Патент USA US2406424код для вставки
2,406,424 Patented Aug. 27, 1946 UNITED STATES PATENT OFFICE 2,406,424. CONTROL SYSTEM George E. King, Swissvale, Pa. assignor to West inghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Application Gotober 17, 1944, Serial No. 559,065 10 Claims. (01. 172—-179) 1 The present invention relates to variable volt age control systems and, more particularly, to electric motor control systems for operating or automatically controlling the operation of mo tors connected to various types of mechanical loads. In certain of its aspects this invention is related to a copending application of G. E. King and W. H. Formhalls, Serial No. 559,068, ?led on the same date as this application and . 2 of the motor, driving the casting machine. Thus, speed regulation at this normal running speed by means of a rotating regulator is not essential. Current limiting control by means of a rotating regulator is, however, provided to limit the ac celerating and braking current. This current limiting rotating regulator is so connected that it circulates current through the field windings of the main generator, supplying the motor when entitled. Control systems (W. E. Case 23,453) and 10 ever the main motor armature current approaches the preselected maximum value. This current also SerialtoNo. a copending 559,066, ?led application on the same of G. dateE. as this is circulated in such a direction with respect to the normal supply currents circulating in these application and entitled Control systems (W. E. ?elds, that the main generator output current is Case 23,417). This invention provides certain improvements 15 limited within the preselected maximum value. The creeping speed is very slow and may, for in variable voltage control systems in which ro example, be about 1.2% of the full ?eld speed tating regulators are employed to regulate cer of the main drive motor. Speed regulation of the tain electric quantities of the system, and the motor at this slow speed by ordinary adjust invention as hereinafter described and as illus trated in the drawing is speci?cally directed. to 20 ments of the excitation of the main ?elds of the generator, is not practicable. To obtain this slow the regulation of the speed of rotation of a di constant speed, a rotating regulator is used to rect-current motor together with provisions for control a separate generator ?eld. When this limiting the motor current whether the motor is control is utilized for creeping speeds, the ?eld operating normally as a motor or during regen erative periods when the motor is being over ‘15125 windings of the main generator which control the running speed are disconnected from the cir hauled by its mechanical load and driven as a cuit. The rotating regulator used to limit the generator. It will be apparent to one skilled in current in the motor functions in this capacity the art that the invention is not limited to speed’ during acceleration and braking at both creeping regulation alone since various modi?cations of and running speeds. the systems may be made to control the motor On some applications it is desirable to operate torque or power in conjunction with the current over a wide speed range with good speed regula limiting features mentioned. It will further be tion and at the same time limit the accelerating apparent that the invention is riot necessarily and braking current. The second form of the limited to motor control since automatic regula~ invention illustrated in the drawing shows a vari tion of the voltage, current or electric power sup able voltage control system of this type. In this plied to an electrical load of substantially any second form of the invention the speed regulat type susceptible of regulation may be had. ing generator, unlike that of the ?rst-mentioned In one form of the invention illustrated, the form of the invention, functions throughout the variable voltage control system is particularly entire speed range to control the speed of the adapted for controlling the speed of a motor used motor. It, further unlike the speed regulating to drive a centrifugal casting machine. Such a generator of the ?rst form of the invention, sup machine usually has ?xed running and creeping plies only the corrective current to the main speeds. After the metal is poured into the mould generator ?eld windings with which it is con to be rotated. the machine is accelerated, by way of example, in 15 minutes to the running speed, 4:5 nected rather than the total current necessary for exciting and regulating the main generator at which speed it may operate for 50 minutes. ?elds. In this second form of the invention the The machine is then decelerated and brought to rest in approximately a 10~minute interval of current limiting features, as previously described, are obtained. The current limiting rotating reg time. It is then again started and brought up to creeping speed where it is operated for about 50 ulator, however, regulates directly the speed reg ulating generator and indirectly the main gen 100 minutes, after which it is again brought to erator rather than directly as in the ?rst form rest, and in due course of time the completed of the invention. In this second form of the casting is removed. invention, the two rotating regulators, that is, the The running speed of the centrifugal casting machine is constant and at the full ?eld speed 55 speed and the current limiting rotating regula 2,406,424 3 4 tors, are connected in effective series circuit rela tionship. By means of this expedient there is considerable ampli?cation of the regulating quan tities thus effecting a quick response. During is connected in series circuit relationship with reversing facilities. Reversing may be obtained by simply adding reversing contactors. Such regulating generator the armature winding of a main generator G. A current limiting regulating generator RCL is utilized to limit the currents circulating in the braking periods the main generator current is series motor generator armature circuit within reversed. Thus, the action of the regulating gen preselected maximum values. A speed regulating erators is to tend to maintain the generator ?eld generator R5 is utilized to control the electrical current and prevent this ?eld current from col~ output of the main generator G when it is desired lapsing too fast. to operate the drive motor M at very slow or In order to simplify the drawing and the ac 10 creeping speeds. An exciter E‘ is provided to companying descriptive disclosure, the two forms supply a constant electrical quantity to various of the invention illustrated are shown without elements of the system. The exciter the speed the current limiting regulator RCL and the main generator G are expedients