US1131282A - Constant-current rectifier system. - Google Patents

Description

G. P. STEINMBTZ. CONSTANT CURRENT RBGTIFIBR SYSTEM.

APPLIOATIQN FILED MAY z3, 1905, 1,1 31,282. Patented Mar. 9, 1915.

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WITNESE: @o n INVENTOR:

@ka/44] Charles P Steinmetz,

C. P. STEINMETZ. CONSTANT CURRENT NEGTIPIER SYSTEM.

APPLICATION FILED KAY 23, 1905.

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IHVEHTOR: Charles Il? Steinm By etz @QM/Vr ftty.

man STATES PATENT onnicn.

P. 'STEINMETL vO1? SCHENECTADY, NEW YORK, ASSIGNOR T0 GENERAL ELECTRIC COMPANY, A CORPORATION OF NEW' YORK.

CONSTANT-CURRENT ECTIFIER SYSTEM.

l Application led May 23,

To all vwhom t may concern Be it known that I, CHARLES P. STEIN- METZ, a citizen of the United States, residing atfSchenectady, county of Schenectady, Stateof New York, have invented certain new and useful Improvements in Constant- Current Rectifier Systems, of which the following is a specification.

This invention relates to' a system of .electrical'distribution in which alternatingcur-vl rent is rectified to produce a. unidirectional current applicable toseries circuits requiring substantially 'constantcurrent.`

Theinvention also relates to the forms of apparatus whereby this result is obtained.

In carrying out my invention I make use of the peculiar property of a, mercury or similar arc, whereby y current is permitted to pass freely through the arc inone direction but is prevented from fiowing in the opposite direction. l f y The details of my invention will be better understood by reference to the following deforces and the current in different parts of scription taken in connection with the drawings forming part of this. specification.v

Figure 1 is aV diagramrepresenting my `improved system of electrical distribution; Ngs. 2 and 3 'are explanatory diagrams; Fig. 4 comprises a group of curves showing various relations between electro-motive the system; and Fig. 5 shows a modified form of reactance device for supplying current to the auxiliary anodes.

Referring to Fig. 1, the mercury rectifier 1 is connected through a transformer 2 to the'sourceof constant potential 3. This transformer 2 is in some respects similar to the ordinary tub transformer for converting constant potential alternating current into constant current, but differs in some particulars, which are hereinafterl pointed out.

The transformer comprises a prlmary coil 4 and a fioating secondary coil 5, the terminals tively, to the anodes 8 and 9 of the mercury. rectifier through reactance devices l0 and 11. The mercury cathode 12 of the rectifier I Specification of Letters Patent.

6 and. 7 of `which are connected, respec- Patented Mar. 9, 1915. 1905. serial No. 261,868.

the secondary 5. The rectifier is also pro-4 versa, to establish a starting arc in-the'lower end-of the rectifier `for the purpose hereinafter pointed out. These electrodes 16 and 17 are supplied with current from the low potential secondary 18 of a transformer, 4the primary 19 of which is connected to the constant potential source 3. A reactance device 2O is connected directly across the terminals of the secondary 18 and is provided with a f Vtap 21 from which a conductor leads to a reactance 22 and then to the cathode 12. These auxiliary anodes 16 and 17, together with their correlating transformer and reactances, operate vto render the space within the rectifier conductive for current from the transformer secondary 5 in va manner hereinafter described more in detail.

The operation of the mercury arc rectifiery of material, projected and'constantly replenished by a high velocity blast issuing from the cathode. The arc, therefore, must be continuous at'the cathode, though'it may be shifted from anode to anode. Any interruption of the cathode blast puts out the arc'by interrupting the supply of conducting va` por. With an alternating impressed E. M. F. the arc, if established, will go out at the end of the half-wave, or if a cathode blast is maintained continuously by a second arc, only alternate half-waves can pass, namely, those for which that terminal is negative from which the continuousblast issues. The arc, with an alternating Aimpressed voltage, consequently rectifies the current, and the voltage range of rectification is'very great.

In Fig. 2 is` shown -diagrammatically a constant-current transformer having a primary 23 and a Secondary\having its termiauxiliary electrodes to the cathode or vice nals I24 and 25 connected respectively the anodes 26 and 27 of a mercury rectier. The cathode 28 of the rectifier is connected through a series circuit 29 to a tap 30 in the lcenter of the transformer secondary. With such an arrangement, an alternating current in the primary' 23 will impress a voltage between the secondary terminals 24 and 25 having the wave form shown in curve I of Fig. 4. The voltages from 30 to 24 and 19 from 30 to 25 are given by curves II and III.

