US2725522A - High speed voltage stabilizer - Google Patents

Description

Nov. 29, 1955 D. M. MURRAY L HIGH SPEED VOLTAGE STABILIZER 4 Sheets-Sheet 1 Filed Sept. 10, 1951 THYR AT Ron: PLATI- VD LTAGI- GRID VOLTAGE RAT GEN.

Nov. 29, 1955 D. M. MURRAY E 2,725,522

HIGH SPEED VOLTAGE STABILIZER Filed Sept. 10, 1951 4 Sheets-Sheet 2 DON/7L o MHGLEHN lV/JIFIPH Y 4 0955? r 1 EU #0: 7519s Br M 44% Nov. 29, 1955 Filed Sept. 10, 1951 D. m. MURRAY ETAL 2,725,522 HIGH SPEED VOLTAGE STABILIZER 4 Sheets-Sheet 3 THYRATROH PLATE.

F r 1 I Nov. 29, 1955 D. M. MURRAY EI'AL 2,7

HIGH SPEED VOLTAGE STABILIZER Filed Sept. 10, 1951 4 Sheets-Sheet 4 United States Patent 2,725,522 HIGH SPEED VOLTAGE STABILIZER Donald M. Murray and Norbert Leo Kusters, Ottawa,

Ontario, Canada, assignors to National Research Council, Ottawa, Ontario, Canada, a body corporate of Canada Application September 10, 1951, Serial No. 245,862 2 Claims. (Cl. 323-47) This invention relates to voltage stabilizers of the elec-.

tromechanical type. a

The term unbalance is used herein to signify the difference between the desired voltage and the actual output voltage of the voltage stabilizer.

It is intended that the phrase directly mechanically coupled be given a narrow interpretation so that it means a connection which allows no relative movement between the connected parts and thus the definition eX- cludes such couplings as gear trains or mechanical linkages.

Our invention comprises a high speed voltage stabilizer which has a wide regulating range and a short, substantially constant response time which is substantially independent of the magnitude of the unbalance.

This stabilizer includes an unbalance detector which is adapted to control the movements of a D. C. motor whose total angular range of rotation is restricted to less than 360 and is directly mechanically coupled to the ratio varying arm of a variable ratio transformer, controlling the output voltage of the stabilizer.

Very high transitory torques may be obtained from the D. C. motor and the detector and control circuit are adapted over a wide unbalance range to cause a torque which varies with the magnitude of the unbalance. The time required for the coupled motor and transformer to effect the correction of an unbalance is very short and is nearly constant since the larger the unbalance the more rapid the movement of the motor to correct it.

A D. C. moving coil meter type of movement provides a motor which is ideal for direct mechanical coupling to a transformer whose ratio is controlled by the rotation of a radial arm. Such as that known by the trade name Variac. The angular range of rotation of such a motor may be made to correspond .to that of the variable ratio transformer with which it is used. Direct mechanical coupling between the motor and transformer provides a linkage of low inertia and is free from the inherent disadvantages of gear trains which have been commonly used heretofore. Conventional D. C. motors are not suitable for this invention because: brushes and commutators introduce drag and magnetic locking of field and armature produces positional inaccuracies.

It is belietved that the use of an unbalance detector producing a D. C. output signal such as the D. 0. bridge described hereafter is a part of the preferred apparatus for putting the invention into practice, although other detecting means may be employed.

In order to eliminate hunting in the stabilizer, arachometer generator is directly coupled to the motor and its output is fed back into the control circuit.

When a D. C. bridge is used a cascade network connected to the output of the bridge reduces :thetime vco'nstant of the detector. I

An illustrative embodiment of the invention is described hereinafter and shown in the accompanying drawings in which:

Figure 1 shows a block diagram of the control circuit.

Figures 2a and 2b show the control circuit in detail.

Figures 3 and 4 show the phase and amplitude relationship respectively of voltages controlling the thyratron.

