US1771463A - Control system - Google Patents

Description

A. PINTO CONTROL SYSTEM July 29, 1930.

Filed April 2, 1926 VOLTAGE Tums INVENTOR MW CPAQJI- Y E N m T Patented July 29, 1930 UNITED STATES PATENT oFFica ANTHONY PINTO, 0! NEW YORK, N. Y., ASSIGNOR 'lO OTIS ELEVATOR COMPANY 01 JERSEY CITY, NEW JERSEY, A CORPORATION 01' NEW JERSEY CONTROL SYSTEM Application filed April 8, 1928. Serial No. 98,859.

The invention relates to control s stems and particularly .to control systems or direct current generators.

Direct current generators have various uses, one of which is to supply current at a variable voltage of either polarity. It is advantageous .to obtain such voltage by controlling the strength and polarity of the enerator separately excited field winding. .t is desirable in certain types of control to obtain a generator E. M. F. of either polarity at a relatively low voltage. This is useful in the control of the hoisting motor of an elevator installation, particularly during the self-leveling operations. It is desirable also to obviate the effect of the time constant of the generator field during the reversal of the generator E. M. F.

One feature of the resent invention resides in minimizing t e time required to bring the generator E. M. F. from a certain value of one polarity to a certain value of the other polarity.

Other features and advantages will become apparent from the following description and appended claims.

The invention involves the polarity of one portion of the generator separately excited field winding being reversed with respect to that of another portion to cause the magnetizing forces of these portions to act in opposition. Then by varying the magnetizing force of either or each of said portions, the net magnetizing force of the winding may be caused to be such that an E. M. F. of either polarity may be obtained, the particular polarity depending upon which one p of said portions predominates.

In carryin out the invention, according to the preferred arrangement, certain connections in the generator separately excited field winding circuit are changed for low voltage operation so as to cause the current in a portion of the field winding to flow in a reverse direction while the direction of the flow of current through the remainder of the winding remains the same. To obtain an E. M. F. of one polarity, the current through said portion is caused to be less than that flowing through the remainder of the windrequired to operate at low values of E. M. F.,

certain condltions arise which tend to cause variations in the value of E. M. F. generated. Due to the residual flux of the generator field, assuming the generator se arately excited field winding connected t e same for low voltage operation as for high voltage operation, the E. M. F. valuesobtained for a definite value of field current during the low voltage operation var considerably depending upon the magnetic state of the machine prior to the low voltage operation and the polarity of the E. M. F. desired. The preferred arrangement of the invention also obviates the effects of the residual flux of the generator and thereby causes more uniform operation during low voltage operating periods.

A system of control directed to similar subject matter is shown in this inventors copending application, Serial No. 60,769 filed October 6, 1925. and division thereof, erial No. 273,290, filed April 27, 1928.

The invention will be described, by way of illustration, as embodied in a system in which manually operable switches are employed for the control operations. This, however, is merely to simplify; the descriptipn and it is to beunderstood t at the invention is aplicable to any type of control system in which it would be useful.

In the drawings Figure 1 is a schematic diagram of a control system embodying the invention; and

Figure 2 is a hysteresis curve employed to illustrate the invention.

The generator is designated as a whole by the numeral 12, its armature bein desi nated 15 and its separatelv excited fie (1 win ing being divided into 0W0 portions desig nated 17 and 18. The generator is illustrated as supplying current to a direct current motor 20, the armature f this motor being designated 21 and its field winding 22. A resistance 27 is provided for controlling the strength of the generator field and therefore the voltage applied to the motor armature. A resistance 28 is provided for controlling the relative values of the current supplied to the enerator field winding portions 17 and 18 uring low voltage operation. It will be understood that a series field winding may be provided on the generator if desired. The source of current for the generator field winding is indicated by wires 200 and 208.

The switches employed are designated as follows IL-reversing switch,

L-field control switch,

LRlow voltage reversing switch,

LF-low voltage control switch.

