US2157830A - Power system - Google Patents

Description

POWER SYSTEM D. w. MGQLENEGAN Original Filed Dec. 29, 1937 Inventor David W. McLenegan, b film 8 Hi May 9, 1939.

SE mm mm Emma mm mm Attorney.

Patented May 9, 1939 rice PATET POWER SYSTEM David W. McLenegan, Caldwell, N. J., asslgnor to General Electric Company, a corporation of New York Application December 29, 1937 Serial No. 182,275

Renewed January 26, 1939 4 Claims.

My invention relates to alternating current power systems having variable speed prime movers or other power devices and particularly to such systems for supplying power to drive auxiliary apparatus on railway cars or other vehicles.

Air conditioningsystems and other auxiliary apparatus utilized on railway cars are commonly provided with power supplied from a suitable electric generator driven by one of the car axles. For most purposes, it is satisfactory to use a direct current generator. However, when air conditioning systems are provided with hermetically sealed compressor units; that is, units in which the motor and compressor are contained in a sealed casing, an induction motor should be used and it necessary to provide a source of alternating current. The speed of an alternating current motor is, dependent upon the irequency of the current supplied and this in turn is determined by the speed of the generator. In order to utilize alternating current supplied from a generator driven by the car axle, it is necessary to provide some arrangement for keeping the range of frequency of the generated current su cientiy narrow for satisfactory operation of the motors. This is particularly true when the motors are employed to drive apparatus such as refrigerant compressors, the reirigeratin capac= ity of which varies with the speed. Accordingly, it is an object of my invention to provide an in proved alternating current power system having a variable speed prime mover such as the axle of a railway vehicle and including an arrangewent whereby the speed of the motors to which the power is sup lied he maintained within a. range substantially narrower than the range of speed oi the prime mover.

Further objects and advantages of my haven- 49 tion will become apparent astlie following description proceeds, and the features of novelty which characterize my invention will be pointed out particularity in the claims annexed to and forming a part oi this specification.

For a better understanding of my invention,

reierence may be had to the accompanying drawing in which Fig. 1 shows a passenger railway car provided with an electrically driven air conditioning system and an alternating current 5 power system embodying my invention for supplying energy to the air conditioning apparatus;

and Fig. 2 is a wiring diagram of the power system utilized on the car shown in Fig. l.

Referring now to the drawing, I have shown railway car provided with a. refrigerant condensing unit it! including a hermetically sealed casing I I in which is arranged a refrigerant compressor driven by an alternating current induction motor. The condensing unit In also includes condensers l2 and a fanl3 driven by analternating current motor it for circulating air over the casing H and over the condensers. The condensing unit is arranged to supply liquid refrigerant to the cooling coils of an air conditioning system including a cooling chamber it within which the evaporator 10 coils are arranged and a motor it for driving a fan to distribute the cooled air from a conduit it through openings it into the upper portion of the passenger space oi? the car. In order to supply alternating current for energizing the compressor 16 motor and the motor i l, I provide an alternating current generator ill driven by a belt W from one of the car axles ii, a spring 22 being provided to maintain tension in the belt 2E2. Other forms of mechanical drive may he used for transmitting g power from the car'axle to the generator, and any other suitable variable speed power device may be used to drive the generator it. in order to provide field excitation for the generator. it! and also for energizing the lighting system of the car and such apparatus as the motor it I provide a direct current generator of the type which is standard on railway cars. The generator 23 is connected to be driven from an axle 2 3 by a belt or any other suitable arrangement, a as spring is losing provided to maintain the belt tension. The alternating current genera-tor it) is arran ed, so that it may operate with a plu rality of numbers of pairs of ileld poles in such manner that the frequency oi the current pro- 35 duced thereby may he changed by changing the number of poles; A dynamoelectrlc machine oil this type is disclosed and claimed in U. 8. Letters Patent Llil loldpril 22, 1824-, Robert W. Wie5sman, assigned to the General Electric Goinpany, 4Q assignee of this invention. A frequency responsive device is provided for changing the number of poles of the alternating current generator iii in accordance with the speed oi the car, so that the frequency of the current produced by the 45 generator it] varies within a narrower range than the range of speeds-cf the car, and furthermore. the compressor motor and the motor i i are designed to be operated at any one of a plurality of speeds, the speeds being selected in mcordance so with the frequency of the current produced by the generator i9, so that the speed of the motors varies within a narrower range than the range of frequency of the generated current. The variation in speed of the alternating current 55 field exciting winding 28.

