US2083297A - Regulating system - Google Patents

Description

June 8, 1937. F. H. GULLIKSEN ET AL 2,083,297

REGULATING SYS TEM Filed Nov. 3, 1934 2- Sheets-Sheet l WITNESSES: INVENTORS.

J1me 1937. F. H. GULLIKSEN ET AL 2,083,297

REGULATING SYSTEM 2 SheetsShet 2 Filed Nov. 3, 1934 INVENTORS. ksen and J l A/Dawon'.

Patented June 8, 1937 UNITED STATES.

PATENT OFFICE REGULATENG SYSTEM Application November 3, 1934, Serial No. 751,361

Claims.

Our invention relates to electrical regulators and it has particular relation to electronic tube regulators for maintaining constant the voltage or other characteristic of an electrical machine 5 or circuit.

One object of our invention is to simplify the equipment and control circuits comprised by alternating-current generator voltage regulators of the electronic tube type.

Another object of our invention is to increase the reliability of operation and improve the quality of performance of such regulators.

An additional object of our invention is to increase the speed of response of such regulating equipments.

A further object of our invention is to decrease the time required by the regulator to settle disturbances in the regulated quantity.

A still further object of our invention is to minimize interruptions in electronic tube regulator service due to tube failure.

An additional object of our invention is t provide a simple form of load compensation for voltage regulators which are applied to self-excited generators.

Our invention itself, together with additional objects and advantages will best be understood throughthe following description of specific embodiments thereof when taken in conjunction 30 with the accompanying drawings, in which:

Figure 1 is a diagrammatic representation of one preferred form of the regulating system of our invention shown as being applied to control the voltage of an alternating current generator;

Figs. 2 and 3 are diagrams of curves illustrating certain characteristics of the thermionic detector tubes comprised by the system of Fig. 1;

Figs. 4 and 5 are diagrams of curves showing the manner in which the excitation-supply rectifier tubes of the system of Fig. 1 are controlled;

Fig. 6 is a diagrammatic representation of one manner in which non-controllable rectiflers may two sets of rectifier tubes 20 and 22.

hunting means comprised by the system of Fi '7.

Referring to the drawings and particularly to Fig. 1 thereof, the electronic-tube regulating system there depicted is shown as being applied to 5 maintain constant the voltage of an alternating current generator Hi the armature windings 12 of which are connected with a three-phase circuit, represented by conductors l4, and the field winding it of which derives its exciting current 10 from one phase of the circuit I4 through a connection which includes a transformer l8, and

The effective current passed by these tubes, which preferably are of the grid-controlled gas-filled variety 15 and which are connected in well-known manner to effect full wave rectification, is controlled by a grid-voltage supply circuit which includes one or more detector tubes 36 energized, through transformers 42 and 46, in accordance with the voltage of the regulated circuit 14. 20

Considering first the excitation-supply recti fier tube circuits, during one-half of each cycle of the alternating current voltage which the machine IU impresses upon the transformer l8, the anode elements 24 of the tubes 20 are subjected, through their connection with the secondary winding 25 of the transformer, to a positive voltage and during the remaining half-cycles the anode elements 26 of the tubes 22 are similarly positively energized. 'From the cathodes 28 of both sets of tubes one connection is made with the machine field winding l6 through which the rectified current passes and returns, by way of a second connection which includes a switch 61, to the mid-point 21 of transformer winding 25. So far as the normal operation of the system is concerned, only one tube in each of the sets 20 and 22 is essential, the second illustrated tube being for the purpose of minimizing interruptions of regulator service due to tube failure.

