‘Sept. 10, 1946. ’ ' ' F. E. CREVER ELECTRIC 2,407,476 CIRCUIT ' Filed June 6, 1944 w“ Figl. nnju J . _ I Inventor: Frederic-k E.Cr~ever~, by ri?e, Attorney. - Patented Sept. 10, 1943 25,407,476 UNITED STATES PATENT OFFICE 2,407,476 ELECTRIC omourr Frederick E. ‘Crever, Scotia, N. Y., assignor to General Electric Company, a corporation of New York Application June 6, 1944, Serial No. 538,933 1 8 Claims. This invention relates to electric circuits and more particularly to improvements in automatic polyphase alternating-current regulating circuits. It is often desirable to provide the main con (Cl. 171-223) 2 line conductors I, 2 and 3 and to a common neu tral point 8. The alternator 4 is provided with a direct-current ?eld winding 9 which is energized .by the armature voltage of a direct-current ex citer Ill. The excitation of the exciter I0 is controlled by a bucking ?eld winding II which is energized in accordance with the voltage of the main al trol element of regulators for polyphase circuits with polyphase voltage response and also with line current response. The latter response is usu ally for obtaining line drop compensation or cir culating current compensation in case of parallel ternating-current circuit in the manner which operation. In accordance with a principal fea will now be described. ture of this invention there is provided a novel 10 Connected across the main alternating-current and simple network fOr obtaining from a poly circuit is a T~connected potential transformer phase circuit a single-phase voltage which is pro I2, the primary of which has its main winding portional to the positive phase sequence compo I3 connected across conductors I and 2 and has nent of the voltage of the polyphase circuit. This single-phase voltage is in quadrature with the 15. the teaser winding I4 connected between line con ductor 3 and the mid-point of main winding I3. current in one of the lines of the polyphase cir The voltage of teaser winding I 4 is, of course, cuit at unity power factor of said circuit. This .866 times the voltage of main winding I 3 so network is made extremely sensitive to changes in regulated voltage by means of a saturated re actor, which, however, introduces a frequency error. In’ accordance with another feature of that the voltages between the two terminals of main winding I3 and the terminal of teaser wind ing I4 are all equal and all displaced 120 degrees. The secondary of potential transformer I2 dif fers from the ordinary three-phase to two-phase T-connected transformer in that the two phases 25 of the secondary do not have equal voltages and and improved electric circuit. the phase I5 which is excited by the teaser wind Another object of the invention is to provide ing I4 has twice the voltage of the phase I6 a new and improved symmetrical phase sequency Which is excited by the main winding I3, and this segregating network. latter half-voltage winding is connected to the A further object of the invention is to provide mid-point of the full-voltage winding of the sec a novel highly sensitive frequency compensated ondary so as to form a T connection. Serially positive phase sequence responsive regulator con connected across the high-voltage secondary trol circuit. Winding I5 are a resistor I1 and a reactor I8 An additional object of the invention is to pro vide a new and improved automatic regulator 35 which have equal ohmic values at the normal fre quency of themain circuit; that is to say, the system. reactance inohms of the reactor I8 is numerical The invention will be better understood from ly equal to the resistance in ohms of the resistor the following description taken in connection with ll. Consequently, the voltage between the junc the accompanying drawing and its scope will be tion point I9 of the resistor and the reactor and pointed out in the appended claims. . 40 the point 20 where the windings I5 and I6 are In the drawing Fig. 1 is a diagrammatic illus interconnected is equal to one-half the voltage tration of an embodiment of the invention which is provided with a pair of differentially-acting , of the winding I5 and is therefore equal to the voltage of the winding I6. Thus, the voltage be control windings and Fig. 2 is a modi?cation tween I9 and the free terminal of the which provides a novel circuit for differentially 45 windingtheI6point will be either twice the voltage of energizing a single control winding. the winding IE or will be zero, depending upon Referring now to Fig. 1 of the accompanying whether the voltage between the points I9 and drawing, which illustrates diagrammatically an 20 is in phase with or in phase opposition with embodiment of the invention as applied to an automatic three-phase generator voltage regu 50 the voltage of the winding It‘, and this depends upon the phase rotation of the main circuit. The lating system, there is shown therein a main main circuit is assumed to have 1—2—-3 phase regulated three-phase alternating-current circuit rotation and with this phase rotation the voltage comprising conductors I, 2 and 3. This circuit between the point I9 and the free terminal of is energized by an alternator 4 having phase wind the Winding I6 will be twice the voltage of the ings 5, 6 and 7 