If now, 24, 25 and 30 are connected withl the corresponding rectifier terminals 26, 27 and 28, and at 28 a cathode blast is maintained, 'those currents will pass for which 28 is negative or cathode, that is, the current iowing through the rectifier from 26 to 28 and from 27 to 28 under the impressed E. M. F.s II and III, give curves IV and V, and the current issuing from 28 will be the sum of IV and V, as shown in curve VI. Such a'rectiiier would, however, not be self-exciting, but would require some outside means for maintaining the cathode blast at 28, for the current in the rst half-wave 31 in curve VI e ioes down to zero at the zero value of M. F. III, before the current of the next half-wave 32 is started by theLE. M. F. II. It is therefore necessary to maintain the current of the first half-wave 31 beyond the y zero value of its propelling impressed electro-motive force III until the current of the next half-wave 32 has started, that is, to overlap the currents -of the successive halfwaves. This is done by inserting reactances 35 33 and 34 into the leads from the transformer, as shown in Fig. 3. The eifectf of these reactances is that the current of the rst half-wave 31 .of curve VI continues to ow beyond the zero of its impressed E. M. F. III or, in other words, until the E. M. F. III has died out and reversed and the current of the next half-wave of curve VI has been started by the E. M. F. II. Thus the twohalf- waves 31 and 32 of the current overlap and each half-wave lasts for more .than half a period or for more than 180.

The current waves resulting are shown in curve VII. rIhe current half-wave 31 starts at `the zero value of its E. M. F. III but rises slower than it would without reactance, following essentially the exponential curve of a starting current, and the energy which is so consumed by the reactance as counter E. M. F., is returned by maintaining the .55 current half-wave beyond the E. M. F. wave,

that is, beyond 180. .By this means a rectiier becomes self-exciting, as each half-wave by over-lapping with the next, maintains the cathode blast until the next half-wave is started. The successive current' half-waves added give the rectified or unidirectional curve VIII. Although I have 'shown separate reactan'ces 10 and 11 in the anode leads, it will be understood that if desired the nec- @5 essary reactive eectmay be produced by menace the transformer secondary itself when suitably designed; or as an alternative construction, the transformer secondary may contain slightly less reactance than. is necessary to produce proper overlapping ofthe current waves and small reactances may be introduced in the leads to make up the balance, thus allowing a certain flexibility of adjustment in the system. During a certain portion of time in each half-wave, from the Zero value of E. M. F., -arcs flow simultaneously between 26 and 28 and between 27 and 28. During the existence of both arcs there can be no potential difference betweenthe recti-` lier terminals 26 and 27, and the impressed .80 E. M. F. between the rectifier terminals 215'- and 27 therefore has the form shown in curve IX, that is, remains zero for X degrees andthen, with the breaking of the arc of the preceding half-wave jumps up to its normal value. The induced E. M. F. of the transformer secondary must, however, more or less completely follow the primary impressed E. M. F. wave or, in other words, have the general shape shown in curve I, and consequently the difference between IX and I must be taken up bythe reactance. That is, during the time when both arcs flow i in the rectifier, the reactive coils 33 and 34 consume the induced E.' M. F. of the trans- 95 former secondary,l and the voltage across these reactive coils is, therefore, as shown in curve X. Thus the reactive coil consumes voltageat the start of the current of each half-wave, at 35 in curve X, and produces 1 00 voltage near the end of the current flow, at a 36. Between this time the reactive coil has practically no effect and its voltage is low,

corresponding tothe variation of the r'ectified alternating current, as shown in curve XI. Thus during this intermediary time the alternating reactive coils merely assist the direct current reactivecoil 37. Since the voltage at the alternating terminals of the rectifier 26 and 27 has two periods of zero 110 value during each cycle, the rectified voltage between 28 and 30 must also have the same zero periods and is indeed the same curve as IX, but reversed as shown in curve XII. Such an E. M. F. wave cannot operate arcs, especially mercuryarcs, since during the zero period of voltage the arcs go out. rIlhe voltage on the direct currentline must never fall below the' counter E. M. F. of the arcs and since the resistance of this circuit is low, -120 about 10%, it follows that the total variation of direct current line voltage must be below 10%, that is, the'voltage practically constant, as shown in dotted lines in curve XII. 'Io overcome this ditliculty a high re- 125 actance 37 is inserted into the direct current circuit which consumes the excess voltage l during that part of curve XII where the rectified voltage is above line voltage, and

supplies the line voltage during the period 139 .A

of zero rectified voltage. The voltage acrossv this reactive coil, therefore, is as shown by curve XIII.