are well known in the art and any 15 driven at a constant speed by any suitable con— suitable form of reversing equipment may be stant speed prime mover or system of prime utilized without departing from the spirit and movers. As shown by way of illustration but not scope of the teachings of this invention. limitation they are connected to a common shaft A principal object of this invention is to pro to be driven by a single prime mover. The con vide a variable voltage drive including a motor 20 stant speed prime mover, however, is not shown in which automatic speed regulation of the motor in an effort to simplify the illustration of the is provided in conjunction with automatic regu invention. lation of the motor current. The main motor M is provided with a single Another object of this invention is to provide separately excited ?eld winding MF which re a variable voltage drive providing two selectively 25 ceives its excitation directly from the exciter. obtained constant running speeds for a motor The main generator G is provided with a differ in conjunction with current limiting protection ential ?eld winding GDF which is utilized at the for the motor. end of braking periods of the motor to buck-down Still another object of this invention is to pro or neutralize the residual voltage of the main vide a variable voltage drive of the character 30 generator. It is further provided with control referred to which provides a wide range of speed ?eld windings GSFi, GSFZ and GSF3. The regulation for a motor in conjunction with pro windings GSFI and GSFIZ are connected (see tection against excessive motor currents. Fig. 3) in opposite legs of a conventional Wheat A speci?c object of this invention is to provide stone bridge circuit which has as its other two a variable voltage drive utilizing rotating regu 35 opposite legs the bridge balancing resistors RI lators for regulating the speed of a motor and and This bridge circuit is connected at its limiting the motor current in which the rotating input terminals l and 2 across the exciter buses regulator controlling the motor currents requires B! and 32. Thus the ?eld windings of the main a certain value of excitation of its ?eld windings generator are excited in accordance with the before a corrective output thereof is obtained. 40 exciter voltage at some constant value depending Other objects and advantages will become ap upon the value of the resistor R3. As shown in parent upon a study of the following disclosure Fig. 2, the ?eld winding GSF3 of the main gen when considered in conjunction with the accom erator is connected in series with the armature panying drawing, in which: circuit of the speed regulating generator RS, Figure 1 schematically illustrates a variable 45 which series circuit includes the series ?eld wind voltage drive providing protection against exces sive currents, in which constant speeds of the motor controlled by the variable voltage system. ing R5! for the speed regulating generator, which by reason of its series connection with the arma ture of generator BS is excited by the armature are selectively obtained; current thereof, and a resistor SR! which is Fig. 2 diagrammatically illustrates a detail of 60 utilized to adjust the resistance of the ?eld cir the invention illustrated in Fig. 1; cuit RS! for the speed regulating generator to Fig. 3 diagrammatically illustrates another impart self-energizing properties to the speed detail of the invention illustrated in Fig. 1; regulating generator. This series circuit also Fig. 4 is a modi?cation of the invention pro includes the contact members CGF2 of the creep viding a wide range of speed control for the motor 55 contactor CGF which functions alternately with in conjunction with protection against excessive the running contactor RGF to selectively control the main generator at running or creeping speeds. Fig. 5 diagrammatically illustrates a detail of A discharge resistor DR shunts the main gen the invention of Fig. 4; erator ?eld GSFB to provide a discharge path Fig. 6 is a detail of one of the rotating regu 60 therefor upon opening of the contact members lators utilized in the variable voltage drives illus CGFZ. trated in the drawing; The current limiting regulating generator RCL Fig. '7 is a curve graphically illustrating the is provided with a series connected armature cur operating characteristics of one of the rotating rent excited ?eld ‘Winding RCLI and a control ?eld 65 winding RCLZ. The control ?eld winding RCL2 is regulators utilized in this invention: and Fig. 8 is a curve graphically illustrating the energized by the drop across the resistor R4 con operating characteristics of the other rotating nected in series in the main motor generator ar regulator utilized in this invention. mature circuit. and thus has a voltage applied Referring now to Fig. 1 of the drawing, the thereacross proportional to the currents ?owing invention illustrated therein corresponds to the 70 in the circuit and of a polarity depending upon ?rst form of the invention hereinbefore generally the direction of the current flow. The series ?eld described. It comprises a main drive motor M winding RCLl has a resistor SR2 connected in which is mechanically connected to drive the series therewith for adjusting the resistance of mentioned centrifugal casting machine (not illus this ?eld circuit, and this assembly, in conjunc trated). The armature winding of this motor 75 tion with the armature member I4 of the current current in the system; I 2,406,424 5 6 limiting generator, is connected across the output with three sets of contact members DFI, DF2 and terminals 3 and 4 of the previously mentioned Wheatstone bridge circuit. The speed regulating generator RS is provided with two di?erentially connected ?eld windings RS2 and RS4 which are respectively connected DF3. The contact members DFI when closed complete the ?eld circuit for the di?erential ?eld winding GDF of the main generator. The con tact members DFZ, which are back contacts, function in conjunction with either the contact across the resistor R4 in the motor generator se ries armature circuit and the motor armature ter members RRZ or CR2 to energize either the CGF or RGF relays depending upon whether the CR minals. Pattern ?eld winding RS3 provides the or RR relay is picked up. The contact members control pattern voltage for the speed regulating 10 DF3 when closed function in conjunction with the generator. It is connected across the exciter Stop push button, the contacts CB2, either the buses BI and B2 by the contact members CGFI of Creep or Run push buttons depending upon the creep generator ?eld contactor CGF. The which is depressed and the CR4 or RR4 contacts, winding RSI for the speed regulating generator, also ‘depending upon which of the Creep or Run as previously described, is series connected and push buttons are depressed, to deenergize either the generator is of the self-energizing type, the RR or CR relays. The run generator ?eld The exciter E, as illustrated, is provided merely relay RGF is provided with a single contact RGFI with a shunt ?eld winding EF. Any suitable ?eld which, as previously described, when closed'en winding system for this machine may be utilized ergizes the Wheatstone bridge circuit and as fol since per se it forms no part of this invention. 