Figures 5 and 6 show cross sections of a type of motor input side of-terminal 101.

2 which may be used in the circuit and Figure 6 is taken along the line 66 of Figure 5.

Figures 7-10 show another-embodiment of the motor.

In the block diagram of Figure l is shown the overall arrangement of the voltage stabilizer wherein parallel line conducting systems are, for simplicity, represented by a single line and the control signal system is distinguished by utilizing such lines terminated in arrows, which indicate the signal direction. A power line is represented as Ill-4.1, the input end being designated at 10 and the output end being designated at 1!. Situated on this line is a mechanically operated, transformer voltage correcting system indicated at 20. To the output side of the voltage correctin system, the line 10-11 is tapped at 101 to supply voltage to a plate power supply 30 and to a filament and field power source 40. The line output voltage is proportional to that voltage appearing at terminal 461 of the power source 40. The voltage at terminal 401 is applied to a D. C. detector bridge 56 which is adapted to operate in such a way that when the voltage at 461 is not at the desired value, and therefore the voltage 11 is not at the desired output value, the bridge supplies a signal output which varies linearly, and in the correct sense, with the error in the line voltage at 11. This voltage is applied to a phase inverter system 6% and the output is applied to a thyratron armature control system 70. This system acts as a control switch for the power supply ltll-Jfil-JtlZ-dtll to the armature windings of the D. C. motor shown at 80. The motor is directly mechanically coupled to the voltage correcting system 20. The armature control system 70 acts to allow power to be ap plied to the motor along the line lll1 70l-702-801, to cause the motor to rotate in such a manner as to correct the voltage error of the line through correcting system Zil. The system so far described may be improved by the addition ofa damping feedback circuit. The motor 89 has a common armature shaft with generator 90 whose output is amplified by the amplifier system and fed back into the armature control system 70 in such a man ner as to oppose the direction'of rotation of the motor. This system supplies adequate damping action for the motor. The plate power supply 3% supplies an output which is applied to the detector bridge 5%, phase-inverter system 60 and to amplifier Sill-ii. The filament and field power supply as supplies rectified field. current to the D. C. motor 8d through rectifier 4G2, and supplies field current to the generator 90. Filament current is supplied by supply 40 to detector bridge 50 (as previously described), phase inverter 6%), thyratron armature control '70 and amplifier 100.

There is now disclosed specifically a circuit which embodies the system disclosed above'. Reference may be had to Figures 2a and 2b which are complementary but are thus broken up in the interests of clarity.

In Figure 2a is shown power line ltlll the mechanica'lly operated voltage correcting system 26, motor 80 and generator 90. In voltage correcting system 29, autotransformer 2 32 is connected across the power line on the A transformer 293 has its secondary connected in series with one of the conductors of the power line and its primary connected to the output contactsof the auto-transformer 102. Output contact 205 is fixed while contact 204 is adapted to travel on both sides of it. Thus the travel of the movable terminal on transformer 292 causes transformer 203 to buck or boost the line input voltage to the desired amount. In the circuit herein shown the transformer 203 is adapted to buck or boost the input voltage by approximately 10% .of the line voltage. The variable contact arm is directly mechanically connected to the motor shaft. Motor 80' has armature connect-ions 801a and 802a and field connections 803a and 804a for field coil 805. The mechanical construction of the motor will be described in more detail hereafter. The motor shaft is directly mechanically connected to the variable contact 204 as shown schematically by the dotted line 201--206. The motor armature connections will be more fully discussed hereafter in relation to the thyratron armature control 70. The motor is protected by ganged switches 818 and 819 and fuses 834 as shown in Figure 10.

Generator 90 has field winding connections 801, 802 and power output connections 803, 804.

Connected across the line -11 is voltmeter 104 and in series therewith is a switch 105 which allows the volt age on either the input or output side of transformer 203 to be measured, while in series with the power conductor containing the output winding of transformer 203 is an amrneter 124 which measures the line output current 20.

