US2799000A - Wide-range saturable-reactor tube-firing circuit - Google Patents

Description

July 1957 1 A. CASANOVA 2,799,000

WIDE-RANGE SATURABLE-REACTOR TUBE-FIRING CIRCUIT Filed 0012. 15, 1953 I RSI Rs r 3 :2 RP! RP 2 2 x 5 5' x lllllllnl l" If GP WITNESSES INVENTOR Louis A. Casanova.

WIDE-RANGE SATURABLE-REACTOR T UBE-FIRING CIRCUIT Louis A. Casanova, Pittsburgh, Pa., assignor to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Application October 15, 1953, Serial 100.386,?20 Claims. (Cl. 321-40) My invention relates toexcitation-means. for ignitron rectifiers orinverters, or'for othercontrolledtubes, and the special feature. of my invention is the provision of means for obtaining a sufiiciently wide range of phasedelays. of rectifier-tubes, or a sufficiently wide range of phase-advances of inverter-tubes, .to. be able to quickly changefrom no.-load to full-load, orfrom no-voltage output to full-voltage output, by phase-control. More particularly, my invention relates to an all-electronic or allsta-tic control-means of the indicated range, specifically providing a phase-angle control-range of at least 100, and preferably at least 115. To provide a reasonable factor of safety, I aim at a phase-adjustment of a. maximum of 120, for most power-interchanging conversionapparatus using my invention for interchanging controllable power between two diverse electric systems. It is conceivable, however, that a. need may arise for such a system in which the phase-angle control extends over a range of 180, or even more, and I contemplate such a systemtwithin the scope of my invention.-

More particularly, my invention relates to ignitrons or other controlled tubes in which firing-capacitors are used, to discharge through saturable series reactors into an ignitor or other make-alive anode or control-circuit. The firing-angles of such tubes may be varied over a phaseangle range of about 60, by means of a controllably saturable. phase-shifting reactor which is connected between the source of excitation-voltage and the firing-capacitor, without making it impossible to initiate the firing-operation of the tubes even when the excitation-voltage falls to approximately one-half of its normal value, meanwhile maintaining stability andan approximately constant voltage-regulation over the entire phase-shift range.

In most rectifier or inverter systems, a phase-shift range of 60 is not enough to eifect a complete loadcontrol from no-load tofull-load, as it is usually necessary to provide a phase-shift of anywhere from 100 to 115 in order to effect a complete load-change in tubecircuits of difiierent descriptions. It is conceivable that there may be some circuits which require a phase-shift control approaching. 180 or even more.

In order to obtain a rapidphase-shift control, while at the same time facilitating adaptation of the control-device to automatic regulation, it is desirable that as much as possible of this phase-shift control, namely 60, shall be. provided for by the above-mentioned controllably saturable phase-shifting reactors. When awider angle of phase-shift controlis needed, this has been provided heretofore by means of mechanically movable phaseshifters, which involve a significant amount of rotorinertia, and consequently involve a slight time-delay in rotating the rotor-members of these phase-shifters.

An important field ofapplication of my invention is in rectifier-devices which replace motor-generator sets. It a rectifier-device is to be able to successfully replace a motor-generator'set, it is obvious that the performance of the rectifier-control must equal that of the motor-generator set. Since the speed of responseof the voltageand control of a. motor-generator set is very high, involving only a change in the field-excitation strength of the generator, it is necessary also for the rectifier-control to be capable of very quickly changing the firing angle from a Zero delay to a delay of anywhere from to more or less, as may be necessary in any particular rectifier-circuit. My invention is particularly needed in such a situation, and inother applications wherein a rapid phase-angle change is needed, over a wide angular range.

Iachieve the objects of my invention by omitting the above-mentioned mechanically rotating phase-shifter, and replacing the same with one or more phase-shifting networks which are. serially connected between the excitation-voltage source and a firing-circuit which is provided with the usual controllably saturable phase-shifting reactor. This phase-shifting network, or each one of said networks, if there are more than one, includes a parallelcapacitor and a parallel-connected saturable reactor, these two. devices having an unsaturated circulating current which is at'least four times larger, and preferably from live to seven or eight times larger (or even more), than the load-currents which are drawn therefrom by the firing-circuit, if there is onlyone such phase-shifting network, or the load-currents which are drawn by the next phase-shifting network, if there are two or more serially connected phase-shifting networks. Each phase-shifting network is provided with a charging-circuit which serially includes its own controllably saturable phase-shifting reactor. Means are provided for controlling the saturations of all of the. phase-shifting reactors, preferably by means of a single variable resistance, which can be either manually or automatically controlled, and this may be accomplished at a very high speed, from one extreme of the adjustment-range to the other.

