US2441987A - Excitation system for vapor electric valves - Google Patents

Description

May 25, 1948. J. L. BOYER EI'AL EXCITATION SYSTEM FOR VAPOR ELECTRIC VALVES Filed July '7, 1944 2' She'ets-Sheet 1 F/y Z.

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EXCITA'IION SYSTEM FOR VAPOR ELECTRIC VALVES Filed July 7, 1944 2 Sheets-Sheet 2 WITNESSESB INVENTORS u John L. B0 er'&

v 5 He 'berT .Rose. M.

ATTORNEY Patented May 25, 1948 .EXOITATION SYSTEM FOR VAPOR ELECTRIC VALVES John L. Boyer, Wilkinsburg, and Herbert A. Rose,

Pittsburgh, Pa,

assignors to Westinghouse Electric Corporation, East Pittsburgh, Pa., .a corporation of Pennsylvania Application July '7, 1944, Serial .No. 543,839

13 Claims. '1

Our invention relates to a vapor electric converter, and particularly to an excitation system for a vapor electric device, such'as a vapor electric valve.

in the operation of vapor electric devices it has long been customary to provide a continuous source of excitation to maintain a cathode spot for the establishment of :the main are in the valve. Heretofore, considerabledifiicultyhas been met'in establishing and maintainingsuch excitation arcs.

It has heretofore been considered desirable to provide mechanical means for starting and restarting the cathode spot forthe excitation arcs. According to our invention, the starting and maintaining of an-excitation arc is accomplished by means of static equipment which is automatically operative without any mechanical wear or adjustment.

In the excitation system according to our inventiomthe vapor electric device is provided'with two excitation electrodes, one in the form-of a make-aliv or high resistance type electrode associated and usually in permanentcontactwith the cathode and theother a main excitation-or keepalive electrode in spaced insulated relation to the cathode.

A source of alternatingcurrent excitation potential is provided and "from this is derived an excitation potential having a high regulation characteristic. This excitation potential is appliedto both the .make-aliveand keep-aliveelectrodes and means responsive to the flow of :current .to the electrodes is provided .for controlling the regulation characteristic so that when nocurrent is flowing to the excitation electrodes, the excitation potential will have sufficient value to initiate a cathode spot through the make-alive electrode and after current has started to flow, the excitationpotential will be reduced to a value just sufficient to maintain the excitation arc and certainly below a potential which will operate the make-alive electrode.

It is, accordingly, an object of our invention to-provlde an excitation system having an excitaand a keep-alive electrode energized from the same potential source.

It is a further object of our invention to provide an excitation system having an automatic regulation characteristic.

It is a further object of our invention-to provide an excitation system which has an automatic restart in the event of failure of the-excitation arc.

Other objects and advantages of our invention will be apparent from the following detailed .description taken in conjunction with the accompanying drawing, in which:

Figure 1 1s a diagrammatic illustrationci a simplified-embodiment of our invention,

means of a rectifier transformer 1| 2 which is preferably connected to the alternating-current circuit'bymeans of a circuit breaker152 and having the phase terminals of the transformerconnected to vapor electric valves ['3 onlyone otwhich is shown for simplicity of illustration.

Each of the valves 13 comprises a container |-4 in which is a vaporizablereconstructingmathode i5 of suitable material such as mercury, and spaced from .and insulated from :the cathode I5 is an anode 156 which 'may, .or rmay p.017, be providedwith a .control shield :or grid I]. A makealiveelectrode l8 .usually in the form of ahigh resistance material .is placed in contact with the cathode L5 and spacedirom the cathode and insulated therefrom .is an: excitation anode or,k;eepalive electrode 1 9.

Excitation wpotential derived .irom any su tabl alt rnating current source herein shown :as th alternating-current circuit Ms connected to the excitation circuit by means nor a circuit breaker 3|. The.alternatingecurrent potential is applied to theprimarywinding zit-of:anexcitatlonztrans- 3. former 2| and the output potential of the transformer 2| is rectified by means of a full-wave rectifier 22 usually of the dry plate type. A capacitor '23 is usually connected across the terminal of the rectifier 22 and serves the dual purpose of smoothing the rectified potential and furnishing a source of stored energy for initiating the cathode spot.

