US2248625A - Electric valve control circuit - Google Patents

Description

ELECTRIC VALVE CQNTROL CIRCUIT Filed March 30, 1940 Carl C. Hersknd, 7 M

y His ttorney.

Patented July 8, 1941 ELECTRIC VALVE CONTROL CIRCUIT Carl C. Herskind, Schenectady, N. Y., assignor to General Electric Company, a corporation of New York Application March 30, 1940, Serial No. 326,925

3 Claims.

My invention relates to electric valve circuits and more particularly to control or excitation circuits for electric valve means of the type employing ionizable mediums, such as gases or vapors.

In the application of electric valve means such as those employing ionizable mediums including gases and vapors, it is frequently desirable to utilize electric valve apparatus of the type having immersion-ignitor control members or makealive electrodes. Electric valves of this type are disclosed and claimed in United States Letters Patent No. 2,069,283, granted February 2, 1937 upon an application of Joseph Slepian et al. In this type of electric valve means, a control member is associated with a cathode and preferably has an extremity of the control member extending into the cathode, which may be a mercury pool. The immersion-ignitor control member is preferably constructed of a material having an electrical resistivity which is large compared with that of the associated cathode, and an arc discharge is established between the anode and the cathode of the electric valve means by transmitting through the control member to the cathode a current of predetermined value sufficient to establish at the surface of the mercury a potential gradient of proper magnitude to effect ionization of the mercury vapor. In accordance with the teachings of my invention described hereinafter, I provide a new and improved control circuit for electric valve apparatus of the above described type.

It is an object of my invention to provide a new and improved electric valve translating circuit.

It is another object of my invention to provide a new and improved excitation circuit for electric valve means.

Itis a further object of my invention to provide a new and improved control circuit for electric valve apparatus of the type employing an immersion-ignitor 'control member in which the life of the electric valve means is substantially increased due to the reduction of the current which the immersion-ignitor control member is required to transmit.

Briefly stated, in the illustrated embodiment of my invention I provide a control circuit for electric valve apparatus including an immersion-ignitor control member in which an inductive network, such as transforming means, produces a periodic voltage of peaked wave form by using a harmonic voltage derived from an associated alternating current circuit, and in which a suitable kunidirectional conducting device is connected between the control member and the inductive network so that only unidirectional current is transmitted to the control member. I also provide in the electric valve means an auxiliary electrode which is connected to the inductive network so that the current furnished by the inductive network is transferred to the auxiliary electrode as soon as an arc discharge is established within the electric valve means. In this manner the current-carrying duty of .the control member is substantially reduced, effecting a substantial increase in the useful life of the electric valve means.

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. Fig. l diagrammatically illustrates an embodiment of my invention a-s applied to a polyphase rectifier, and Figs. 2 and 3 represent 'certain operating characteristics of the arrangement shown in Fig. 1.

Referring now to Fig. 1 of the drawing, I have diagrammatically illustrated my invention as applied to a polyphase electric valve converter for energizing a direct current load circuit I from a polyphase alternating current supply circuit 2 through electric translating apparatus comprising a transformer 3 having primary windings 4 and groups of secondary windings 5 and 6, including a plurality of electric valve means I-i2. A suitable interphase transforming means I3 may be connected between the groups of secondary windings 5 and 6 in the usual manner, so that the -translating apparatus operates as a double three phase system.

The electric valve means l-IZ are of the type comprising an ionizable medium, such as a gas or a vapor, and each includes an anode I4, a cathode I5 which is preferably of the self-reconstructing type, such as a mercury pool cathode, a make-alive or an immersion-ignitor control member I6, and is also provided with a suitable auxiliary electrode II. The auxiliary electrodes I1 may take the form of baies interposed between the cathodes I5 and the anodes I4 and may serve several functions. One of these functions is the transfer of exciting current from the control members IB after the initiation of arc discharges and another function is the propagation or extension of the arc discharges from the 'cathodes I5 to the anodes I4. valve means is rendered conductive at the desired time during the cycle of operation by transmit- Each electric ting to its associated control member I6 a current of predetermined magnitude.