Also connected across the line 10-11 are the control circuit terminals 106 and 107. These are connected on the output side of the voltage correcting transformers 202 and 203 whereby the output voltage is measured and controlled so that errors in the control correction may be compensated by the control circuit itself and so that the various power source of the control circuit will be at a steady voltage.

Circuit breakers 108 and 109 are connected in line 1011 in series with transformer 103. Fuse 110 and switch 111 are connected in series with control circuit terminal 106.

The control circuit which includes elements 30, 40, 50, 60, 70 and 100 is shown in Figure 2b. Terminals 106 and 107 supply power for filament supply which in turn supplies powers to the various filaments through transformer 302 and transformer 403, 404, and 405'. The field supply for the motor 80 is also obtained from terminals 106 and 107 through rectifier bridge 402.

Filament supply for generator amplifier system 100, rectifier 301, and phase inverter 60 is obtained from secondary winding 406 of transformer 302 while filament supply for the sensitive electronic element in the detector ridge is obtained from secondary Winding 407 of the same transformer. filament voltage to rectifier elements in the thyratron system 70. The terminals 106 and 107 are connected to two opposed terminals of the rectifier bridge 402 while the motor field winding terminals 803a and 804a are connected to the other two opposed terminals.

Connected to the main output winding 303 of the transformer 302 are the twin anodes of the full wave rectifier tube 304 of rectifier system 301. The winding 303 is centre-tapped and the line connected thereto forms the negative supply voltage for the control system as a whole. The output of the rectifier tube 304 is filtered in the cathode circuit by the choke coil 305 and the condenser 306 and is then applied to the plates of amplifier system 100, phase inverter system 60 and detector bridge 50.

An attenuating circuit composed of variable resistors 307 and 308, fixed resistor 309 and condenser 310 supplies voltage to terminals 311 and 312 through a transformer 313 for a purpose to be specified hereinafter.

The detector bridge 50 is composed of a temperature limited diode 501 and voltage reference tube 502 forming two arms and connected to the cathode reference voltage. The other two arms of the bridge are connected to the plate reference voltage and are composed of resistance 503 on the one hand and resistance 504 in series with condenser 505 on the other hand. The condenser 505 is in parallel with the secondary of transformer 313. Connected across the bridge is resistance 506 there being a variable contact 507 which is adjustable to vary the resistance value on each side of the contact. Between the variable contact 507 and the arm of the bridge containing diode 501 is connected a condenser 508.

Before continuing with the description of the circuit as a whole, it is proposed to explain the operation of the bridge, whose elements have just been referred to, in detail.

Transformers 403 and 404 supply The temperature limited diode 501 is the detector element of the bridge. The suggested tube is either a Sorensen 2ASl5 or a Westinghouse R0585. The plate current of this tube varies with filament voltage, but only slightly with plate voltage (Rp:4 to 7 meg). In operation the tube may be considered as a resistance varying approximately linearly with filament voltage. In the bridge 50 the voltage reference tube 502 is used as a balanced reference for the tube described above. The output of the bridge as a result of unbalance in the diode 501, is taken at 507. The value of resistance on the detector side of contact 507 is from 10 to 15 times the resistance on the reference side, depending on the setting of contact 507 on the resistance 506. Operating with such a large attenuation factor allows the condenser 508 to be connected as described to form a cascade network which effectively reduces the time constant of the detector by a factor of about 10.

The diode 501 is a square law detector and the ripple is large, and depends on the speed of response of the detector. In the embodiment described herein, the peak ripple value is about 20% of the D. C. plate voltage. In order to eliminate this ripple as far as possible the output of transformer 313 is connected across condenser 505 as heretofore described, with resistance 308 being adjusted to equalize the ripple and bucking voltages and resistance 307 and capacitance 310 being adjusted to give the desired phase shift.