Referring now to Fig. 1, it will be noted that the reactances 10 and 11 correspond respectively to the reactances 33 and 34 of Fig. 3, the functions of which have been set forth bin detail in the preceding discussion. Similarly, the reactance 13 of Fig. 1 corresponds in function to the reactance 37 of Fig. 3. In addition to these features Fig. 1 shows one means contemplated by me for starting the first discharge through the mercury rectifier. This starting means comprises the two auxiliary electrodes 16 and 17 which are 4supplied with current from the secondary 18 of a transformer, and comprises also an arrangement of reactance devices 20, 22, whereby these two auxiliary electrodes 16 and 17 may alternately pass current to the main cathode 12, and -furthermore may maintain an overlapping phase relation of these successive current waves so that the cathode 12 is at all times energized or excited by current from these auxiliary electrodes. After the rectifier has once been -started the auxiliary electrodes may be cut out of circuit entirely and the rectifier will maintain itself in a conductive condition because of the effect produced by the reactances 10 and 11 in the manner previously discussed, but on the other hand, the continuous use of the auxiliary electrodes 16 and 17 requires the expenditure of only a small quantity of energy and has the advantage that if the consumption circuit is accidentally opened or is subjected to marked fluctuations from any cause the auxiliary exciting means serves to bridge over these disturbances and prevents the rectifier from being extinguished.

By the construction above described the circuit which supplies current to the auxiliary anodes is effectively insulated from the constant potential source 3, so that there yis no danger of introducing the high potential arc current into the constant potential circuits.

When desired, I may combine the reactance and transformer as in the apparatus shown in Fig. 5, which consists of a primary coil 19 adapted for connection to the constant potential source 3 and wound in two sections on the two legs of an iron core 20 having a magnetic shunt 202. A second coil 18 is wound in two sections on this core and is provided with a tap from which a circuit may be completed through the reactance 22 to the rectifier cathode 12. The terminals of this coil 18 may beconnected respectively to the starting electrodes 16 andv 17. The magnetic shunt 202 extends into proximity to the respective end pieces of the rectangular core, and its ends lie respectively between the Sections of-the prilin each.

mary coil and between the sections of the secondary coil. By this arrangement leakage paths of low reluctance are afforded for the primary and secondary fluxes. The leakage path for the alternating primary flux, including as it does the wide air gaps on either side of the shunt 202, is of greater reluctance than the local leakage paths for the individual secondary coils. It may be noted that due to the action of the rectifier l fed by the secondary coils, current flows alternately in said coils and is unidirectional The leakage path for each secondary coil is thus across the adjacent corner of the shunt 202 and so includes a wide air-gap between the end of the shunt 202 and the main coil.

Although I have described an apparatus for starting a rectifier tube from an alternating current circuit it should be understood that I may also start it by the use of a storage battery connected between one of the auxiliary electrodes and the cathode, or I may if desired start the tube by'tilting it so that the mercury in the cathode cup flows the entire length of the anode chamber and draws an are from one of the anodes when the tube is restored to its original position. Such a method of starting is particularly applicable to the construction of tube shown in Fig. 3. v

The rectifier itself embodiescertain features which I consider of importance. As the conditions for successful operation to produce constant current are somewhat different from those which exist when the rectifier is operated on constant potentialcircuits, I nd it advantageous to inclose each of the anodes 8 and 9 in a separate tube. I also find it advantageous to use as a cathode an amalgam of a refractory metal such, for instance, as gold or silver. Such a refractory metal has no appreciable vapor tension at the temperature of the mercury arc, and so does not take part in the conduction of current between the electrodes. The presence of such a metal reduces the vapor tension of the mercury and so makes the rectifier run cooler and thereby renders the rectifying arc less liable to strike back. By the expression strike back I mean the action which takes place when a mercury arc reverses so that a carbon electrode becomes momentarily a cathode. Such an action produces a short circuit through the rectifier between carbon electrodes and bv the disintegration of the carbon is likely to ruin the tube.

I find it desirable to use a higher magnetic density in the transformer than is ordinarily employed in constant current transformers of the tub type. and furthermore I find it desirable to so adjust the angular relation between the weight supporting are #S8-and .the lever arm 39 that the i transformer will deliver from its secondary a current which tends to decrease slightly in quantity as the voltage across the consumption circuit decreases. rlhis adjustment is rendered desirable because of the fact that the overlapping of the current curves caused by the reactances l0 and 11 increases with a decrease of load and tends to make the rectified current increase when the number of translating devices in the series circuit decreases. llhis adjustment of the transformer may be easily' effected by shifting the weight supporting arc 38 about a pivoted connection 40 in the manner well known to persons skilled in the art. in exact compounding' may thus be effected so that the current through the translating devices is substantially constant under. all conditions of load.

