US2467784A - Variable voltage generator - Google Patents

Description

April 1949- F.. D. SNYDER I 2,467,784

VARIABLE VOLTAGE GENERATOR Filed March 20, 1947 VG MF LM IHVHI K H ITNESSES- I INVENTOR figzfif d fieaer/ck D. Snyder.

- fut/5 ATTORNEY Patentecl Apr. 19, 1949 VARIABLE VOLTAGE GENERATOR Frederick D. Snyder, Milton, Mass, assignor to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Application March 20, 1947, Serial N0. 735,860

9 Claims.

My invention relates to a Ward-Leonard type of speed control for a direct-current motor.

In certain applications utilizing a variable voltage source of direct current for a motor, it is often highly desirable to obtain slow and smooth successive motor accelerations from the same slowest speed to any preselected higher speeds.

One broad object of my invention is the provision of automatically slowly and smoothly accelerating a direct-current motor from standstill, or a given slow inching speed to a selected high speed.

Another object of my invention is the provision of substantially automatically successively accelerating a direct-currentmotor from a selected slow speed to any higher speed, within the range of the control apparatus, selected between successive accelerations.

It is also an object of my invention to smoothly accelerate a motor by means of a Ward-Leonard control from a given low speed to any preselected higher speed.

A further object of my invention is the provision of substantially automatically altering the speed of a direct-current motor back and forth from one fixed low speed and a selected higher speed.

Other objects of my invention will become more apparent from a study of the following specification and the accompanying drawing, in which the single figure constitutes a diagrammatic showing of my invention.

In my system of control, I provide a manually operable rheostat 42 having an adjustable control, or lead 43, for preselecting any one of a plurality of given speeds for motor LM, the load driving motor, and I provide a motor-operated rheostat 19 of the same design characteristics as rheostat 42.

During acceleration of motor LM, the arm 23 is slowly moved counterclockwise to increase the voltage of generator VG. The arrangement is such that when arm 23 holds a position on rheostat [9 corresponding to the speed setting of lead 43, the movement of the contact 2] on rheostat l9 ceases. The motor LM thus continues to operate but at a fixed speed determined by the setting of lead 43.

A still better understanding of my contribution to the art may be had from a study of typical operating cycles. If the circuits shown in the figur are considered as deenergized, except for buses l, 9 and I6, and the attendant wishes to use the apparatus he actuates the Slow push button, or switch, 6. This operation establishes a circuit from bus I through conductor 2, actuating coil 3 of relay 4, contacts 5, closed by the Slow push button, or switch, 6, stop push button I, conductor 8 to bus 9. The starting always is to proceed through a preliminary slow speed so that the Slow push button 6 is the manually operable starting switch as well.

Operation of relay 4 causes the closing of contacts I0. The relay 4 thus remains actuated independent of the position of switch 6, which may thus be released as soon as relay 4 has operated. The relay 4 also closes contacts l2. This operation establishes a circuit from energized conductor 2 through actuating coil ll of the main starting contaotor C, through contacts 12 to energized conductor 8. The operation of contactor C causes the closing of contacts l3, l4, and I5 to thus connect the motor M of the motor generator set MG to the buses I, 9 and I6.

The motor M thus presently brings the variable Voltage generator VG and the exciter generator EG to full speed. To obtain the requisite slow speed for the load driving motor, it is, of course, important that the excitation of the variable voltage generator at this stage of operation be a minimum. How this is accomplished will become apparent presently.

From an inspection of the figure, it will be apparent that the negative terminals of the generators VG and EG are connected together. Conductor 20 will thus be at the same negative potential, and the respective potentials of conductors l8 and 24 will thus be dependent of the voltage of the exciter generator EG and the voltage of the variable voltage generator VG. Since the exciter field EF and its series-connected rheostat I1 and the motor field MF are directly across the exciter armature terminals, namely conductors l8 and 20, the voltage of generator EG will be at full value and the motor LM will be fully excited. The generator field GF will however be energized at a minimum value by a circuit which may be traced from conductor I8 through all of the sections of the generator field control rheostat I9, the generator field GF to conductor 20.

The resistance value of rheostat I9 is controlled by the position of the contact 2|, connected to lead 22, and mounted on the arm 23 actuated by the rheostat motor RM. The arm 23 during this stage of operation is in the position shown. This is the all-resistance-in position. Why the arm 23 must necessarily be in the position shown for this stage of operation will become apparent hereinafter.

Since the excitation of the field GE is a minimum, the voltage across conductors 24 and is a minimum. The motor LM thus operates at its slow, or inching, speed.