In order to stabilize the regulating actions and to permit uncontrollable rectifier units, which are less expensive and of longer life, to be used to rectify one-half of the alternating-current wave, we connect the grid elements 32 of the tubes in set 22 only with the machine-voltage errordetecting circuit from which is supplied a potential E3 for'adjusting the magnitude of exciting current supplied to the machine field winding I6 by controlling the point in each positive half cycle of anode voltage at which conduction is instituted. The grid elements 30 of the remaining set of tubes 20 are connected, when tubes are used, as in Fig. 1, instead of copper-oxide or other non-controllable rectifiers, shown at 20 in Fig. 6, by means of suitable resistors 3|, directly to the tube cathodes, in a manner to render these tubes conductive during substantially the 5 full duration of each positive half cycle of their anode voltage. As will be more completely explained, the inductance characteristics of the machine field winding I6 tend to automatically maintain a substantially equal division of load 10 between the two sets of rectifier units so that, in the illustrated application, our control ofthe one set only affords practically the same range of adjustment as does the previously employed control of both sets.

Considering now the voltage-error detecting circuit of our improved regulating system, in order to eliminate the necessity for a standard potential battery or other equivalent'source of reference voltage in these circuits, we prefer to utilize one or more detecting devices 86in the form of filament-controlled tubes, two of which are shown in the diagram of Fig. 1. The purpose of the illustrated duplication is merely to minimize interruptions of service due to tube failure. Each of these tubes comprises an anode element 44 and a cathode or filament 40 which is supplied, through the transformer 42,

with an energizing voltage which varies directly with that of the circuit H to be regulated. The tube anode elements 44 have impressed upon them, by means of a transformer 46 which is also energized by the voltage of circuit l4 and in the secondary winding circuit of which a rectifier 48 is connected, a rectified or pulsat- 35 ing uni-directional current. A. capacitor 50 and a resistor 6| are connected in parallel across this anode-voltage supply circuit for the detector tubes to partially filter or smooth out the voltage pulsations. The current drawn by 40 these tubes is passed through a resistor 63, the

voltage drop Ea across which thus varies in accordance with the temperature of the tube filaments' 40, and a second capacitor 64 connected in parallel with the tubes. This capacitor serves 4 to produce cyclic pulsations of current through the resistor,- which pulsations are superimposed upon the average value of the resistor voltage drop. The control potential Es impressed-upon the excitation-supply tube grids is made up of voltage E2 and a secondcomponent E1, in the form of a portion of the relatively constant voltage appearing across the capacitor 60 and the resistor II, which opposes voltage E2. As is indicated by the simplified curves of Fig. 4, this latter ,voltage is somewhat the greater and hence maintains the grids at an average potential which is negative with respect'to the tube cathodes. In Fig. 4 the major reference line 56 60 applies to the excitation-supply tube cathodes 26, the curve E. indicates the voltage impressed upon the anode elements 26 of the tubes 22, and the curve E. represents the critical values of negative potential which, when impressed upon 65 the grid elements 32 of the tubes, prevent an institution of tube conduction. No attempt has been made to represent the individual alternating-current ripple components of the two voltages E1 and E2. The .major or direct current component of voltage E: is controlled by the .detector tubes 36 and its altemating-current component is determined by the current drawn by the capacitor 64.

To more readily displace the phase position 76 of the ripple in control voltage E: from that of the anode voltage E. of the excitation supply tubes by the amount, which, as is shown in Fig. 4, is most advantageous for controlling the conduction starting point of these tubes, we prefer to supply it, as indicated by the diagram of Fig. 1, from a diflerent phase of the circuit l4 than that which supplies the tube anode circuits. It will be understood, however, that, if desired, other expedients may be utilized for accomplishing the same result.

The detector tubes 36 are, in the system of Fig. 1, preferably operated at an anode voltage sufllcientlyhigh to saturate or place them in a condition in which all of the electrons emitted by the cathodes are attracted to the anodes. In the diagram of curves of Fig. 2, which show the manner in which the current Ip through the tube varies with changes in the anode voltage Ep when different values of energizing voltage E: are applied to the cathode orfilament element, such a saturating voltage Epl is indicated by the dotted line which identifies a region in which changes in the value of anode voltage have little effect upon this tube current. At such a voltage, however, a change in the magnitude of the filament heating voltage from E1: to En or En eifects, as indicated by the wide separation of the curve of Fig. 2, a substantial'change in that current.