An exemplary form of embodiment of my invention is shown in the accompanying drawing, the single figure of which represents a simplified circuit-diagram of circuits and apparatus illustrative of the principles of application of my invention.

I have shown my invention as a conversion-apparatus for interchanging controllable power between an alternating-current system, such as a three-phase system AC, and a direct-current system DC having terminals While I have illustrated the AC system as being-a three-phase system, it could also be a single-phase system, or a polyphase system of a difierent number of phases. Furthermore, while I have shown the second electric system as a DC system, it is to be understood that this second system could be either a direct-current system or an alternating-current system having a dilferent frequency than the system marked AC. In general, it is desirable thatat least one of these systems should be an alternating-current system having a self-sustained frequency and having a normal voltage which is subject, at times, to voltage-fluctuations, and it is to be understood that the system marked AC is a power-line having such characteristics. The power may be interchanged in either direction, between these two systems, depending upon the tube-control.

My conversion-apparatus is shown as a double threephase rectifier-system, using a main transformer MT, having a delta primary which is energized from the AC system, and having two star-connected secondary windings which provide the consecutive secondary phases numbered 1 to 6; The star-points of the two secondary windings are connected by an interphase transformer IT, the midpoint of which is connected to the negative directcurrent load-terminal The six secondary phases 1 to 6 aroused to energize the anodes of six ignitrontubes, of which'only two tubes are shown, namely the tubes T1" and"T4 which are connected to the diathe auxiliary bus XAC.

metric opposite secondary phases 1 and 4, respectively. The other tubes will be connected to the other secondary phases, as will be well understood. Each tube has a main anode A, a mercury or other vaporizable cathode C, and an ignitor or other makealive anode I, with suitable numericalsuffixes corresponding to the secondary phase-number. The cathodes are all connected together in a common circuit which is the positive terminal of the DC load-circuit.

It is usually convenient and economical to provide an auxiliary transformer XT, which energizes an auxiliary alternating-current bus XAC from the main alternatingcurrent power-line AC, transforming the power-line voltage from whatever value it may have, for example 6900 'volts, to some convenient standard auxiliary voltage, such as 230 volts. Various equipments are energized from So far as my present invention is concerned, I have shown an excitation-transformer ET as having a delta primary winding which is energized from this auxiliary bus XAC, and as having a dog-leg or 'zig-zag connected secondary winding providing secondary or controlling-circuits which are being used in any particular case.

Each diametrically connected pair of tubes, such as T1 and T4, is provided with a firing-capacitor Cr, which discharges through a serially connected, constantly saturable series reactor Xs, which is connected between one terminal 11 of the firing-capacitor CF and a circuit 12 which is in turn serially connected, through a positivewave contact-rectifier or other asymmetrically conducting device RS1, to the ignitor I1 of the first tube T1. The other terminal of the firing-capacitor CF is indicated at 13, and this terminal is serially connected through a positive-wave rectifier RS4 to the ignitor I4 of the diametrically connected tube T4. A shunt-connected circuit-device must be provided for completing the circuits for the two opposite-polarity currents which are drawn by the ignitors I1 and I4. In the illustrated system, this is done by means of shunt or parallel-connected negative-wave rectifiers Rm and Rm, which are connected between the cathode-bus and the circuits 12 and 13', respectively. The usual firing-circuit contains not only the firing-capacitor CF and the saturable series reactor Xs, but also a controllably saturable phase-shifting reactor XPSl, which is serially connected between the terminal 11 of the firing-capacitor CF and a charging-circuit 14 for this capacitor. The degree of saturation of the phase-shifting reactor XPSI is controlled by means of a direct-current saturating-coil 15.

As has been previously pointed out, and as has been known in the art, the firing-circuit which is contained between the conductors 14-13 and the respective ignitors I1 and I4 is known, and it is known to be stable, and to maintain a fairly constant firing-voltage on the ignitors, throughout phase-angle changes of as much as 60, in a 60-cycle system. It is known that the related magnitudes of the capacitive reactance of the firing-capacitor Crand the unsaturated inductive reactance of the series reactor Xs may easily be chosen, largely by empirical methods, so that the firing-operation of the tubes T1 and T4 will commence, even through the AC line-voltage should drop to 50% of its normal value. This condition is usually imposed, so that the rectifier will be able to start under low line-voltage conditions, with a generous margin of safety, under all operating-conditions.

In accordance with my present invention, I provide one or more phase-shifting networks, which are serially connected between the excitation-transformer secondaryphase 14' and the firing-circuit input-terminals 14-13, respectively. Each of these phase-shifting networks is and Rat, as is well known in the art. 75,

capable of providing an extra 60 of phase-shift adjustment, in addition to the 60 which is provided by the firing-circuit. In most rectifying systems, including the system which is illustrated, only one of these phase-shifting networks is needed, so as to give a total phase-angle adjustment of including the 60 of adjustment which is provided by the firing-circuit. It is to be understood, however, that if a wider phase-angle adjustment is needed, it is possible to serially add as many phase-shifting networks as may be needed, in order to secure the total overall range.

