US3480822A - Method of rectifying heavy high-voltage currents and a device for realization thereof - Google Patents

Description

NOV. 25, 1969 NASTJUKHA ETAL 3,480,822

METHOD OF RECTIFYING HEAVY HIGH-VOLTAGE CURRENTS AND A DEVICE FOR REALIZATION THEREOF Filed Feb. 28, 1967 INVENTORS fl amnd'r I. Mari nib eta! M/nm, ill nm flmmk dLw ATTORNEY5 United States Patent US. Cl. 313-161 6 Claims ABSTRACT OF THE DISCLOSURE A gas-discharge valve for rectifying heavy high-voltage currents, comprising a cold hollow solid-state cathode operating in arc discharge duty characterized by a low voltage of the discharge. The are gas-discharge valve is essentially fashioned as an enclosed hermetically-sealed metal chamber having an insulated anode inserted thereinside. The anode and cathode form a gas-discharge gap in which there is created a pressure p (mm. Hg) satisfying the condition ap 3 cm. mm. Hg, Where a" is a dimension determining the size of the cathode cavity, and the product of the pressure by the distance d between the anode and the bottom of the cathode cavity is less than pal corresponding to the left-hand branch of Paschens curve (pd pd When cut in an AC. circuit having a low load resistance, this device provides for rectification of alternating currents. To start the are valve at a preset moment of time, when it is cut into pulse circuits, the valve is provided with a firing arrangement.

The present invention relates to electrical devices designed for conversion of high-voltage current and, particularly, to a cold-cathode arc valve.

Widely known are devices for rectifying alternating current with the aid of an arc discharge where the rectifying properties of a gas-discharge gap are determined by a difference in physical qualities or states of electrodes. Thus, for example, a gas-discharge arc gap with a hot cathode (gas diode thyratrons) possesses rectifying properties due to high emissivity of the hot cathode. However, the limited density of thermoemission current does not allow the hot cathodes to be used in the region of heavy currents. Gas-discharge devices with a mercury-pool cathode (mercury rectifiers, ignitrons, excitrons) are used in the region of these currents. The rectifying properties of these devices are explained by the fact that an arc can be easily initiated on a mercury-pool cathode. In spite of a great number of advantages, however, the mercury-pool cathode, brings about certain difficulties in the manufacture and operation of said rectifiers. It requires the introduction of additional screens in the rectifier chamber and makes its operation very sensitive to temperature. The latter circumstance makes it necessary that the temperature of operation be maintained by valves with the aid of a thermostat system at a certain level and within only a narrow range. A system of this kind consumes a large amount of power. When ignitrons operate in pulse circuits, the pool cathode limits the permissible rectified currents the value of which is not more than 10 ka.

Devices with a hollow cold cathode are also known that operate in the region of a normal glow discharge. Owing to the properties of the glow discharge, however, these devices operate in the current range up to tens of milliamperes at a voltage drop of several hundreds of volts. The pressure of the filling gas in glowdischarge devices usually amounts to tens and hundreds of millimeters of mercury, which limits their frequency characteristics.

The object of the present invention is to eliminate the above-mentioned disadvantages.

Another object of the invention is to provide a device for rectifying heavy high-voltage currents which would make it possible to operate in pulse duty and to sharply increase the operating currents in this duty as far as several tens of kiloamperes at a voltage of up to 10 kv. with maintenance of the unidirectional conductance, i.e., an arc valve with improved frequency characteristics.

According to the above-mentioned and other objects, the invention is essentially a means for rectifying heavy high-voltage currents, which utilizes the sharp difference in arc discharge firing potentials at different polarities of the gas-discharge gap electrodes. This diflFerence is attained by creating a condition in the anode-hollow cold solid state cathode gap that would enable the hollow cathode effect to appear during an abnormal glow discharge that precedes the arc discharge. This condition is: the product of the inner size (for example, diameter) of the hollow cathode at (cm.) by the pressure of the filling gas p (mm. Hg) is less than 3 (ap 3 cm. mm. Hg). In this case, another condition should also be satisfied: the product of pressure p (mm. Hg) by the distance between electrodes d (cm.) corresponds to the values which are ni the region of the left-hand branch of Paschens curve (pl pd The device according to the invention comprises a hollow cold solid state cathode, an insulated anode, a means for setting up a required gas pressure in the anode-hollow cathode gap, and a firing arrangement located outside the hollow cathode and communicating with the latter through a hole.

Hereinafter, the invention will be explained by an exemplary embodiment thereof and the accompanying drawings, in which:

FIG. 1 is the arrangement of the anode-hollow cathode system; and

FIG. 2 is the arc valve with a hollow cold solid state cathode, according to the invention.

The general operation of the device with a hollow cold solid cathode, according to the present invention, is based on the properties of an abnormal glow discharge in the anode-hollow cathode system. In a gas-discharge gap with such electrodes we have the anode A (FIG. 1)-hollow cathode K system in the case of one polarity, and the anode K-plane cathode A system in the case of the opposite polarity.

