US2248624A - Electric valve control circuits - Google Patents

Description

'July 8, 1941. c. c. HERSKIND ELECTRIC VALVE CONTROL CIRCUITS Filed Ma rch 30, 1940 2 Sheets-Sheet 1 Fi$.2a.

OUTPUT VOLTAGE OF TRANSFORMER I2 VOLTAGE IMPRESSED ACROSS CONTROL a m m m Inventor Carl C. Herskind M v His Attorney.

July 8, 19 41. c.-c. HERSKIND ELECTRIC VALVE CONTROL CIRCUITS Filed March 30, 1940 2 Sheets-Sheet 2 Inventbr:

m W n x" H /W p .w a/ c y b Patented July 8, 1941 ELECTRIC VALVE CONTROL CIRCUITS Carl C. Herskind, Schenectady, N. Y., assignor to General Electric Company, a corporation of New York Application March 30, 1940, Serial No. 326,924

8 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, such as a gas or a vapor.

It is frequently desirable to utilize electric valve apparatus of the type having immersion-ignitor control members or make-alive electrodes. Electric valves of this type are disclosed and claimed in United States Letters Patent No. 2,669,293, granted February 2, 1937 upon. an application of Joseph Slepian et al. In electric valve means of this type, a control member is associated with a cathode of the self-reconstructing type, such as a mercury pool cathode. The control member has an extremity thereof extending into the mercury and is constructed of a material, such as boron-carbide or silicon-carbide, which has a specific electrical resistivity relatively large compared with that of mercury. An arc discharge is established by the transmission of current of a predetermined value to the control member, resulting in the establishment of a cathode spot which eliects ionization of the mercury vapor and in turn establishes an are discharge between the anode and cathode of the electric valve means, thereby transmitting current in the anode-cathode circuit. The cathode spot upon the surface of the cathode is effected by establishing a predetermined potential gradient at the surface of the mercury. In accordance with the teachings of my invention described hereinafter, I provide new and improved control circuits for electric valveapparatus of the type described above.

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

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

It is a further object of my invention to provide new and improved control circuits or excitation circuits for electric valve apparatus, using immersion-ignitor control members, in which means is provided for continuously producing a periodic voltage for energizing the control members irrespective of the state of ionization of the medium, and in which current is transferred from the control members each cycle upon the initiation of an arc discharge within the electric valve means.

Briefly stated, in the illustrated embodiments of my invention I provide control circuits for electric valves of the type employing immersionignitor control members in which energizing current is transmitted to the control members periodically to render the electric valve means conductive periodically. The electric valve means is also provided with an auxiliary electrode, such as auxiliary anode or baffle, which is connected to the excitation circuit to effect transfer of excitation current from the control member to the auxiliary electrode each cycle upon the establishment of an arc discharge within the electric valve means, thereby reducing the duty imposed upon the ,immersion-ignitor control member.

For a better understanding of my invention, reference may be had to the following description taken in connection with the accompanying drawings, and its scope will be pointed out in the appended claims. Fig. 1 diagrammatically illustrates an embodiment of my invention as applied to a bi-phase rectifier for, energizing a direct current load circuit from an alternating current supply circuit, and Figs. 2a and 2b represent certain operating characteristics of the arrangement shown in Fig. 1. Fig. 3-diagrammatically illustrates a modification of my invention as applied to a polyphase'rectifier system. Fig. 3a represents certain operating characteristics of the arrangement shown in Fig. 3.

In Fig. l of the drawings, I have diagrammatically illustrated my invention as applied to an electric valve converting system for energizing a load circuit, such as a direct current load circuit I, from a polyphase alternating current supply circuit 2 through electric translating apparatus comprising a transformer 3 and electric valve means 4 and 5. The electric valve means 4 and 5 are preferably of the type employing an ionizable medium, such as a gas or a vapor, and each comprises an anode 6, a selfreconstructing cathode such as a mercury pool cathode 1, and a make-alive or immersion-ignitor control member 8, preferably constructed of a material having an electrical resistivity large as compared with that of the mercury pool cathode l. The immersion-ignitor control members 8 may be constructed of boron-carbide or silicon-carbide or other suitable material.

