US1147026A - Electrode for vapor electric apparatus. - Google Patents

Description

C. A. KRAUS L R. D. MAILEY.

ELECTRODE FOR VAPOR ELECTRIC APPARATUS.

APPLICAUON FILED 1AN.8,1914.

19147,@2@ PatentedJuly 2U, 1915.

2 SHEETS-SHEET l.

C. A. KRAUS & R. D. MAILEY.

ELECTRODE FOR VAPOR lELECTRIC APPARATUS.

APPLICATION FILED 1AN.8. 1914.

Lmp. Patented July 20, 1915.

2 SHEETS-SHEET 2.

UNTED STATES PATENT FFlE.'

CHARLES A. KRAUS, 0F NEWTON HIGHLANDS, AND ROY D. MAILEY, 0F LYNN,

, MASSACHUSETTS.

ELECTRODE FOR VAPOR ELECTRIC APPARATUS.

Specification of Letters Patent.

Patented July 20, 1915.

Continuation in part of application Serial No. 569,699, led June 30, 1910. This application led January 8. 1914. Serial No. 811,083.

To all w71 om it may concern.'

lle it known that we, )nannies A. KnAUs and Ror l). Mmm-zr, citizens of the United States, and residents, respectively, of Newton l-lighlands and Lynn, in the counties of Middlesex and Essex, both in the State of Massachusetts, have invented new andvuseful Improvements in Electrodes for Vapor lClectric Apparatus, of which the following is a specification.

Our invention relates to the construction of vapor electric apparatus, and has for its object the control or suppression of undue agitation of the liquid mercury cathode usually present in such apparatus, and is addressed particularly to the class of apparatus which is of large capacity and requires therefore. a insider-able body of mercury for the cathode.

For the illustration of our invention we take the case of a mercury arc rectifier which is a characteristic example of vapor electric apparatus. The rectifier consists essentially of a gas-tight container with two anodes of solid metal, and a cathode of liquid metal, mercury' heilig invariably employed in practice. As is well understood, the solid anodes allow the current to. flow in one direction only, and these anodes are connected directly to two outer terminals of a source of alternating current between which terminals there is located a suitable reactance. rlhe middle or neutral point of the reactance is connected through a load circuit with the liquid metal cathode. lf the cheek valve action of either of the anode-s fails so that current may enter as well as leave a surface, an arc will be formed directly between the two anodes and since there is no considerable reactance in a circuit directly from one anode to the other, the current is liable to reach abnormally high value. '.lhis phenomenon is commonly termed short-circuit arcng and when it occurs subjects the apparatus to, possible injury and interrupts the operation of the rectifier. The exact nature of the phenomena which .underlie short-circuit arcing in a rectifier is not clearly understood, although it is generally considered that proximity of the anodes to the surface of the mercury cathode is a factor. As a result, rectifier-s have been usually constructed in such a manner as to place the anodes at such a distance that short-circuit arcing is not likely to result. However, such a disposition ofthe anodes with respect to the mcrc ury surface is not free from serious objection. The mercury vapor itself offers convsiderable resistance to the passage, of the current, and while the potential difference between an anode and the cathode may be as low as 8 volts when the anode is placed near the cathode surface, this potential difference increases rapidly as the length of the vapor path is increased. Fall of potential in the vapor path not only reduces the efficiency of the rectifier on account of increased loss of energy, but reduces the capacity of a rectifier of given dimensions, since the greater the loss of energy within the rectifier the larger must be the surface through which heat may be withdrawn. A further disadvantage from placing the anodes at a great distance from the cathode lies in the fact that under such conditions the potential drop at the anode surface is increased by the presence therein of foreign gases from which a rectifier can never be completely freed. The presence of foreign gases at the anode surface materially i11- creases the potential loss or drop at that point. On the other hand, if the anodes can be placed near to the mercury cathode surface, the circulation of mercury vapor displaces the foreign gases from the immediate neighborhood of the anodes which consequently act more economically and with only the potential fall normally due to their substance and structural characteristics. On the other hand, when the anodes are placed at great distance from the cathode, the mercury vapor displacing foreign gases circulates them into the neighborhood of the anode in increased concentration and thus produces an abnormally high potential fall at the anodes. Another difficulty which results from the accumulation of foreign gases in the neighborhood of the anodes, is that the are is liable to skip, and this difficulty becomes accentuated when the ,rectifier is operated continuously for a long time because by continued use gases are driven out of the electrodes and also -out 4of the walls of the container when, as is preferable, these are made of metal. yUltimately the gas pressure about the anodes will reach a value such that the are does not strike through it to the electrode. Then the rectier operates only intermittently and its service is seriously impaired.