The output signal from the bridge contact 507 is subjected to amplification and phase inversion in phase inverter system 60. The tube used is a cathode coupled phase inverter 601 composed of twin triodes 602 and 603. The grid of triode 602 is connected to the detector bridge as shown so that the grid voltage is held constant with respect to the cathode reference voltage by the voltage reference tube 502. The output of the bridge from contact 507 is applied to the grid of tube 603. The tubes have a common cathode resistance 604 and have plate resistances 605 and 606 respectively. The circuit including bridge 50 and inverter system 60 is so adjusted that for a balance condition the plates of triodes 602 and 603 are at equal potential and are constant with respect to the cathode reference voltage no matter what the plate reference voltage is. The advantages from this arrangement will be discussed hereafter in connection with the thyratron armature control 70. The tube 601 must have a high gain and in the embodiment disclosed a 6SL7 was used. Such a circuit is described in detail in Electronics, November 1943, by Walter Richter. The output of the phase inverter contains a large 240 cycle ripple at the plates of tubes 602 and 603 remaining after the elimination of the 120 cycle detector ripple at condenser 505. This is filtered by parallel T networks 607 and 608 respectively between plates and ground. Network 607 is composed of resistances 609, 611 and 613 and capacitances 615, 617 and 619 while network 608 is composed of resistances 610, 612 and 614 and capacitaces 616, 618 and 620. The point of symmetry 621 of the network is grounded at 622 while their output is taken at 623 and 624 respectively.

A coupling network 703 couples a phase shifted portion of the line voltage, obtained from terminals 106 and 107, in series with the output of the phase inverter system, obtained from terminals 623 and 624. The line voltage component is added in series by means of transformer 718 whose secondaries 704 and 705 are in the output circuits of terminals 623 and 624 respectively. A phase shift of the line voltage is obtained from condenser 706 and resistance 707, in conjunction with resistances 719a and 720a, while the resistances 70S and 709 in series and parallel respectively with the primary winding of transformer 703 arbitrarily fix the amplitude of the transformer output voltage. It has been found that the amplitude of this phase shifted voltage affects the gain of the voltage regulator system as a whole, a decrease in the amplitude acting to increase the gain. The amplitude should not be allowed to become too small since the thyratron operation will become erratic and aifect the accuracy of the stabilizer. 1n the circuit disclosed specifically herein, the lower limit for this amplitude is ten volts.

The thyratron armature control utilizes a symmetrical system having thyratrons 710 and 711 respectively whose cathodes are each connected through parallel diode-resistance networks to a common grounding lead at 712. The control grids of thyratrons 710 and 711 are connected to the windings 704 and 705 respectively to receive the respective combined outputs therefrom. The plate circuit of thyratron 710 includes secondary 801 of the armature supply transformer 103 and the armature winding of the motor. The plate circuit of the thyratron 711 includes secondary 802 of the armature supply transformer 103 and the armature winding of the motor. Connected to the cathode of tube 710 is one end of the motor armature windings and a parallel resistance-diode network 713 composed of resistances 714 and 715 and diodes 716 and 717 connected as shown. The diodes are usually combined in a tube such as the 6AL5. The other end of the network 713 is connected to commongrounding lead 712. The diodes supply what is almost a short circuit in parallel with the resistors when the voltage at 712 is positive with respect to cathode and are open circuited when the polarity is reversed. symmetrically in the thyratron system 70, between the cathode of tube 711 and 712 is a network 717 composed of resistances 719 and 720 and diodes 721 and 722 so that the diodes form a short circuit when the lead 712 is positive with respect to the cathode and an open circuit when the polarity is reversed.

Resistances 723 and 724 are included in the respective screen grid circuits in order to attenuate the current flow therein.

It will also be noted that the motor armature and the symmetrical resistance-diode network form a closed circuit which will be discussed hereafter.

