US2254703A - Electric valve control circuits - Google Patents

Description

Sept. 2, 1941.

H. DE B. KNIGHT ELECTRIC VALVE CONTROL CIRCUITS Filed Jan. 23, 1939 Fig.2.

Inventor": Henry de Bo yne Knight,

by His Attohney.

' such as boron-carbide or silicon-carbide.

Patented Sept. 2, 1941 ELECTRIC VALVE CONTROL CIRCUITS Henry de Boyne Knight, Rugby, England, assignor to General Electric Company, a corporation of New York Application January 23, 1939, Serial No. 252,469 In Great Britain February 23, 1938 '7 Claims.

My invention relates to electric valve circuits, and more particularly to control or excitation circuits for electric valve means of the type employing an ionizable medium and an immersionignitor control member.

In electric valve means of the type employing an immersion-ignitor control member which is associated with a self-reconstructing cathode, such as a mercury pool cathode, the are between the anode and the cathode is initiated by passing through the immersion-ignitor control member current of predetermined magnitude. The immersion-ignitor control member is constructed of a suitable material having an electrical resistivity relatively large with respect to that of the associated mercury pool cathode. The immersionignitor control member may be constructed of a poorly conducting or semi-conducting material, The design and dimensions of the ignitor control members are determined by various considerations. In the systems employed heretofore, the ignitor current has been supplied generally from a grid controlled hot cathode rectifier, in which applications it is desirable to design the ignitor to maintain the current at a relatively low value.

This may be achieved by making the ignitor control member small in diameter at the point where it comes in contact with the cathode. Furthermore, the voltage to be applied to the ignitor should be maintained at a low value, and for this reason the length of the control member should be reduced as much as possible.

On the other hand, in the case of a mercurypool type rectifier designed for relatively large currents, additional factors come into consideration, as, for example, heat dissipation, mechanical forces on the ignitor due to the movement of the mercury during transport and in operation, and the tendency to cause changes in the mercury level and, therefore, changes in the point of contact between the ignitor and the mercury, due not only to action of the cathode spot but also caused by the evaporation of the substance of the cathode. It has been found that these factors necessitate an ignitor of robust design and having a minimum length.

The above stated requirements are obviously conflicting, and various attempts have been made heretofore to produce an ignitor control member so shaped as to compromise satisfactorily between the two sets of conditions. Ignitors so built are, however, costly to produce and diflicult to make with accuracy. In accordance with the teachings of my invention described hereinafter,

I provide new and improved control systems for electric valves employing immersion-ignitor. control members and in which the necessity for making the above stated compromise is obviated.

It is an object of my invention to provide new and improved electric valve circuits.

It is another object of my invention to provide new and improved electric valve control circuits.

It is a further object of my invention to provide new and improved control or excitation circuits for electric valve translating apparatus.

In accordance with the illustrated embodiments of my invention, I provide new and improved control or excitation circuits for electric valve means of the type employing an immersion-ignitor control member. I employ a main or power electric valve means having an ignitor control member of simple, robust design, for example, a cylindrical conductor of semi-conducting material long enough and sufliciently thick to cope satisfactorily with the conditions imposed on a heavy duty rectifier, but requiring a relatively high starting current. The starting current is supplied by means of an auxiliary electric valve means of the controlled type having a mercury pool cathode, since this type of electric valve is better adapted to transmitting large peak currents than those of the hot cathode type. The ignition of the arc in the main or power electric valve means is controlled by controlling the ignition of the arc in the auxiliary electric valve means. In one embodiment of my invention, I provide a control electric valve or electronic discharge device of the thyratron type or hot cathode type which controls the energization of the immersion-ignitor control member of the auxiliary electric valve. In accordance with another illustrated embodiment of my invention, I provide an auxiliary electric valve of the type having an immersion-ignitor control member and a grid which control the energization of the immersion-ignitor control member of the main or power electric valve means. A source of current establishes a cathode spot on the cathode of the auxiliary electric valve during practically the entire positive half cycles of voltage of an associated alternating current supply circuit and the grid renders the auxiliary electric valve conductive at the desired time, thereby obtaining precise and positive control of the conductivity of the power electric valve and making it possible to supply at the precise time a relatively large starting current for the power electric valve.

For a better understanding of my invention, reference may be-had to the following description taken in connection with the accompanying drawing, and its scope will be pointed out in the appended claims. Figs. 1 and 2 diagrammatically illustrate various embodiments of my invention as applied to electric translating apparatus for transmitting power between an alternating current supply circuit and a direct current load circuit.