, fore, four effective field poles.

motors is, therefore, much more narrow than the variationin speed of the generator l9, and the speed of the devices driven by the motors is, therefore, substantially uniform.

The arrangement and mode of operation oi the power system will readily be understood by reference to Fig. 2, in which I have indicated at Ha the motor within the casing H shown in Fig. 1 to drive the compressor of the refrigerating machine. The motor Ha is provided with a low speed field exciting winding 2'5 and a high speed The fan motor I4 is provided with a low speed field exciting winding 29 and a high speed field exciting winding 30. The two windings are connected to be supplied in parallel, the low speed windings being connected to three-phase supply lines 3!, and the high speed windings to three-phase supply lines 32. Lines 3! and 32 are arranged to be connected by switches 33 and 3 3 respectively, to three-phase alternating current supply lines 35, which are connected to three terminals of a manually operable switch 36; Three-phase alternating current power is supplied to the switch 36 either from three-phase lines 3'5 connected to the alternating current generator 59 or from three-phase lines 38 connected to receive power from a receptacle 39 when the train is in the station.

The generator 19 comprises a salient pole rotor having a plurality of field exciting windings 3d, which are connected so that opposite pairs or" windings are in series, the pairs shown on the vertical axis being connected to slip rings 4i and 42 at the right end of the rotor, and the pairs on the horizontal axis to slip rings 43'and 44 at the left end of the rotor. The field excitin winding has been illustrated with eight coils providing a full number oi eight field poles. When the generator is operating with its full number of poles, the magnetic flux in adjacent poles is in opposite directions as indicated by the arrows. erator with one-half its fullnumber oi poles, the current in the group of coils connected in the left-hand rings 43 and 44 is reversed, it being evident that then the polarity of each oi the coils of the reversed group is the same as that of the adjacent coil of the other group. This connection provides four groups of coils, each group comprising two coils in which the direction of magnetic flux is the same and there are, there- Each of the salient poles is provided with a short-circulting ring or jacket 45 to damp-the flux changes produced by the reversal of the fields when changing the number of poles of the generator. The stator of the generator 49' is provided with a plurality of field exciting windings 4E and H arranged to provide either a single-Y connection for the lower range of speeds, or adouble-Y connection for the upper range of speeds. This change in the connection of the stator windings compensates for the change of voltage due to the change in speed. In order to change the number of pairs of poles on the rotor of the generator 89, I provide solenoid operated switches 48 and 49; and in order to change the connection of the windings of the stator, I provide solenoid operated switches 50 and 5|.

In the railway air conditioning system illustrated, the switches 50 and 5| in addition to eifecting a change of the connection of the gen- When it is desired to operate the genof switch 48.

of switches is prevented by interlock contactors comprising the top arms of switches 48 and 49.

Operation of the pair of switches 48 and 5| con- 1 costs the generator is with its full number of poles and with its stator winding in single-Y. This is the connection for the lower range of train speeds. The pair of switches 49 and 50 connects the generator with one-half its full number of poles and with its stator winding in double-Y. This is the connection for the upper range of train speeds. In addition to an electrical interlock effective through the top arms of the switches 48 and '49 to prevent concurrent actuation of the two pairs of switches, a. me-

. chanical interlock 53 is provided to prevent concurrent actuation of the switches 50 and 5|.