It will be seen from observation of the circuit just de scribed that the A. C. component of the thyratron grid voltages obtained from windings 704 and 705 causes the thyratrons to fire alternately allowing plate current to flow therein so that armature current is supplied to the motor. The armature terminals and the secondaries .801 and 802 are so arranged that the secondaries 801 and 802 tend to give opposite rotation to the motor. In the balanced condition, it is arranged that both thyra'trons are firing slightly and there is an equal impulsion to move in either direction. This vibration efiect prevents static friction between the transformer arm and the coils of the transformer 202 and prevents a consequent inaccuracy in the reaction. However, on the occurrence of an unbalance in the line the D. C. component of the grid signal applied to one of the thyratrons is raised due to the output of phase inverter system 60 while the other is lowered. This causes the appropriate thyratron to tire for a longer period than the other, and with the circuit adjustment herein disclosed, for any substantial unbalance, the other thyratron will not be firing at all due to the setting of the balance D. C. grid level. This balance is such that when any substantial lowering of: the grid of the second thyratron due to the signal from the opposite grid, will act to prevent the firing of the thyratron and therefore the armature current of the motor will only be flowing in one direction. The motor therefore turns and through the rotation of shaft 204801 causes a correcting voltage to be applied to the line to remove the unbalance. The removal of the unbalance removes the asymmetry from the thyratron action so that the motor, having completed its correcting, stops.

The operation of the diode-resistance networks 713 and 717 will now be discussed. Networks 713 and 717 work in conjunction with thyratrons 710 and 711 respectively.

6 Suppose that thyratron 710 is firing. At such a time its cathode is positive with respect to the grid, but as the currentcuts off, the inductance of the motor causes a negative voltage at the cathode of 710 which decays for the next half cycle unless clipped by network 713. For successive firing of thyratron 710 a back E. MsF. is built up in motor 80 as the armature picks up. speed, this back E. M. F. causes the cathode of 710 torise with respect to the grid thus tending to reduce the firing interval and therefore the interval of application of armature current to the motor. The short across network 717 at this point, ensures that the full back E. M. F. is applied to thecathode of 710. The use of the networks .hasbeen found to assistpin damping the motor operation in .the case. where the line unbalance is causedby a step change in voltage. The damping effect of. the network when there is a cyclical unbalance is doubtful and its value seems to be chiefly in'connection with step changes.

There is a voltage range switching for the regulator provided, by double pole triple throw switch 112 which controls the .thyratron cathode voltages and the detector tube filament current; The switch 112 controls the D. C. grid level of the thyratrons with respect to the phase inverter plates and therefore the relative voltage between grids and thyratronsof tubes 710 and 711 respectively by means of resistances 113, 114, 115 and 116 and this level controls the time of firing angle of the thyratrons at balance. Fine adjustment for this control setting is obtained by potentiometer 117 in series with the resistances. The detector tube filament current is controlled by switch 112 through an attenuation system composed of resistances 118 to 121 while potentiometer 122 allows for the fine adjustment of the attenuator. The resistances and potentiometer may be so arranged that the filament current is the same for three different desired voltages, the control switch 112 setting the correct resistance combination, and potentiometer 122 allows for interpolation between the three range systems. 'It is thus seen that the value of the voltage to be maintained may be switched without causing any unbalance in the bridge, since the attenuation system is adapted to keep the bridge conditions the same regardless of the voltage input thereto.

The D. C. current from the thyratrons 710 and 711 varies linearly withD. C. grid signal over the most useful range. The non-linear effect as the firing approaches 0 is overcome by having the balance condition in the thyratron system with both thyratrons firing slightly. Such a balance is obtained at all settings by proper adjustment of the potentiometer 117 and proper selection of the resistances 113 to 116. i

In order to provide adequate damping for the system a rate generator is attached to the shaft of the motor 80. This generator receives its field supply at terminals 301 and 802 from transformer 405 and its output is taken at terminals 803 and 804.