As is known, in the system of electrodes with a double or hollow cathode operated in abnormal glow discharge duty, the current density proves to be, with other conditions being equal (the filling gas pressure and the voltage of discharge), several orders higher than in the case of an ordinary plane cathode. We have discovered that, owing to a little width of the cathode drop region and, consequently, to a large electrical field at the cathode, the transition of the glow discharge to the arc discharge takes place in a system of this kind at voltages much lower than in the case of a plane cathode. In addition, it is known that in the pressure region corresponding to the left-hand branch of Paschens curve a plane cathode system develops a high-voltage glow discharge which is characterized by a high discharge voltage drop. A positive volume charge arising during the high-voltage glow discharge precludes a further increase of the current, the result of which is that the transition to an arc discharge takes place in a plane cathode system at very large voltage and current values. Thus, there exists a pressure region in which a rectifying eflect occurs in an anode-hollow cathode system with the latter operated in the arc-discharge duty. The region of filling gas pressures is determined, on the one hand, by the condition of the hollow cathode effect existence, i.e. ap 3 cm. mm. Hg, and, on the other hand, by the condition of the high-voltage glow discharge occurrence, i.e. pd pd If, in a gas-discharge gap formed by the system of electrodes shown in FIG. 1, a pressure is set up which corresponds to the above conditions and this system is connected to an AC. circuit with a low load resistance, rectification of alternating current can be accomplished.

The advantages of a hollow solid state cathode can be seen most clearly in the region of heavy currents over 1000 a. during operation in pulse circuits. In this case, to initiate an arc discharge in the above rectifying system at a given moment of time, an additional ionization should be produced in the hollow cathode. As a result, owing to the properties of a hollow cathode the initiated volume charge will facilitate the transition of the discharge to the arc form. The additional ionization can be produced by a lowpower discharge in an auxiliary igniting device.

In so far as an arc discharge can be initiated under the conditions of a low pressure the charged particles are recombined at the electrodes after the discharge ceases and when the voltage polarity is changed. The interelectrode space is rapidly being deionized, the electric strength is being restored, and no arcback takes place. No pressure increase occurs after the passage of a current pulse except for a relatively short aging process. Moreover, a decrease in the gas pressure has been noticed in the discharge chamber after the passage of a current pulse.

One possible design version of a hollow-cathode arc valve according to the present invention includes an enclosed metal chamber 1 (FIG. 2) and a base 2 on which chamber 1 is secured by means of a rubber gasket 3. This chamber and base serve as a hollow solid state cold cathode for the rectifier. A copper anode 5 extends into chamber 1 through an insulator 4 and is cooled by water through pipes 6. The cathode is cooled with running water that comes into a jacket 7. The air is evacuated from the chamber by a forepump through a number of holes 8, a forechamber 9 with a vacuum valve 10. The pressure of a gas (for example, air, hydrogen, or some other gas) is set up with the aid of an adjustable means 11 through a pipe 12. The value of pressure is measured by a thermocouple pressure gauge 13. In its simplest form, the purposes of the means for setting up a required gas pressure can be served by a needle valve. In case hydrogen is used as a filling gas, a heated palladium capillary may be employed as the adjustable means. In a soldered-off rectifier, the gas pressure may be set up with the aid of a titanium hydrogen generator.

To initiate an arc discharge, use is made of a firing arrangement located outside the hollow cathode. The firing device consists of an additional chamber 14 communicating with the interior of the main chamber 1 through a hole 15. Inside the firing chamber an insulated electrode 16 is provided to which a positive trigger pulse is applied. To facilitate the firing of an auxiliary discharge, use is made of a small ring-shaped permanent magnet 17. Electrode 16 is cooled with running water through pipes 18.

When operated in pulse duty with the filling gas pressure ranging from 10- to 10- mm. Hg, the rectifier enables single-polarity current pulses with an amplitude of 50 ka. to be generated at the voltage of 10 kv. The pulse repetition frequency amounts to several cycles per second, the average current is up to 200 a. The current pulse duration is 1 msec. and more. It has been found that when the rectifier was connected to an inductive shorting circuit, currents with an amplitude of ka. were obtained at a current pulse duration of 300 msec.

We claim:

1. A gas-discharge arc valve for rectifying heavy highvoltage currents, comprising a cold hollow solid-state cathode made as an enclosed hermetically sealed metal chamber; an insulated anode extending into said hollow cathode; means for creating in said chamber a gas pressure of such a value that would satisfy the conditions under Which the product of pressure p (mm. Hg) by a dimension a (cm.) determining the size of the cavity of the cathode is less than 3 cm. mm. Hg (ap 3 cm. mm. Hg) and the product of the pressure by the distance d between said anode and the bottom of said cavity of said cathode is less than pd corresponding to the left-hand branch of Paschens curve (pd pd 2. A valve as claimed in claim 1, in which said cathode forming said chamber is made cylindrical.

3. A valve as claimed in claim 2, in which said anode made as a disc is coaxially disposed inside said chamber near the upper side thereof.

4. A valve as claimed in claim 3, comprising a firing arrangement designed for switching on the valve.

5. A valve as claimed in claim 4, in which said firing arrangement communicates with said chamber and consistsof an additional discharge chamber, an insulated electrode to which a trigger pulse is applied, and a permanent magnet which creates a magnetic field in said additional discharge chamber.

6. A valve as claimed in claim 3, with means for cooling said cathode and anode by running water.

References Cited UNITED STATES PATENTS 2,660,687 11/1953 Coleman 313161 3,290,542 12/1966 Lafferty 313-231 X JAMES W. LAWRENCE, Primary Examiner RAYMOND F. HOSSFELD, Assistant Examiner US. Cl. X.R. 313187, 198, 217

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