighting Company, Inc., a corporation of Delaware Application May 14, 1941, Serial No. 393,380

8 Claims.

This invention relates to electrical systems and more particularly to a system for providing a controlled source of direct current for fluorescent lights on railway cars.

An object of this invention is to provide a stabilized constant direct current voltage when there is available power with variable voltage. A further object is to provide a booster set for producing a variable voltage in series with a variable source to provide a constant voltage for a load. Another object is to provide apparatus of the above character which will produce a booster voltage in series with a voltage source to maintain a controlled output voltage on a load. A further object is to provide apparatus of the above character which is simple and sturdy in construction and which is inexpensive to manufacture and efficient in operation. Another object is to provide apparatus which is light in weight, dependable in operation, and which does not require constant attention and service. A further object is to provide a method of operating apparatus of the above character. Other objects will be in part obvious and in part pointed out below.

The invention accordingly consists in the features of construction, combinations of elements, arrangements of parts, and in the several steps and relation and order of each of the same to one or more of the others, all as will be illustratively described herein, and the scope of the application of which will be indicated in thefollowing claims.

In the drawings:

Figure 1 is a circuit diagram of one embodiment of the invention with certain details omitted for clarity;

Figures 2 and 3 are similar to Figure 1 but show other embodiments of the invention; and,

Figure 4 is a vertical elevation partly in' section of the motor generator set of Figure 1.

The present application is related to the co pending application of John J. Kennedy, Serial No. 368,801, filed December 6, 1940, entitled (Electrical system. I

Under some circumstances, it is desirable that a reliable source of direct current be provided and that the voltage be maintained constant even though there are variations in the load and in other conditions of use. When such a source of current is desirable and the only available source of power is a variable source, it is important that a reliable, eflicient translating means be provided to translate the power available into the proper term for use. At times this problem is present on railway cars, such as coaches, Pullman cars, and the like, where each car is provided with its own individual electrical system, and where certain of the equipment requires a constant voltage supply. Generally, the railway car system includes a set of storage batteries, lighting and other equipment, and an axledriven generator to supply power for the equipment, and for charging the batteries. Additional equipment is provided under some circumstances for supplying power to the systern when the car is stationary in the yard, and in some systems means is provided for driving air-conditioning equipment directly from axle when the car is traveling at a proper speed. In all systems the equipment should be light in weight and sturdy, and it should be efiicient and dependabe in operation. Furthermore, it is diflicult to insure that the equipment will receive proper attention during use,- and it is therefore desirable that the equipment operate with a minimum of adjustment and repair.

On railway cars the battery is usually a 32- volt set, and the axle-driven generator is regulated to give a charging value best suited to the particular installation, usually with the generator voltage adjusted to a value between 37 and volts. At times the battery voltage may be as low as 28 volts, and the voltage of the system may vary between this low value and the maximum voltage of 45 volts, depending upon the condition of charge of the battery and upon whether or not power is being supplied by the axle-driven generator.

It has been found that fluorescent lights are well suited for railway lighting, and it is therefore desirable to provide for their use by furnishing a reliable and eflicient source of voltage. Fluorescent lamps can be operated with direct current voltage, and illustratively, such lamps use 60 volts for lamps of 15-inch length, and 80 volts for lamps of 18-inch length. It is an object of this invention to permit the use of fluorescent lamp units of this character by providing a reliable source of direct current voltage which is automatically maintained constant. In the present embodiments power is derived from the battery-generator system, and the voltage at the voltage. Thus, the total voltage on the load is the sum of the voltage of the battery-generator system and voltage of the booster set, and this total voltage is maintained constant and is availtial field winding which partially neutralizes the effect of the main field winding. The current carried by this difierential field winding is varied with variations in the battery-generator voltage with th result that the magnetic field of the booster generator is reduced when the batterygenerator voltage increases and is increased when the battery-generator voltage falls. Additional means is provided to compensate for other variable conditions and to stabilize the voltage.

Referring particularly to the left-handside of Figure 1 of the drawings, a generator 2 is provided with a controller 4 which maintains the proper current in the generator field 6. One side of the generator is connected through a line i and an automatically operating switch in to a line H and a, set of batteries I2; this line H is connected through a switch 9 to a line 8, The other side of the generator is connected through a line I4 to the other side of the batteries. Lines H and M are the main power lines of the battery-generator system which carries a' load 16 consuming direct current. When switch 9 is closed, the voltage across lines 8 and M is the same as that of lines II and I4, and this voltage varies depending upon the state of charge of the setof batteries and the starting and stopping of the charging action of they generator. Connected across lines 8 and I4, and thus adapted to be energized by the voltage of the batterygenerator system, isa direct current motor I8 having a main shunt field winding ll, a starting winding IQ for producing high starting torque, a compensating current winding 5| and an armature 20. The main shunt field winding H is formed by four separate winding units in the form of separate coils and designated Ila, I11), I10 and Nd, and these units cooperate in producing th main magnetic field for the motor. Armature 20 is connected through a shaft 22 to drive the armature 24 of a booster generator indicated at 26 and having a main shunt field winding 25, a series fieldwinding and a differential field winding 21. The generator output leads are connected in series with the load lines of the battery-generator system, and according ly, one side of the armature is connected through the series winding 23, a line 29 and winding 5! to line 8, and the other side of the armature is connected to line 28. Line 28 and line It extend to the right and supply direct current to a load 32, which in this embodiment is a bank of fluorescent lights and their attendant auxiliaries.