In order to actuate the pair of switches 48 and iii during the lower range of train speeds and the pair ofswitches 49 and 5|! during the upper range of speeds, I provide a switch 54 operated by relay contactor 55 in accordance with the frequency of the voltage supplied by the generator to the lines 31. In its upper position, the switch 54 connects the solenoids o! the switches 48 and Si in parallel between lines 56 and 51 through the top arm of switch 49, so that the switches 48 and 5! will be actuated upon closing of the thermostat 52. The line 67 is connected to one of the terminals of the direct current generator 28 and the line 58 is connected to the other terminal through a. line 58a when the thermostat is operated. The pole changing operation can be e!- system is being supplied from the station source through the lines 38 does not operate the pole In its lower position, the.

changing switches. switch 54 connects the coils of switches 49 and 50 across the lines 55 and 51 through the top arm The switch 54 is actuated by a relay employing a series non-linear resonant circuit including a resistance element 58, a saturable inductance element 59 and a capacitance element. arranged in series across lines 8|, which are connected to be energized across one phase of the windings of the generator IS. A second capacitance element 62 is provided to change the critical frequency for operatib'ri of the relay in such manner that the relay may eflect a change in the connections of the generator in accordance with the speed of the train although the relay itself is responsive to the frequency of the voltage'produced by the generator. A relay. of this type is described and claimed in a copending application, Serial No. 182.268, filed De-,

cember 29, 1937, in the name of Chauncey G. Suits and assigned to the same assignee as the present application. I do not, therefore, claim herein anything described or claimed in the said Suits application. The operation of the frequency responsive relay will be explained more fully hereinafter.

Direct current is supplied by the generator B for energizing the cont? )1 circuits and the field of the alternating current generator l9 and any and 34 respectively. One of the coils 19 and auxiliary apparatus, such as the motor It and a plurality of lights 63. The generator 23 is of the type commonly employed on rail-lay cars, and is provided with a shunt field winding Gil and a field regulator 85. A. storage battery 86 is provided to supply direct current when the train is not in motion. The battery is permanently connected across the supply line Etc and a line 6'6. A cutout 58 is provided to connect the battery to the generator for changing whenever the voltage of the generator is greater than that of the battery, this arrangement being standard for railway lighting circuits. The lights 63 may be connected across the lines 56a and 61 by a switch 59, and the motor It may be connected across the lines 56a and 61 by a switch It in the event it is desired to run the motor continuously. A switch 10a is provided so that the circuit of the motor 16 may be opened to prevent automatic starting of the motor and draining of the battery when the car is out of service.

When .the thermostat 52 calls for cooling, it moves to the left and connects a coil "ll across the battery to actuate a switch 12, the coil it being across the battery through the line 55a and a line 13. The upper contact of the switch 12 closes a holding circuit for the coil it. The

bottom contact connects the motor 86 across the battery, and an intermediate contact llconnects the field exciting winding of the generator i9 across the direct current generator 23 between the line 56a and a connection 16 through a line 16. The other intermediate contact indicated at 11 connects a line 18 to the line 56a to energize one sideof coils 19 and 8B of the switches 33 80 is energized by being connected between lines 13 and 18, the coil selected depending upon the position of a switch 8!, and the corresponding one of the switches 33 and 34 is, therefore, operated to connect either the high or low speed windings of the motors Hit-and H to the supply V circuiting the battery when the coil is short-cirspeed, so that the frequency of the generator I9 is halved and the generator supplies current at a frequency which increases with the increase of speed up to full car speed. It is readily apparent that even with this reduction the range of the alternating current generator frequencies, there is still a wide variation of frequency and it is in order to reduce still further the range of motor speeds that the alternating current motors are provided with the two speed windings, as shown,

making it possible to operate the motors within a range of speed more narrow than the range of frequency of the current supplied by the generator. In this manner, it is possible to operate the compressors or fans driven by the motors with relatively small speed variation.

