US2008675A - Electric discharge apparatus - Google Patents

Description

July 23, 1935.

E. G; BANGRATZ ELECTRIC DISCHARGE APPARATUS Filed Jan. 6, 1935 Fly:

WITNESSES:

2% Wm 1M INVENTOR Ernest 6-. Banyr'azz.

ATTORN Patented July 23, 1935 A UNITED srArEs PAT NT OFFICE.-

nmcrnro DISCHARGE. APPARATUS Ernest G. B angratz,'WilkinsburgQPaQ assignor and to Westinghouse Electric & Manufacturing Company, East E'ittsburgh, Pa, a corporation I of Pennsylvania Application January 6, 1933, Serial No. 650,519

My invention relates to electric discharge apparatus and it has particular relation to electric discharge apparatus utilized in the operation of electric discharge devices of the type incorporating a starting electrode.

The electric discharge devices utilized in the apparatus of the type to which my invention particularly applies, in general, comprise a plurality of principal electrodes between which an elec-' trical discharge is-to pass. 'The discharge may be initiated by impressing a large potential between these principal electrodes. I-Iowever; in the practice of my invention it is initiated by the cooperation of a starting electrode and one of the principal electrodes. The starting electrode is, disposed adjacent to or in contact with the principalelectrode with which it is to cooperate and it generally has a resistance which is high comparedto the resistance of the cooperative electrode. To start the discharge between'the principal electrodes, a heavy current is transmitted between the starting electrode and its cooperative electrode. I

In the electric discharge devices that are utilized in the preferred practice of my lnven tion, at least one of the principal electrodes is a conductive liquid or a suitable solid and the start-,

ing electrode is immersed therein. When a solid is utilized it is preferably a metal of the type that has a comparatively high vapor tension at a relatively low temperature such as lead or tin. I

More specifically, one of the principal electrodes in these electric discharge devices is mercury and the starting electrode is-a rod of ma.- terial having a resistivity high compared to mercury which is immersed in the mercury. To initiate a discharge'between the principal electrodes of an electric discharge device of this type, a current is transmitted between the starting electrode and the mercury. This current is of such polarity that the starting electrode is positive electrically with respect to the mercury.

While the theory of the operation of the electric discharge devices'of the type discussed hereinabove, is, largely conjectural, it appears that the discharge is initiated bythe ionization effect of a series of minute sparks which pass in the space between the'mercury and the starting electrode when current is transmitted through thefstarting electrode. It will appear at once from this con-.

sideration that to properly initiate the discharge,'

the starting electrode should not be wetted by the mercury nor should it amalgamate with the mercury and in experimenting with the electric dis- (iUl. 250-27.5)

charge devices discussed herein, I have verified this conclusion.

It will be seen from the above-discussion that considerable care must be taken in selecting the electrodes that are utilized in the electric discharge devices and in providing for the transmission of a starting current between the starting electrode and the mercury. Since these'currents are, in general, comparatively large, problems of considerable difilculty have arisen in providing the necessary starting apparatus. In accordance with the teachings of the prior art, the starting current is transmitted directly from the power source through the electrodes in question. However, since the electrode'is deleteriously affected by the reverse current which must necessarily pass therethrough when the discharge is initiated between the principal electrodes, a'rectifier is or-. dinarily connected series with the starting electrodes in the'starting circuit. The rectifier is so connected thatit passes current only in a direction such that when it is energized, the

starting electrode is positive relative to the mercury and by reason of thepassage of current therethrough, a discharge is initiated between the principal electrodes. When the discharge is once initiated, the rectifier prevents the. passage of current through the starting electrode in the opposite direction and thereby protects the electrode from the deleterious efiects of the reverse current. By reason of the magnitude of the starting current, the problem of providinga suitablerectifier'is not at allinconsiderable and adds to. the cost and the maintenance of the beginning of a. positive half-cycle of principal potential, the discharge is initiated. If. the starting current is interrupted during this positive half cycle', it has no eifect on the principal discharge and the principal discharge continues until the potential between the principal electrodes is reduced to a value below the ionization potential.