The manually operable speed selecting rheostat 42, and the resistor 44 connected in series with the rheostat, are connected directly across conductors l8 and 20. The rheostat 42 is similar in electrical and some mechanical characteristics to the motor-operated rheostat l9 and the particular position of the connecting arm 43 on the resistor sections of rheostat 42 normally determines the high-speed setting for the motor LM, but since contacts 41 are, at this stage of operation, open, the position of the arm 23 has no ef feet in selecting a high-speed setting.

The resistor 44 has a resistance value so selected with reference to the resistance value of the resistor 45 that when the voltage drop from junction 30 through the actuatin coil 3| of the contact making voltmeter V to the junction 32 is zero for the particular high-speed selection made by the arm, the movable contact 25 of the voltmeter V holds the position shown with reference to contacts 2%. However, since contacts M are open, junction 3i? will be sufliciently positive with respect to junction to effect the operation of the contact making voltmeter V. Contact 25 will thus remain in the position shown.

The contact making voltmeter, which may be of any standard design, will, since the potential drop is from junction 32 to junction 30., actuate its movable contact 25 clockwise to engage contact 50. This will, however, be of no effect since the contacts 48 of the limit switch 49, are open. The motor LM is thus, by reason of the low voltage of generator VG slowly and smoothly accelerated from zero speed to the inching speed.

Voltage relay 33 has its actuatin coil connected directly across the conductors 24 and 20. Its characteristics are 50 selected that it is not actuated as long as the voltage of generator VG is such as to provide only an inching speed for motor LM.

To effect the fast or selected speed of operation of motor LM, the Fast push button, or switch, 35 is actuated. This operation closes a circuit from conductor 2, through coil 33 of relay 34, switch 35, conductor 36,.contacts 3'! of voltage relay 33, conductor 39, switch 5, contacts I of relay 4, and the Stop switch 'I to conduGEQr 8.

Operation of relay 34 closes contacts 40. This operation makes the energization of coil 33 independent of the position of contacts3'i. Relay 34 also closes contacts 4|. This operation shunts a portion of rheostat 42 to thusmake the speed setting of the arm 43 efiective. Junction 30 thus becomes more positive since the resistance drop across resistor 44 in relation to the drop across resistor 45 is increased. A current thus flows from junction 36 through coil 3| to junction 32.

This current flow through the actuating coil 3| of the contact making voltmeter causes the contact 25 to engage contact 26. A circuit isfthus established from conductor 18 through contacts 25 and 26, the contacts 21 of the high voltage limit switch 28, field 29, and the rheostat motor RM to conductor 20. The rheostat motor RM thus operates the arm 23 counterclockwise shifting the contact 2! connected to lead 22 to shunt more and more resistor sections of the rheostat l9.

The voltage of generator VG thus slowly and gradually increases, thus increasin the speed of motor LM. As soon as the arm 23, has moved to such a; position in its counterclockwise movement that the voltage of generator VG has risen to such an extent that the voltage of junction 32 is equal to the voltage of junction 3|], the motor RM stops because contacts 25 and 26 move to the position shown. Since the drop of potential between junctions 33 and 32 is a function of the position of arm 43 on rheostat 42, it is apparent that contact 24 will always come to rest at a point on rheostat i9 that has a direct relation to the setting of arm 43 on rheostat 42.

As the voltage of generator VG is increased, as above stated, the coil 48 of the voltage relay will cause this relay 38 to pick up to close contacts All and open contacts 31. The closing of contacts 47, thereafter makes the energization of contactor C independent of the position of contacts 52.

A small counterclockwise movement of arm 23 causes the closing of contacts 48 of the lowvoltage limit switch 49. If the speed setting of arm 43 is changed to a lower speed, namely'in a clockwise direction, then the junction 32' becomes more positive and in consequence contact 25 will move to engage contact 50. This operation establishes a circuit from conductor. l8 through contacts 25 and 53, the contacts 430i limit switch 43, field 5i, and motor RM to conductor 23. The direction of motor RM is thus reversed and the arm 23 moves to the left or clockwise in proportion to the extent of the clockwise setting of arm 43.

My control not only provides for effectively at will changing the speed of motor LM to any selected value either up or down from a given value, but also provides voltage regulation to compensate for changes in load on the motor. If the load on the motor increases, the motor will operate at a different point, a lower point, on the voltage regulation curve of the generator. This means that the potential drop between junctions 3i and 32 increases. The result will be that the generator excitation of generator VG will be increased in proportion to the greater load. On a decrease in load, the reverse will take place. The contact making voltmeter thus not only provides for a function to obtain the selected speed from a motor but also provides for Voltage regulation.