In order to select the motor speeds and make the range of speeds of the motors more narrow than the range of frequency of the supplied current, I provide a relay it? for energizing a coil 83 to operate the switch 38. Any suitable fre quency responsive device or relay may be utilized to operate the switch iii and select the one of the switches 33 and 3 3 which is to be operated. I prefer, however, to employ relay utilizing a series non-linear resonant circuit of the type disclosed and claimed in U. S. Letters Patent 2,021,753, Chauncey G. Suits on November 1935, and assigned to the Feneral Electric Company, assignee of this invention. The relay is connected to be responsive to the frequ icy of the voltage across one phase of the lines and comprises a non-linear resonant circuit including a saturable inductance element a resistance element 85, and a capacitance element St connected in series between two of the lines The operating coil of the relay ti is connected across the capacitance 86. A circuit of this type may be designed to have a characteristic such that the voltage across the capacitance falls suddenly at a critical value of frequency. On an increase of frequency from minimum to maximum, the relay 82 will be picked up to energize the coil 83 and pick up the switch ill thereby actuating the switch 34 and connecting the high speed windings of the motors i la and Hi. When the critical value of frequency is reached, the relay 82 will drop out thereby causing the switch hi to drop out and actuate the switch 33 to connect the low speed windings of the motors to the lines 35. It will be evident that the operation of the motors with their high speed windings at frequencies in the lower portion of the range of frequency will approximate the speeds of operation of the mo-.

tors with the low speed windings at frequencies in higher portion of the range of frequencies. Any suitable arrangement for providing two speed ranges for the motors may be employed. However. I prefer to use motors provided with two wi'ndingsas shown, the windings being arrangedto provide a difierent'number of effective poles. For example, in the system illustrated in which the generator is provided with an arrangement for halving the number of its field poles, I prefer toprovide motors having high and low speed windings giving a ratio of speeds of 3:2. For example, the motors might be provided with a four-pole high speed winding and a six-pole low speed winding.

In order to prevent excessive speed of the motors; for example, in the event the train speed should become excessive, I provide a switch 81 having an operating coil 88 arranged to be actuated by a relay 89 when in its drop out position. The relay 89 is connected across a capacitance 90 of a non-linear resonant circuit including a saturable inductance element 9! and a resistance element 82 connected in series with the capacitance 90 across one phase of the supply lines 35. The non-linear resonance circuit is designed to pick up the relay 89 at all normal frequencies of the voltage across the lines 35, so that the coil 88 is normally deenergized. The critical frequency of the non-linear circuit is selected so that the relay drops out at a value of frequency corresponding to the maximum frequency permissible for energlzatlon of the motors. When the relay 89 drops out the coil 88 of the switch 8! isenergized and the switch 81 is picked up j to open the circuits of the coils l9 and 80 thereby preventing actuation of either of the switches 33 and 34 so that the motors Na and M cannot be current supplied to the motors, I provide a reversing switch 93, which is arranged to reverse two of the supply lines 35, and I provide a phase rotation responsive device M for actuating the switch 533. The device 9d comprises a small polyphase induction motor 95 having a relatively high resistance squirrel cage rotor, or it may be any other suitable device having similar characteristics. The three phase windings of the motor are connected to the lines 35. When the phase rotation is in one direction the motor 95 rotates in a clockwise direction and moves the switch 93 to its upper position through a train of gears 95 and a rack 9i. When the phase rotation is in the opposite direction, the motor turns in a counter-clockwise direction and moves the switch to the position shown in the drawing. It will, therefore be evident that the same direction of phase rotation will be maintained in the lines 35 leading to the motors regardless of the direction bf phase rotation at the terminals of the switch 36.