Electric valve means 4 and 5 are provided with auxiliary electrodes 9 and 10, respectively. In electric valve means 4 the auxiliary electrode 9 is represented as being of the baffle type interposed between the anode t and the cathode l and has several functions. One of these functions is to effect transfer of excitation current from the control member 8 to itself upon the initiation of an arc discharge within the electric valve means 4. Another of its functions is the propagation or extension of the are discharge irom the vicinity of the cathode I to the anode 6 upon the proper encrgization of the control member 8.

In electric valve means 5 the auxiliary electrode I is represented as having a difierent form, that is of smaller dimensions than the baffle 9 of electric valve means 4, and is positioned somewhat nearer the cathode 1 One of the principal functions of the auxiliary electrode I0 is to effect transfer of the excitation current from the control member 8 to itself upon the initiation of an arc discharge Within the electric valve means, or to effect transfer of the excitation current to itself upon the establishment of an arc discharge between the anode 6 and the cathode I.

I provide an excitation circuit I I for supplying energizing or exciting current to the immersion-ignitor control members 8 to render the electric valve means 4 and conductive periodically. The excitation circuit II comprises means for continuously producing a periodic voltage to efiect the proper energization of the control members 8, irrespective of the state of ionization of the mercury vapor of the electric valve means 4 and 5. This energizing means may comprise a transformer I2 energized from a suitable source of alternating current correlated in phase and frequency with respect to the voltage of circuit 2. In the arrangement of Fig. 1, this source of current is derived from the alternating current circuit 2 through a suitable phase shifting means, such as a rotary phase shifting device I3. Transformer I2 is preferably of the type designed to furnish a periodic voltage of peaked wave form. The transformer I 2 may be arranged to operate on the saturation principle, such as that disclosed and claimed in United States Letters Patent No. 2,080,250, granted May 11, 1937 upon an application of Burnice D. Bedford, and which is assigned to the assignee of the present application.

The excitation circuit II which energizes control members 8 of electric valve means 4 and 5 also includes unidirectional conducting devices, such as electric discharge devices I4 and I5, so that only unidirectional currents are transmitted to the control members 8. Electric discharge devices I4 and I5 are also preferably of the type employing an ionizable medium, such as a gas or a vapor, and each comprises an anode I6 and a cathode I'I. These discharge devices may also include a grid I8 which may be connected to thecathode I I. The cathode heating elements may be energized from suitable transformers I9 energized from a suitable source of alternating current. Current limiting resistances and ZI are connected in series relation with the anode-cathode circuits of electric discharge devices M'and I5 and control members I3 of electric valve means 4 and 5, respectively.

As a means for eifecting transfer of excitation current from the control members 8 to the auxiliary electrodes 9 and I 0 upon the initiation of arc discharges within the electric valve means 4 and 5, I provide suitable connections 22 and 23. These connections are preferably interposed between the anodes I6 of electric discharge devices I4 and I5 and auxiliary electrodes 9 and I 0 of electric valve means 4 and 5, respectively.

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 bi-phase rectifier to transmit unidirectional current to the load circuit I from the alternating current circuit 2. In general terms, the electric valve means 4 and 5 conduct current alternately to supply the unidirectional current to the load circuit I. The magnitude of the voltage impressed across the load circuit depends upon the phase relation of the times of initiation of the arc discharges relative to the applied anode-cathode voltages of the electric valve means 4 and 5. As the times of initiation of the arc discharges are advanced toward the zero point of the positive half cycle of applied anodecathode voltage, the magnitude of the direct current voltage is increased and, conversely, as the times of initiation of the arc discharges are retarded in time, the direct current voltage is decreased.