I provide an inductive network or a plurality of inductive networks which produce periodic voltages of peaked wave form which are impressed on the control members I6 of electric valve means 1-I2. 'Ihese inductive networks may comprise a transformer I8 having primary windings I9 and a plurality of secondary windings 26 which produce a voltage of fundamental frequency, that is of the same frequency as the voltage of circuit 2. The transformer I8 may be energized from the supply circuit 2 as shown in Fig. 1. In order to produce a resultant periodic voltage of peaked wave form, I provide a second inductive network which may comprise transformers 2| and 22 having primary windings 23, 24 and secondary windings 25, 26, respectively. The primary windings 23 and 24 are arranged in a Y connection and are connected to be energized from supply circuit 2. The secondary windings 25 and 26 are arranged in an open delta connection so that the voltages appearing across the open terminals are third harmonic voltages relative to the voltage of circuit 2. The third harmonic output voltages of the secondary windings 25 and 26 are combined with the fundamental voltage of secondary windings 20 of transformer I8 through connections 2l, 28 and 29. The resultant voltage furnished by this arrangement is a periodic voltage of peaked wave form.

As a means for supplying to the immersionignitor control members I6 only unidirectional impulses of current, I provide a plurality of unidirectional conducting devices 30-35 inclusive, associated with electric valves 'I-IZ, respectively. Unidirectional conducting devices 3U-35 may be electric valve means and are preferably of the type comprising an ionizable medium, such as a gas or a vapor. The control members or grids thereof may be connected to the cathodes 37 thereof.

In order to relieve the duty imposed on the immersion-ignitor control members I6, I provide a plurality of conductors 38 for connecting the auxiliary electrodes Il to the inductive networks above described.Y Upon the initiation of an arc discharge within the respective electric valve means, the current is by-passed by the circuits including conductors 38 thereby relieving the duty imposed upon the control members I 6, Current limiting resistances 39 may be connected in series relation with the control members I6.

The feature of employing an excitation circuit which continuously produces a periodic voltage for energizing the immersion-ignitor control members and for transferring the current to the auxiliary electrode during each cycle of voltage applied to the anode-cathode circuit is disclosed and broadly claimed in my copending patent application Serial No. 326,924, filed March 30, 1940, which is assigned to the assignee of the present application.

To control the phase relation of the energizing impulses transmitted to the control members I6 relative to the respective anode-cathode voltages, I provide any suitable phase shifting arrangement, such as a rotary phase shifter 40. In this manner, the magnitude of the output voltage of the electric valve means, and hence the power supplied thereby, may be controlled or adjusted. Transformers 4I may be employed to supply cathode heating current to the filaments of the cathodes for the unidirectional conducting devices 30-35.

The operation of the embodiment of my invention shown in Fig. 1 will be explained by considering the system when it is operating as a rectifier to transmit power to the direct current circuit I. Due to the connection of the secondary windings 5 and 6 of transformer 3 and the interphase transformer I3, the electric valve converting system will operate as a double three phase rectifier, each winding transmitting load current for electrical degrees during each cycle of voltage of circuit 2, but for only 60 electrical degrees with any one other winding of another group. In other words, two electric valve means of the group 'I-I 2 are always conductive, but any one valve will conduct current for only 60 electrical degrees with any one other electric valve.

The electric valve means 'I-I2 are rendered conductive at the desired times during the cycle of operation by the excitation circuits connected to the control members I6 comprising the transformers I8, 2| and 22 and unidirectional conducting devices 3--35, The transformers I8, 2I and 22 produce periodic voltages or currents of peaked wave form which are transmitted through the unidirectional conducting devices 30-35 to the respective associated control members I6 to render the electric valve means conductive. As soon as an arc discharge is established within the electric valve means, due to the establishment of a cathode spot upon the cathodes I5, the currents furnished by the excitation circuits are transferred from the control members I6 to the auxiliary electrodes I'I, thereby decreasing the duty imposed on the control members. The unidirectional conducting devices 30-35 assure that only unidirectional currents are transmitted to the control members I6.