The make-alive electrode |8 and the keep-alive electrode I9 are connected in parallel to the positive terminal 24 of the direct current, both being connected across the rectified potential by means of a return connection 25 from the cathode l of the vapor electric device to the negative terminal of the rectifier. To facilitate the initiation of the cathode spot, a saturable reactor 26 is connected in series with the make-alive electrode [8 while it is desirable to place an impedance 2'! usually in the form of a linear reactor in series with the keep-alive electrode l9.

In order to provide a, high regulation characteristic for the excitation potential, the excitation transformer 2| is provided with a magnetic bridge herein illustrated as a third leg 28 of the transformer 2|, said third leg 28 having an air gap 29 therein.

In the operation of this simplified form of our invention, the output potential of the transformer 2| will be rectified and charge up the capacitor 23 across the terminals of the rectifier 22. When this potential reaches sufficient value, the saturable reactor 26 will saturate permitting a sudden flow of current to the make-alive electrode |8. This flow of current will establish a cathode spot on cathode l5 after which an arc will establish to the keep-alive electrode IS.

The flow of current through the secondary winding of the excitation transformer 2| shifts the flux to the magnetic bridge 28, and thus materially reduces the secondary potential of the excitation transformer 2|. The potential is then slow the value which will produce saturation of the saturable reactor 26, so that current will flow substantially only to the keep-alive electrode I9. However, in the event of cessation of current flow to the excitation electrodes, the magnetic current will again flow through the secondary winding of the transformer 2| and reestablish the potential sufficient to reinitiate the cathode spot, thus automatically maintaining excitation in the event that the excitation arc should be extinguished for any reason.

In the modification according to Fig. 2, the excitation transformer |2| is of the three-legged variety with the primary and secondary windings being distributed over two of the loss while the third leg is interlinked with the connection |27 to the keep-alive electrode l9. An impedance preferably 32 in the form of a capacitor is connected in series between the source and the primary winding of the transformer |2|.

In the operation of this form of our invention, the application of potential to the primary winding I20 will produce a high potential which is rectified and applied to the excitation electrodes l8 and IS in the manner as hereinbefore described. However, the fiow of current to the keep-alive electrode [8 will change the magnetization characteristic of the transformer |2| and producing high voltage drop across the series impedance 32 and thus materially reduce the terminal voltage of the excitation transformer |2|. The magnetic interlinkage [21 between the transformer |2| and the connection to the keep-alive electrode l9 substantially replaces the stabilizing 1E, impedance 2i, as shown in connection with Fig. 1.

The modification of our invention, according to Fig. 3, is particularly designed to save space requirements of the excitation system. A directcurrent excitation potential of the right value for controlling the keep-alive electrode 29 is provided, and this source may be connected to a plurality of keep-alive electrodes 25. While this directcurrent potential may acquired from any source, we have shown it as being derived from the alternating-current source by means of a suitable transformer and a full-wave rectifier Separate transformers are then provided for each of the make-alive electrodes iii. The primary winding of the maize-alive transformer 35 has connected in series therewith a suitable impedance 35, preferably in the form of a capacitor, while the secondary potential is directly connected across the maize-alive electrode l8 and the cathode lb of the device.

In the operation of this form of the device, the direct-current potential will be applied to the keep-alive electrode l8 and if no current is flowing thereto, the secondary or output potential of the make-alive transformer 35 will apply high potential to the 1nake-alive electrode l8. However, as soon as current flows to the keep-alive electrode, the winding 3? connected in series between the direct-current source Hi2 and the keepalive electrode it will modify the impedance of the transformer so that the major portion of the primary voltage will appear across the series connected impedance thus reducing the makealive potential to a value insufficient to supply current through the make-alive electrode 18.

