US2454129A - Vapor electric device - Google Patents

Description

Nov. 16, 1948. v V J. B'OYER'ETAL 2,454,129

: VAPOR ELECTRIC. DEVICE Filed Oct. 25, 1947 q v 2 Sheets-Sheet 2 WITNESSES: I Ffi iJfillggENTgRs d 4 ar n 0 5 0152;: L.5ayer. I

ATTORN EY Patented Nov. 16, 1948 UNITED STATES PATENT OFFICE VAPOR ELECTRIC DEVICE John L. Boyer, Wilkinsburg', and Robert J. Ballard, West Newton, Pa., assignors to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Application October 23, 1947, Serial No. 781,632

8 Claims. (Cl. 250 27.5)

Our invention relates to a vapor electric device and Particularly to a vapor electric valve for operation in a frequency changer system. In the operation of vapor electric devices such as frequency changers, it is customary to initiate the cathode spot periodically in phase with the low frequency system and to maintain the oathode spot by means of a holding electrode over a predetermined angle of the low frequency circuit.

Difficulty has been experienced because the holding anode requires an exceptionally high current to maintain the cathode spot during the conducting interval. We have discovered that this high current is due to the rapid deterioration of the load current in the high frequency circuit and the residual high ionization, or rather the presence of a large number of negative electrons and positive ions in the vapor space of the valve. In order to carry a current, the holding electrode must collect negative electrons, and since it has no preference in this matter, it collects the negative electrons from the charged space vof the converter rather than from the cathode spot so that the cathode spot may be extinguished. Such a result is undesirable as it produces an arc-through or short circuit in the low frequency system.

In a normal converter the holding electrode will operate quite satisfactorily with a current of the order of two amperes, but in a conversion circuit a current of thirty amperes during the high frequency conducting interval has been found necessary in order to satisfactorily maintain the cathode spot. We have found that this high holding current may be materially reducedby providing a deionizating grid between the holding electrode and the major portion ofthe vapor space to inhibit flow of electrons from the space to the holding electrode.

We prefer to make this deionizing electrode in the form of a graphite grid having relatively large openings therein and spaced immediately above the cathode and its associated holding electrode so that the deionizing grid shields the holding electrode from a major portion of the ionized vapor in the valve chamber.

It is, accordingly, an object of our invention to provide a vapor electric valve having a de-.

ionizing grid adjacent to the cathode.

It is a further object of our invention to provide a vapor electric valve requiring a relatively.

pro-

2 will be apparent from the following detailed description taken in conjunction with the accompanying drawings in which:

Fig. lis afragmental sectional elevation of a vapor electric valve embodying our invention; and

Fig. 2 is a schematic illustration of a vapor electric converter utilizing a valve according to our invention.

In the exemplary embodiment of our invention, the vapor electric Valve comprises a closed container I usually of metal in which is a cathode 2 usually consisting of a pool 3 of mercury in the base of the container l. A make-alive electrode 4 is provided for periodically initiating an electron emitting condition on the cathode, usually called a cathode spot and the make-alive electrode 4 is preferably energized by a peaking circuit 5 at the frequency of the low frequency potential.

In order to maintain the cathode spot for a determined interval of the low frequency potential, a holding electrode 6 is provided adjacent to the surface of the cathode pool 3 and it is sup plied with potential from an exciting transformer I over a predetermined interval of the low potential frequency, usually a period of the order of of the low frequency potential.

Cooperating with the cathode 2 is a suitable anode 8 usually composed of graphite and being supported in spaced insulated relation to the container and the cathode pool 3. Usually one or more control electrodes 9 and 10 are placed about the anode 8 and they are supplied with control potential at the high frequency rate from a control source ll so that the anode 8 carries several cycles of the high frequency potential during the period that the holding electrode 6 is maintaining a cathode spot.

Usually a cathode shield I2 is placed between the active portion of the cathode surface 2 and the openings I3 in the control grids 9 and in so thatthere is little possibility of droplets of cathode material being thrown from the cathode surface and into the openings 13 of the control grids 9 and Ill. The control grids 9 and Hi are usually provided with relatively small openings It so that the electron attenuation is very great in the con trol grids, thus permitting positive control of the anode 8 by the control grid potential.

The rapid decay of the anode current at the high frequency rate leaves the vapor space of the converter highly ionized or at least containing a large number of negative electrons and positive ions which must be neutralized before the space becomes non-conducting.

We have found that there is a tendency of the negative electrons to flow from the ionized space to the holding electrode 6 and that they flow with greater ease than the electrons emitted by the cathode 2 so that the holding electrode current tends to be completely supplied from the ionized space so that the cathode spot is extinguished. The extinction of the cathode spot in one of the pair of concurrently excited valves results in a misfire in this valve. The misfire in this valve prevents commutation in the companion valve and results in an arc-through therein which produces a short circuit on the low frequency circuit.