connected respectively to the 55 the invention, novel frequency compensating means is provided for the circuit. An object of the invention is to provide a new winding I 6 so that the voltage between these 2,407,476 it points will be a measure of the positive phase se quence voltage of the main circuit in that it wil disappear for negative phase sequence voltages. If the main circuit has the opposite phase rota tion, network will respond to the negative resonant circuit connected across the resistor ll. As shown, this consists of a capacitor 32 and a reactor 33 in the form of a step-up auto~ transformer. These devices are tuned to res chance at the normal frequency of the system so that they have extremely high net reactance phase sequence voltage of the circuit. and do not vaffect the operation of the circuit Point IE5 is connected to one of the input ter at normal frequency. However, if the frequency minals of a full-wave recti?er 2i and the free departs from normal, then the frequency corn terminal of winding it is connected to the other input terminal of the recti?er 2!. The direct 10 pensating circuit is no longer resonant and the departure from resonance compensates for the current output terminals of this recti?er are conchange in voltage held by the saturated reactor nected to the bucking control field winding l l for so that even though the reactor saturates at a the eXciter It. different voltage dependent upon the frequency, The exciter it‘ is provided with a series wind~ ing 2?; which is sufficiently strong to cause it to 15 the primary voltage maintained is independent of frequency. The action of the frequency com~ self-excite and build up to its ceiling voltage. pensator produces no substantial shift in phase However, before it can reach its ceiling voltage, the output voltage of the positive phase se the voltage of the alternator will reach a pre quence network over an appreciable range or vari 1eterrnined normal value at which the ampere ation in frequency. turns of the bucking winding l i will be suf?cient Hunting of the system is p ‘evented by an anti ly strong to limit further increases in excitation hunt control winding for the exciter which voltage of the exclter. The exciter is also is energized through a stabilizing transformer 35 preferably a high-speed high-ampli?cation ma whose pil .' ing is connected across the chine, such as an amplidyne which is provided armature of the exciter. When desired, manual with cross armature reaction excitation as de control of the volt-age of the exciter, and hence of scribed and claimed in Patent 2,227,992, granted the alternator, may be obtained. by closing a January 7, 1941, on a joint application of M. A. switch which connects the anti-hunt winding Edwards and E. F. W. Alexanserson and assigned across the armature of exciter it] through a to the assignee of the present application. In order to increase the sensitivity of the buck 30 manually operable rheostat El, thus providing shunt ?eld rheostatic control. ing ?eld circuit and also to decrease the peak The operation of. most of the elements of Fig. 1 inverse voltage on rectifier 2i, capacitor 23 is 135 already been largely covered in connection connected across bucking ?eld ll. Resistor 21’! with the above description. In general, if the has a high value and its purpose is to prevent 35 alternator and the exciter are being driven at spurious oscillations. rated speed by a suitable prime mover, or prime The sensitivity of the regulator system is in movers, and if the switch is open, the system creased by connecting a saturated reactor ‘25 in will maintain the voltage of the output circuit series with the input terminals of the recti?er l, 2, substantially constant at a value deter 2 I. The voltage drop through the impedance net mined by the adjustment of the saturated reactor work which supplies the rectifier 2| is reduced 25 for wide variations in load and power factor to a minimum by means of a series capacitor and for appreciable variations in speed. Thus, 2% so that the current in the winding H which any decrease in voltage will cause the current is supplied by the impedance network produces in the bucking winding to decrease more rapidly, a minimum amount of voltage drop in the cir— that is, by a larger percentage, than the current cuit through which it flows. decreases in the boosting winding, thus decreas A boosting ?eld winding 2'4 and recti?er 2:13, ing the net bucking ampere-turns of the two ?eld which is connected across the output of the posi windings allowing the series ezrciter to build tive phase sequence network before it goes up to a higher voltage and thus to restore the through saturated reactor Eli, are interconnected by wire 22 for the purpose of preventing polarity 5 O voltage of the main circuit to normal. Simi larly, an increase in voltage of the main circuit reversal. of the exciter and to supply additional will increase the bucking ampere turns faster speed of response in the boosting direction. than it increases the boosting ampere turns so The output voltage of the positive sequence that there is a net increase in bucking ampere network being in phase with the voltage of wind turns and the voltage of the exciter is conse