The exceedingly rapid manner in which the tube current is thus caused to vary is indicated by the curve of Fig. 3. Within the voltage range which includes E12, a high factor of amplification is thus obtained. Such a filament-controlled detector being essentially a temperature-actuated device, indicates the root-mean-squared value, instead of the average as does an anodecontrolled rectifier tube, of the alternating current voltage and thus, in addition to being highly sensitive, provides a character of response which is especially desirable when the generator wave form is subject to deviations or changes.

The conversion, by detector tubes 36. of changes in the voltage of the regulated circuit l4 into much larger changes in the direct-current component of voltage E2 which forms a part of the excitation tube control potential effects acorresponding shift in the position of the axis 60 of this potential E: with respect to the tube anode voltage axis I6 and the critical grid voltage curve E By increasing this separation an increase in the regulated voltage delays the point of tube current conduction to reduce the current passed by the tubes 22, and, by decreasing this separation, a decrease in the regulated voltage similarly initiates conduction at an earlier point in each posltivehalf cycle of tube anode voltage to thereby increase the eflective current passed by these tubes.

As before pointed out, such adjustments are accompanied by comparable changes in the effective current passed by the opposition connected rectifiers 20 even though these tubes are conductive throughout their entire corresponding hali cycles of anode voltage; as indicated by the shaded area of Fig. 5. This substantially equal division of current results from the predominating inductance characteristics of the machine field winding I 6 in which changes in current during succeeding half cycles of energizing voltage are balanced by action of the energy stored in the magnetic field -surrounding the winding. This field of energy causes to be set up counter-electro-motive forces which oppose the passage of current through the continuously conducting tubes 20. Control of the exciting current supplied to machine winding I6 is thus as satisfactorily effected as were the rectifier units 20 (Fig. 1) or 20' (Fig. 6) also to be influenced by a regulated quantity responsive control voltage, an arrangement which would require a doubling of the minimum permissible current capacity of the detector output circuit and which further would not permit non-controllable units (20') to be employed.

In placing the complete regulating system shown in Fig. 1 into operation, the regulated generator I0 is excited, during its starting period, from a separate source of direct current, indicated in the form ofa battery 65, which may be connected to the field winding l6 by shifting the transfer switch blade 61 to its upper position. As

soon as the generator voltage has reached its substantially normal value, switch 81 is returned to the lower position illustrated in which the field winding I6 is connected for self-excitation through the rectifier tubes comprised by our improved regulating system.

In operation of the system, as long as the magnitude of the voltage supplied by the generator to the regulated circuit I4 is of the normal or desired value, the filaments oi the detector tubes 38 are heated to an intermediate temperature and the control voltage impressed upon the grids of the excitation-supply tubes is of such character that they supply to the generator field winding that value of exciting current which maintains the generator voltage at this desired value.

Upon the occasion of a decrease in this regulated voltage, the voltage impressed upon the detector filaments corespondingly decreases and the tubes pass a smaller value of anode current. The resulting lowering of this current correspondingly so modifies the rectifier tube control potential as to raise the value of exciting current supplied to the machine field winding and restore the voltage of machine l0 back to its desired value.

In a similar manner, upon the occasion of a rise in the voltage of the regulated circuit ll,

the temperature of the detector filaments is increased, and these detectors draw more current. This so modifies the control voltage E: as to lower the existing current and restore the voltage 5 and thereby requires that the detector filament operate at correspondingly changed temperatures to maintain their control of the excitation-supply tubes.

By duplicating the detector tubes 36, we have found that interruptions in service due to tube failure may be greatly minimized. In the filament supply circuit of these parallel connected devices we connect a resistor 68 which functions to'so increase the voltage across the filament of one tube in case of failure of the other as to cause this remaining operative tube to continue to maintain the regulated voltage at its normal value. To produce this desired efiect the resistor must of course be rather closely adjusted in resistance value.