The manner in which the excitation circuit furnishes the control voltages and the manner in which the currents are transferred between the control members I6 and the electrodes II may be more fully explained by referring to the operating characteristics shown in Figs, 2 and 3. Curve A of Fig. 2 represents the voltage of one phase of the transformer I8, such as the voltage of secondary winding 2U associated with unidirectional conducting device 30. Curve B represents the third harmonic voltage furnished by secondary windings 26 of transformer 22; and curve C represents the resultant periodic voltage of peaked wave form provided by the combination of the voltage of fundamental frequency and the third harmonic voltage. In Fig. 3 the dotted curve C represents the positive portion of the voltage of peaked wave form which is furnished by the associated part of the excitation circuit. The heavy curve D represents the actual current transmitted to the immersion-ignitor control member I6 of electric valve means 'I for that condition where the electric valve means 'I is rendered conductive at time a. That is, the immersion-ignitor control member I6 conducts current furnished by the unidirectional device 3U from the excitation circuit until the current reaches a value sufficient to establish a cathode spot upon cathode I5. The cathode spot is established at time a and the current is immediately transferred to the auxiliary electrode Il, Immediately upon such transfer, the current transmitted by the control member I6, of course, decreases substantially and the current transmitting duty is reduced. It will be understood, that as soon as the control member I6 has performed its duty during each cycle of operation the current is transferred therefrom. Furthermore, due to the presence of the unidirectional conducting device 3Q, the negative portion of the periodic voltage of peaked wave form furnished by the excitation circuit is suppressed, affording a further protection to the immersion-ignitor control member I6. In this manner, during each cycle of operation or during each cycle of Voltage of circuit 2, the control members I6 conduct current only until arc discharges are established, at which time the currents are transferred to the auxiliary electrodes.

When the auxiliary electrodes I1 are arranged in the form of a baiile interposed between the anodes I4 and the cathodes I5, the auxiliary electrodes not only assist in the transfer of current from the control members I6 after the initiation of an arc discharge but also assist in the propagation of the arc discharge to the anodes.

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 modiiic'atio-ns 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 direct current circuit, electric translating apparatus connected between said circuits and including an electric valve means of the type employing an ionizable medium capable of supporting an arc discharge and comprising an anode, a cathode, an immersion-ignitor control member and an auxiliary electrode, means for supplying energizing current to said immersionignitor control member comprising one inductive network energized from said alternating current circuit for producing a voltage of fundamental frequency, a second inductive network energized from said alternating current circuit for producing a periodic voltage of triple frequency and means responsive to the resultant of the fundamental voltage and the triple frequency voltage to impress on said control member a periodic voltage of peaked wave form, and means for connecting said auxiliary electrode to said inductive networks to effect transfer of current from said immersion-ignitor control member to said auxiliary electrode upon the initiation of an arc discharge within the electric valve means.

2. In combination, an alternating current circuit, a direct current circuit, electric translating apparatus connected between said circuits and including an electric valve means of the type employing an ionizable medium capable of supporting an arc discharge and comprising an anode, a cathode, an immersion-ignitor control member and an auxiliary electrode, means for supplying energizing current to said immersionignitor control member comprising one inductive network energized from said alternating current circuit for producing a voltage of fundamental frequency, a second inductive network energized from said alternating current circuit for producing la periodic voltage of triple frequency and means responsive to the resultant of the fundamental voltage and the triple frequency Voltage to impress on said control member a periodic voltage of peaked wave form, a unidirectional conducting device connected between said control member and said inductive networks so that only unidirectional current is transmitted to said control member, and means for connecting said auxiliary electrode to said inductive networks to eiect transfer of current from said control member to said auxiliary electrode upon the initiation of Ian arc `discharge: within said electric valve means.

3. In combination, an alternating current circuit, a direct current circuit, electric translating apparatus connected between said circuits and including an electric valve means of the type employing an ionizable medium, capable of supporting an arc discharge and comprising an anode, a cathode, an immersion-ignitor control member and an auxiliary electrode, an excitation circuit for supplying energizing current to said control member comprising :a transformer energized from said alternating current circuit for producing a voltage of fundamental frequency, a transformer having a Y-connected primary winding and an open-circuit delta secondary winding for producing a voltage which is a third harmonic of the voltage of said alternating current circuit, means for interconnecting said transformers to produce a periodic voltage of peaked wave form, means for connecting said transformers to said control member comprising a unidirectional conducting device, and means for connecting said auxiliary electrode to said transformers to effect transfer of current from said immersion-ignitor control member to said auxiliary electrode upon the initiation of an arc discharge within said electric valve means.

CARL C. HERSKIND.

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