The specific forni of mercury rectifier shown in Fig. l is well adapted for use on high potential circuits, as it will readily stand a pressure of many thousand volts between an'odes without causing an arc to strike between them. Each anode is carried in the top of a comparatively narrou7 chamber which is separated by a considerable distance from the mercury cathode and furthermore is shielded from the direct cathode blast by a bend in the walls of the chamber as clearly shown in Fig. l. By making these chambers small a relatively high temperature is produced in and around the anodes, thus preventing the condensation of mercury at these points and so decreasing the liability of arcing between anodes. A mercury condensation chamber il is located directly above the mercury cathode l2 and serves to receive the direct cathode blast and to relieve the anode chambers of eX- cessive mercury vapor pressure. This condensing chamber 41 is connected to the main body of the tube through a constricted opening or neck, but l make no claim to that feature herein as the same is the invention of and is described and claimed in the application of Joseph L. R. Hayden, Serial No. 284,333, filed oct. 25, 1905.

What l claim as new and desire to secure by Letters Patent of the United States, is

1. ln a system of electrical distribution, the combination of a source of constant potential alternating current, a transformer connected thereto and adapted to deliver current of varying potential from its secondary, a single phase vapor rectifier connected' to said transformer secondary, reactances for maintaining said rectifier conductive for currents of one direction, a series circuit containing a plurality of translating devices, a reactance in series with said devices, and means for passing current from said rectifier through said last named reactance and said translating devices.

2. The combination of a vapor rectifier, a

meines high voltageV constant current source for supplying current thereto, a constant potential alternating current circuit and means connected to said circuit for rendering said rectifier conductive for current from said transformer.

3. The combination of a constant potential circuit, a constant current transformer connected thereto, a rectier tube supplied by current from said transformer, and means for exciting said rectifier tube by energy from said constant potential circuit.

4c. A. vapor rectier having a mercury cathode and a plurality of anodes, means for supplying alternating current to said anodes and for maintaining the supply substantially constant, supplemental anodes, and means for supplying alternating current at constant potential to said supplemental anodes to render the rectier conductive. l

5. The combination of a transformer having relatively movable coils, a source of constant potential for supplying current to one of said coils, a vapor rectifier connected to the other of said coils, a tap at or near the center of said last named coil, a constant current series circuit connected between said tap and said vapor rectifier and a reactance device in said circuit.

6. The combination of a transformer having relatively movable coils, a source of constant potential connected to one of said coils, a vapor rectifier connected to the other of said coils, a tap at or near the center of said last named coil, a constant current circuit connected between said tap and said rectifier, and inductive devices for maintaining said rectifier conductive for current from said source.

7. rlhe combination of a constant current transformer having a suitable winding, means for supplying energy to said transformer from a source of constant potential, a vapor rectier connected to the terminals of said winding, a tap from an intermediate point of said winding, a series consumption circuit connected between said tap and said rectifier, and a constant potential circuit for supplying current to said rectifier to render it conductive for current from said transformer.

8. The combination of a single phasev vapor rectifier having a cathode and a plurality of anodes, a consumption circuit connect'ed to said cathode, translating devices in said circuit having an appreciable counter prising a plurality 9.'The combination with. an alternating current circuit, and a current-rectifying device, of a transformer in rposed between the circuit and the rectifying device com-- of coils arranged to form two secondary-circuits. that are traversed respectively by currents of uniform direction, anda magnetizable core for the coils adapted to provide a leakage path for uxes between the coils pertaining respectively to the two secondary circuits.

10. vThe combination with an alternating current circuit, and a current-rectifying device, of a transformer interposed between the circuit and the rectifying device'comprising a lurality of coilsarranged to form two secon ary circuits that are traversed respectively by currents of uniform direction, and a magnetizable core for the coils adapted-to provide leakage paths for ytluixes surrounding lthe ...coils pertaining respectively to the two secondary circuits, th said paths `'having a common portion in which the leakrespectively by currents of uniform direction, and means providing a low reluctance leakage path between the coils pertaining respectively to the two secondary'circuits.

12. A transformer comprising a plurality of secondary coils and low reluctance leakvage paths between the said coils.

In witness whereof I have hereunto set my hand this 22nd day of May, 1905.

CHARLES P. STEINMETZ.

Witnesses:

BENJAMIN B. HULL, Human Onronn.-

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