20 lows energizes the main generator ?eld windings The control equipment, which cooperatively GSFZ and GSFI to operate the motor at its run functions to provide selectively obtained opera ning speed: The creep relay CR is provided with a tions of the system as well as functioning in part plurality of contacts CR! to CR4. Contacts CRI to protect the system, comprises a main circuit when closed provide an energizing circuit for the breaker CB of the single-pole type for opening “a timing relay TR across the exciter buses BI and the main motor armature circuit on power failure, B2; the contact members CR2 when closed pro overload and loss of motor shunt ?eld. Creep vide, in conjunction with the back contact mem relay CR. and run relay RR are provided for se bers DFZ, an energizingr circuit for the creep gen lecting the creeping or running speeds. Creep erator ?eld contactor CGF across the exciter generator ?eld contactor CGF and run generator 3 i) buses 13! and B2; the contact members CR3 when ?eld contactor RGF are provided respectively for closed complete, in conjunction with the contact energizing the circuits for the main generator members CB2 of the main circuit breaker CB, the ?elds GSF3, GSFI and GSF2 for obtaining the creeping and running speeds of the motor. Dif ferential ?eld relay DF is provided for closing the Stop push button and the contact members RRII, a holding circuit for the operating coil of the creep relay CR; and ?nally the contact members ?eld circuit for the ?eld winding GDF of the main generator G to neutralize the generator CR4 which function in a similar capacity to the contact members RR4. The run relay RR is pro residual voltage and prevent the motor from vided with a similar group of contacts as the relay creeping. A time relay TR is provided to time the CR. These contacts are numbered RRI to RR4 operation of the DF relay. A voltage relay VR 40 and function in a capacity similar to that of the is provided to prevent the operation of the relays contacts of the creep relay. The creep generator TR and DF until the generator voltage has ?eld contactor CGF is provided with the con dropped to a low value. A ?eld loss relay FL has tact members CGFI and CGF2. The contact its coil connected in series in the bus B2 and thus members CGFI connect the pattern ?eld winding senses a loss of exciting current for the motor ?eld RS3 of the speed regulating generator RS across winding MF. Creep and Run push buttons, so the exciter buses Bi and B2. The contact mem designated in the drawing, respectively control the energization of the CR and RR relays to effect creeping and running speeds of the motor. ' A. Stop push. button, so designated in the drawing, is pro 50 vided to deenergize either of the creep or run re lays depending upon which is energized at the in stant the Stop button is depressed. The relay FL has one set of contact members bers CGFZ, as hereinbefore described, complete the circuit for the creep generator ?eld winding GSF3 across the speed regulating generator RS. Before proceeding with the discussion of the operation of the control system, an understand- ing of the function and characteristics of the regulating generators RCL and RS should be had. Both of these generators as illustrated are FL! which control the energization of the operat 55 series generators. The following discussion is ing coil of the main circuit breaker CB. The directed to the generator RS. In Fig. 7 of the main circuit breaker CB has a set of main con tacts CBI which, when closed, complete the series motor generator armature circuit. It also is pro drawing the saturation curve of a series gener ator is drawn. Stable operation of a series gen~ erator is obtainable only if the resistance of the vided with an auxiliary contact CB2 which when 60 ?eld circuit is less than that of a line tangent to closed, in conjunction with the Stop push but the saturation curve, that is, tangent to the in ton and either the contact members RR3 or itial substantially straight line portion of the CR3, establishes holding circuits for either the saturation curve. If the resistance is higher the RR or CR relays. The voltage relay VR is pro~ generator voltage cannot build up. If the re vided with one set of contact members VRI sistance is lower the generator open circuit volt which when closed establish a holding circuit age will be that determined by the intersection of for the timing relay TR. This circuit is effective the line with the saturation curve. If the resist~ only during running speeds of the motor since ance line of the field circuit is as designated by RL when the motor is operating at creeping speeds in Fig. '7 the generator can theoretically have an the voltage across the motor armature terminals m open circuit voltage equal to the ordinate of any is of such a low value that this relay does not pick of the points of tangency, for example, the points up. The relay TR is provided with one set of con PI and P2. ' tact members TR! which, when closed, connect While this would be undesirable in a standard the operating coil of the relay DF across the ex generator, it is an ideal characteristic for a reg~ citer buses BI and B2. The relay DF is provided 75 ulating generator since then the purpose of the 2,406,424 7 8 control ?eld windings, that is, the pattern ?eld RS3 and the di?erentially connected windings netomotive forces of the pattern and differen tially connected ?elds thereof are neutralized. If the speed of the motor rises, the converse of RS2 and RS4, becomes that of locating the the above-discussed function proper operating point of a series generator in cluding a series armature current excited held U! place. and armature, keeping this operating point con obviously takes The current limiting regulating generator RCL has self-energizing properties similar to those of stant and supplying the required amount of the speed regulating generator. In addition, this power to the connected ?eld windings of the main regulating generator requires a certain value, of generator. With the resistor R8 in the pattern ?eld circuit selected to provide the desired ex 10 excitation of its ?eld circuit before an electrical output thereof