Motor l8 tends to operate at constant speed throughout a wide range of variation in the supply voltage and, illustratively, this motor is of the type shown in United States Letters Patent 2,134,900, Lewis H. Von Ohlsen. Accordingly, the main field winding I! is connected in series with -rent characteristics.

are connected in series with resistance units 42a and @217, and winding units no and H11 are con-- two pairs of resistance-units designated 520, Mb,

520 and 42d, which are Thyrite resistors, or any other material having similar voltage and our- Winding units Ila. and 91b nected in series with resistance units 420 and 42d; in this manner two series circuits are formed which are connected in parallel across lines 8 and Id. The connection between line 8 and wind ing H is completed through a manually adjustable variable resistance unit l5 which is adjusted to set the speed of the motor at the proper value.

By providing this adjustment, it is unnecessary to change the air gap of the motor.

The magnetic section of the motor i8 is liberal the circuit of the main field windings, the field current varies at a rate more rapid than does the impressed voltage. Due to the unsaturated condition of the iron, this current variation is accompanied by a substantially proportionate variation in the field flux with the result that a small variation in voltage causes a relatively great variation in the field fiux. Illustratively, if the voltage across lines 8 and I4 increases, there is a substantially greater increase in the field current, and in the magnetic fiux, and this increase in magnetic fiux is suificient to hold the motor speed constant.

As explained in detail in the above-mentioned patent, Thyrite resistance units have a negative resistance-temperature coefficient, and units @211,

. Mb, 420 and 42d are so designed and positioned that the changes in resistance due to temperature changes compensate for changes in resistance in the field winding l1. As pointed out above, the main field winding I! is divided into four separate winding units which are evenly spaced about the motor casing, and the Thyrite units 42a, 42b, 42c and 42d are also evenly spaced as they are mounted on the four arms of the motor frame. Thus, in the resistor units, heat is produced and is readily dissipated the same as in the field windings, and the proper field current flows at all times.

When it is desirable to provide power for the load 32, switch 9 is closed, and it is important that upon the closing of switch 9 power will be available without undue delay. Motor i8 is therefore provided witha starting winding 19 which is so designed as to make the motor start rapidly. When the motor is running at full speed, a change in load causes a change in the armature current which flows through winding I9, and due to the unsaturated condition of the iron parts of the motor, these variations in current tend to cause variations in the field flux. This is undesirable particularly because of the fact that variations in field flux have an inverse effect upon motor speed. That is, an increase in load tends tocause an increase in this field flux which in turn tends to cause a decrease in motor speed, and conversely a decrease in load tends to cause an increase in motor speed. In addition to the effect of winding I9, an increase in the mechanical load upon the motor tends to slow down the motor due to factors such as armature and other losses.

To compensate for these effects, motor 18 is provided with the compensating current windin which opposes the main motor field winding l1 and the starting winding I9. carries the load current fiowing through the booster generator armature to line 28, and this current varies when there are variations in the current drawn by the load 32. During the starting period of the booster set and until load 32 draws a current, winding 5| carries only the current of the booster generator main field winding 25, andthe effect of this small current upon the magnetic field of the motor is negligible. Thus, during the time that there is no load, the effective magnetic field of the motor is the sum of the effects of the currents in starting winding l9 and the main field winding I'I. When load 32 starts drawing current, the current fiows through winding 5| to line 28, and this current tends to oppose the effect of the currents in field windings l9 and I1. Thus, the load current, by flowing through winding 5i, is effective to reduce the total field flux produced by the motor field windings. The effect of this current in winding 5| is suificient to neutralize the factors, such'as the increase in current in winding l9, armature resistance, etc., tending to reduce the motor speed, and the motor speed tends to remain constant.