It is seen, therefore, thatthe output of the It is to be'noted that the starting electric discharge devices of 'the type utilized in the practice of my invention cannot be varied by varying the current transmitted through the starting electrode. It can however, be varied by adjusting the point in thehalf cycle of positive principal potential at which the starting current is transmitted through the starting electrodes. If this point occursearly in the half cycle, {the maximum current is transmitted through the electric discharge device and if it occurs late in the half cycle, current of smaller magnitude is transmitted through the electric discharge device.

Ashas been explained hereinabove in accordance with the practice of the prior art, rectifiers are utilized in the starting circuit. Since rectifiers do not per se lend themselves with facility to phase-shift operation, the rectifiers of the type that are ordinarily utilized with electric discharge devices discussed herein are equipped with control electrodes and the phase shift is applied to the control electrodes. However, the current that must necessarily be transmitted through the rectiflers is of considerable magnitude and in con sequence thereof, the rectifiers must have considerable current-carrying. capacity. For this reason the grid currents transmitted by the rec -'tifiers are not at all inconsiderable.

starting'apparatus which shall not involve the use of rectifiers.

Another object of my invention is to provide for electric discharge devices of the type incorporating starting electrodes, starting apparatus for precisely and accurately controlling the current output.

A further, object of my invention is to provide for electric discharge devices of the type incorporating starting electrodes, apparatus for supplying starting current to the starting electrodes at the precise point in the half cycles of positive principal potentialat which it is desirable that the starting current be supplied to provide the necessary-or desirable output current.

A still further object of my invention is to provide for electric discharge devices of the type incorporating starting electrodes, simple and inexpensive apparatus for applying starting currents of high peak'values but of such short duration as to require conductors of comparatively small capacity for transmission.

A more specific object of my invention is to provide for a system of the type incorporating a plurality of electric discharge devices equipped with starting electrodes, apparatus for providing starting current to the starting electrodes ,of a type such that the starting point of each of the electric dischargedevices shall be independently adjustable. 1

More concisely stated, it is an object of my invention to provide for a system of the type in-' ratus that I provide for electric discharge devices incorporates a plurality of capacitors. Each capacitor is associated with a starting electrode of one electric discharge device and to prepare for the initiation of a discharge in a particular device, the capacitor is charged to a high potential independently of the device. After .being charged, the capacitoris connecteddirectly between the starting electrode and the electrode cooperative therewith and the starting current is transmitted through the starting electrode and its associated element. To reduce the required current carrying capacity of the conductors through which the charging and discharging currents are transmitted, it is desirable that these currents be of as short duration as possible and for this reason as little as possible resistance is connected in series with the capacitor and the I have found in the practice of my invention that .a peak current of from 50 to 100 amperes may be attainedby utilizing a capacitor of reasonable magnitude and in the ordinary charging and discharging circuits that I have utilized this peak current passes for so short an interval of time that conductors of comparatively small resistance are not deleteriously affected by transmitting the current. v

The novel features that I consider characteristic of my invention are set forth with particular--.

ity in the appended claims. The invention itself, however, both as to its organization and its meth- -od of operation, together with additional objects and advantages thereof, will best be understood when read in connection with the accompanying drawing, in which Figure 1 is a diagrammatic view showing a preferred embodiment of my invention; and

Fig. 2 is a view in section of a portion of an electric discharge device utilized in the practice of my invention showing a certain defective feature which might arise in the operation thereof.

The apparatus shown in Fig. 1 comprises a plurality of electric discharge devices I and 3, each device incorporating an evacuated chamber '5 in which a solid anode! of any proper material such as carbon, and a cathode 9 of mercury are disposed. A starting electrode I I is immersed in the mercury. As has been explained hereinabove, the starting electrode l should have a resistivity high compared to theresistivity of the mercury and should not be wetted or amalgamated with the mercury.