The excitation circuit II, and in particular the transformer I2, continuously produce periodic voltages of peaked wave form for energizing the control members 8 of electric valve means 4 and 5. The phase of the peaks of voltage of transformer I2, of course, may be adjusted by means of the rotary phase shifting device I3, and hence the magnitude of the output voltage impressed on direct current circuit I may be controlled thereby. The transformer I2 continuously produces the voltage of peaked wave form, irrespective of the state of ionization of the mercury vapor of the electric valve means 4 and 5, thereby assuring at all times a source of voltage for efiecting the desired energization of the control members 8. Of course, unidirectional currents are transmitted to the control members 8 by virtue of the operation of the electric discharge devices It and I5. During each cycle, as soon as the current transmitted by the electric discharge devices I4 and I5 attains the value sufiicient to establish are discharges within the electric valve means I and 5, the exciting currents are transferred from the control members to the auxiliary electrodes 9 and I0, respectively, thereby reducing the current transmitting duty imposed upon the control members 8. This current transfer is effected by virtue of the lower impedance to the flow of current offered by the circuits for the auxiliary electrodes 9 and II! as compared with that of the circuits for transmitting current to the control members 8.

The above operation may be more fully explained by referring .to the operating character istics shown in Fig. 2a. Referring particularly to the operation of the electric valve means 4 including the auxiliary electrode 9 in the form of a baffle, curve A represents the open-circuit voltage of peak-ed wave form supplied by the transformer I2 in excitation circuit II. This Voltage attains the maximum value c. The operating characteristics of curve B show the output voltage of the transformer I2 in dotted form. The shaded portion of curve B represents the Voltage applied to the immersion-'ignitor control member 8. At time a the voltage applied to the control member 8 and hence the current transmitted. thereto is not sufiicient to effect the establishment of an arc discharge. As the voltage and current increase, at time b, the current has attained a value sufficient to establish an arc discharge and the current is thereupon transferred to the auxiliary electrode or bafiie 9, thereby reducing the current-carrying duty imposed on the control member 8. The larger portion of the exciting current is transferred to the bafiie 9 which not only maintains the arc discharge Within the electric valve means 4 after initiation, but also assists in the extension of the arc discharge to the anode 6. Curve represents the relative magnitudes of the currents conducted by the control member 8 and the baffie 9. In curve C of Fig. 2a the current i represents the magnitude of the current conducted by the control member 8 and i represents the current conducted by the baffle 9. An inspection of these curves reveals that maintenance of the arc discharge within the electric valve means a is assured by the baffle 9 which transmits a substantial arc-maintaining and arc-propagation current, whereas the amount of current which the immersi-on-ignitor control member Bis required to transmit is relatively small. This current transfer takes place every cycle upon initiation of the arc-discharge.

The manner in which the auxiliary electrode iii of electric valve means 4 operates to relieve the current transmitting duty on control member 8 may be explained by referring to the operating characteristics shown in Fig. 2b. The dotted curve thereof represents the voltage produced by transformer I 2 and the heavy curve D represents the voltage impressed across and hence the current transmitted by the immersion-ignitor control member 8. As soon as the arc discharge is established between the anode 6 and the oathode l, the auxiliary electrode Ill transfers the current to itself, reducing the current through the control member 8.

In Fig. 3 I have diagrammatically illustrated another embodiment of my invention as applied to a polyphase electric valve converting system where only the control and excitation circuits are shown. With the exception of the main or power transmitting electric valves 2435, the associated power transmitting apparatus are not illustrated. It is believed that the connections of the associated power circuits will be apparent to those skilled in the art. Electric valve means 2435 are represented as being of the same type as electric valve means in Fig. 1 and each comprises an anode 36, a mercury pool cathode 31, an immersion-ignitor control member 38 and an auxiliary electrode 39.

Suitable sources of periodic voltage for energizing the control members 38 are provided by an inductive network, such as a plurality of transformers 40 and 4| including primary windings 42, 43 and secondary windings M, 45, respectively. The voltages furnished by. windings Ml and 45 may be either sinu-soidal or of peaked wave form. A suitable phase shifting means, such as an auto-transformer 46, may be interposed between the alternating current supply circuit 2 and the transformers Ill] and ll to afford any desired phase shift in the control voltages. The transforming means 49 and ll, of course, may be of the type designed to produce voltages of peaked wave form. interposed between the transformers 49 and 4!, which constitute excitation circuits for the control members 38 of electric valve means 2435, I provide a plurality of electric discharge devices 41-58 which serve to transmit only unidirectional currents to the control members 38 and which are also of the controlled type, thereby providing a means for initiating the energization of the control members 38 at predetermined times during each cycle of the periodic voltages supplied by secondary windings 49 and 45. The control electric discharge devices 41-58 are preferably of the type employing an ionizable medium and each comprises a control member or grid 59, the conductivity of which is controlled by means of a plurality of control circuits to be described immediately hereinafter.