As indicated above, booster generator 26 is provided with three field windings, and the total field flux is automatically regulated to cause the booster generator to produce the proper booster voltage at all times. The iron parts of the booster generator 26 are liberal in design so that the iron is worked below the saturation point on the magnetization curve and an increase in field current is accompanied by a substantially proportionate increase in magnetic fiux. Thus, by properly designing the field windings and controlling the currents through each winding, the total field flux is automatically regulated to compensate for the various changes inconditions. Accordingly, the load current from winding 5| of the motor flows through series winding 23 of the booster generator, and when there are changes in the load, the total field flux of the'booster generator is changed to compensate for voltage drop due to armature reaction, etc.

The main shunt field winding 25 is connected by leads 82 and 84 across lines 28 and i4, and during operation this voltage is maintained sub stantially constant, and this winding tends to maintain a substantially constant field flux. The voltage is stabilized by the use of a ballast lamp 36 which is connected in line 84 in series with field winding 25. Ballast lamp 36 has the characteristic that there is a large resistance change for small changes in current value, and a ballast lamp is selected which is of a proper size that it carries a current somewhat under its normal rating to give it long life. By using a ballast lamp in this manner a decrease in voltage across lines 28 and I4 does not cause a proportionate change in the current in field winding 25, and the voltage tends to remain constant.

As has been outlined above, the voltage between lines 8 and i4, which is the voltage of the battery-generator system, may vary during operation between limits such as 28 and 45 volts, and the booster generator produces a booster voltage which is automatically regulated to maintain constant the voltage between lines 28 and M. This variation in the output voltage of the booster generator is controlled by neutralizing a portion of the main field flux and this is accom- Winding 5| plished by controlling the current flowing through the differential winding 21. "Diiferential winding 21 is connected in series with the motor field winding i1, and the series resistors 42a,- 42b, 42c and 42d. As indicated above, this current varies at a rate more rapid than does the impressed voltage, and winding 21 is so constructed and arranged that its current neutralizes the proper amount of the field flux at all times. 11- lustratively, if the voltage across lines 8 and I4 increases, the current through winding 21 increases, and this causes adecrease in the total field flux of the booster generator. This decrease in the field flux causes a proportionate decrease in the booster voltage which is substantially equal to the increase in voltage across lines 8 and [4.

In this embodiment the output voltage across lines 28 and i4 is 60 volts, and the booster voltage i maintained at a value to'hold this output voltage within permissible limits. The booster set starts rapidly when switch 9 is closed, and the voltage builds up immediately to the proper value. The voltage is stable and does not vary substantially due to sudden changes in the load and in the supply voltage.

In the embodiment of Figure 2, the four winding units for the motor field winding I! are replaced by a single winding unit I I1, and the four Thyrite resistors are replaced by a single Thyrite resistor I42. Furthermore, the resistance unit l5 and the ballast lamp 36. are omitted. In other respects the embodiment of Figure 2 is the same as that of Figure 1. The embodiment of Figure 3 is similar to the embodiment of-Figure 2 but a separate Thyrite resistor 242 is provided for the field winding 221 of the booster generator 226. In this way the motor and the booster generator are adjusted and operated independently, and the characteristics of one may be changed without varying the characteristics of the other.

The booster set or electromotive device of Figure 1 is shown in cross-section in Figure 4. The shell construction, generally indicated at 54, includes-a cylindrical casing 52 mounted at the bottom upon two brackets 53 and carrying at its ends a pair of heads 55. At the ends the casing is provided with hand-holes 51 which are covered by two band-like hand-hole covers 59, and these hand-hole covers are clamped by means (not shown) to form a substantial seal around the ends of the casing.

The heads 55 carry a pair of ball bearing assemblies 56 and 58, and these ball bearing assemblies have their inner races clamped to the opposite ends of the shaft 22. Shaft 22 supports at the right the booster generator armature 24 and at the left the motor armature 20; Mounted on the head at the left of armature 20 is the motor brush-assembly 62 which engages the motor commutator, and likewise mounted at the right of armature 24 is a generator brush-assembly 64 which engages the generator commutator. Surrounding armature 20 is the motor field assembly 60 and in a like manner, surrounding armature 24 is the generator field assembly 58. Each of these field assemblies is built up of four poles which are held in place by suitable cap screws 68, extending through the casing wall, and each pole carries coils forming part of the field windings.

The four poles of the'field assembly 60 carry the four main motor field 'coils of the winding H with the upper pole in Figure 4 carrying coil no and the lower pole carrying coil 110. Starting winding I! and series winding 5| are for convenience and simplicity applied to alternate sets of poles with the coils of winding l9 mounted on the two poles shown in Figure 4, and with the coils of winding i mounted on the-other two poles which are not shown. The booster generator shunt field winding is formed by four coils. The series field winding 23 andthe compensating winding 21 are each divided into two coils; one shunt coil and one compensating or difierential coil is mounted on each of the set of two poles shown, while one shunt coil and one series coil is mounted on each of the other two poles (not shown).