It will be noted that, as shown in Fig. 1, if the starting electrode l I is not wetted by the mercury 9 and does not amalgamate therewith, the meniscus l3 of the mercury in the region in which it is in contact with the starting electrode ll recedes from the starting electrode and a minute gap starting electrode H and the mercury 9, minute,

sparks are generated in the region l5 between the meniscus l3 and the starting electrode II and by I reason of the ionization produced by, the minute,

sparks, the discharge between .the principal electrodes I and 9 of the electric discharge devices I or 3 is initiated.

{It is to be noted that if the startingelectrode H is not of proper character and the mercury 9 amalgamates or wets the electrode, the meniscus of the mercury in the region of the electrode will assume a form such as the meniscus I l of the mercury IQ of the tube 2 I shown in Fig. 2. In the electric discharge device 2| no gap is provided between the mercury I9 and the starting electrode 23 and I have found in experimenting with the electric discharge devices of the type discussed herein that if such a situation exists, the starting electrode fails to function properly.

As to the proper materials which may be utilized for starting electrodes, I have found that silicon carbide, boron carbide, boron and silicon yield satisfactory results. From the present state of my work with the electric discharge devices, it appears that carborundum (that is tosay, silicon carbide) yields highly satisfactory results and boron carbide and boron appears to be far more satisfactory even than silicon car= bide.

To return to the apparatus shown in Fig l, the electric discharge devices I and 3 are energized from an'alternating current power supply source (not shown) through a suitable transformer 25. The secondary 21 of the transformer 25 is equipped with-a plurality of terminal, taps 29 and 3| and a mid-tap 33. The terminal taps 29 and 3! of the secondary 21 are connected to the anodes lof the electric discharge devices I and 3 while the-mid-tap 33 of the transformer 25 is connected to the cathodes 9 of the electric discharge devices l and 3 through the load 95 which-is to be energized by the output of the assumed that the system is in 'the' condition shown inFig. 1, the left-hand capacitor 3! is connected in a circuit extending fromrthe midtap 33 of the transformer 25 through the conducting segments 39 of onedisk 4i through the left hand capacitor 37, through the conducting segments 390i a second disk M to one terminal tap 3i ofthe secondary 21. If the conducting segments 39 are properly adjusted on their drive shaft 45, a positiveimpulse of current will be transmitted [to the left hand capacitor 31 and it will be charged to a predetermined potential.

After the capacitor 3! is so charged, the conducting segments 39 of. the disks 4| through which it was charged aredisconnected fromthe brushes 9? and ,the capacitor 31 remains for .a short interval of time in its charged condition.

However, at a predetermined interval of time after this event occurs, the brushes 49 of theother associated sectored disks are connected to the conducting segments 53 of these disks and the capacitor is discharged through the starting electrode H and through the mercury 9 cooperative therewith.

As has been explained hereir'iabove, the sec.- tored disks 4| and 5| rotate in synchronism with the power source. If the left hand capacitor 31 is now discharged at a time such that the positive half wave of potential is being applied to the principal electrodes 1 and 9 of'the corresponding 'rate shafts which electric'dis'charge device, the device is energized and 'current corresponding in magnitude to the point at which the .device was energized is transmitted between its principal electrodes 1 and 9 and, therefore, through the load 35.

It is to be noted that the output of the electric discharge device may be adjusted by the simple expedient of shifting the segments 53 associated with the starting electrode H relative to'the segments '39 through which the-capacitor is charged. As is apparent, the segments may be mounted on simple disks 5I and 4| equipped with suitable It is to be observed also that a shifting scheme of the type shown in Fig. 3 of Patent No. 7633;482, to P. H. Thomas may be utilized for adjusting the position of the sectored disks M and 5t. In such a case, the sectored disks should not be mounted directly on the shaft of the synchronous motor (53 but they should be mountedon sepamay be suitably rotated by a device such as is shown in the patent and should 55. associated with this capacitor are shown in, Fig. 1 in a position corresponding to that in which the capacitor 37 is discharged.