Periodic voltages for the control of the conductivity of the electric discharge devices -58 may be obtained by means of suitable control or excitation circuits comprising a plurality of transformers 6E and BI including primarywindlugs 62 and 63, and secondary windings 64 and 85, respectively. In the arrangement of Fig. 3,

l8 secondary windings 64 and B5 of transformers 60 and GI are shown as each being connected through a pair of conductors to the oathode and the grid of the respective electric discharge devices ll58. It will be understood that the groups of secondary windings 64 and 55 may be arranged to have neutral connections which are connected to the common connection for cathodes 3! of electric valve means 2l35. Current limiting resistances 66 and 67 may be connected in series relation with the grids 59 to protect the input circuits to the electric discharge devices 67-59. The phase of the periodic voltages impressed on the grids 59 of electric discharge devices l'i--58 may be controlled or adjusted by means of any suitable arrangement, such as a rotary phase shifter 68 connected between the transformers 69 and SI and the alternating current supply circuit 2.

The embodiment of my invention shown in Fig. 3 operates in substantially the same way as that explained above in connection with the arrangement of Fig. 1. 'Ihe electric valves 24-45 are rendered conductive in a predetermined order or sequence by the proper energization of the associated control members 38. Unidirectional currents are transmitted to the control members 38 from. the excitation circuits, comprising transformers 4E! and ti, through the control electric d scharge devices tl58. The discharge devices 4'l-58 are preferably rendered conductive at a time when the excitation current is sufficient to establish an arc discharge within the associated main or power electric valve means 24--35. In this manner, the average current which the control members 38 is required to transmit is still further reduced. As soon as the arc discharge is established within the electric valve means 24-35, the current is transferred to the auxiliary electrodes 39 which maintain the are discharges. The magnitude of the output voltage, and hence the power output of the electric valve means 24-35, is controlled by means of the rotary phase shifter 5.3 which determines the time during the cycle of voltage of circuit 2 at which the respective electric valve means are rendered conductive.

Curve E of 3a represents the voltage supplied by one of the windings 44 and 45, as for example windin Mi associated with electric discharge device l'i and electric valve means 24. Curve F represen s the voltage and the current supplied to control member 38 of electric valve means 24. At time 1 the grid voltage furnished by secondary winding 84 of transformer 60 is proper to render electric discharge device 41 conducting. Current'is thereupon conducted to control member 38 from winding 44 through electric discharge device 4?. At time 5/ an arc discharge is established within electric valve means 24 and the excitation current. or the principal part of it, is transferred to the auxiliary anode 39. It

will be understood that the current which control member 38 is required to conduct is there fore maintained at a small value without sacrificing precision of control.

While I have shown and described my invention as applied to particular systems 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, 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 comprising a saturable inductive device for continuously producing a periodic voltage for efiecting energization of said control member, a unidirectional conducting device connected in said excitation circuit for transmitting only unidirectional impulses of current to said control member, and means exclusive of said unidirectional conducting device and connected between said saturable inductive device and said auxiliary electrode for effecting transfer of current from said control member to said auxiliary electrode during each cycle of the voltage of said alternating current circuit upon initiation of an are discharge vvithin said electric valve means.

2. In combination, an alternating current cir cuit, a direct current circuit, electric translating apparatus connected between said circuits and including 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 comprising a winding for continuously producing a periodic voltage to energize said control member during each cycle of voltage of said alternating current circuit, a unidirectional conducting device connected between said control member and said winding to transmit only unidirectional impulses of current to said control member, and means exclusive of said unidirectional conducting device for connecting said auxiliary electrode to said winding to effect the transfer of excitation current from said control member to said auxiliary electrode during each cycle of voltage of said alternating current circuit upon the initiation of the arc discharge occasioned by the transfer of current through said control member.