scribed above, when the car leaves the station. manual switch 36 is'closed in its lower position thereby connecting supply lines 35 to the alternating current generator leads 3?. As soon as the car attains sufficient speed, the voltage of the direct current generator 23 will build up, and will rise toa value sufficient to close the cutout 58 and connect the generator to charge the bat tery 68. Should there be a demand for cooling, the thermostat 52 will pick up the switch it and, since the switch 54 is in its drop out position, the coils of the switches 49 and E] will be connected across the generator between the lines 55 and 5f and the switches 49 and 59 will be picked up. The

actuation of the switches 49 and 50 connects the generator with its minimum number of poles, so that a relatively low frequency voltage is produced. However, at the speed at which the direct current generator 23 builds up, this frequency will be sufllcient to actuate the relay 55 and pick up switch rod indicated at Hli will continue to move upwardly a short distance after the switch arm v This arrangehas engaged the upper contacts. ment assures the maintaining of switch arm in engagement with the upper contacts during the interval when the generator connections are being changed and, therefore, prevents the dropping out of the switch due to the decrease of voltage during the interval of change. The generator is now connected to supply the motor lines 35, and the relay 32 will be picked up to actuate During the operation of the power system dethe switch 8! and connect the coil 80 between the lines 18 and 13 through an interlock arm I02 of switch 33. The switch 34 is, therefore, actuated to connect the high speed windings 28 and 30 of the motors to the power supply. The motors Ila and I4 will then operate the condensing unit III to supply refrigerant to the coils within the cooling chamber 55 and the cooled airwill be circulated by operation of the fan It and delivered to the passenger compartment. As the train speed increases, the frequency of the current supplied by the generator will increase until the critical frequency of the relay 82 is reached when the relaly 82 will drop out deenergizing the coil 83 to cause the switch 8! to drop out and deenergize the coil Bil. When the coil 80 is deenergized, the high speed switch 34 opens. Switch 8! in its drop out position energizes the coil 19 of the switch 39 through an interlock arm Hi3 of the switch 3t and the switch 33 is, therefore, actuated to connect the low speed windings of the motors to the supply lines 35. The increase in frequency of the supplied current is, therefore, compensated by the reduction of the speed of the motors and the refrigerating apparatus is, therefore, driven at about the same range of speed as was effective with the high speed windings during the lower range of frequency; As the generator frequency increases, it will increase to a value which is the critical value for the resonant circuit of the relay 55 when only the condenser 60 is connepted therein. Relay.55 will, therefore, drop out thereby deenergizing the switch 54 which drops out disconnecting the switches 48 and 5| and energizing the switches 49 and 50. so that the generator is connected with one-half its full number of poles and with its windings in double- Y. When the switch 49 is picked up, the upper arm thereof connects the capacitance 62 in parallel with the capacitance 60 of the relay 55 and thereby changes the characteristic of the nonlinear resonant circuit, so that the relay 55 will not be picked up until the frequency is reduced and a frequency is reached less than one-half the critical frequency of the circuit with only the.

capacitance 50. The reduction of the frequency due to the halving of the number of effective poles of the generator causes the relay 82 to be picked up since the frequency has fallen below its critical drop out value and the motors are, therefore, connected so that their high speed windings are energized by picking up of the switch 34. As the train speed continues to increase, the frequency of the current supplied by the generator I9 will again reach the critical frequency of the relay 82 and the relay will drop out to transfer the motors from their high speed to their low speed windings thereby lowering the speed of the motors and compensating for the increase in frequency of the generator l9. The system will continue to operate with the generator l9 connected with its minimum number of poles and the motors connected with their low speed windings until the train speed is again reduced or until the train speed becomes excessive and causes operation of the over-frequency relay 89 to disconnect the motors from the lines 35. When the train speed is decreased from the normal full speed, the mo-- tors and generator will be connected in a sequence which is the reverse of .that just described. The motor windings will change from low to high speed when the frequency of the generator decreases to the critical pick up frequency of the relay d2. When there is a further decrease of train speed, the critical speed for the relay 55 will arouses be reached and the relay 38 will pick up and energize the switch it which will change the generator connections from the lower number of poles to the full number of poles. This change will increase the frequency or the current supplied and the relay 32 will drop out thereby reconnecting the motors with their low speed winding energized. As the train speed is decreased still further, the critical pick up value of frequency tor the relay 82 will be reached again, the relay will pick up, energize the switch iii and transfer the motors from their low speed to their high speed connection. when the train speed is still further reduced, the voltage of the direct current generator 23 will fall sufilciently to open the cutout B8 and deenergize the control circuits thereby stopping operation oi the power system.