A four-pole generator is illustrated for convenience of description and it is preferred to group the coils for the north and south poles N and S together to form the portion 17 and those for the north and south poles N and S together to form the por tion 18. The coils forming the portion 17 are connected in series relation as are those forming the portion 18. High voltage operation is obtained with switches LR and LF open and switch L in its right-hand position, as illustrated. With switch L in this position, field winding portions 17 and 18 are connected to act cumulatively. With the blades of reversing switch R thrown to the left into engagement with contacts 66 and 67, a circuit is completed for the generator separately excited field winding as follows :-by way of wire 200 through resistance 27, reversing switch contacts 66 and 201, wire 202, blade 203 and contact 120 of switch L, wire 204 through field winding portion 18, contact 122 and blade 205 of switch L, wire 206 through field winding portion 17, contacts 207 and 67 of reversing switch R, to wire 208. Assuming that the flow of current through the generator field winding is in such direction as to provide field poles of a polarity indicated in the drawings, an E. M. F. of a certain polarity is generated at the generator brushes 19. By throwing the blades of reversing switch R to the right to engage contacts 105 and 106 the current through the generator field winding is reversed, reversing the polarity of the E. M. F. generated. A suitable switching arrangement (not shown) is provided for short-circuiting resistance 27 to bring the generator excitation, and therefore the generator E. M. F., up to full value.

During low voltage operation, in systems such as those in which the generator separately excited field winding is connected to the source in the same manner during low voltage operation as during high voltage operation with thedesired low values of generator E. M. F. obtained by'permitting onl a small amount of current to flow througfi the winding, if the same values of current are supplied to the winding for obtaining an E. M. F. of the same polarity as the E. M. F. prior to low voltage operation as for obtainmg an E. M. F. of opposite polarity. variations in the value of the E. M. F. obtained occur due to the varying efi'ects of residual flux of the generator field. As such small values of current effect the production of low values of flux, the residual flux present forms a large percentage of the total flux and therefore affects the value of the generated E. M. F. markedly. In order that the effects of the residual flux may be clearly seen, reference may be had to the assumed hysteresis curve shown in Figure 2. This figure illustrates the conditions when a small current is supplied to the separately excited field winding of a generator. The magnetizing forces due to this small current are represented as NI and NI, depending on whether the polarity of the generator E. M. F. remains the same as before low voltage operation or is reversed. Assume that the generator armature E. M. F. has been of a value V and that later, in order to obtain low voltage, it is reduced to a value V of the same polarity by decreasing the value of the generator field current to a certain amount. If the excitation of the generator field winding is reversed, however, the E. M. F. of the generator for the same value of exciting current is of a value V which value is much less than the value V The values V and V of the generator E. M. F. may also vary during operation of the system depending upon the previous magnetic state of the machine. Obviously, such differences in the numerical values of the E. M. F. generated are very undesirable in certain types of control systems. These varia tions cannot be satisfactorily merely by adjusting the amount of resistance in series with the separately excited field winding. For example, if the amount of resistance were decreased in order to raise the value of V the value V also would be increased. Similarly, if the amount of resistance were increased in order to lower the value of V the value of V also would be lowered. It the effects of residual flux are eliminated for low voltage operating conditions, the system may be adjusted so as to obtain more uniform operation. This desired result may be attained by reversing the polarity of certain of the field poles.

As has been previously explained, switch L is in its right-hand position during high voltage operation and the current flows through the field coils in such manner as to provide poles of alternate polaritv as indicated. To obtain low voltage operation, switch L is operated to its other position where its switch corrected blade 203 engages contact 141 and its switch blade 205 engages contact 140. It will be assumed that reversing switch R remains in its left-hand position and that resistance 27 has been 'reincluded in circuit to reduce the generator voltage. Upon operation of switch J to the left to obtain low voltage 0 eration, although the direction of the flow 0 current through the coils for poles N and S (winding rtion 17) is not affected, the current through the coils for poles N and S (windingportion 18) is reversed. Thus N becomes a south pole and S becomes a north pole. If these poles were excitd equally with the winding connected for low volta e operation, the value of the total E. M. F. at t e generator brushes 19 would be substantially zero, since a the voltagesgenerated in (part of the generator armature wmding woul be balanced out by a voltage of equal value but op osite polarity generated in the remainder o the winding. owever, a difference inthe valuesofthe magnetizing forces due to the winding portions is obtained by connecting resistance 28 in parallel with one of the wlnding portions so that an E. M. Fiat the generator brushes is obtained.