3. In combination, an alternating current circuit, a direct current circuit, electric translating apparatus connected between said circuits and including 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, excitation means energized from said alternating current circuit for continuously producing a periodic voltage for energizing said control member to render said electric valve means conductive at a predetermined time during each cycle of voltage of said alternating current circuit, a unidirectional conducting device connected between said excitation means and said control member to transmit unidirectional current to said control member, means exclusive of said unidirectional conducting device and connected between said excitation means and said auxiliary electrode to permit transfer of current from said control member to said electrode upon the initiation of an arc discharge (between said anode and said cathode occasioned by the energization of said control member, and means for controlling the time of energization of said control member by said excitation circuit relative to the voltage of said alternating current circuit.

4. In combination, an alternating current circuit, a direct current circuit, electric translating apparatus connected between said circuits and including 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, excitation means comprising means for continuously producing a periodic voltage to energize said control member irrespective of the state of ionization of said medium, a control electric discharge device connected between said excitation means and said control member and comprising an anode and a cathode, and means connected between said electrode and the anode of said control discharge device to permit transfer of current from said control member to said auxiliary electrode during each cycle of the voltage of said alternating current circuit upon the initiation of an arc discharge within said electric valve means occasioned by the energization of said control member.

5. In combination, an alternating current circuit, a direct current circuit, electric translating apparatus connected between said circuits and including 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 a baflle interposed between said cathode and said anode, said bafile being arranged to operate as an exciting anode and to assist in the extension of the arc discharge from said cathode to said anode upon the energization of said control member, excitation means comprising means for continuously producing a periodic voltage to energize said control member to render said electric valve means conductive during each cycle of voltage of said alternating current circuit, a control electric discharge device connected between said excitation means and said control member and including an anode and a cathode, and means connected between said baffie and the anode of said discharge device to permit transfer of the current from said control member to said bafile during each cycle of the voltage of said alternating current circuit upon the initiation of an arc discharge within said electric valve means.

6. In combination, an alternating current circuit, a direct current circuit, electric translating apparatus connected between said circuits and including 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, excitation means comprising means for continuously producing a periodic voltage to render said electric valve means conductive periodically, an electric discharge device of the controlled type having a grid and being connected between said excitation means and said control member, means for energizing said grid to render said electric valve means conductive, and means exclusive of said electric discharge device and connected between said excitation means and said auxiliary electrode to permit transfer of current from said control member to said auxiliary electrode during each cycle of the voltage of said alternating current circuit upon the initiation of an arc discharge within said electric valve means.

7. In combination, an alternating current circuit, a direct current circuit, electric translating apparatus connected between said circuits and including 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, excitation means comprising means for continuously producing a periodic voltage to render said electric valve means conductive periodically, an electric discharge device connected between said excitation means and said control member and comprising a grid for initiating energization of said control member through said discharge device, means for impressing on said grid a variable control voltage to determine the time during each cycle of voltage of said alternating current circuit at Which said electric discharge device is rendered conducting, and means exclusive of said electric discharge device and connected between said excitation means and said auxiliary electrode to permit transfer of current from said control member to said auxiliary electrode during each cycle of the voltage of said alternating current circuit upon the initiation of an arc discharge within said electric valve means.

8. In combination, an alternating current circuit, a direct current circuit, electric translating apparatus connected between said circuits and including a pair of electric valve means each being of the type employing an ionizable medium capable of supporting an arc discharge and each comprising an anode, a cathode, an immersionignitor control member and an auxiliary electrode, excitation means comprising means energized by alternating current for continuously producing an alternating voltage of peaked wave form to energize the control members alternately, means connected between said excitation means and the control member of each of said electric valve means and each comprising in series relation a unidirectional conducting device and an impedance element, and means connected be tween said excitation means and each of the auxiliary electrodes to permit transfer of current from the control member to the associated electrode during each cycle of voltage of said alternating current circuit upon initiation of an arc discharge within the electric valve means occasioned by the energization of the associated control member.

CARL C. I-IERSKIND

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