My invention has been shown herein as applied to a particular system. Specifically, it has been shown as applied to a full-wave rectifying system.

Its application to a-half-wave rectifying system is apparent and systems wherein my invention is applied .to such apparatus are equivalents which lie within the scope of my invention. It is to be noted, moreover, that my invention resides specifically in the application of a capacitor for initiating a discharge in electric discharge devices Moreover it is to be kept in mind that while, as I shown and described herein, it may be advantageous' to charge the starting capacitors 3! through the principal secondary 27 of the transformer 25 an auxiliary secondary may be provided for this purpose.

In certain electric discharge devices constructed in accordance with the teachings of the early prior art, the discharge is initiated by impressing a potential between the starting electrode and one principal electrode in contact with .each other and then separating the electrodes, thereby producing a spark. Insofar as my invention applies to devices of this .type it is to be regar d as including within its scope applications to the e specific embodiments of my invention, I am fully principal electrodes between which an electric discharge isto pass and a starting electrode disposed in contact with one of said principal electrodes for initiating said discharge; a capacitor, means for charging said capacitor and means for establishing a direct metallic connection from said capacitor, after it has been charged, to said starting electrode and to said principal electrode in contact therewith thereby to discharge said capacitor through said starting electrode and to initiate-the electric discharge between said principal electrodes.

2. In combination with an electric discharge device of the type incorporating a plurality of principal electrodes between which a discharge is to pass and a starting electrode having an electrical resistance that is high in comparison with the resistance of one of said principal electrodes disposed in contact with said principal. electrode to cooperate therewith to initiate said discharge; means for storing electrical charges, means for charging said storing means, and means for estab:

lishing a direct metallic connection between said storing means, said starting electrode and said principal electrode in contact therewith to discharge said storing means, after it has been charged, through said starting electrode and said principal electrode in contact therewith thereby to initiate a discharge between said principal 'tion between said starting electrode, said liquid and said storing means to discharge said storing means, after it has been charged, through said starting electrode and said liquid thereby to initiate a discharge between said principal electrodes.

4. In combination'with an electric discharge device of the type incorporating a plurality of principal electrodes between which a discharge is to pass, at least one of said electrodes being normally a liquid, and a starting electrode immersed in said liquid to cooperate therewith to initiate a discharge said startingelectrode'having a resistivity that ishigh in comparison with the resistivity of the liquid, being incapable of amalgamating with said liquid and of being wetted by said liquid, means for storing electrical charges, means for establishing a direct metallic connectionbetween said storing means, said liquid and said principal electrode to charge said storing means and means for discharging said storing means, after it has been charged, through said starting electrode and said liquid thereby to initiate a discharge between said principal electrodes.

5. In combination with an electric discharge device of the type having a pluralityof principal electrodes between which a-discharge is to pass and means for initiating said discharge said.

means including a mercury electrode and an electrode immersed in said mercury; means forstoring electrical charges, means for charging said storing means and means establishing a direct metallic connection between said storing'means, said mercury and said starting electrode discharge for said storing means, after it has been charged,

through said mercury and-said electrode im-v mersed therein thereby to initiate said discharge between said principal electrode.

6. In combination with an electric discharge device of the type having a plurality of principal electrodes between which adischarge is to 'pass and means for initiating said discharge said means including a mercury electrode and an electrode immersed in said-mercury; said electrode being of a type such that it does not amalgamate with mercury nor is it wetted thereby; means for storing electrical chargesjf means for charging said storing means and means for establishing a direct metallic connection between said mercury electrode, said electrode -immersed therein and said starting means to discharge said storing means, after it has been charged, through said

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