The illustrated phase-shifting network comprises a parallel capacitor CP and a parallel-connected, constantly saturable reactor XP, both of which are connected across the terminals 14 and 13, respectively. The parallel-connected capacitor CP and reactor XP have an unsaturated circulating current which is several times, and preferably from five to eight times, the load-current which is drawn by the firing-circuit, more or. less. Probably never less than one-fourth of said circulating current would be withdrawn from the parallel-connected capacitor C2 and reactor Xp, to charge the firing-capacitor CF. The phaseshifting network also includes a second controllably saturable phase-shifting reactor XPs2, which is serially connected between the circuit 14 and the secondary terminal 1' of the excitation-transformer ET. The saturation of this phase-shifting reactor XPs2 is controlled by means of a direct-current saturating-coil 16. The circuit 13 is connected to the secondary terminal 4' of the excitationtransformer ET.

The above-described apparatus makes it convenient to provide a single control, for controlling the two saturatis, in cases using more than one phase-shifting network in addition to the firing-circuit. Conveniently, these two saturating- coils 15 and 16 are connected in series, and are energized with controllable direct-current by any suitable means, such as a battery-circuit represented by the terminals B+ and B-, and a serially connected rheostat or variable resistance 17, which can be controlled either manually or by means of an automatic regulator (not shown). It is possible, by suitable switching-means, which is the ordinary means for varying a resistance such as 17, to vary the magnitude of the direct-current saturating-current from its full value to zero, or vice versa, with practically no time-lag, and hence it is possible to change the ignition phase-angle of the controlled rectifier-tubes T1 and T4 with speeds of response which rival or exceed the speeds which are obtainable with motor-generator sets.

The operation of the pulsed-current ignitor-circuits, with non-linear inductances connected therewith, such as the inductances Xs, Xrsi, XP, and Xpsz, and with their non-sinusoidally charged and discharged capacitors, such A as CF and CP, defies strict mathematical analysis, and even analysis by means of the calculating board. The performance of such circuits is largely unpredictable, and must be empirically determined, and the design-constants must be largely determined, or at least checked, by test. It has been found that the illustrated circuit operates in the manner which has been described.

It will be understood that the ignitor-tubes T1 and T4 could have been replaced by other types of tubes, each tube having a main anode and-cathode circuit and a control-circuit. It will also be understood that these tubes,

by a proper phasing of the excitation-voltages therefor,

could be used either for rectifier-operation or inverteroperation.

It will also be understood that the control-element of the tube T1 does not need to be an ignitor I1 or other make-alive element; but if it is-an ignitor, it should be protected against the negative portions of ,the controlvoltage, as by the contact-rectifiers such as Rsr, R54, Rm

v It will be noted that the so-called firing-capacitor Cris a parallel-connected capacitor, which is connected in parallel-circuit relation across theterminals of the impressed single-phase control-source. It will further be noted'that the .so-called series reactor Xs is actually connected in a parallel circuit, Xs"Rs1-I1C1RP4, across the terminals 12, 13 of theparallel-connected capacitor Cr, and that nearly all of thevoltage-drop in this parallel circuit occurs in the substantially constantly saturable reactor Xs. It will be understood that th control-circuit I1-C1 of the tube T1 could be supplied or energized in any way from the output-side of the phase-shifting network which is made up by a controllably saturable reactor XPS1, in the energizing-circuit for a parallel-connected capacitor CF and constantly saturable reactor Xs. I thus use two (or more) similar, serially connected, phase-shifting networks, XPS2CPXP, and XPS1CF-XS- In each network, the controllably saturable reactor controls the phase-lag which must occur, in each half-cycle, before the capacitor reaches the instantaneous voltage-value necessary to saturate the constantly saturable reactor, and that the constantly saturable reactor thereafter holds or regulates the capacitor-voltage at approximately this value, until near the end of that half-cycle.

It is contemplated that the previously mentioned changes and equivalencies are within the scope of my invention, in its broader aspects.

I claim as my invention:

1. A conversion apparatus for interchanging electric energy between two different electric systems, at least one of said systems being an alternating current system, said apparatus comprising at least one tube having a main anode-cathode circuit and a control circuit, main circuit connections for connecting the main anode-cathode circuit of each tube between the systems for energy inter change therebetween, excitation means for providing an alternating current excitation voltage having a predetermined phase relation to the voltage of said alternating current system, a plurality of serially connected phase shifting networks, serially connected between said excitation means and the control circuit of each tube, each phase shifting network including a capacitor and a substantially constantly saturable reactor connected in parallel across the capacitor, each phase shifting network also having a charging circuit which serially includes a controllably saturable phase shifting reactor for charging its capacitor, and means for controlling the saturations of all or": the phase shifting reactors.