Asimilarduplication of tubes in each of the excitation-supply rectifier sets 20 and 22 also minimizes interruption of service due to tube failure, inasmuchas an inoperative condition of one of the tubes in each or both of these sets is found not to detrimentally effect regulator operation, the change in excitation supply circuit impedance being compensated for by a readjustment which the detector circuits automatically make in the character of the control voltage Ea.

We have discovered that the system just described is inherently stable in operation and exhibits no tendency to hunt or overshoot in its corrective actions. We believe that such stability is the result of the before-discussed inductive balancing action between the two sets of excitation-supply rectifier units when taken in combination with the action of the ripple-amplifying capacitor 54 in the control voltage supply circuit. This capacitor appears to introduce a slight delay in the attainment by the detector tube circuit of its final or newly adjusted condition upon a change in filament temperature. In any case, the regulator of Fig. l exhibits a; high degree of generator from zero to 125 percent of its rated capacity.

Considering now the modification of our invention depicted by Fig. 7, the. regulating system there shown controls the voltage of an alternating-current generator l0 which has its field winding 15 energized by means of a separate generator or exciter 10. The exciter field winding II is supplied with a unidirectional energizing current from the generator output circuit l4 through a connection which includes a transformer l8 and a pair of rectifiers, in the form of grid-controlled gas-filled electronic tubes 12 and 14, which are connected to effect full wave rectification.

The grid elements 15 of these tubes have impressed upon them a direct current control voltage E: which is supplied through a circuit which includes a two-element detector tube 36, the oathode or filament 40 of which is energized by a voltage Er derived from the regulated circuit l4 through a transformer 42 as in the system of Fig. 1. The anode element 44 of the tube has impressed thereon a unidirectional potential supplied also from the regulated circuit through a transformer 18 and a full wave rectifier 19. Between the rectifier and the detector tube, filtering apparatus, in the form of a capacitor and a resistor 82, is disposed in well known manner.

As in the case of the system of Fig. 1, the excitation-supply rectifier tube control voltage is made up of two components, E which comprises the drop across a'portion of the resistor 82 and which tends to make the tube grids positive, and E5, which comprises the voltage drop across a resistor 83 through which the current drawn by the detector tube 36 passes and the polarity of which opposes that of component E4 and tends to make the tube, grids negative. Both voltages E4 and E5 contain small alternating-current ripples no attempt to represent which has been made in Fig. 8.

During normal'operation of the regulating system the magnitude of component E5 slightly exceeds that of E4 thereby making the sum Es a relatively small value of unidirectional voltage which renders the grid elements I5 of the rectifier tubes negative. Except during periods of exciter field current change when, as will be further explained, there is set up in an anti-hunting resistor 85 a stabilizing potential Es, the voltage- E1 impressed upon the tube grids is the same as the detector circuit output voltage E0.

5 The operation of the system of Fig. 7 simulates that of a vibratory contact type of regulator in that adjustment in the current supplied to exciter field winding ll may under certain conditions be effected by rendering the rectifier tubes 12 and II' alternately completely conductive and completely non-conductive, the relative values or ratio of these conducting and non-conducting periods being varied in such manner as to maintain the voltage of machine ill at its desired value. The

15 manner in which the illustrated circuits efiect such operation will be understood by reference to Fig. 8, in which curve E. represents the wave of anode voltage impressed upon each oi the rectifier tubes and curve E; the critical grid voltage necessary to maintain the tube in a non-conductive state.

When the voltage 01' regulated circuit i4 is of the normally desired value, the grid control potential E7 varies, as indicated in Fig. 8, between two limits such as are indicated by the parallel lines 81 and 88, this variation resulting from correspondingly slight fluctuations in the detector filament heating voltage which each conducting and non-conducting period of the rectifier tubes 12 and I4 causes. When this control potential is of the value 81, conduction starts at an early point in each positive half cycle of the anode voltage of the rectifier tubes and continues during the remainder of that half cycle as is indicated by the shaded area 9| in Fig. 8. However. when, as a result of such conduction, control voltage E1 has been shifted to the value indicated by line 88, the rectifier tubes are prevented from becoming so completely conductive.