If the motor is operating at the full speed determined by the setting of arm 43 and, the attendant wishes to go back to the slow or inching speed, he merely again actuates switch 6. Openin of switch 3 causes relay 34 to drop out to open contacts 40 and M. The opening of contacts 4H prevents reenerg'ization of relay 34 upon release of switch 5. Relay 4 remains reenergized because its holding contacts Ill areclosed. The energization of contactor C is thus independent of the position of contacts 47.

The opening of contacts ii establishes the allresistance-in condition for rheostat 42.? The consequence is that arm 23. is moved to the position shown. The motor thus slowly and smoothly decelerates from the set high speed to the inching speed. Switches 8 and 35 may thus'be alternately operated to change the speed of the motor.

either from the inchin speed to the selected high speed or from the selected high speed to the inchin speed. 2

If it is desired to stop from the inching speed, the operation of the Stop switch] causes the rapid successive operation of relay 4 and contactor C. v i

Ifthe motor LM is operating at, a selectedhigh speed andthe .Stop switch is actuated lthestopping operation is gradual. The opening of switch 1 causes the relay 4 and 34 to drop out; but, since the voltage of generator VG is high, the voltage relay 38 is energized and contacts 41 are closed. The contactor C thus remains energized.

The deenergization of relay 34 opens contacts 4| to thus cause operation of the rheostat motor RM to move the arm to the position shown.

When the arm 23 is in the position shown, the voltage relay 38 drops out opening the circuit for coil I I of the contactor. The whole system except buses I, 9 and [6, thus becomes deenergized.

From the foregoing, it will be apparent that I have provided a motor-control scheme which is very accurate and comparatively simple to build and is of utility in many applications requiring variable voltage control.

While I have shown and described one embodiment of my invention, it is apparent that others, particularly after having had the benefit of the teachings of my invention may devise similar control schemes for accomplishing the same or similar results. I, therefore, do not wish to be limited to the exact showing herein made but Wish to be limited onl by the scope of the claims hereto appended.

I claim as my invention:

1. In a system of control for a direct-current motor, in combination, a, direct-current generator operating at substantially constant speed, a direct-current motor connected to said generator, a source of constant potential direct current, a field winding for the generator, a manually adjustable rheostat, a motor-operated rheostat, said generator field winding being connected through said motor-operated rheostat to said source of constant potential direct current, means for causing the operation of said motor-operated rheostate from an all-resistance-in position to positions including less and less resistance in the circuit of the generator field winding to thus accelerate the motor, and means operable when the resistance of the motor-operated rheostat has decreased to substantially equal the adjusted resistance value of the manually adjustable rheostat for stopping the change in resistance value of the motor-operated rheostat.

2. In a system of control, the combination of, a source of potential, a series circuit connected to said source, said series circuit including an adjustable resistor and a resistor of fixed resistance value, said adjustable resistor being adjustable to any resistance value within its range, a. second series circuit connected to said source, said second series circuit including a variable resistor having substantially the same characteristics as said adjustable resistor, a second source of potential, a second resistor of fixed resistance value, said second resistor being connected across said second source, an electromagnetic device responsive to the difference in voltage drop across said resistors of fixed resistance value, means for gradually varying the resistance value of said variable resistor from a given high value in the direction of its lower values, and switching means responsive to substantially equal voltage drop across said resistor of fixed resistance value for efiecting a stopping of the variation of resistance value of said variable resistor.

3. In a system of control, a source of constant potential and a source of variable potential having a, common negative potential, an impedance of fixed impedance value connected across said source of variable potential, a variable impedance in normal use varying from a given maximum toward lower values of impedance, means responsive to said variation of impedance of said variable impedance for increasing the voltage of said source of variable potential from a. given minimum toward higher values, a series circuit including an adjustable impedance and an impedance of fixed impedance value, and means responsive to the difference in potential drop across said two impedances of fixed impedance values for controlling the variation of the impedance value of said variable impedance.

4. In a system of control, in combination, voltage producing means having a first terminal at a given negative potential and a second terminal at a given positive potential, and a third terminal, a first circuit across said first two terminals, means for gradually varying the current flowing in said first circuit, means responsive to an increase in the current flow in said first circuit for altering the value of the positive potential of the third terminal as a function of the current changes in the first circuit, a second circuit across said first two terminals, a regulating circuit across the third terminal and the first terminal, and means responsive to the voltage drop across said third terminal and a selected portion of the second circuit for controlling the means for varying the current in the first circuit.