In order to prevent the flow of electrons from the ionized space to the holding electrode 6 we have provided a deionizing grid l5 usually of conducting material immediately above the cathode 2 and the holding electrode 6 so that the cathode 2 and holding electrode 6 are shielded from the major portion of the ionized space. Preferably the ionizing grid is composed of a plate of graphite having a plurality of relatively large passages l6 therein. The passages 16 may be of considerable dimensions as the only purpose of the grid H5 is to prevent flow of electrons to the holding electrode 6 and, consequently, a relatively low attenuation rate is permissible.

While we have found that a deionizing grid [5 a ionizing grid 5 on a common support I l with the cathode baffle i2 and to insulate the deionizing grid l5 from the baffle support I! b means of an insulating tube 18.

The improved valve according to our invention, is particularly useful in such circuits as frequency converters, a typical example of which is shown in Fig. 2. A plurality of valves according to our invention, are utilized for converting low frequency energy from a low frequency source to a high frequency potential for use in a high frequency circuit such as induction heaters or electric furnaces.

The low frequency potential is supplied to the valves in pairs by means of a suitable conversion transformer 20, and conversion is accomplished by means of a grid control system operating alternate valves at the desired high frequency potential, the commutation of the high frequency being assisted by means of a resonant transformer 2|, the primaries 22 of which are connected in series between the low frequency transformer 2i! and the conversion valves. The secondary 23 of this transformer 2| is in a tuned circuit which is preferably a portion of the load circuit 24.

The impulses to the make-alive electrodes 4 of the various converter valves are supplied by a wave-distorting impulsing system 5 in which a capacitor 25 is charged at the low frequency rate and discharged through a saturable reactor 26 to produce peaked impulses at the low frequency rate. One of these impulses is applied to the make-alive electrode 4 and the alternate impulses, preferably short circuited through a pogrid above said pool and larity responsive device, usually a unidirectional conductor 21.

A holding electrode is supplied from the low frequency source 1, preferably by two succeeding half waves so that the holding electrode 6 is operative over a period of the order of of the low frequency potential.

The grid control circuit II for the anode 8 is supplied with a high frequency potential and this high frequency potential may be either self-exciting-that is, taken from the frequency of the load circuit 24or it may be separately excitedthat is, provided from an outside source (not shown) of the desired frequency.

While for the purpose of illustration We have shown and described a specific embodiment of our invention, it will be apparent that changes and modifications can be made therein without departing from the true spirit of our invention or the scope of the appended claims.

We claim as our invention:

1. A vapor-electric device comprising an evacuated container; and anode and a cathode in spaced insulated relation in said container, an

- ionizable vapor in said container, means for pcriodically initiating a cathode spot on said cathode, cathode spot maintaining means operative to maintain said cathode spot for a predetermined interval after initiation, a control grid between said anode and cathode and electron collecting means interposed between the major portion of said ionizable vapor and said cathode spot maintaining means.

2. An arc-discharge device comprising an evacuated container, an anode in spaced insulated relation in said container, a cathode spaced from said anode, a control grid adjacent said anode, a make-alive electrode in contact with said cathode, a keep-alive electrode adjacent the surface of said cathode, an ionizable medium filling the space between said anode and cathode, and a conducting grid interposed between said keep-alive electrode and the major portion of said ionizable medium.

3. An are-discharge device comprising an evacuated container, an anode in spaced insulated relation in said container, a cathode spaced from said anode, a control grid adjacent said anode, a make-alive electrode in contact with said cathode, a keep-alive electrode adjacent the surface of said cathode, an ionizable medium filling the space between said anode and cathode, and a grid like structure of conducting material held in insulated relation above said cathode and said keep-alive electrode.

4. An electric valve comprising a closed container, a cathode including a pool of vaporizable reconstructing material for producing an ionizable vapor in said container, an anode in spaced insulated relation to said cathode, a control grid about said anode, a make-alive electrode in contact with said cathode, a keep-alive electrode in spaced proximity to the cathode, a shield interposed between the anode and cathode, and a deionizing grid mounted in spaced relation between the cathode and the shield.

5. An arc-discharging device comprising a closed container, a pool of mercury in said con tainer, an anode supported in said container in spaced insulated relation to said pool, a control grid about said anode, a make-alive electrode extending into said pool, a keep-alive electrode adjacent the surface of the pool and a deionizing said keep-alive electrode.

6. A vapor-electric device comprising an anode and cathode in a container, an ionizable vapor in said container, means for periodically initiating an electron emitting condition on said cathode, electron collecting means mounted adjacent the surface of the cathode, said electron collecting means being operative to maintain the emitting condition on said cathode, an electron barrier mounted adjacent the cathode and said electron collecting means and interposed between said electron collecting means and the major portion of the space in said container.

7. An arc-discharge device comprising a closed container, an anode and cathode in said container, an ionizable vapor in said container, a make-alive electrode in contact with said cathode, an auxiliary anode adjacent said cathode,

and a grid separating said cathode and auxiliary anode from the major portion of said ionizable No references cited.

Images