The previous description has been based on the assumption that the thermostat 52 was continuously calling for cooling. It will m understood, however, that under normal operation of the air conditioning system, the thermostat may not call for cooling until the car attained substantial speed. However, as soon as there is a demand tor cooling and the thermostat operates to pick up the switch 12, the generator and motors will be connected in the necessary relation to provide the desired speed of the motors at the car speed existing when the thermostat is oper ated.

From the foregoing, it is apparent that l have provided a power system for railway cars and other vehicles which makw possible the opera tion of alternating current auxiliary devices on the car at speeds within ranges materially less than the range of speeds of the car and, furthermore, that the desired speed of the motors is maintained regardless of the changes of speed 01 the vehicle.

While I have described my invention in connection with an air conditioning system for railway cars, other applications will readily be apparent to those skilled in the art. I do not, therefore, desire my invention to be limited to the particular construction shown and described, and I intend in the appended claims to cover all modifications within the spirit and scope of my invention.

What I claim as new and desire to obtain by Letters Patent of the United States is:

1. A power system including an alternating current generator, 9. variable speed device arranged to drive said generator, said generator having a plurality of pairs of field poles, an alternating current motor, said motor having field exciting windings providing two ranges of speed, means for supplying to said motor current produced by said generator to energize said motor, means dependent upon the speed of saitL device for changing the effective number of pairs of said field poles to vary the frequency of the current produced by said generator and for maintainin the range of frequency of the current produced by said generator more narrow than the range of speed of said device, and dependent upon the frequency oi the current produced by said generator for selecting either oi said ranges of speed 01 said motor.

2. A power system including an alternating current generator, a variable speed device arranged to drive said generator, said generator having a plurality of pairs of field'poles, means for changing the effective number of pairs of said field poles to provide a range of frequency of the current, produced by said generator more narrow than the range of speed of said device, an alternating current motor having windings providing two ranges of speed, means dependent upon the speed of said device for actuating said pole changing means, and means dependent upon the frequency of the current produced by said generator for selecting either of said ranges oi. speed 01' said motor during operation Oif said gerl erator with either number of efiective pairs oi field poles.

3. A power system including an alternating current generator, a variable speed device ar= ranged to drive said generator, said generator having a plurality of pairs oi field poles, an alternating current motor, said motor having wind.- ings providing two ranges of speed, means for supplying to said motor current produced by said generator to energize said motor, means responsive to the frequency of the current produced by generator for changing the effective numleer of pairs of said field poles to vary the frequency the current produced by said generator and. for maintaining the range of frequency or the current produced by said generator more narrow than the range of speed of said device, and means dependent upon the frequency of the cur rent produced by said generator for selecting either of said ranges of speed or said motor.

4. A power system including an alternating current generator, a variable speed device arranged to drive said generator, said generator having a plurality of pairs of field poles, an alternating current motor, said motor having windings providing two ranges of speed, means for supplying to said motor current produced by said generator to energize said motor, means responsive to the frequency of the current produced by said generator for changing'the effective number of pairs of said field poles to vary the frequency of the current produced by said generator and for maintaining the range of frequency of the current produced by said generator more narrow than the range of speed of said device, means dependent upon the frequency of the current produced by said generator for selecting either of said ranges of speed of said motor, and mean; for connecting to said motor a source of alternating current other than said generator and for rendering inoperative said generator pole changing means.

DAVID W. McLENEGAN.

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