ing which in turn is in phase with the volt quently reduced. age of winding it, is in quadrature with the volt The positive phase sequence response of the age of phase l of the armature of the alterna system insures that the action of the regulating tor ll so that it will be in quadrature with the system will be in the proper direction regardless current in the line 3 at unity power factor oper ation of the alternator it. Therefore, when a sim 60 of how unbalanced the voltages of the three phase circuit are. ple resistor to is connected in series with the output of the positive phase sequence network and current is circulated through it from a cur rent transformer Si in line 3, the voltage drop in the resistor 39 will be in quadrature with the voltage of the positive phase sequence network during unity power factor conditions. This volt age will then add or subtract from the positive phase sequence network voltage depending upon whether the line current is leading or lagging and thus circulating current compensation may readily be obtained when the generator 4 oper ates in parallel with other generators. The control circuit is compensated for vari ations in input frequency by means of a parallel In the modification shown in Fig. the opposed ?eld windings Z] and M of Fig. l are replaced by a single control ?eld winding 38 which is energized by a differential current obtained from recti?er El and a recti?er 39 which is energized from an auxiliary current source in the form of a small alternator The output terminals of the rectifiers 2i and 39 are connected with addi tive cumulative polarity in a closed series cir suit and the winding is connected across this circuit. As long as the output currents of the two recti?ers 2! and 359 are equal, the control winding 38 will be deenergized, but as soon as the output currents of the recti?ers become un 2,407,476 5 6 equal, the controlwinding 33 will carry the dire fercnce betWeenthe output currents of the two fora-it isaimed in-the appended‘. claims to cover recti?ers and this di?'erence current will ?ow the-true,spiritand'scope of the invention; all such changesand modi?cations as fallwithin in opposite directions depending upon which rec ti?er has the greater output current. Current limiting resistors 4| and 42- are con nected in the input side of the recti?er 39 and in the common series circuit for the outputs of. both recti?ers and also a smoothing reactor 43 is connected. in the latter circuit. ' - / What I .claim as new and desire to secure by Letters Patent of the United States is: 1. A symmetrical phase sequence network comprising, in combination, a T-connected trans~ former having a three-phase primary winding and a two-phase secondary winding, one of the 10 phases of said secondary winding having half the .Due to the extreme sensitivity of the circuit voltage of the other and having one terminal resulting from the saturation of the reactor 25, thereofconnected tothe mid-point of said other small variations in voltage of the alternator 4h phase, a»resistor and an equal ohmic value re will-have very little effect on the regulated out-put actor-connected in series across said other sec voltage of the main alternator 4. 15 ondary phase,» and output terminals connected The operation of Fig. 2 is generally the same respectively to the free terminal of the lower as that of Fig. 1 in that the. circuit is so adjusted voltage secondary phase and to they junction of that, at normal voltage of the’ main alternator the saidresistor and reactor. ~ > ' l difference in output currents of the recti?ers 2| 2. A symmetrical phase sequence network and 39 will energize control winding 38 with the 20 comprising, in combination, a T-connected trans proper amount of current to provide the neces former having a three-phase primary winding sary excitation for the main alternator. If now and a two-phase secondary winding, one of the the alternator Voltage departs from this normal phases of said secondary winding having half value even slightly, there will be a relatively large the voltage of the other and having one terminal change in output current of the recti?er 2| thus 25 thereof connected to the mid-point of said other causing a relatively large change in current in phase, a resistor and an equal ohmic value re the winding 38 and this change will be in such actor connected in series across the higher volt direction as to restore the voltage of the alter age secondary phase, output terminals connected nator substantially to normal. . respectively to the free terminal of the low volt In Fig. 2 the anti~hunting ?eld winding 34 of age secondary phase and to the junction of said the eXciter has been omitted and the secondary resistor and reactor, and frequency compensating Winding of the stabilizing transformer 35 has means comprising a parallel resonant circuit con been connected directly in series with the single nected across said resistor. differentially energized control winding 38 so 3. In combination, a polyphase alternating that changes in voltage of the exciter will, by current circuit, means for regulating the voltage means of the stabilizing transformer 35, induce of said circuit, a control element for said regu voltages in the circuit of the winding 38 which lating means, means including an impedance are of such direction as to counteract the change network for deriving from said circuit a single in exciter voltage and thus prevent overshooting phase voltage which is proportional to the posi or hunting of the regulator system. 