US1955325A - Elevator control system - Google Patents

Description

April 17, 1934. w, ws 1,955,325

ELEVATOR CONTROL SYSTEM Filed Dec. 17, 1929 fZaZ.

INVENTOR W/'///0m R. flay/L9 ATTORNEY Patented Apr. 17, 1934 ELEVATOR CONTROL SYSTEM William R. Davis, Wilkinsburg, Pa., assignor to Westinghouse Electric & Manufacturing Company, a corporation of Pennsylvania Application December 17, 1929, Serial No. 414,700

5 Claims.

My invention pertains to the art of compounding or adjusting the compounding of generators whereby certain voltage characteristics may be obtained under varying load conditions.

In the present disclosure, my invention is more specifically applied to the generator of a variablevoltage or Ward-Leonard system for controlling an elevator hoist motor.

It has been common to compound separately excited generators by providing an additional field winding thereon and connecting the same in series relation with the armature whereby its effect upon the field varied with the load. Various degrees of compounding and difierent voltage characteristics have been obtained by connecting the series field winding, either cumulatively, to aid the separately excited field winding, or differentially, to oppose the separately excited field winding and. by varying the magneto-motive force of the series field winding. The intensity of the magneto-motive force produced by the series field winding may also be varied by adding or removing turns upon the series field winding. However, a more common and convenient method of varying the eiiect of the series winding has been to provide a resistance in shunt thereto. By varying the value of the resistance, more or less current is shunted away from the series winding and its effect varied accordingly. Hence, by providing the series winding with more than the necessary number of turns and selecting a shunt resistance of the proper value, it is possible to obtain any desired degree of compounding.

In practice, the shunt resistance must be of very low value and is usually a metallic strip having a resistance of a fraction of an ohm. Consequentially, it has been very difficult to determine the correct value of such low-resistance shunt. Furthermore, after the shunt resistance has been selected, changes in temperature will cause slight changes of the relative resistances of the series winding and its shunt resistance which are sumcient to disturb the compounding adjustment of the generator.

In elevator systems of the variable-voltage or Ward-Leonard type, it is customary to adjust the compounding of the generator by providing a suitable resistance in shunt to the series winding so that it is over-compounded suificiently to compensate for the drooping speed characteristics of the elevator motor. In elevator systems, however, rapid changes of armature current occur during acceleration and deceleration and it has been found that, under such conditions, the overcompounding obtained in the manner above set forth is slow in becoming effective. During steady-current conditions, the winding and its shunt resistance carry definite portions of the total armature current, and the degree of compounding remains constant, except for the variations of relative resistance mentioned above. But, when the armature current changes rapidly, the non-inductive resistance being connected in shunt to a winding which has inductance, will tend to carry more than its normal portion of the current, and the degree of compounding will be diminished during a certain interval of time, depending upon the rate of change of current and the inductance of the winding.

It is, therefore, an object of my invention to provide a compounding effect upon a generator which will react rapidly to changes in the current output of the generator.

An object of my invention is to provide an adjustment for the compounding of generators which will be conveniently and readily adjustable.

A further object of my invention is to provide a generator-compounding adjustment which will remain constant in its adjustment, whereby the compounding effect on the generator will not vary or lag under changing conditions.

More specifically, it is an object of my invention 'to provide means whereby the compounding of the generator of a variable-voltage elevator system may be more easily and conveniently adjusted, which will remain constant under varying temperature conditions and which will not tend to lag when the armature current changes rapidy.

In practicing my invention, instead of using a low resistance in shunt relation to the series field winding, I regulate the compounding efiect of the series field winding by setting up a counter-magnetomotive force from a second series field winding connected differentially. In elevator practice, the generators are commonly provided with a difierential series field winding used as a flux killer to overcome the effect of the residual magnetism in the generator field iron, and, in accordance with my invention, this same winding may be utilized to regulate the compounding by providing a suitable resistance in series therewith to regulate the counter-magnetomotive force set up thereby.

Other objects of my invention will become evident from the following detailed description, taken in conjunction with the accompanying drawing, in which:

Figure 1 is a diagrammatic view of a compoundwound generator in which the compounding is adtill justable by means of a difierential field winding in accordance with my invention;

Fig. 2 is a diagrammatic view similar to Fig. 1 except that the resistance for varying the excitation of the differential field winding is connected in a difierent manner.

Fig. 3 is a diagrammatic view of the usual variable-voltage elevator system showing the compound-wound generator provided with a differential field winding used as a fiux killer in the usual manner, and also showing the application of my invention thereto for adjusting the compounding by means of the differential field winding.