occurs. In Fig. 6 a single field citing current in the pattern ?eld RS3, and the pole of the machine is illustrated to show the circuit closed, voltage in the regulating gener manner in which this function is obtained. As ator armature rises rapidly because the excita~ Will be apparent from Fig. 1, this generator- has tion of the pattern ?eld RS3 is added to the ef fect of the series ?eld. This voltage excites the 15 but a. single control ?eld winding for the reason that such a single control ?eld winding is all generator ?eld GSFS causing voltages to appear that is required in the instant application. It across the differentially connected ?elds RS2 will, however, be apparent that any suitable num and RS4 which, if the selected speed of the mo ber of ?eld windings functioning, for example, in tor is correct, a resulting differential voltage neu the manner of those of the speed regulating gen tralizes the pattern. ?eld. The regulating gen erator RS may be provided for different applica erator thus reaches a steady point of operation tions. In order to provide current limiting con-1 because there is no forcing of the ?elds and due trol for the motor some means must be employed to the self-energizing properties of this gener to eifect operation of the current limiting regu-v ator the series ?eld can just maintain this steady state condition. 25 lating generator RCL only when the load current exceeds a safe maximum value. To accomplish As previously noted, the speed of the motor is this the regulating generator RCL is given spe to be regulated at creeping speed, thus, an indi cial characteristics such as illustrated graphical sired, cation since, of thethe counter counter voltage voltage of indicates the motorthe de ly in Fig. 8. This characteristic differs from that parture in speed of the motor from the desired 30 of the speed regulating generator RS by having an extended low voltage or zero voltage interval value. This is obtained by connecting the ?eld which extends equally on both sides of the ordi winding RS4 across the motor armature termi nate designated generator volts. A character nals to ‘be energized by the voltage drop across istic of this type can be obtained by providing the these terminals, and by connecting the ?eld ?eld poles of the generator with a magnetic shunt winding RS2 across the resistor Rllv in series in such as l2 in Fig. 6 which saturates at a smaller the motor generator armature circuit. In this flux density than the main ?eld pole l6. Numeral manner the ?eld winding RS4; has applied there M designates a portion of the rotor spaced from across a voltage proportional to the motor arma the ?eld pole by a small arcuate air gap, and ture terminal voltage and the ?eld winding RS2 numeral Iii designates a non-magnetic insert in has applied thereacross a voltage proportional the circuit of the ?eld pole which, in effect, pro to the load current of the motor armature. vides a small air gap. The pole structure com When the motor is operating at normal speed the prises a base portion in good magnetic contact excitation of the ?eld Winding RS4 is greater with the stator l8 and a pole shoe portion 20 ad than the excitation of the ?eld, winding RS2. By having the ?eld winding RS4 differentially con 45 jacent to the armature. The windings of the generator are arranged on the main pole 16. The nected with respect to the ?eld winding RS2, the air gap formed by the non-magnetic insert [0 differential voltage resulting from the differen~ carries both the pole and the shunt magnetic tial action of the ?eld windings and RS4 neutralizes the action of the ?eld winding RS3. ?ux, and hence does not in?uence the division Thus the excitation of the main generator ?eld 50 of the flux. It primarily determines the low or winding GSFS, which utilized for operating zero voltage interval previously mentioned, and the slope of the characteristic curve beyond the the motor at creeping speeds, is maintained at low voltage interval. Because of this gap, sub a constant value. stantially all the ?ux flows through the magnetic Considering now an increase in load of the motor M causing its speed to drop, it will be ap 55 shunt since the reluctance of this path is low parent that the motor armature terminal volt and almost none of it is forced across the motor generator armature circuit to generate a voltage age will drop ‘while at the same time the motor armature current will rise. This causes the e:.~ as long as the field excitation of RCLZ is in citation of the ?eld winding RS2 connected sufficient to saturate the magnetic shunt. The across the resistor Rd to increase, while at the 60 magnetic shunt I2 is so proportioned that it same time the excitation of the ?eld winding saturates at an excitation corresponding to the RS4 is decreasing. The differential voltage thus termination of the low or zero voltage interval obtained is smaller than the pattern voltage. As and then becomes unable to carry more ?ux. a result the excitation of the speed regulating Consequently, after the saturation of the mag generator is increased to increase the excitation 65 netic shunt, an increasing ?eld excitation forces of the generator ?eld winding GSFS to bring the flux across the air gap to the armature so that motor up to a speed indicated by the pattern now a. voltage is generated. The action after the voltage. The speed thus increases until the ao magnetic shunt has saturated is similar to that tion of the differentially connected ?elds again of the speed regulating generator RS. neutralizes the pattern ?eld and generator RS 70 By connecting the series connected armature due .to the self~energizing properties thereof I4, the self-energizing ?eld winding RCLI and the tuning resistor SR2 across the output termi again maintains this new condition. At this nals 3 and 4 of the conventional Wheatstone time the speed is exactly the same as before the bridge circuit it is possible to control the excita load on the motor changed because the regulat ing generator can be at balance only if the mag 75 tion of the main generator ?eld windings GSFI 2,406,424 10 and GSFZ in such a manner that the current circulating in the series motor generator arma ture circuit never exceeds a preselected maximum For example, if the current in the motor ‘ value. generator series circuit should rise beyond the a voltage having an electrical current which cir culates in the bridge circuit in such a direction as to decrease the excitation of the generator ?elds GSFI and GSFZ thus controlling the max preselected maximum value, the drop across the resistor R4 and, consequently, the voltage across circuit. As the motor approaches the running speed the accelerating current diminishes and the current limiting regulating generator