To obtain a generated E; M. F. of the same polarity as obtained during the preceding high voltage operation, resistance 28 is connected in parallel with .winding portion 18 by moving the blade 211 of switch LR into engagement with contact 144. This causes the current in field winding portion 18 to be less than that in field winding portion 17.-

The magnetizing force due to portion 18, therefore, is less than that due to portion 17. To reverse the polarity of the E. M. F. generated, switch L is, maintained in its lefthand position and the blades of switch R are maintained in engagement with contacts 66 and 67. The blade 211 of switch LR, however, is disengaged from contact 144 and moved into engagement with contact 175, thus connecting resistance 28 across field winding ortion 17. Thus, the current in field win ing portion 17 becomes less than that supplied to field winding portion 18. By utilizing a large magnetizing force for each pole and by employing a resistance 28 of such ohmic value as would cause a proper difference in the values of these magnetizing forces, an E. M. F. of the desired low value may be obtained. The large magnetizing forces may be obtained by short -circuiting a portion of resistance 27 as by the engagement of blade 210 with contact 142 of switch L, the amount of resistance short-circuited being adjustable to suit the requirements of the particular system.

When the switch L was movedto its lefthand position for low voltage operation, the current supplied to field winding Iplortion 18 was reversed while that supplied to eld winding portion 17 was maintained in the same direction as was previously supplied to the whole field winding. Thus, upon the shunting of field winding portion 18 by resistance 28, fieldwinding portion 17 predominated so that a voltage was generated of the same. polarity as that obtained immediately precedmg the low voltage operation, and upon the shunting of field winding portion 17 b resistance 28. field winding portion 18 pre ominated so that a voltage of opposite polarity was generated. It is to be noted that, to obtain a reversal of the generator E. M. F., the current through the field winding portions is not reversed, the direction of the current supplied to the-field winding portion 17 remaining in the direction tending to cause the generation of an E. M. F. of the same polarity and the direction of current supplied to the field winding portion 18 remaining in a d1-.

rection tending to cause the generation of an E. M. F. of the opposite polarity.

By short-circuiting a portion of resistance 28 by moving blade 212 of switch LF into engagementwith contact 146, voltage of higher value may be obtained durin ow voltage operation. Assume, for exam e, that switch LF is closed and that the bla e 211 of switch LR is in engagement with contact 144. Thus, only a portion of resistance 28 is connected in shunt with field winding portion 18. The current supplied to field winding portion 18 is considerably less than that supplied with the whole of resistance 28 connected in shunt therewith, and as a consequence, its opposing magnetizing force is considerably less. A higher voltage is obtained, therefore, at the generator brushes 19. Upon the openin of switch LF, the current supplied to field wlnding portion 18 is increased while that supplied to field winding portion 17 is decreased, thus decreasing the value of the E. M. F. generated.

The portion of resistance 27 controlled by blade 210 of switch L is maintained shortcircuited by the engagement of this blade with contact 142 during low voltage opera-- tion, regardless of the polarity of the E. M. F. generated, so that large magnetizingforces are employed for the pole pieces. In this manner, the iron of the various parts of the magnetic circuit of the generator field structure is worked on the high portions of the hysteresis loop where the effect of residual flux is practically'nil, and E. M. F.s may beobtained, during low voltage 0 eration, the values of which are not efiecte by residual flux and are practically the same for the same value of excitation current.

The transfer of resistance 28 from across one winding portion to the other to control the polarity of the E. M. F. generated simply causes a reapportionmentof the amount of current supplied to each windingportion. Thus, upon the transfer of resistance 28, the predominating voltage generated in one portion of the generator armature winding delOO creases and the opposing voltage generated in the remaining portion of the enerator armature winding increases with t e result that the so termed opposing voltage is caused to )redominate and an E. M. F. at the enerator brushes is obtained of opposite polarity. Due to the fact, however, that the current in one winding portion is simply decreased while that in the other is increased, the change in the values of the opposing magnetizing forces of the winding portions occurs very quickly. Consequently, the change in the relative values of the opposing voltages generated in the generator armature winding portions and therefore the establishment of a. generated E. M. F. of opposite polarity also occurs quickly. Thus, the time required to bring the generator E. M. F. from a certain value of one polarity to a certain value of the other polarity is minimized with the result that the over-all operating efiiciency of the s sterm in which the arrangement is employe is raised considerably.