Referring more specifically to the drawing, I have illustrated in Fig. l a compound-wound generator G having an armature G, a shunt or separately excited field winding GF, and a cumulative series field winding GCF. An additional field winding GDP is provided and is so connected that its magnetomotive force is in opposition to that 6f field windings GF and GCF. The effect or the differential field Winding GDF may be controlled by providing a suitable resistor R1 in series therewith. By varying the resistance of resistor R1, or selecting a suitable value thereof, it is possible to vary or set up any degree of opposing magnetomotive force whereby the cornpounding efiect of the cumulative series field winding GC'F may be adjusted to suit the requiremerits of any particular installation. The use of the resistor R1 in Fig. 1 does not involve any of the 'diificulties attending the use of a shunting resistance for diverting a portion of the armature current because its purpose is not that of diverting any particular portion of current away from the series cumulative field winding GCF but to determine the degree of excitation of the differential field winding GIDF. The resistor R1 may have a higher order of resistance which is not so difiicult to determine and wherein slight changes of resistance caused by temperature changes will not materially effect the compounding adjustment. Furthermore, the windings GCF and GDF, being closely associated with the field structure, will both be exposed to the same temperature conditions.

Another advantage of my method of adjusting the compounding is that the compounding ef fect does not lag during sudden changes of armature current. By the application of my invention, the low-resistance non-inductive shunt may be emitted, and the inductive efiect of the difierential field be made such that it will cause the gen erator to be overcompounded during such periods.

'Ihave shown in Fig. 2 an embodiment of my invention very similar to that shown in Fig. 1, except that the connection of winding GDF through its adjusting resistance is modified somewhat. Instead of using a simple resistor in series with the differential field winding, as in Fig. 1, I provide a resistor R2 connected in shunt to the winding GCF, and the desired degree of excitation of the difierential winding GDF is obtained by connecting the end thereof to the proper intermediate point on the resistor R2. The connectioh of resistor R2 in shunt to the cumulative series field winding GCF, as shown in Fig. 2, avoids the difficulties encountered with the prior resistors shunting the cumulative winding since its resistance is comparatively high and is readily determined and adjusted. Furthermore, the use of resistor R2, connected as shown in Fig. 2, is not to shunt any appreciable portion of the current away from the winding GCF but merely to apply a certain potential to winding GDP, as determined by the designed characteristics thereof, hence, a slight variation of its resistance does not materially disturb the compounding.

Although my invention is capable of general application, I believe it has special utility in connection with elevator systems of the variablevoltage or Ward-Leonard type in connection with the low-voltage operation of the elevator generator and I have illustrated its application to such system in Fig. 3.

The system shown comprises an elevator car C suspended by a cable Ca which passes over a hoisting drum D to a suit-able counterweight Cw, in the customary manner. The hoisting drum D is directly coupled to an elevator motor EM having an armature 'EM and a separately excited field winding EMF.

The armature of the motor EM is energized from the generator G, being connected in loop circuit with the generator armature G. The control of the motor is accomplished by varying the excitation of the generator field. The generator is of the compound-wound type having a separately excited field winding GF and a cumulative series field winding GCF. The generator is also provided with an additional winding GDF which is so connected that it opposes the Windings GF and GCF. The generator armature is driven by the shunt motor lVi shown connected directly across the line conductors L1 and L2, control apparatus being omitted for the sake of greater simplicity in the drawing. The shunt field winding of theelevator motor EM may be excited from any suitable source of directcurrent power and is shown as being connected directly across the line conductors L1 and L2.

The direction of movement or" the car C is controlled by controlling the direction of current supplied to the separately excited field winding .GF or" the generator G, through the agency of upv and down direction switches l and 2, respectively, which switches are, in turn, controlled by manipulation of a car switch CS carried on car C. 7

But the system can be most readily described and understood by considering an assumed operation thereof.

Assuming the elevator car C to be standing at a fioor level, the attendant on the car may start the car upwardly by movement of the handle to the left, thereby completing a circuit for the lip-direction switch 1, which extends from the line conductor L1, through conductor 4, fixed concircuit which extends from the line conductor L1, through conductor 11 contact member 1) of rip-direction switch 1, conductors 12 and i3, generator shunt field GF, conductor 14, winding of series relay e1, conductor. 15, contact member a of up-direction switch 1 and, by way of conductors l6 and 17, to the other line conductor L2.

The generator G, therefore, supplies voltage in one direction to the elevator motor armature EM to causethe motor to move the car upwardly.

It will be observed that, simultaneously with the closing of contact members a and b of updirection switch 1, its contact members 0 were Lia opened and members d were closed. The opening of contact members 0 breaks the circuit through which differential field GDF was connected across the generator armature as a flux killer and which extends from the generator armature G, through winding GCF, conductors 27 and 29 differential winding GDF, conductor 31, contact member 0, of relay 42, conductor 34, contact member 0 of down switch 2, conductor 46, contact member 0 of up switch 1, conductor 25, resistor R4, conductors 26 and 24, to the other side of armature G of the generator.