ceases to function. the control ?eld Winding RCL2 for the current limiting regulating generator, is su?icient to pro imum value of current in the motor generator Pressing the Stop push button drops out relay duce an electrical output of this machine. By 10 RR and as a consequence, the relay RGF, thus properly determining the polarity of the various disconnecting the bridge circuit from the exciter elements connected in the conventional bridge and deenergizing the generator ?eld windings circuit, the output current of this generator is GSF: and GSFE. The generator Voltage de circulated through each of the ?eld windings GSFI and GSFZ of the main generator in a 15 creases until it is less than the counter voltage of the motor. The motor then generates a cur direction opposite to that supplied by the exciter rent in the reverse direction through the gen E. As a result the excitation of these ?elds is erator trying to drive it as a motor and speed reduced, and the voltage output, and consequently up the motor generator set. When the regen the current in the motor generator armature cir cuit is reduced to a safe value. 20 erative current approaches the preset maximum The operation of the system may be described as follows. Upon starting of the prime motor (not shown) the various generators of the system are rotated at a constant speed. Rotation of the armature of the exciter E causes a voltage to be applied across the exciter buses BI and B2. As a consequence the motor ?eld winding MB‘ is energized. When the exciter voltage builds up the ?eld loss relay FL closes closing the circuit to the circuit breaker CB under voltage release coil. The circuit breaker now closes connecting the motor armature to the main generator arma ture. With building up of the exciter voltage the differential ?eld relay DF, connected across the exciter buses through the contact members T'Ri, picks up and connects the generator differ ential ?eld across the generator armature to neu tralize the residual generator voltage. Pressing the Run push’ button completes a cir cuit from the exciter bus B2 through the contact members CB2 of the main circuit breaker, the Stop push button, the contact members DF3, the back contact members of the Run push but ton, the normally closed contact members of the Creep push button, the contact members CR4 value, the current limiting regulating generator again circulates a current in the bridge circuit through the generator ?elds which this time tends to maintain the generator voltage and prevent it from collapsing too rapidly and thus limits the maximum regenerative current. As the motor approaches zero speed the voltage re lay VR drops out deenergizing the operating coil of the TR relay. After a time delay the TR relay drops out and energizes through its contact mem bers TRI the differential ?eld relay DF, thus connecting the generator differential ?eld across the generator armature bringing the generator voltage doWn near zero and causing the motor to stop. Pressing the Creep button causes the creep relay CR, time relay TR, differential ?eld relay DF and creep generator ?eld contactor CGF to operate in their sequence. These circuits are substantially the same as those traced in con nection with the running operation of the vari able voltage drive and hence are not again traced. The contactor CGF when closed ener giZes the pattern ?eld RS3 of the speed regulat ing generator through its contact members CGFI and completes the circuit for the ?eld winding of of the creep relay CR and the coil of the run the main generator GSF3 to the armature of the relay RR, to the exciter bus Bl. The run relay speed regulating generator RS. The speed regu thus picks up, closing its contact members RRI, lating generator armature circulates a current RRZ, RR3 and opening its contact members RRA. through the connected generator ?eld GSF3 and Closing of the contact members RRI causes the the generator voltage builds up starting the mo TR relay to pick up, opening its back contact tor. It should be noted that the current limit members TR! which drops out the di?erential ing regulating generator is free to limit the ac _ relay DF. When the differential relay DF drops celerating and regenerative current by means of out its contact members DFZ close, establishing a circuit through these contact members and the 55 the bridge-type circuit, as previously described. If the creeping speed is very low there Will not contact members RR2 for the coil of the relay be sufficient generator voltage to pick up the RGF across the exciter buses BI and B2. Ener VR relay. Thus the timing relay is held in only gization of the relay RGF closes the contact through the contact members CR! which e?ect members RGFI thereof which complete the con nection of the input terminals l and 2 of the 60 its energization. Thus when the Stop push but ton is depressed to bring the motor to rest, the Wheatstone bridge circuit across the exciter buses timing relay after a short time delay drops out BI and B2 and energizes the run generator ?elds and applies the differential ?eld GDF by means GSFI and GSF2. The generator voltage builds of the DF relay to neutralize the residual voltage up circulating a current through the motor ar or the main generator G. mature circuit, the motor starts, and the cur The embodiment of the invention illustrated rent increases in value until it approaches the in Fig. 4 corresponds to the second form of the maximum set by the current limiting regulating invention generally discussed in the opening par generator RCL. As the generator voltage in agraphs of this speci?cation. This embodiment creases, the voltage relay VR picks up forming again utilizes the speed controlling and current with its contact members VRI, now closed, a limiting regulating generators discussed in con holding circuit for the timing relay TR. If dur nection with Fig. 1 of the drawing. Hence a ing this interval, the current builds up in the further description of these machines and their motor generator armature circuit to a value above the preset maximum value, the current characteristics is believed unnecessary in con limiting regulating generator RCL will produce 75 nection with Fig. 4. 