Referring to Fig. I of the drawing, my invention is there illustrated as applied to electric translating apparatus for transmitting power from an alternatin current supply circuit I to a direct current load circuit 2, through an electric valve means 3 which is of the type employing an ionizable medium such as a gas or a vapor and which includes an anode 4, a mercury pool cathode 5, and an associated immersion-ignitor control member 6. The immersion-ignitor control member 6 is constructed of a semi-conducting or poorly conducting material, such as silicon carbide or boron carbide, the specific electrical resistivity of which is substantially greater than that of the associated mercury pool cathode. The immersion-ignitor control member 6 is of robust design and construction, arranged to withstand substantial mechanical strain due to mechanical forces or due to the ordinary electrical operation of the electric valve means, but requiring a sub stantially large starting current.

In order to effect energization of the immersion-ignitor control member 6, I provide an exciter or control circuit I which is connected between the anode 4 and the cathode 5. The control circuit 1 comprises a serially connected impedance element, such as a resistance 8, and an auxiliary electric valve means or auxiliary electronic discharge device 9 which is also of the type having an immersion-ignitor control member II), a mercury pool cathode II and an anode I2. The immersion-ignitor control member II) of the auxiliary electronic discharge device 9 is energized by means of a circuit I3 which is connected across the anode I 2 and the control member II] and comprises a resistance I4 and a control electric valve I5 of the hot cathode type having a control grid I6 which renders the electric valve means l5 conductive. The electric valve means I5 is preferably of the type employing an ionizable medium. A periodic voltage of predetermined phase displacement relative to the voltage of the alternating current supply circuit I is impressed on the control grid I6 in order to control the conductivities of the electric valve means 3 and 9. This periodic control voltage may be supplied from a source of alternating current II, or may be connected to the alternating current circuit I through a suitable phase shifting device such as a rotary phase shifter I8. A suitable source of negative unidirectional biasing potential, such as a battery I9, may be employed.

The operation of the embodiment of my invention shown in Fig. 1 will be explained by considering the system when it is designed to transmit unidirectional current to the load circuit 2. Electric valve means 3 is rendered conductive during each positive half cycle of voltage of circuit I to transmit direct current to the load circuit 2. The time during each positive half cycle of voltage at which the electric valve means 3 is rendered conductive is determined by the time of energization of the immersion-ignitor control member 6. The auxiliary electronic discharge device 9 conducts unidirectional current to the control member 6 from the supply circuit I at the desired time to render the electric valve means 3 conductive. The electronic discharge device 9 in turn is rendered conductive by the control electric valve means I5 which in turn is controlled by the rotary phase shifter I8. Since the electronic discharge device 9 is of the mercury pool cathode type, a relatively large starting current is transmitted to the control member 6 in order to assure positive and accurate starting of the electric valve means 3. Of course, as soon as the electric valve means 3 is rendered conductive, the voltage appearing across the anode and cathode thereof decays so that current is no longer transmitted to the control member 6.

Fig. 2 diagrammatically illustrates another embodiment of my invention which is similar in many respects to that shown in Fig. 1, and corresponding elements have been assigned like reference numerals. In the embodiment of my invention shown in Fig. 2 I provide an auxiliary electric valve means or electronic discharge device 20 which is preferably of the type employing an ionizable medium, such as a gas or a vapor, and is particularly illustrated as employing mercury vapor as the ionizable medium. The auxiliary electronic discharge device 20 comprises an anode 2|, a mercury pool cathode 22, an immersion-ignitor control member 23 and a control grid 24. The electronic discharge device 20 is connected across the anode 4 and the control member 6 of the electric valve means 3 and transmits relatively large amounts of unidirectional current to the control member 6 from the alternating current circuit I in order to render the electric valve means 3 conductive. A suitable current limiting or controlling impedance, such as a resistance 25, may be connected in series relation with the electronic discharge device 20. The control member 23 of the electronic discharge device 20 maintains a cathode spot on the cathode 22 so long as the control member 23 is properly energized and the control grid 24 renders the electric valve means conducting, that is, establishes an arc discharge between the anode 2| and the cathode 22, thereby effecting precise and accurate control of the time at which theteleotronic discharge device 29 conducts curren As a means for supplyin current to the control member 23 in order to maintain a cathode spot on cathode 22, I provide a control circuit which may comprise a transformer 26, a unidirectional conducting device 27 and a current limiting resistance 28. The circuit transmits a substantially unidirectional current to the control member 23 and that current may be controlled so that the cathode spot is maintained during substantially the entire positive half cycles of voltage of circuit I. The time during which the cathode spot is maintained may be controlled by means of a rotary phase shifting device 29 which is energized from a suitable source of alternating current 30. Of course, the rotary phase shifter 29 tmay be connected to alternating current circui In operation the rotary phase shifter 23 is adjusted in order that a cathode spot is maintained on the cathode 22 during substantially the entire positive half cycles of voltage of circuit I. Of course, the electric valve means 3 will not be rendered conductive until current is transmitted to the control member 6 by the electronic discharge device 20. The electronic discharge device 20 will not conduct current until a suitable voltage is impressed on the control grid 24 by means or the rotary phase shifter l8. By the proper positioning of the rotary phase shifter IS, the times during the positive cycles of the voltage of circuit I at which the electronic discharge means 20 is rendered conductive, are controlled to control the amount of current transmitted by the electric valve means 3. The control circuit transmits only unidirectional current to the immersion-ignitor control member 23. The circuit including the transformer 26, unidirectional conducting device 21 and the phase shifter 29 transmits to the control member 23 a series or train of discrete impulses of unidirectional current which are correlated in time relationship with respect to the voltage of the alternating current circuit I. These impulses are transmitted to the control member during alternatev half cycles of voltage of circuit I. Since the cathode spot is maintained on the cathode 22 during substantially the entire positive half cycles of voltage of circuit I or for a predetermined interval of time prior to the time at which it is desired to render the electronic discharge device 20 conductive, the electronic discharge device 20 may be rendered conductive at precise times and a sufliciently large starting current may be transmitted to the immersion-ignitor control member 6 of the power electric valve means 3, thereby permitting the use of a rugged and substan tial construction of the immersion-ignitor control member 6.