. The four Thyrite resistors 42a, 42b, 52c and dare spaced about the right end of the casing 54, and as shown at the lower right-hand portion of the figure, they are rigidly held in place by screws extending through the longitudinal arms of the casing frame. A suitable terminal box (not shown) is mounterLnpon the side of the casing, and access may be had to the terminal box through a door to connect the booster set to the battery-generator system and to the load. This terminal box also includes the manually adjustable variable resistance unit l5 (see Figure 1) which is in series with the main motor field winding IT, and which maybe adjusted to set the speed of the motor at the proper value.

As many possible embodiments may be made of the mechanical features of the above invention and a the art herein described might be varied in various parts,- all without departing from the scope of the invention, it is to be underportion of said electromotive device having a magnetic field which is varied to control the output voltage, a main field winding to produce the major portion of said magnetic field, a stabilizing ballast lamp connected in series with said main field winding across the lines which supply power to the load, a differential field winding to neutralize a portion of the field flux produced by said main'field winding with the result that the magnetic flux is thereby reduced, and means controlling the supplying of current to said difierential field winding.

2. In an electrical sy' tern, means constituting a source of electrical power, and an electromotive device in series with said source to provide a controlled output voltage for a load, said electromotive device including, an armature, and a field assembly producing a magnetic field for said armature and comprising, a series field winding adapted to carry load current, a main field assembly to produce the main field flux and carrying current derived from the output voltage impressed upon the load, and an auxiliary field winding to carry a current tending to produce'a flux opposing said main field flux and tending to produce a fiux varying with changes in the voltage of said source.

3. In'an electrical system, a booster set comprising, a constant speed motor connected to be driven by power available from the voltage source, a generator having its output leads connected in series between the voltage source and the load, said generator having a main field winding connected across the output lines supplying power to the load, a stabilizing resistor in series with said field winding andhaving the characteristic that its resistance changes rapidly with changes in the current flowing through it, and a differential field winding to neutralize a portion of the flux produced by said main field Winding.

4. In an electrical system for a railway car of the character wherein a variable source of direct current is available, a generator for providing a variable booster voltage in series with the voltage source, which booster voltage supplements the voltage source to provide a substantially constant output voltage for a load, said generator comprising, a generator frame having iron parts which are liberal in design so that the iron is worked magnetically along the substantially straight-line portion of the magnetization curve of the iron, a set of main field windings to produce substantially constant magnetic flux, a set of auxiliary field, windings to produce magnetic flux which is counter to the main magnetic flux so that when the magnetic flux of the auxiliary field windings is increased the total magnetic flux of the generator is decreased, and means to supply current to said set of auxiliary field windings comprising means to exert an efiect which is a function of the voltage of'the voltage source and another effect which is a function of the load current with the, result that the magnetic flux of the auxiliary field windings is increased with variations in the voltage of the voltage source and the load current at a rate sufiicient to maintain substantially a constant output voltage for the load.

5. In electrical apparatus of the character described, an electromotive device comprising, an armature having a current winding, a main field winding formed by two pairs of field winding units, current control means formed by two pairs of Thyrite resistor units, circuit means forming two parallel circuits with each circuit formed by a pair of said field winding units and a pair of said resistor units connected in series, a variable resistor connected in series with said parallel circuits so that it may be adjusted to regulate the current flowing therethrough, current coils to carry current to start the motor and to compensate the speed of the motor for changes in load, and a frame construction including longitudinally extending arms upon which are mounted said Thyrite resistor units.

6. In electrical apparatus of the character described, an electromotive device comprising, an armature having a current winding, a main field winding formed by a plurality of field Winding units, current control means formed by a plurality of resistor units having the characteristic that their conductivities vary with the potential impressed upon them,- circuit means forming a plurality of parallel circuits with each circuit including at least one of said field winding units and at least one of said resistor units connected in series, variable resistor means connected in series with said parallel circuits and adapted to be adjusted to regulate the current flowing therethrough, and a frame construction including longitudinally extending arms upon which are mounted said resistor units.

7. In an electrical system which includes means constituting a source of voltage, the combination with said voltage source of a booster set comprising, a constant speed motor connected to be driven by power available from said voltage source and including means to vary the magnetic field of the motor when there are changes in the voltage of the voltage source, and a generator having its output leads connected in serieswith the voltage source and a load, said generator including means to maintain a substantially constant main magnetic field and means to produce compensating e'fiects tending to vary said main magnetic field to compensate for variations in the current delivered to the load and in the voltage of the voltage source.

8. Apparatus as claimed in claim 7 wherein the main magnetic field for the motor is produced by a set of field windings which are connected in series with a set of compensating field windings on said generator by a circuit including a plurality of Thyrite resistor units.

LOUIS H. VON OHLSEN. JOHN J. KENNEDY.

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