This output is applied to amplifying system as shown across a filter condenser 1003 in parallel with resistance 1004 and potentiometer 1005. The amount of damping feedback is controlled by the setting of potentiorneter 1005, the amplifying system utilizing a twin triode connected for amplification.

It will be noted that the plate voltage of the amplifier stages is controlled by the selection of resistance 1014 while capacitance I015 supplies a grounding filter to eliminate ripple and surge voltages from the amplifier plate supply.

The first stage of the feedback amplifier uses cathode resistor 1012 having condenser 1006 serving as an A. C. ground and plate resistor 1007. The output of the first stage is applied from the plate through blocking condenser 1008 to the grid of the second stage, which is grounded through resistance 1009. In the circuit of the second stage is cathode resistor 1010. The amplifier output is applied to transformer 1011 and the output is applied between ground 622 and grounding lead 712 so that the effect of the generator output is to vary the level of the thyratron cathodes with respect to the grids so that the time of firing is affected in such a way as to oppose the direction of motor travel, as shown in Figure 3 and Figure 4.

In order to ensure that the control circuit is in full operation before the motor begins to operate a thermal delay relay 123 is placed in series with the primary of transformer 103 so that armature current cannot fiow to the motor until a set time after the control circuit is witched on. The relay is operated by current from the output of transformer 408.

Since the speeds involved are low (the maximum velocity being equivalent to a few hundred R. P. M.) a generator having a small positional error should be used. The drag cup type rate generator is the most suitable because of the convenience in coupling the A. C. signal to the desired part of the circuit.

in selecting a model it was found that the 60 cycle varieties had too much positional error. Therefore a 400 cycle type operated at 60 cycles with reduced voltage is used and is coupled to the amplifier system as disclosed above.

Figure 3 shows the phase relationships of the thyratron voltages while Figure 4 shows the same voltage amplitudes plotted against time.

The circuit constants and tube types of the circuit above described are tabulated below:

SS-Variac driving motor N.R.C.

90-Rate generator Bendix CK-Z HB-Hammond 710 special (separate secondaries) lM-Simpson voltmeter-l50 v. 105-Microswitch-BZ2RQ1 IQS-Heineman circuit breaker AMl2-25 amp. 109-Heineman circuit breaker AMl2-25 amp. ill-Toggle switch 112-Mallory 3123] 113-47k 114-2.7k 115-271; 115-150-2 watt wire wound 116-1 meg. i17-50k wire wound 3 watt 190-532 ll9-l0-4.8 watt wire wound 120-.7-1esistance wire #32 Cromel 121-.7 resistance Wire #32 Cromel 122-2k wire wound 4 watt 190-514 MES-Edison thermal delay-Model 501 I'M-Simpson ammeter-0-25 amp. Mil-General Radio Variac V-S 203-Hammond 23777 57.5- v. 207-Pilot light-mounting-dialco PLNS49-85410 bulb Sill-Hammond 270B Sim-6X4 MES-Ham. choke 154 306-2-lO f.-450 v. 307-.l #f.200 v. 307-200 wire wound 4 watt 190-508 303-201; wire wound 4 watt 190-524 309-k-2 watt 312-.005 ,lLf.6UO v. 313-Harnmond 330 402-Rectiiier bridge-Federal .3 amp. 103B5SCLX1 Wis-Hammond 167C irth-Hammond 167C 405-Hammond 167k SUI-Sorensen 2AS15 502-5651 503-47k 504-1 meg.