While I have shown and described my invention as applied to a particular system of connections and as embodying various devices diagrammatically shown, it will be obvious to those skilled in the art that changes and modifications may be made without departing from my invention, and I, therefore, aim in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. In combination, an alternating current circuit, a load circuit, electric valve means connected between said circuits and comprising an anode, a cathode and a control member of the immersion-ignitor type, an excitation circuit for energizing said control member connected between sail anode and said control member and comprising an electric valve means including an anode, a cathode and an immersion-ignitor control member, means for energizing said second mentioned control member comprising means for transmitting to said control member discrete impulses of unidirectional current to maintain a cathode spot on said second mentioned cathode during substantially the entire positive half cycle of voltage of said alternating current circuit, and means for controlling the conductivity of said second mentioned electric valve means to effect energization of said first mentioned control member.

2. In combination, an alternating current supply circuit, a load circuit, electric valve means connected between said circuits and including an immersion-ignitor control member, an excitation circuit for energizing said control member and including an auxiliary electronic discharge device for energizing said control member and including an anode, a cathode, animmersion-ignitor control member and a control grid, means including a rectifier for transmitting discrete impulses of unidirectional current to said control member for maintaining a'cathode spot on said cathode during substantially the entire positive half cycles of voltage of said alternating current circuit, and means'for energizing said grid to render said electronic discharge device conducting to efiect energization of said first mentioned control member.

3. In combination, an'alternating current supply circuit, a load circuit, electric valve means connected between said circuitsand including an immersion-ignitor control member, an excitation circuit for energizing said control member and including an auxiliary electronic discharge device for energizing said control member and including an anode, a cathode, an immersion-ignitor control member and a control grid, means for energizing said control member comprising a source of current for energizing said second mentioned immersion-ignitor control member and a unidirectional conducting device for transmitting to said control member discrete impulses of unidirectional current to maintain a cathode spot on said cathode during substantially the entire positive half cycles of voltage of said source, and means for impressing on said grid a periodic voltage to render said electronic discharge device conducting at predetermined times during the cycles of voltage of said alternating current circuit.

4. In combination, an alternating current circuit, a load circuit, electric valve means connected between said circuits and including an immersion-ignitor control member, an excitation circuit for energizing said control member and including an auxiliary electronic discharge device for energizing said control member and including an anode, a cathode, an immersion-ignitor control member and a control grid, means for supplying discrete impulses of unidirectional current to said second mentioned control member to maintain a cathode spot on the associated cathode during substantially the entire half cycles of voltage of said alternating current circuit, and means for energizing said grid to render said electronic discharge device conducting.

5. In combination, an alternating current circuit, a second circuit, electric translating apparatus connecting said circuits and comprising an electronic discharge device including an anode, a cathode, an immersion-ignitor control member associated with said cathode and a control grid, means for supplying to said control member discrete impulses of unidirectional current timed with respect to the voltage of said alternating current circuit to establish a cathode spot on said cathode during each cycle of the voltage of said alternating current circuit, means for impressing a potential on said control grid to maintain said discharge device nonconducting, and means for modifying said potential to permit the flow of current between said anode and said cathode.

6. In combination, an alternating current circuit, a second circuit, electric translating apparatus connected between said circuits for controlling the transfer of power therebetween and including an electric discharge device of the type employing an ionizable medium and comprising an anode, a cathode, an immersion-ignitor control member and a control grid, means for energizing said control member comprising means for transmitting to said control member a series of discrete impulses of unidirectional current timed with respect to the voltage of said alteran anode, a cathode, an immersion-ignitor control member associated with said cathode and a control grid, means for transmitting current to said control member during alternate half cycles of voltage of said alternating current circuit to establish a cathode spot on said cathode during each cycle of the voltage of said alternating current circuit, means for impressing a potential on said control grid tending to maintain said discharge device nonconducting, and means for modifying said potential to initiate the flow of our- 10 rent between said anode and said cathode.

HENRY DE BOYNE KNIGHT.

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