In practice, the presence of the before-mentioned alternating-current ripples in the control potential E7 somewhat modifies the described action in that. these ripples introduces combined magnitude and phase-shift control efiect which varies the conductivity of the excitation-supply tubes without necessitating the extreme on and oil" action except for large regulated voltage variations.

Hence, when the voltage of circuit i4 is of the normal or desired value, the tube conductivity characteristics are automatically maintained such as to cause exciter Hi to supply to field winding ii of machine it the proper exciting voltage to keep the machine voltage at this desired value.

Upon the occasion of a drop in the voltage of regulated circuit I, the average temperature of the filament l0 oi the detector tube 36 is correspondingly lowered, so that the tube draws less current through resistor 83 and thus reduces the e0 magnitude of control-potential component Es- This makes thegrid control voltage E1 less negative with the result that the ratio of the conductive to non-conductive periods of rectifier tube operation, when the control variation is this extreme, is correspondingly raised, the amount being sufiicient to restore the machine voltage back to its desired value.

In a similar manner, a rise in the regulated voltage increases the average temperature oi the detector filament which, in'turn, raises the magnitude of component E5 and renders the grid control voltage E1 more negative. This, in turn, decreases the ratio of conducting to non-conducting periods, when the control variation is this extreme, oi the excitation supply tubes and lowers the voltage of machine ill by an amount appropriate to restore it to the desired value.

The value 01' voltage which the regulator will maintain may be changed by adJusting the position of a tap connection Bl along the detectorcircuit resistor 88. Such an adjustment varies the value of the control potential component E5 and thereby requires that the detector filament operate at correspondingly changedtemperatures to maintain its control of the excitation-supply tubes.

In the system of Fig. 7, which is more completely described and claimed in our copending application Serial No. 751,362, filed November 3,

1934, and assigned to the same assignee as this invention, we have also disclosed a highly improved iorm oi stabilizing or anti-hunting means which prevents overshooting oi the corrective actions without substantially detracting from the speed of response 01' the regulating system. These means comprise the before mentioned resistor connected in the grid control circuit or the excitation supply tubes which resistor is connected in series with a capacitor 82. The series-connected resistor and capacitor are, in turn, energized by the voltage appearing across a second capacitor 94 which together with a series connected resistor is directly influenced by the voltage appearing across the field winding ll of the machine excitor 10.

The manner of operation of these anti-hunting means may be best explained by reference to the curves of Fig. 9 which are drawn'to illustrate the action resulting from a sudden drop in the regulated voltage Er which takes place at time ti. Upon the occasion of this drop, the regulating system just explained functions to increase the current supplied to and hence the voltage appearing across the exciter field winding H. As a result, there is drawn through the resistor 85 a current which acts to charge capacitor 84 to a value of potential higher than that previously existing. The general manner in which this increase takes place is indicated by curve 81 of Fig. 9. It will be noted from this curve that there is an appreciable delay before the capacitor attains the new value of charge corresponding to the raised exciter field voltage.

As this voltage across capacitor 94 rises, it

causes to be forced through the resistor 85 a current which charges capacitor 92, this current causing to appear across the resistor a stabilizing voltage E. which varies in the general manner indicated by curve E. of Fig. -9. The. polarity of this voltage is such as to oppose or retard the corrective action instituted by the regulator. In the specific instance under course of explanation, it combines with the voltage E6 to make the control potential E1 of a greater negative value and thereby so prematurely decreases the efiective conductivity of the rectifier tubes 12 and 14 as to prevent the regulator initiated increase in machine excitation from being continued until the regulated voltage is raised above the desired value.

Upon the occasion of an increase in the reguiated voltage and a corresponding reduction in the exciting current supplied through the rectifier tubes, an action exactly similar to that above explained takes place, with the exception that the capacitors 94 and 92 force discharging currents through their associatedresistors and the control voltage E1 is made oi a lesser negative value than Ea to thereby appropriately arrest the corrective action. In both instances, however, this retarding force does not come into effect until an appreciable time after the corrective action has been instituted, with the result that the regulator is much quicker in settling the disturbed quantity than were the anti-huntinginfiuence to be directly proportional to the magnitude of the corrective action, as in comparable anti-hunting systems developed in the past. The performance of one. such comparable system is indicated by the dotted sections of the curves of Fig. 9, which show the undesirable retarding eifect on regulating action which such comparable systems have exerted.