609-2-100k-in series 610-2-100k-in series 611-1001;

612-1001; 613-2-100k-in series 61'4-2-lO0k-in series 615-3300 int-mica 616-3300 uni-mica 617-6600 #411. combine 2-3300 ,uptf. 618-6600 #111. combine 2-3300 muf. 619-3300 i-mica 620-3300 uni-mica 706-.5 f.-600 v. 707-l0k-2 watt 714-22k-2 watt 715-22k-2 watt 716-6AL5 718-Hammond 333 719a4.7k-2 watt 719-22k-2 watt 720a-4.7k-2 watt 720-22k-2 watt 72i-6ALS 725-2500 ,unf. mica 801a-Microswitch-B2RSTC 802a-Microswitch-B2RSTC 1001-6SL7 1003-.1 nfi-ZOO v. 1004-4.7k

1005-5k wire wound 4 watt 190-520 1006-25 f.-25v.-246006 1008-5 ,Lbf.600 v. 1009-1 meg. 1010-1.2k Hill-Hammond 332 1012-47 k 10142.7k-2 watt HHS-Second section of C1 In Figures 5 and 6 are shown a motor construction suitable for use in the circuit already described. As best seen in Figure 5 the static portions comprise an annular magnetic inner ring 806 and an annular magnetic outer ring 807 concentric therewith connected and supported by magnetic side, base and centre members 803, 809 and 810 respectively and a field coil 811 which surrounds centre member 810 and lies adjacent the side members 808. There is therefore an annular air gap of uniform size between rings 806 and 807 and in this gap moves the armature coil 812. The coil is mechanically mounted on a hollow spindle 813 and the coil and spindle are adapted to rotate together and therefore the axis of the spindle is made the centre of curvature of the annular air gap. Mechanical means (not shown) are provided to limit the extent of rotation in either direction so that the armature coil 812 does not contact the centre member 810, and this limiting permits a total extent of rotation of about 270. The spindle is mounted on support members 814 for rotation.

Causing the magnetic field and the polarity of rings 806 and 807 is field coil 815 which surrounds the centre member 810, passes between this member and side memher 808 and rests on base member 809. The leads 816 and 817 for the armature coil are brought out through the hollow spindle 813 and connected to switches 818 and 819 shown in Figure 2b. These switches are ganged and adapted to switch the armature supply coils 801 and 802 out of the circuit when so desired. The leads from the field coil 815 (not shown) are connected to terminals 803, 804 as shown in Figure 2:1.

It will be noted that one of the advantageous features obtained by using a motor with approximately a 270 movement is that this extent of rotation corresponds approximately to the full voltage sweep on the Variac transformers at present in use. That is, the full movement of a Variac arm is about 270 to run through the whole range of output voltages possible with the Variac, and it is therefore possible, as shown herein to directly mechanically couple the shaft of a motor of the type disclosed, to the Variac and to obtain the advantages of low inertia discussed heretofore. There are also substantial advantages to the simplicity of design and construction and the reduction of frictional effects on the motor operation. Also directly mechanically coupled to the motor spindle is the rate generator 90 which is not shown in detail since its construction is well known, although a schematic diagram of one of the possible motor-generator-Variac arrangement is shown in Figures 7 to 10, wherein an alternative form of motor which has a more uniform field is shown.

The motor has an inner pole member 822 having a cylindrical exterior and a crescent shaped outer pole member 823 whose concave surface is cylindrical and adjacent to and concentric with the exterior surface of member 822. An outer ring 824 forms the magnetic path between these members and this is connected to inner pole member 822 by core connector 825 and to outer pole member 823 by core connector 826. The core connectors are each surrounded by field coils 833 having the general shape of a vertical annulus and in this connection attention is particularly directed to Figure 10 where the general field coil arrangement is shown in perspective. It will be noted in Figures 7 and 8 that the outer pole member is shaped so as to complement the coils in filling the annular area between the annular air gap and the outer ring.

Referring now to Figure 9 it is seen that armature coil 827 is mounted on a spindle 828 to move in the annular air gap and that the coil leads 829 are led into the armature through the hollow centre of the spindle 828. C- operating rollers and roller arms 830 and cams 831 actuate switches that open the motor circuit to limit the extent of the motor spindle rotation so that armature coil 827 does not contact core connector 825. Concentrically mounted with the motor spindle, is a standard Variac 832 and attached to the motor spindle 828 is the arm 829 of the Variac 202 (see also Figure 2a) which mechani cally effects the voltage correction shown at 20 of Figure l. Leads 829 are connected to switches 818 and 819 in Figure 2b, while the field coil 833 is connected by leads (not shown) to terminals 803 and 804 of Figure 201.