5. In a system of control, in combination, voltage producing means having a first terminal of a given negative potential, a second terminal of a given positive potential, and a third terminal the positive potential of which is to be varied, a first circuit including an electromagnetic device the energization of which is to be varied and a variable impedance, means for causing a gradual diminution of the impedance value of the variable impedance from a given maximum value toward a given minimum value to thus increase the energization of said electromagnetic device from a given minimum to a maximum value, means responsive to the rise in energization of said electromagnetic device for increasing the positive potential of the third terminal, a second circuit including an impedance of fixed impedance value and an adjustable impedance connected across said first and second terminal, and means responsive to the positive Voltage of the third terminal in relation to the voltage drop across said impedance of fixed impedance value for controlling the means for causing a gradual diminution in the impedance of the variable impedance.

6. In a system of control, in combination, voltage producing means having one terminal at a given negative potential and a second terminal at a given positive potential, and a third terminal, a first circuit across said first two terminals, means for gradually varying the current flowing in said first circuit, means responsive to an increase in the current flow in said first circuit for altering the potential of the third terminal as a function of the current changes in the first circuit, a second circuit across said first two terminals, a regulating circuit across the third terminal and the first terminal, and means responsive to the voltage drop across said third circuit and a selected portion of the second circuit for controlling the means for varying the current in the first circuit.

7. In a system of control, the combination of, a generator driven at a constant speed, a motor connected in a loop circuit with the generator, an exciter driven at a constant speed and excited to produce substantially a constant voltage, said exciter having its negative terminal connected to "the negative terminal of the'generator, said generator having a field winding and -a rheostat therefor connected in series circuit across the exciter terminals, a motor for controlling the resistance value of the rheostat, a circuit including a resistor having substantially the same resistance value as the generator field winding, and an adjustable rheostat having generally the same electrical characteristics as the first-mentioned rheostat connected in parallel to the enerator field winding and its control rheostat, asecond resistor, having substantially the same resistance value of the first-mentioned resistor, connected across the generator terminals, and means responsive to the difierence in voltage drop across said'two resistors for controlling the operation ofthe motor for actuating the rheostat of the generator field winding.

8; In a system of control, the combination of, a generator driven at a constant speed, a motor connected in a loop circuit with the generator, an exciter driven at a constant speed and excited to produce substantially a constant voltage,

said exciter having its negative terminal conneoted to the negative terminal of the generator, said generator having a field winding and a rheostat therefor connected in series circuit across the exciter terminals, a motor for controlling the resistance value of the rheostat, a circuit including a resistor having substantially the same resistance value as the generator field winding, and an adjustable rheostat having generally the same electrical characteristics as the first-mentioned rheostat connected in parallel to the generator field winding and its control rheostat, a second resistor, having substantiallythe same resistance valueof the first-mentioned resistor, connected across thegenerator terminals, a contact making voltmeter having one terminal connected to the positive terminal of the generator and its other terminal connected at the junction of the adjustable rheostat and second-named resistor Whereby said voltmeter hand is actuated from a neutral position either clockwise or counterclockwise depending on the sign of the difference of the voltage drop across said two resistors, and means responsive to the operation of said voltmeter to cause the motor for the generator field rheostat to operate either in one-directiono1z the other'ditrection or not at all depending 'on the positionof the voltmeter hand.

9. In a system of control, the combination-of, a generator driven at a constant speed, a motor connected-in a loop circuit with the generator, an exciter driven at a constant Speed and ex? cited to produce substantially a constant voltage, said exciter having its negative terminal connected to the negative terminal of the generator, said generator having a field winding and-a-rheostat therefor connected-in series, circuit across the exciter terminals, a motor for controlling-the resistance value of the rheostat, a circuit including a resistor having substantially the same resistance value as the generator field. winding, and an adjustable rheostat havinggenerally the same electrical characteristics as the first-mentioned rheostat connected in parallel to the: generator field winding and its control rheostat, a second resistor, having substantially thesame-resistance value of the first-mentioned resistor, connected across the generator terminals, a contact making voltmeter having one terminal connected to the positive terminal of the generator and its other terminal connected at the junction ofthe adjustable rheostat and second-named,res-istor whereby said voltmeter hand is actuatedfrom a neutral position either clockwise or counterclockwise depending on the sign of the difference of the voltage drop across said two resistors, and means responsive to the operation of said voltmeter to cause the motor for thegeneratorvfield rheostat to operate either in one direction-orthe other direction or not at all depending'on the position of the voltmeter hand, and means for open-circuiting the adjusting circuit-.ofthe adjustable rheostat whereby the voltage ofthegenerator will be caused to be a minimum.

FREDERICK D SNYDER;

REFERENCES CITED Name Date Howe Apr.- 5, 1932 Number

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