40 tive phase sequence voltage of said circuit and When it is desired to control the voltage of the which’ is in quadrature with one of the line cur main alternator 4 manually, a switch 44 is moved rents of said circuit at unity power factor, means to the left, thus connecting the alternator 49 to for vectorially adding to said single-phase volt a recti?er 45 whose output terminals are con age another single-phase voltage which corre nected across the resistance of the manually op 45 sponds in phase and is proportional in magnitude erated ?eld control rheostat 37. The switch 44 to said line current, and means for energizing when moved to the left also connects the control said control element in accordance with the vec ?eld winding 38 between the moving contact of tor sum of said single-phase voltages. the rheostat 3i and an intermediate point on a voltage divider 493 which is connected across the armature circuit of the exciter Ill. Thus, any operation of the rheostat will cause a change in energization of the control Winding 38 which in turn will cause a change in the eXciter voltage and this action Will continue until the change in exciter voltage causes the voltage divider 46 to produce a voltage substantially equal to the changed voltage of the rheostat. In this manner very stable operation of the manual voltage con trol circuit is obtained. In Fig. 2 the exciter has also been provided with a conventional series winding 41 for provid ing a predetermined amount of the excitation of this machine. In some instances this series ?eld winding can be so strong that it tends to saturate the exciter and under these circumstances the 65 4. In combination, a polyphase alternating current circuit, means for regulating the voltage of said circuit, a control element for said regu lating means, means including an impedance net work for deriving from said circuit a'single-phase Voltage which is proportional to the positive phase sequence voltage of said circuit, means in cluding a series saturated reactor for energizing said control element in accordance with said sin gle-phase voltage, and means for compensating said network for the effect of frequency changes on said saturable reactor. 5. In combination, an automatic electric reg ulator, an electroresponsive control element therefor, a pair of recti?ers having their output terminals connected with cumulative polarity in a closed series circuit, means for energizing said recti?ers in such a manner that their relative control winding 38 will normally act to hold the energizations Vary With variations in a regulated voltage of the exciter down to the required value quantity, and means for connecting said electro corresponding to the normal voltage of the main responsive control element across said circuit so alternator 4. 70 as to be energized by the difference between the While there have been shown and described recti?er output currents. particular embodiments of this invention, it will 6. In combination, an automatic electric regu be obvious to those skilled in the art that various lator, an electroresponsive control element there changes and modi?cations can be made therein for, a pair of recti?ers having their output termi Without departing from the invention and, there 75 nals connected with cumulative polarity in a 2,407,476 closed series circuit, means for energizing one of said recti?ers with a substantially constant al ternating voltage, means for energizing the other of said recti?ers with an alternating voltage which varies in accordance with the magnitude CI of a regulated quantity, and means for connect ing said electroresponsive control element across said circuit so as to be energized by the difference between the recti?er output currents. '7. In combination, a dynamo-electric machine, ' a ?eld winding for controlling the excitation of said machine, a pair of recti?ers having their output terminals connected with cumulative po to variations in the voltage of said dynamo-elec tric machine, and means for connecting said ?eld winding across said circuit so as to be energized by the di?erence between the recti?er output currents. 8. In combination, a dynamo-electric machine, a ?eld winding for controlling the excitation of said machine, a pair of recti?ers having their out put terminals connected with cumulative polarity in a closed series circuit, means for energizing said rectifiers in such a manner that their rela tive energizations vary with variations in an op erating condition of said machine, and means for connecting said field Winding across said cir larity in a closed series circuit, means for ener gizing one of said recti?ers with a substantially 15 cuit so as to be energized with the difference be tween the recti?er output currents. constant alternating voltage, means for energize ing the other of said rectifiers with an alternat ing voltage which varies non-linearly in response FREDERICK E. CREVER.