2. A conversion apparatus for interchanging electric energy between two different electric systems, at least one of said systems being an alternating current system, said apparatus comprising at least one tube having a main anode-cathode circuit and a control circuit, main circuit connections for connecting the main anode-cathode circuit of each tube between the systems for energy interchange therebetween, excitation means for obtaining an alternating current excitation voltage from said alternating current system, a plurality of serially connected phase shifting networks, serially connected between said excitation means and the control circuit of each tube, each phase shifting network including a capacitor and a substantially constantly saturable reactor connected in parallel across the capacitor, each phase shifting network also having a charging circuit which serially includes a controllably saturable phase shifting reactor for charging its capacitor, and means for controlling the saturations of all of the phase shifting reactors.

3. A conversion apparatus for interchanging electric energy between two diiferent electric systems, at least one of said systems being an alternating current system, said apparatus comprising at least one tube having a main anode-cathode circuit and a control circuit, main circuit connections for connecting the main anode-cathode circuit of each tube between the systems for energy interchange therebetween, control circuit means including a capacitor and a saturable series reactor connected between said capacitor and the control circuit of each of said tubes in a circuit'extending in parallel across said capacitor, said' control circuit means also including a charging circuit which serially includes a controllably saturable phase shifting reactor for charging said capacitor, excitation means for obtaining an alternating current excitation" voltage from said alternating current system, at least one phase shifting network serially connected between said excitation means and said control circuit means, each phase shifting network including a parallelconnected capacitor and a substantially constantly saturable reactor connected in a circuit extending in parallel across the associated capacitor, each phase shifting network having a charging circuit which serially includes a controllably saturable phase shifting reactor for charging its parallel-connected capacitor, and means for controlling the saturations of all of the phase shifting reactors.

4. A conversion apparatus for interchanging electric energy between two different electric systems, at least one of said systems being an alternating current system, said apparatus comprising at least one tube having a main anode-cathode circuit and a control circuit, main circuit connections for connecting the main anode-cathode circuit of each tube between the systems for energy interchange therebetween, control circuit means including a capacitor and a saturable series reactor connected between said capacitor and the control circuit of each of said tubes in a circuit extending in parallel across said capacitor, said control circuit means also including a charging circuit which serially includes a controllably saturable phase sifting reactor for charging said capacitor, excitatation means for obtaining an alternating current excitation voltage from said alternating current system, at least one phase shifting network serially connected between said excitation means and said control circuit means, each phase shifting network including a parallel-connected capacitor and a substantially constantly saturable reactor connected in a circuit extending in parallel across the associated capacitor, each phase shifting network having a charging circuit which serially includes a controllably saturable phase shifting reactor for charging its parallelconnected capacitor, the substantially constantly saturable reactor of each phase shifting network having an unsaturated circulating current which is at least several times larger than the load currents which are drawn therefrom by the circuit which is energized thereby.

5. A conversion apparatus for interchanging electric energy between two different electric systems, at least one of said systems being an alternating current system, said apparatus comprising at least one tube having a main anode-cathode circuit and a control circuit, main circuit connections for connecting the main anode-cathode circuit of each tube between the systems for energy interchange therebetween, control circuit means including a capacitor and a saturable series reactor connected between said capacitor and the control circuit of each of said tubes in a circuit extending in parallel across said capacitor, said control circuit means also including a charging circuit which serially includes a controllably saturable phase shifting reactor for charging said capacitor, excitation means for obtaining an alternating current excitation voltage from said alternating current system, at least one phase shifting network serially connected between said excitation means and said control circuit means, each phase shifting network including a parallel-connected capacitor and a substantially constantly saturable reactor connected in a circuit extending in parallel across the associated capacitor, each phase shifting network having a charging circuit which serially includes a controllably saturable phase shifting reactor for charging its parallel-connected capacitor, the parallel-connected capacitor and substantially constantly saturable reactor of each phase shifting network having such related magnitudes that the operation of the controlled tube can be initiated, and stability and an approximately constant voltage regulationmain- References Cited in the file of this patent UNITED STATES PATENTS 2,266,714 Mittag Dec. 16, 1941 Mye 1's fl May 4, 1943 Meyers May 23, 1944 Mittag June 13, 1944 f Cox et al. Mar. 26, 1946 Casanova Dec. 19, 1950 Geiselman Apr. 24, 1951 Gieselman Sept. 18, 1951

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