From the foregoing considerations 1t is apparent that any means tending to reduce the liability to short-circuit arcing which docs not involve an increase of the distance between anode and cathode, will be of utility in the construction and operation of mercury arc rectifiers and analogous apparatus. Ve have found that the suspension of the check valve action at the anode is due in most cases at least to the presence of liquid mercury on the anode surface. If an arc is established in a space in which two independent electrodes are located, of which one at least is composed of mercury, and a substantial difference of potential exists as between them, an arc will start across between these electrodes and if, in the rectifier, liquid mercury is deposited upon an anode, it immediately becomes possible for a cathode arc to form thereon, whereupon a short-circuit arc results. The mercury which acts asthe cathode in a rectifier is in violent motion and drops of the liquid metal are thrown about to considerable distances within the rectifier. of this agitation the tendency to form shortcircuit arcs increases because o f the increased probability of drops of liquid mercury reaching and lodging upon the anodes. For. this reason short-circuit arcing 1s more frequent at higher currents than at low currents and increases in frequency with the depth and'superfcial area of the mercury cathode.

Our invention, therefore, has for 1ts object the reduction of the tendency to form short-circuit arcs and attains this object bydamping or suppressing the agitation of the mercury cathode surface.

In the drawings hereto annexed which illustrate our invention, Figure 1 is a vertical section of the lower part of a vapor electric apparatus, and Fig. 2 is a horizontal section taken on the line 2 2 of Fig. l.

The essence of this improvement lies in the provision at or near the surface of a mercury cathode of a solid obstruction to the movements of ebullition and agitation of the mercury itself. We may, and preferably do, employ the cathode lead connections to assist in furnishing such an obstruction and may employ also either indeendently or in connection with the cathode ead construction, solid obstructions to violent ebullition and spattering.

Referring to the drawings, which illustrate an example of our improvements, A represents a rectifier container, D the mercury cathode, D a container therefor, B the main anode, and C the auxiliary anode for maintaining the arc. The cathode lead` comprises a, plate or disk E of suitable metal,

l/Vith an increase in the violencesuch as iron or steel, preferably having a continuous surface without perforations, and this extension or baffle E is firmly secured to the cathode lead connection E which extends to the container wall to pass through it to the outside electrical connection. The damper E is preferably placed near the surface of the mercury cathode l) and will in most cases suiiice to suppress and control the agitation of the mercury while it ofiiciates also as a conducting surface of metal to carry away the current from the cathode.

Considered with reference to the electrical functions of the components of such an aparatus, the mercury which in the specific illustration shown lies underneath the extension E, does not contribute at all to the operation of the apparatus. The current passes through the mercury on top of the extension E to the said extension and thence through the other portions of the electrode lead; the heat generated in the mercury does not penetrate to any considerable extent into the lower portion of the mercury mass. Strictly speaking, therefore, the mercury cathode is that which lies between the surface of the mercury pool and the conductive lead immersed in the mercury or upon which the mercury rests. As that portion of the mercury between the upper surface of the conductor and the mercury surface vis a seat and origin of agitations, the proportions of this functionally active cathode are important in respect to the extent and violence of the agitations which may take place. If, for instance, the depth and diameter of the mercury overlying the conductive lead are of the same or nearly the same order of magnitude, the agitating effect of the current and the heat developed thereby may form a stationary wave (that is to say, an undulatory oscillation of which the wave crest does not progress as in a medium of indefinite extent) and this stationary wave may under such dimensional conditions be the wave fundamental to the body of the mercury. The fundamental wave under such circumstancesy is the maximum; it is represented by a single central crest surrounded by an annular depression succeeded in the oscillation by a single central depression surrounded by an annular crest. In the case of a mercury cathode, such a fundamental wave presents the maximum of peril to the operation of the apparatus. If the ratio of depth to horizontal extent of the actually effective cathode mercury be progressively changed so that the ratio of depth to diameter diminishes, -a proportion will eventually be reached which is completely prohibitive of the formation of a fundamental wave. While not exactly determined, this ratio would probably, in the case of mercury, be found to `be in the region of 1 to 6. Therefore, in order to insure a condition in which Vthe formation of the fundanwntal wave is impossible, we bring the extension E very close to the surface of' the mercury so that the actually effective cathode consists of a Avery thin sheet of mercury overlying the extension which is, as above explained, to all practical and functional intents and purposes the bottom of the mercury cathode space. With an extension E several inches in diameter and a depth of mercury over it, little, if any more than one-eighth of an inch, it will be clear that the formation of a fundamental Wave is not even remotely possible. The agitations and ebullitions are necessarily local; that portion of the mercury on which the cathode spot rests will be irregularly agitated and no general upward leap of the mercury can take place. It is perhaps,` more strictly correct, therefore, to say that the undulation-dampening means are not so much inherent in the extension E itself as v in the proportions of the effective cathode which lies between this extension andthe surface of the mercury, these proportions being, of course, determined by the diamet-4 ric extent of the extension E and the depth at which the upper surface of the extension is placed in the mercury.