In the modification, according to Fig. 4, the regulation characteristic of the excitation potential is controlled by means of a variable reactor 2%] connected in series with the excitation transformer dl. When no current is flowing to the excitation electrodes, the potential will operate to produce a current to the make-alive electrode H? which current is interlinked by means of winding 2 with the variable reactor it to produce saturation of the reactor id and a consequent high potential applied to the transformer 4|. However, once the cathode spot has been established, the current will flow through the keepalive electrode thus reducing the flow of current through the make-alive electro i8 and desaturating the reactor which then absorbs the major portion of the available potential and thus reduces the output potential of the excitation transformer ll to a value instdficient to produce current flow through the make-alive electrade It.

While the regulation characteristic obviously will be variable with various types of make-alive electrodes l8, we have found that it is desirable to have a regulation characteristic 56 substantially as graphically illustrated in Fig. 5, in which the no-load terminal potential of the excitation transformer is of the order of 300 volts and having a rapidly drooping characteristic to zero potential at a current of the order of 20 amperes.

Instead of utilizing a, direct-current keep-alive are as shown in Fig. 3 it is sometimes desirable to utilize an alternating current keep-alive are in which case two keep-a1ive electrodes l9 are provided as shown in Fig. 6 and supplied with current of the desired potential by a transformer Hit the winding fill in the return circuit 25 then serves the dual purpose of controlling the potential of transformer 35 and as a stabilizing reactor to maintain the. keep-alive, arc, through current zero.

Where it is desired to avoid the necessity for two entrance bushings one of the exciting elec: trodes. 19 may be eliminated, as shown in Fig. T, by utilizing two half Wave rectifiers 45 com nected between the secondary terminals. of trans.- former I33 and the exciting electrode 19. Care must; be exercised to rovide the winding 31 with sufilcient energy storage. capacity to maintain the are through potential zero.

For p rposes of llustration, we have shown and described specific modifications of our in:- vention. t will be apparent that. changes and modifications can be made thereiflwithsut departing from the spirit of our invention.

We claim as our invention:

1. An excitation system for an arc discharge device having at least a main anode and cathode, comprising a makeealive electrode and a keep-alive electrode cooperating with said cathe ode, a source of alternating control potential, a transformer energized from said source, an impedance connected in series with the input of said transformer, means for rectifying the output of said transformer, connections for impressing said rectified output on said makeealive and keep-alive electrodes in parallel, and means responsive to flow of current to said keep-alive electrode for modifying the potential appearing across said impedance.

2. An excitation system for an arc discharge device having at least a main anode and cathode, comprising a make-alive electrode and a keepalive electrode cooperating with said cathode, a source of alternating control potential, a transformer energized from said source, a capacitor connected in series with the input of said transformer, means for rectifying th output of said transformer, connections for impressing said rectified output on said make-alive and keep-alive electrodes in parallel, and means responsive to flow of current to said keep-alive electrode for modifying the potential appearing across said capacitor.

3. An excitation system for a vapor electric device having a main anode and a vaporizable cathode comprising a make-alive electrode and a keep-alive electrode in said device, a source of alternating control potential, a transformer energized from said source, a variable reactor connected between said source and the input of said transformer, a full-wave rectifier for rectifying the output of said transformer, connections for impressing the output of said rectifier on said make-alive electrode and said keep-alive electrode in parallel, and Winding means in series with said keep-alive electrode for varying the reactance of said variable reactor.

4. An excitation system for a vapor electric valve having a vaporizable cathode comprising a make-alive electrode in contact with the oathode, a keep-alive electrode in spaced insulated relation to the cathode, a source of alternatin excitation potential, transformer means energized from said source, means for rectifying the output potential of said transformer means, connections for impressing the rectified output of said transformer on both said make-alive electrode and said keep-alive electrode, and means responsive to current fiow to said keep-alive electrode for reducing the output potential of said transformer.