These prior art systems introduce, as shown by curve section 98, a corrective-action retarding potential which is directly proportional to the rate of change of the correction and which thus seriously slows it down, as shown by curve section- 99. In our improved antihunting system, however, the regulator is left substantially unhampered until some appreciable later time, represented by the peak of the curve E when the maximum retarding influence is first exerted. Substantial benefits in regulator response are in this manner made possible.

The tube duplication expedients of the system of Fig. 1 are also applicable to the regulator of Fig. 7 for the purpose of minimizing interruptions. in service due to. tube failure.

We have found that the described regulating systems may be given a rising characteristic with machine load increase by inserting in the excitation and detector-tube supply circuit a resistor, as shown in Fig. 7 at 80, in'- which a voltage drop proportional to the machine exciting current is set up. Since as the load on the regulated machine is increased greater excitation is required to maintain the voltage at asubstantially constant value, this resistor causes the voltage of circuit It to be maintained above that impressed upon transformer 42, which latter voltage the regulator keeps constant, by an amount proportional to the machine load. The magnitude of this resulting rising characteristic may be raised by increasing the resistance of the compensating resistor and lowered by decreasing the value of this resistance.

Although we have shown and described certain specific embodiments, of our invention, we are fully aware that many modifications thereof. are possible. Our invention, therefore, is not to be restricted except insofar as is necessitated by the prior art and by the scope of the appended claims- We claim as our invention:

1. Regulating apparatus for an alternatingcurrent dynamo-electric machine comprising a circuit for supplying an exciting current to the machine, a grid-controlled rectifier tube for adlusting the magnitude of said current. a detector tube having an anode and a filamentary cathode, a circuit energized by the voltage of said machine and including a rectifier and an impedor for impressing a unidirectional potential between the elements of said detector tube, means for energizing said cathode by a current determined by a characteristic of the machine to be maintained constant, and means for impressing the voltage drop across said impedor upon the grid of said grid-controlled tube.

2. Regulating apparatus for an alternatingcurrent dynamo-electric machine comprising a circuit for supplying an exciting current to the machine, a grid-controlled rectifier tube for adjusting the magnitude of said current, a detector tube having an anode and a filamentary cathode, a circuit energized by the voltage of said machine and including a rectifier and, an impedor for impressing a unidirectional potential between the elements of said detector tube, means for energizing said cathode by a current determined a common energizing voltage which varies in.

accordance with the regulated quantity, and a quantity-coiitrol circuit through which the anode currents of all of said tubes fiow, the combination of an impedor connected in series with said cathode-energizing circuit to raise the voltage applied to the remaining tube cathodes in the event of failure of one or more of them.

4. In a regulating system comprising a pair of parallel-connected detector tubes of the filamentcontrolled type, a circuit for supplying to both of said tubes a common filament-heating voltage, which varies in accordance with the regulated quantity, and a quantity-control circuit energized by the combined current passed by said two tubes, the combination of an impedor connected in series with said cathode-energizing circuit, said impedor functioning, in the event that one tube fails, to raise the filament-heating voltage applied'to the remaining tube by an amount sumcient to compensate for the loss of current in the quantity-control circuit due tosuch failure.

5. In a system comprising an electrical generator having a field winding, a circuit through which the generator supplies exciting current to said winding, and a regulator energized by the voltage of the generator through a. circuit a por-' tion of which is common with the excitingcurrent supply circuit and adapted to so adiust said exciting current as to control the generator voltage, the combination of load-compensating means for the regulator comprising an impedor serially connected in the commonportion of the field current and regulator supp y circuits.

FINN H. GUI .LIKSEN. JOHN W. DAWSON.

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