11 £2,406,424 The variable voltage drive of Fig. 4 is, as previ ously mentioned, adapted to provide a wide range of speed control for the motor. This is accom plished by utilizing the electrical output of the speed regulating generator for regulating pur poses only. That is, only corrective current is supplied to the control ?eld windings GSFI and GSFZ of the main generator by this speed regu lating generator. Thus the speed may be varied 12 windings GSFI and GSFZ and starts the motor. The motor then begins to accelerate to a speed determined by the setting of the rheostat R. During this accelerating period the motor arma ture currents are high and the armature terminal voltage relatively low. As a result, the differen tial voltage resulting from the di?erential action of the differentially connected ?elds RS2 and RS4 is insu?icient to neutralize the pattern volt age. An electrical output of the generator RS over a considerably wider range before satura tion of this relatively small machine occurs. thus follows, which is circulated in such a direc Referring now to Figs. 4 and 5, the main gen tion through the fields GSFI and GSFZ as to erator G now is provided with but two control increase their excitation. In other words, the ?eld windings GSFI and GSFZ. The current generator RS forces the ?elds of the main gen limiting regulating generator RCL, like that of 15 erator G to rapidly accelerate the motor. If the Fig. 1, again has the series armature current ex motor is driving a substantial mechanical load, the armature currents will in all probability, at cited ?eld RCLI and the control ?eld RCL2. The speed regulating generator RS, like that of Fig. 1, has the differentially connected voltage and cur rent responsive ?eld windings RS4 and RS2, re spectively, and a pattern ?eld RS3. ‘Unlike Fig. 1 this generator is provided with two series arma~ ture current excited ?elds RSla and RSIb which least during the early portions of the accelerat ing period, rise above the maximum value deter mined by the characteristics of the current limit ing regulating generator RCL. This machine thus generates a voltage having a current ‘which is circulated in the second electrical bridge cir function as does the single ?eld of the RS gen cuit in a direction to reduce the excitation of erator of Fig. 1 to impart self-energizing proper 25 the series armature current excited ?elds RSla and RSlb or the generator RS to thus reduce ties to the machine. 7 The manner in which the regulating generators this generator’s amplifying characteristics and ‘are connected in the system is readily observed consequently, its electrical output. As follows, in Fig. 5. Here the main generator ?eld windits forcing action on the generator ?elds GSFI ings are again connected in the opposite legs of 30 and GSF? decreases and the main generator the Wheatstone bridge circuit with the resistors voltage drops. This continues until the arma— RI and R2 forming the other two legs. The pat ture currents of the motor are within permissible tern ?eld winding RS3 is connected in series with values and thereafter the current is maintained a speed controlling rheostat R from the positive substantially at this constant level throughout jexciter bus Bl to the input terminal l of this 35 the accelerating period. Thus a heavily loaded bridge circuit. It thus, upon pressing of the Start motor may be accelerated in the minimum pos push button and closing of the contacts CI of sible time without the possibility of overloading the contactor C which is held in at the contacts the system elements. . C2, is energized by a current indicative of the ‘W hen the Stop button is pressed, the energizing current ?owing in the bridge circuit which cur— circuit for the bridge network is opened at con rent is indicative of the selected speed of opera tacts Ci, thereby deenergizing the pattern ?eld tion of the motor M. Thus the pattern excita R’ and also removing this source of excitation tion of the speed regulating generator is estab for the main generator ?eld windings GSFI and ' lished. ‘Each of the self-energizing ?eld windings If under these conditions the motor is RSla and RSIb arevconnected in opposite legs r overhauled by the load to which ‘it is connected, of 'asecond Wheatstone bridge circuit which has the motor functions as a generator and tends to ‘for its other two legs the resistors R6 and R1. drive the generator as a motor. Since the pat One armature terminal of the speed regulating tern ?eld has been deenergized, the excita generator RS is connected to the input terminal tion resulting from the yet energized ?elds RS2 5 of the second bridge circuit, and the other 50 vand RS4 now acting cumulatively reverses the armature terminal is connected to the output electrical output of the regulating generator RS terminal 3 of the ?rst bridge circuit. The re to rev‘ersely excite the main ?eld windings GSFI sistor SRl, which establishes the desired resist— and As follows the main generator volt ance of the self-energizing ?eld circuit, is con age rapidly drops and tendsto build up in the nected between the other input terminal 6 of opposite direction to thus in e?ect aid the regen the“ second bridge circuit and the other output erative action‘of the motor. The current limit terminal 4 of the ?rst bridge circuit. The arma ing generator RCL again functions to produce an ture of the current limiting regulating generator electrical output in such a direction as to oppose RCL, its series connected armature current ex cited ?eld winding RCLI and the series resistor SR2 for this circuit are connected across the the currents circulating in the self-excited ?elds RSia and RSlb. With increasing currents the electrical currents of the RCL generator are greater in magnitude than those of the RS gen circuit. Thus in a manner similar to the speed erator. Thus the current in the series ?elds RS‘la regulating generator the current limiting regu and RSlb reverses and consequently the current lating generator supplies only corrective current 65 in the ?elds GSFl and GSFZ is reversed. The output terminals ‘land 8 of the second bridge to the series ?eld RSIa and RSlb of the speed regulating generator. excitation of the generator ?elds is now there fore'in a direction to maintain the generator volt The operation of this system is as follows. Depressing the Start push button energizes the age thereby preventing regenerative currents in excess of the preset maximum value. contactor C which then closes its contacts Cl and 70 The variable voltage drives of this ‘invention provide automatic overload current protection C2. Closure of contact members C2 provides a holding circuit for this contactor until the Stop push button is operated. Closure of the contact 'members Cl completes the energizing circuit for the bridge network containing the generator ?eld which results not in'aitime wasting shutdown of the system but which limits thecurr'erits'within permissible values, providing maximum ‘accelera tion of the motor for the given mechanical load 2,406,424 13 14 it is driving. Further, this automatic overload said main generator for limiting the electrical protection is provided by means of a simple, small rotating regulator which requires a minimum of maintenance e?ort and which, for the most part, eliminates the complications of relay or contactor output thereof to a predetermined Value. 