5. An excitation system for a vapor electric valve having a vaporizable cathode comprising relation to the cathode, a, source of alternating excitation potential, transformer means enersized. from, said source, means for rectifying the output potential of said transformer means, a capacitor connected across, the rectified potential of said transformer, connections for connestin Said make-alive electrode and said keepalive electrode in parallel across, said rectified a saturable mpedance in series with a -a ive elec rode, and means responsive to current flow to said keep-alive electrode to reduce the rectified potential to a value insufficient. to produ satu at n of said saturable imnedaucc-v A exc t n s stem ora. por electric de e having at least a main anode and a vaporizable cathode QQmPrisir g a resistance type electrode as cciat d with he. cat od a. eep-a i el u', dc spac d om said cathode, a sourc f a e hatin ex itin p ntia a o r e f r tu ent ex itin potential, onn ctions for imp ing the potential of said direct-current source on said keep-alive electrode, a transformer energized from said so rce of alte na i p tent nections for impressing the output of said transformer on s d make-alive electrode and windin rnexansv associated with said transformer and cone tcd. ser es with said keep-alive electrod for controlling, the output potential of said transformer.

7. An excitation system for a vapor electric device comprising a make-alive electrode for initiating a cathode spot in the device, a keep-alive electrode for maintaining the cathode spot, a

source of alternating excitation potential, transformer means connected between said source and said electrodes, said transformer means having a high no-load output potential and a relatively low outputpotential under load conditions.

8. An exciting system for a vapor-electric valve comprising a make-alive electrode in said valve, a keep-alive electrode, a source of alternating control potential, means for energizing both said electrodes from said source, and means controlled by current flow to said electrodes for producing a high regulation characteristic to said control potential.

9. An exciting system for a vapor-electric valve having a vaporizable cathode comprising a makealive electrode in contact with said cathode, a keep-alive electrode in spaced relation to said cathode, a source of alternating control potential, a transformer energized from said source, rectifying means for rectifying the output of said transformer, connections for connecting said electrodes in parallel across the rectified output of said transformer and a shunt flux path in said transformer for producing a rapidly drooping current voltage characteristic in the output potential of said transformer.

10. An excitation system for a vapor-electric device having a main anode and a vaporizable cathode, comprising a resistance type starting electrode in permanent contact with said cathode, a keep-alive electrode in spaced insulated relation to said cathode, a source of alternating excitation potential, transformer means energized from said source, means for rectifying the output potential of said transformer means, circuit means for connecting said starting electrode and said keep-alive electrode in parallel across the rectified potential of said transformer, and means responsive to current flow to said keep-alive electrode to materially reduce the terminal voltage of said transformer means.

11. An excitation system for a vapor-electric device having a main anode and a vaporizable cathode, comprising a resistance type starting electrode in permanent contact with said cathode, a keep-a1ive electrode in spaced insulated relation to said cathode, a source of alternating excitation potential, transformer means energized from said source, means for impressing a unidirectional output of said transformer on said starting electrode, an auxiliary winding on said transformer, means including said auxiliary winding for impressing keep-alive potential on said keep-alive electrode, said auxiliary winding being energized by current flow to said keep-alive electrode to change the regulation characteristic of said transformer.

12. An exciting system for a vapor-electric valve having a main anode and a vaporizable cathode comprising a resistance type starting electrode in permanent contact with the oathode, an auxiliary exciting electrode in spaced insulated relation to the cathode, a source of alternating potential, means for deriving a unidirectional potential from said source, circuit means for impressing said unidirectional potential on said auxiliary exciting electrode, transformer means for deriving a high potential from said source, circuit means for impressing said high potential on said starting electrode and regulating means responsive to current flow to said auxiliary exciting electrode for reducing the output potential of said transformer means.

8 13. An exciting system for a vapor-electric valve havin a main anode and a vaporizable cathode comprising a resistance type starting electrode in permanent contact with the cathode, an auxiliary exciting electrode in spaced insulated relation to the cathode, a source of alternating potential, circuit means for impressing a potential derived from said source on said auxiliary exciting electrode, transformer means for deriving a high potential from said source, circuit means for impressing said high potential on said starting electrode and regulating means energized by current flow to said auxiliary exciting electrode for controlling the output potential of said transformer means.

JOHN L. BOYER.

HERBERT A. ROSE.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,190,774 Edwards Feb. 20, 1940 2,246,181 Morton June 17, 1941 2,266,714 Mittag Dec. 16, 1941 2,267,398 Edwards et al Dec. 23, 1941 2,291,092 Cox et al July 28, 1942 2,313,526 Edwards Mar. 9, 1943 2,361,254 Willis Oct. 24, 1944

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