It is to be understood that the above described arrangement is suitable for use with various types of generators and that these generators may be of other pole numbers, afour-pole generator being chosen merely for convenience of description. It is further to be understood that the ortions of the field winding may be arrange in different circuit relations and that the coils may be grouped differently to eflect the desired result.

As many changes could be made in the above construction and many apparently widely different embodiments of this invention could be made without departing from the scope thereof, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

What is claimed is:--

1. In combination; a generator having a field winding; 21 source of current; means for connecting the whole of said winding to said source; means for reversing the flow of current through a portion of said winding; and means for alternatively causing more or less current to be supplied to said portion than to the remaining portion of the winding to cause the generation of E. M. F.s of different polarities.

2. In combination; a generator having a field winding; :1 source of current for said winding; means for connecting the whole of said winding to said source so as to cause the magnetizing force due to one portion of said winding to assist the magnetizing force due to another portion of said winding; means for reconnecting said portions to said source so as to cause their magnetizing forces to act in opposition; and means for varying the magnetizing force of at least one of said portions, with the portions reconnected to said source, to cause the generation of E. M. F.s at the generator terminals of different polarities.

3. In combination; a generator having a field winding divided into twoportions; a source of current for'said winding; means for connecting the whole of said winding to said source so as to cause the magnetizing forces due to said portions to act cumulatively; means for reconnecting the Whole of said winding to said source so as to cause the magnetizing forces due to said portions to act in opposition; and means for causing, with the winding so reconnected, the magnetizing force due to one of said portions to predominate to obtain an E. M. F. at the generator terminals of one polarity or the magnetizing force due to the other portion to predomi- Hate to obtain an E. M. F. at the generator terminals of the other polarity.

4. In combination; a generator havin a field winding, said windin being divided into two portions; av source 0 current for said winding; means for connecting said wind. ing to said source in such manner that each generator pole piece has an adjacent pole piece of like polarity; a resistance; and means for controlling the polarity of the E. M. F. of said generator with said field winding so connected, said means comprising means for connecting said resistance alternatively in shunt to one portion or to another portion of said winding.

5. In combination; a generator having a field winding; a source of current; means for connecting the whole of said winding to said source; means for reversing the connections for a portion of said winding with respect to the remainder of the winding; a resistance; and means for connecting said resistance in parallel with either the portion for which the connections are reversed or the remainder of said winding to cause the generation of terminal E. M. F.s of different polarities.

6. In combination; a generator having a field winding; a source of current; means for connecting the whole of said winding to said source to cause the generation of an E. M. F.0f certain value; means for reversing the connections for said whole winding to reverse the polarity of the E. M. F. generator; means for reversing the connections for only a portion of said winding; a resistance; and means for connecting said resistance alternatively in parallel with said reversed winding portion or the remaining winding portion to cause the generation of E. M. Es of different polarities and of lower value than said certain value.

7. In combination; a enerator having a field winding, said win ing being divided into two portions; a source of current for said winding; means for connecting said winding to said source in such manner that each generator ole piece has an adjacent pole piece of like p arit a resistance; means for controlling the po arity of the E. M. F. of said generator with said field winding so connected, said means comprising means for connecting said resistance alternatively in parallel with one portion or another portion of said winding; and means for varying the amount of said resistance so connected.

, 8. In combination; a generator havin a field windin a source of current meansIor connecting the whole of said winding to said source; means for reversing the connections for a portion 0; said windmga resistance;

and means for connecting said resistance in parallel with either the portion for which the connections are reversed or the remaining ortion of said windin and means for var mg the amount of sai resistance to vary t e E. M. F. of the generator.

9. In combination; a enerator havin a field windin a source 0 current meansor connecting t e whole of said windin to said source to cause the generation of an M. F.

of certain value; means for decreasing. said E. M. F. to a lower value, said means comprising means for reversin the connections for a portion of said win mg, a resistance, and means for connecting a ortion of said resistance in parallel with eit er the portion for which the connections are reversed or the remaining portion of said winding; and means for increasin the amount of said resistance so connecte to further decrease the E. M. F. of the generator.

In testimony whereof, I have signed my name to this specification.

ANTHONY PINTO.

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