4. In a variable voltage drive, the combination of, a drive motor, a main generator for energizing the drive motor, ?eld winding means for the main systems which function in this capacity. generator, means for supplying a constant elec The foregoing disclosure and the showings trical current to a ?rst portion of the ?eld wind made in the drawing are merely illustrative of the ing means, a regulating generator having an elec principles of this invention and are not to be in trical output controlled in accordance with cer terpreted in a limiting sense. Numerous modi? 10 tain electrical quantities of the motor for ener cations of the variable voltage drives as well as gizing a second portion of the ?eld winding means, the system elements are possible, the results of and means for selectively utilizing the regulating which may be predicted from the teachings of generator and the means for supplying a constant this disclosure. The only limitations are to be electrical current to control said main generator. determined from the scope of the appended 15 5. In a variable voltage drive, the combination claims. of, a drive motor, a main generator for energizing I claim as my invention: the drive motor, ?eld winding means for the main 1. In a variable voltage drive, the combination generator, means for supplying a constant elec of, a motor, a main generator for energizing said trical current to a ?rst portion of the ?eld wind motor, ?eld windings for said generator, an elec 20 ing means, a ?rst regulating generator having an trical bridge circuit, means for supplying elec electrical output controlled in dependence of cer trical energy to the electrical bridge circuit, two tain electrical quantities of the motor for ener of the ?eld windings for said main generator gizing a second portion of the ?eld winding means, being connected in opposite legs of the bridge cir~ means for selectively utilizing the ?rst regulating cuit, a ?rst regulating generator responsive to generator and the means for supplying a constant electrical quantities of said motor for regulating electrical current to control said main generator, the electrical output of said main generator, a a second regulating generator including at least second regulating generator responsive to the one control ?eld winding, means for providing electrical current supplied to said motor by said electrical properties in the second regulating gen main generator for controlling the excitation of erator such that said ?eld winding must be ex said ?eld windings in said bridge circuit to pre cited above a predetermined minimum value be vent excessive motor currents, and means for ren fore an electrical quantity is generated, means for dering said regulating generator ineffective to energizing the control ?eld winding in depend regulate said current until a predetermined max ence of an electrical quantity of the motor, and imum current value is reached, 2. In a variable voltage drive the combination of, a motor, a main generator for energizing the motor, ?eld windings for the main generator, an circuit means connecting said second regulating generator with said ?rst portion of the ?eld winding means for the main generator. 6. In a variable voltage drive, the combination electrical bridge circuit, means for supplying elec of, a motor, an armature winding and a ?eld trical energy to the electrical bridge circuit, cer~ 40 winding for the motor, a main generator, an tain of the ?eld windings of the main generator armature winding and a plurality of control ?eld being connected in opposite legs of the electrical windings for the main generator, circuit means bridge circuit such that the ampere turns in each connecting the armature winding of the main leg are equal, a ?rst regulating generator respon generator and the armature winding of the motor sive to electrical quantities of the motor for con in series circuit relationship, an electrical bridge trolling the excitation of said certain of the ?eld circuit, two of said plurality of control ?eld wind windings, a second regulating generator responsive ings for the main generator being connected in to the motor armature currents for controlling the opposite legs of the electrical bridge circuit, a ?rst regulating generator, and means for render ?rst regulating generator, an armature current ing the second regulating generator ine?ective to excited voltage sustaining ?eld winding and a plu control the ?rst regulating generator until a max 50 rality of control ?eld windings for the ?rst regu imum motor armature current is reached. lating generator, circuit means connecting two of 3. In a variable voltage drive, the combination the control ?eld windings of the ?rst regulating of, a motor, a main generator for energizing said generator in the series armature circuit of the motor, ?eld windings for said main generator, main generator and motor to be energized in ac an electrical bridge circuit, two of the ?eld wind cordance with di?erent electrical quantities there ings for said main generator being connected in of, a second regulating generator, an armature opposite legs of said bridge circuit, means for current excited voltage sustaining ?eld winding supplying electrical energy to said bridge circuit, and a control ?eld winding for the second regulat a ?rst regulating generator responsive to selected ing generator, ?eld poles for the windings of the electrical quantities of said motor for controlling second regulating generator, magnetic shunts of the electrical output of said main generator, a lesser cross-sectional dimension than the ?eld second regulating generator having ?eld poles poles, shunting said ?eld poles; circuit means and magnetic shunts shunting the ?eld poles connecting the control ?eld winding of the second which magnetic shunts saturate at lesser flux regulating generator in the series armature cir densities than the ?eld poles, ?eld windings asso cuit of the main generator and motor to be ener ciated with said ?eld poles, said second regulating gized in accordance with an electrical quantity generator having the characteristic of producing thereof, circuit means for electrically connecting abruptly increasing electrical outputs upon satu said ?rst regulating generator to energize a third ration of the magnetic shunt, means for energiz control ?eld winding of the main generator, cir ing the ?eld windings of the second regulating cuit means connecting the second regulating gen generator in dependence of the magnitude of the erator across the output terminals of the elec electrical current supplied to said motor by said trical bridge circuit, means for supplying electri main generator, and circuit means