As herein shown a rate generator 902 is for convenience mounted inside the Variac coils and its armature is connected to the motor spindle 828 to rotate therewith. There is of course, no necessity of mounting the generator inside the variac but if the relative sizes permit, it contributes to the compactness and simplicity of the device.

In both motor types above described the armature coil is wound on a form, the coil then treated to give it mechanical strength and the form removed. This formless coil has a very low inertia and allows the motor a very rapid response time.

The specifications of the regulator described in detail above and using the last described motor are as follows:

Voltage (out)settings 110-115-120 v. Voltage (in)-output setting 10% Current-amps. max.

Accuracy0.1% (not considering drift due to tube aging or effects of a considerable variation in ambient temperature) Speed of response-98% correction in .10 sec. for a step change up to 5 volts Stability-20% overshoot for a step voltage change Weight of regulator-450 1b.

It is seen that there is herein described in general a voltage regulator designed to have wide linear range of response and a rapid response time and described in detail an apparatus which meets these requirements.

We claim:

1. A high-speed voltage stabilizer for an alternating current supply system comprising, a source of alternating current, a variable output transformer energized by said source and having a ratio-varying arm, a direct-current meter-type motor having a moving-coil armature directly mechanically coupled to said ratio-varying arm to vary the ratio of said transformer, said armature coil having a pair of flexible leads for conducting current thereto throughout its range of movement, a pair of grid-controlled rectifiers, a first armature energizing circuit energized from said source through one of said rectifiers and tending to rotate said armature in one direction, a second armature energizing circuit energized from said source through the other rectifier and tending to rotate said armature in the opposite direction, a voltage-sensitive circuit responsive to the voltage at the output of said transformer and producing a signal varying according to the degree of unbalance between the transformer output voltage and a desired output voltage, and means including circuit connections from said voltage-sensitive circuit to the grids of said grid-controlled rectifiers for rendering one of said rectifiers effective to operate said motor in one direction in response to a change of output voltage from said desired value in one direction, and for rendering the other rectifier effective to rotate said motor in the opposite direction in response to a change in voltage from said desired value in the opposite direction.

2. A high-speed voltage stabilizer for an alternating current supply system comprising, a source of alternating current, a variable output transformer energized by said source and having a ratio-varying arm, a direct-current meter-type motor having a moving-coil armature directly mechanically coupled to said ratio-varying arm to vary the ratio of said transformer, said armature coil having a pair of flexible leads for conducting current thereto throughout its range of movement, a pair of gridcontrolled rectifiers, a first armature energizing circuit energized from said source through one of said rectifiers during alternate half-cycles thereof and tending to rotate said armature in one direction, a second armature energizing circuit energized from said source through the other rectifier during the remaining half-cycles thereof and tending to rotate said armature in the opposite direction, means applying equal biasing voltages to the grids of said rectifiers to effect energization of said armature equally by said energizing circuits, and means including a voltage-sensitive circuit responsive to the voltage at the output of said transformer and being responsive to an increase in output voltage above a desired value to increase one of said biasing voltages and decrease the other, and responsive to a decrease in output voltage below said desired value to vary said biasing voltages in the opposite sense.

References Cited in the file of this patent UNITED STATES PATENTS 1,985,927 Jansen Ian. 1, 1935 2,095,234 Adair Oct. 12, 1937 2,239,768 Artzt Apr. 29, 1941 2,380,784 Patin July 31, 1945 2,453,451 Moseley Nov. 9, 1948 2,504,017 George et a1. Apr. 11, 1950

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