`Either in addition to the cathode lead eX- tension damper or independently, We may provide a damper of solid material, which consists of granules or small fragments of solid material F preferably of porcelain or fused quartz, which We have found very satisfactory for the purpose. The effect of this layer of granulated material is to prevent thc spatterimgr motions of the mercury or its .agitation either in the form of Waves or ejected drops. Not only does the presence of these granules greatly reduce the tendency to form short-circuit arcs, but it improves the action of the rectifier in other respects. The are becomes much steadier and less likely to go out when the current is small. The thickness of the granular layer may be very considerable, as much as an inch in depth, and we find on the whole that a thick layer is more effective than a thin one.

W e claim 1. In a vapor electric apparatus, the com-1 the mercury.cathode-pool and substantially 4of the mercury `cathode-pool and substantially coextensive in horizontal extent with the mercury cathode-pool, the ratio of depth to horizontal extent of said cathode-pool being such as to preclude the formation therein of a fundamental stationary Wave, and a layer of solidl granules of insulating material fioating on the mercury cathode.

4. In a vapor electric apparatus, the combination of an anode, a mercury cathode, a-

container therefor, and a layer of solid granules floating on the mercury cathode.

5. In a vapor electric apparatus, the combination of an anode, a mercury cathode, a container therefor, and a layer of solid granules of insulating material floating on the mercury cathode.

6. In a vapor electric apparatus, the combination ofan anode,.a mercury cathode and a conductive cathode lead having an extension constituting in effect the bottom of the mercury cathode pool and substantially coextensive in horizontal extent with the mercury cathode pool, the ratio of depth to diameter of said pool above said extension expressible by a fraction not greater in value than 7. In a vapor electric apparatus the combinationof an anode and a mercury cathode of which the ratio of depth to diameter is expressible by a fraction not greater in value than 2 and a layer of solid granules floating on the mercury.

8. In a vapor electric apparatus, the combination of an anode and a mercury cathode of which the ratio of depth to diameter is expressible by a fraction not greater in value than 1.1 and a layer of solid granules of insulating material floating -on the mercury.

9. In a vapor electric apparatus, the combination of an anode, a mercury cathode and a conductive cathode lead having an extension constituting in effect the bottom ofthe mercury cathode pool and substantially coextensive in horizontal extent with the mercury cathode pool, the ratio of depth to diameter of said pool above said extension expressible by a fraction not greater in value than QT, and a layer of solid granules floating on the mercury.

1.0. In a vapor electric apparatus. the combi nati on of an anode, a mercury cathode and a conductive cathode lead having an extension constituting in effect the bottom of the Signed by us at Boston, Massachusetts,

mercury catllxlode poolland substatiiallly cothis second day of January, 1914.

extensive in orizonta extent Wit t e mer- 'cury cathode pool, the ratio of depth to di- AAlgAUs v 5 ameter of said pool above said extension expressible by a fraction not greater in value Witnesses:

than if, and a layer of solid granules of insu- CHARLES W. WooDBnRRY,

lating material floating on the mercury. FLORENCE A. COLLINS.

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