connecting said cal energy to a third control ?eld winding of the second regulating generator to effect a control of 75 ?rst regulating generator, to the electrical bridge 2,406,424 15 16 circuit and to the ?eld winding of the motor; and means for selectively connecting said ?rst regu lating generator ‘and said electrical bridge cir~ circuit, and means for controlling the second ‘regulating generator in dependence of an elec trical quantity of the motor. ‘ 9. In a variable voltage drive, the combination cuit to said means for supplying electrical energy. of, a motor, a main generator for energizing the '7. In a variable voltage drive, the combination motor, a pair of control ?eld windings for the of, a motor, an armature winding and a ?eld main generator, a ?rst electrical bridge circuit, winding for the motor, a main generator, an said pair of control ?eld windings for the reg armature winding and a plurality of control ?eld ulating generator'b'eing connected in opposite legs windings for the main generator, circuit means connecting the armature winding of the main 10 of the electrical bridge circuit, a ?rst regulating generator, said ?rst regulating generator being generator and the armature winding of the motor controlled in dependence of electrical quantities in series circuit relationship, an electrical bridge of said motor, circuit means including a second “circuit, two of the control ?eld windings of the electrical bridge circuit‘connecting said ?rst reg ulating generator across the output terminals of of the electrical bridge circuit, a ?rst regulating ‘generator, an armature current excited voltage the ?rst electrical bridge circuit, a pair of arma sustaining ?eld winding and a plurality of control ture current excited ‘?eld windings for the ?rst ?eld windings for the ?rst regulating generator, regulating generator, said armature current ex_ two of the control ?eld‘windings being differen cited ?eld windings forming opposite legs of the " tially connected, circuit means connecting one of 20 second electrical bridge circuit, a second reg ulating generator having ?eld poles and mag said differentially connected windings to be ener gized in accordance with the voltage drop across netic shunts for the ?eld poles of smaller ?ux the motor armature, circuit means connecting capacity than the ?eld poles, control windings the other of the differentially connected windings on the ?eld poles, said second regulating gen to be energized in accordance with the electrical 25 erator being connected across the output ter current traversing the series armature "circuit of minals, of the second electrical bridge circuit, the main generator and motor, a second regulat and means for energizing the control windings ‘ing generator, an armature current excited of the second regulating generator in dependence voltage sustaining ?eld Winding and a control of an electrical quantity of the motor. ?eld winding for the second regulating genera 30 10. In a variable voltage drive, the combina tor, ?eld poles for the windings of the second tion of, a motor, ‘an armature Winding and a regulating generator, magnetic shunts of lesser ?eld winding for the motor, a main generator, cross-sectional dimension than the ?eld poles, an armature winding and a pair of control ?eld fshunting the ?eld poles; circuit means connecting windings for the main generator, circuit means the control ?eld Winding of the second regulat 35 connecting the armatures of the main generator ing generator to be energized in accordance with and motor in series circuit relationship, a ?rst the electrical current traversing the series arma electrical bridge circuit, said pair of control ?eld ture circuit of the main generator and motor, windings for the main generator being connected circuit means electrically connecting the ?rst in opposite legs of the electrical bridge circuit, regulating generator to energize a third control 40 a ?rst regulating generator, a pair of armature ?eld winding of the main generator, circuit means ‘current excited voltage sustaining ?eld windings connecting the second regulating generator across and a plurality of control ?eld windings for the the output terminals of the electrical bridge cir ?rst regulating generator, a second electrical cuit, means for supplying electrical energy to a bridge circuit, said pair of armature current ex third control ?eld winding of the ?rst regulating 45 cited ?eld Windings forming opposite legs of said ‘generator, to the electrical bridge circuit and to second electrical bridge circuit, said ?rst regulat the motor ?eld winding; and means for selectively ing generator being connected in series with the connecting the third ?eld winding of the ?rst second electrical bridge circuit across the output regulating generator and the electrical bridge cir terminals of said ?rst electrical bridge circuit, a main generator being connected in opposite legs cuits to said means for supplying electrical energy. 50 second regulating generator, an armature cur 8. In a variable voltage drive, the combination rent excited voltage sustaining ?eld winding and of, a motor, a main generator for energizing the a control ?eld Winding for the second regulat motor, a pair of control ?eld windings for the ing generator, said second regulating generator main generator, a first electrical bridge circuit, being connected with the armature current ex said, pair of control ?eld windings for the reg 55 cited ?eld winding thereof across the output ulating generator-being connected in opposite legs terminals of the second electrical bridge circuit, of the electrical bridge circuit, a ?rst regulating means for exciting two of the control ?eld wind generator, said ?rst regulating generator being controlled in accordance with electrical quan titles of said motor, circuit means including a second. electrical bridge circuit connecting said ?rst regulating generator across the output ter minals of the ?rst electrical bridge circuit, a pair of armature current excited ?eld windings for the ?rst regulating generator, said armature current excited ?eld windings forming opposite legs of the second electrical bridge circuit, a second regulating generator connected across the output terminals of the second electrical bridge ings of the ?rst regulating generator in depend ence of certain of the electrical quantities of said motor, means for exciting the control ?eld wind ing of the second regulating generator in ac cordance with an electrical quantity of the motor, and means for supplying direct current of con stant value to a third control ?eld winding of 65 the plurality of control ?eld windings for the ?rst regulating generator, to the ?rst electrical bridge circuit and to the motor ?eldwinding, GEORGE E. KING.