The closing of contact members d of up-direction switch 1 completes a circuit from line conductor Ll, by way of conductor 43, through the winding of relay 42, conductor 44, contact members of of up-direction switch 1 and conductor 17, to the other line conductor L2. The energization of the winding of relay 42 causes it to pull up and close its contact members d, thereby completing a circuit from armature conductor 27, through conductor 29, differential field winding GDF, conductor 31, contact member d of relay 42, conductor 32, adjusting resistor R3 and conductor 33, whereby differential field winding GDF is connected in parallel with cumulative field winding GCF through the adjustable resistor R3, in a manner similar to that shown in Fig. 1. By suitably proportioning resistor R3, the intensity of the counter-flux set up by differential field winding GDF may be controlled as desired, and any degree of compounding or over-compounding of generator G may be obtained.

Assuming that the elevator car is to be stopped at any desired floor level, this operation may be performed by moving the car switch CS to its original or off position, as shown in the drawing, thereby deenergizing the up-direction switch 1 to open contact members a and b which deenergizes the generator-separately-excited field winding GF'. When the up-direction switch 1 becomes deenergized, its contact members d will also open, thereby tending to interrupt the compounding adjustment circuit by which winding GDF was connected in shunt relation to winding GCF through resistor R3. The interruption of this circuit will be delayed, however, since it will be maintained through the contact members of delay relay 41 which contact members are connected in parallel with the contact members (1 of up-direction switch 1. Delay relay 41 is slow to open its contact members since it is connected in series relation to the generator field winding GP through a resistor associated therewith and will not release until the excitation of this field winding has diminished to a certain predetermined value. When relay 41 releases, the winding of relay 42 will be deenergized, and the compounding adjustment circuit will be broken at the contact members (1 of relay 42. The contact members 0 of relay 42 will now be closed, thereby completing a circuit from the differential field winding GDF, through conductor 31, contact member 0 of said relay, conductor 34, contact member 0 of switch 2, conductor 46, contact member 0 of switch 1, conductor 25, resistor R4 and conductor 26, to the other side of the generator armature so that any voltage produced by the armature as a result of residual magnetism in the generator field iron will be killed, and the voltage supplied to the elevator motor armature EM will be reduced to zero.

I have described an operation of an elevator system to which my invention has been applied and have shown that the differential field winding GDF on the generator acts alternatively as a flux killer, in the usual manner, when the car is stopped and as a compounding adjuster, in accordance with my invention, when the car is running. It will be seen that the low resistance in shunt with the field winding GCF of the elevator generator, for regulating the compounding thereof, has been eliminated. My invention makes use of counter-flux to adjust the over-compounding of the generator instead of merely bypassing a portion of the series current. The difficulties attending the use of the low-resist ance shunt are thereby avoided. During rapid changes of armature current, the inductance of the differential field winding causes the series field to be over-compounded, hence, during periods of acceleration or deceleration of the elevator car, this eifect tends to speed up the acceleration or deceleration and to eliminate undesirable rough changes of speed.

Although, in Fig. 3, I have shown a series resistor R3 for adjusting the degree of energization of GDP similar to Fig. 1, it is obvious that an adjusting resistor may be connected in the manner shown in Fig. 2, and described in connection therewith.

Although I have shown and described certain specific embodiments of my invention, I am fully aware that many modifications thereof are possible. My invention, therefore, is not to be restricted except insofar as is defined in the appended claims.

I claim as my invention:

1. In combination with a compound-wound generator having a cumulative series field winding, a differential field winding for setting up a counter-magnetomotive force in the field, and means for adjusting the intensity thereof whereby the desired degree of compounding may be obtained.

2. The combination with a compound-wound generator having a cumulative series field winding, of a differential field winding for setting up a counter-magnetomotive force in the field, and means for adjusting the intensity thereof whereby the desired degree of compounding may be obtained, said means comprising a resistor connected in series with said differential field winding.

3. The combination with a compound-wound generator having a cumulative series field winding, of a differential field winding for setting up a counter-magnetiomotive force, and means for adjusting the intensity thereof whereby the desired degree of compounding may be obtained, said means comprising a resistor connected in shunt to the cumulative series winding and means for connecting one end of the differential winding to any desired point on said resistor.

4. The combination with an elevator system of the variable-voltage type including a compound wound generator having a cumulative series field winding, a differential field winding and means for connecting the same across the armature of the generator when the elevator is stopped whereby it acts as a flux killer to destroy the residual magnetism, of means operable when the elevator car is running for connecting the differential field winding in shunt relation to said cumulative field winding, and means for adjusting the intensity of energization of said differential field winding whereby said differential field winding will set up a suitable opposing or counter-magnetomotive force, for determining the degree of compounding of said generator.

/5. The Combination With .an elevator system of the variable-voltage :type including a compound-wound generator having a cumulative series field winding, a differential field winding, means for connecting said diirerential winding across the armature .01" .the generator when the elevator is stopped whereby it acts as a flux killer to destroy the residual magnetism, of means for delaying such connection of the differential winding until the generator field has diminished to a predetermined value means 015- erable when the elevator car is running for connecting the differential field Winding in shunt re-

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