US1919263A - Rectifier - Google Patents

Description

C. G. SMITH July 25, 1933.

RECTIFIER Filed April 12, 1928 IIV w 17201621 for l" I SrzziZ/ '1? g QM Patented July 25, 1933 UNITED STATES PATENT OF CAMBRIDGE, MASSACHUSETTS, A

3155 TO BAYTHEON INQ, CORPORATISN 0F I'TKIASSAGHUSETTS RECTIFIER Application filed April 12,

The present invention relates to glow discharge rectifiers, particulary of the full wave type and for use with high voltage.

V In prior art gaseous rectifiers for high voltage work, one of the causes of tube failure appears to reside in the cracking of the envelope in the region of the seal about the lead-in wires and is the result of gas or air leakage with attendant heat caused by electrolysis at these places. In order to minimize the probability of this form of rupture, I propose to maintain the effectiveness of the seal to the extent of absolutely precluding the passage of gas or air even under conditions of intense electrolysis which ordinarilyaccompany high electric l stress and for this purpose, provide a novel form of stem.

In addition to the above, a further cause of failure is present for upon the application of high voltage, e. g. of the order of 500 volts or more, to a full wave rectifier, i. e. a double anode-single cathode or double cathodesingle anode type, there is marked tendency for the reverse current flowing between two of the electrodes to be greatly increased when current is passing across the other set of elect-r"?des. The reverse current represents a loss of energy, and, in addition, has the dis advantage of deleteriously affecting the rectilied current component. In order to isolate the useful from the parasitic current w thin the rectifier, I propose to segregatethe two discharges in the manner described hereinafter.

Accordingly, one object of my invention is to provide a glow discharge rectifier capable of withstanding high voltage and be eflicient in operation. A more specific object is to improve the type of seal and the manner in which the electrodes are secured in the stem. An exemplary embodiment of the apparatus forming the subject of my invention shown on the drawing in which numeral 1 designates an envelope of glass terminating in reentrant stem and press 2. Within the envelope and supported from the press in upright position there is a hollow cathode 3 of relatively large diameter, made of thin sheet refractory metal, as nickel. The top end of 1928. Serial Ito. 289,526.

the cylinder is closed by a metallic plate l, also refractory and flanged about the periphery for securing to cathode. Projecting into the lower region of the hollow electrode are two anodes 5 of carbon preferably in red form and anchored in pr-determined relation to one another by a tight fitting bushing or thi'mble i of insulating material as lavite. The bushings have an axial bore with a flared or enlarged portion the top. The bottom of the cathode is closed by a metallic disk 7 containin two apertures, the peripheral edges of which are bent over to grip the inner surface of the upstanding columns 6 about the larger diametral dimension. Thus around the active surface of each anode 5 is annular space 13. This space has a radius such that at the pressure of the particular gas used, the gap is insulating because of its relation to the mean free path of the gas. The annular space is also sudiciently deep so that any bombardment of the anodes will not injure the insulation. In order to lower the center of gravity of the cathode as a whole, the bottom closure 7 should be dished in the manner shown, the central portion carrying the anodes extending well into the cathode chamber.

The cathode is preferably divided into two compartments or sections partitioned len gthwise by barrier 8 of refractory metal. This barrier may be solid or perforated. It is preferably a wire gauze. This gauze prevents the main current from increasing the back current but at the same time allows sufficient ionizing agencies to wander back and forth so that starting in one compartment is easy while the other is subjected to reverse current.

The members 6 are supported from the press by a surrounding body of glass 9 formed integral by fusing with the stem 2. By fitting the lava members inside the tubes 9 instead of embracing the exterior surface as heretofore, the advantage of reducing the necessary amount of lava, is obtained. Depending from the lower surface of the stem, there are appendages or projections 10, preferably of the same material as the stem, fused about the lead-in conductors 11 which pass to the electrodes. These extensions are sealed over each wire and provide an additional obstruction to the passage of air in case lealrage occurs in the main body of the press where the high potential gradient and temperature may give rise to electrolysis and rupture. If desired, the conductors may pass loosely through the stem, the seal being made at the tip end of the extension. The portion of the wire above the seal may be coated with magnesium oxide 14 to insulate it. This is a better insulator than. glass, hence, wherever the wire and glass touch, the glass will be protected. Due to the fact that members are removed from the region of discharge and their arrangement facilitates circulation of air between the projections, the seal at this point is cool and therefore quite effective and permanent. After the envelope has been evacuated in the usual manner, a gas of the monatomic group is admitted, preferably helium at a pressure ranging between S and 1.0 111. m. Hg; the tube is then capped. If desired, a trace of alkali metal vapor, e. g. cmsium, may also be added, having the twe fold function of reducing the starting potential, hence losses, and removing the deleterious impurities without absorbing any of the useful gaseous content. The vapor may be conveniently derived from chemicals, e. g. caesium chloride combined with calcium chips, held in a capsule 12 and heated in any suitable manner, e. g. by electrical bombardment or eddy currents. Upon the application of a relatively high voltage, e. g. 550 volts, a glow discharge is initiated between each anode and the cathode, producing a rectified direct current in the output circuit.

Experience has shown that while the back current at a given voltage becomes less as the gas pressure is lowered, the magnitude of this current remains of practical importance even with a pressure as low as 5 m. m. Hg. It has been noted that under conditions of high voltage, the back current to one anode is greatly augmented when the normal current flows to the other anode, perhaps due to an interchange of ionization effects. lVhatever the cause, I have found that by segregating the discharges from one another, e. g. by partition 8, the back current in one con'ipartment is rendered substantially independent of the normal current flowing 1n the other compartment, thus m1n1m1zing the reversal of current. In View of the fact that for high voltage work the pressure of gas is relatively low, e. g. 5 m. m. Hg, calling for the strict conservation, the anode material should be such as to restrain gas clean-up i. e. the permanent entrapment of gas molecules in the metal. For this material I prefer carbon which also offers relatively small disintegration under bombardment.

From the foregoing it is evident that I have provided a glow discharge device constructed in manner to withstand relatively high voltage without rupture 0r undue energy loss. While the novel stem has been shown. and described in connection with a rectifier, it is apparent that its utility is not limited thereto but has broad application to all forms of electrical apparatl'ls embodying a combined envelope and stem through which high voltage leads pass.

I claim:

1. A gaseous rectifier comprising an evacuated envelope containing a gas filling, a large area cathode structure constituting a plurality of adjacently positioned compartments, small area anodes cooperating with the interior surfaces of said con'ipartments to maintain therewith unidirectional gaseous discharges, the adjacent compartments be ing separated by a metallic mesh barrier for preventing the discharge in one compartment from extending into the adjacent compartment, but securing a mutual ionizing influence between the compartments.

2. A gaseous rectifier comprising an evacuated envelope containing a gas filling, a large area cathode structure constituting a plurality of adjacently positioned compartments, small area anodes projecting into the interior of said compartments to alternately maintain unidirectional gaseous discharges with the interior surfaces of said compartments, the adjacent compartments being separated by a metallic mesh barrier for preventing the discharge extending over the interior surfaces of the cathode structure in one compartment from extending onto the interior surfaces of the adjacent compartment, but securing an ionizing influence of the small area anode in one compartment on the gas in the other compartment to facilitate starting of the discharge in the other compartment.

CHARLES G. SMITH.

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