US1677689A - Vapor electric device - Google Patents

Description

July 17, 1928.

L. T. ROBINSON ET AL VAPOR ELECTRIC DEVIC E Filed Nov. 19, 1925 mm v \vRA. b

Q K M m eC e w 0 VVT z b Patented July 17, 1928.

- UNITED STATES 1,677,689 PATENT OFFICE.

LEWIS '.l'.. ROBINSON AND CAMILLE A. SABBAH, OI BCHENEC'I'ADY, NEW YORK, A8-

BIGNOBS '10 GENERAL ELECTRIC COMPANY, A CORPORATION OF NEW YORK.

VAEOR ELECTRIC DEVICE.

Application filed November 18, 1925. Serial llo. 70,201.

Our invention relates to vapor electric devices wherein current is transmitted between a cathode and an anode alternately charged to positive and ne ative polarities, and has for its principal ject the provlsion of a method and means for preventing the transmission of inverse current throug the anode when it is charged to a negative potential.

In the operation of vapor electric devices,

such as the mercury rectifier, current is transmitted between a positively charged anode and the cathode through an electric are which carries a multitude of positive ions. The presence of positive ions in the vicinity of the anode is desirable when it is positively charged and is transmitting current because these ions reduce space charge and facilitate the transmission of current through the device. When the anode is charged to a negative polarity and is not transmitting current, however, thepresence of positive ions in the vicinity of the anode is undesirable for the reason that they are attracted to the anode and tend to raise its temperature to a point at which electrons are emitted. These electrons ionize the surrounding vapor, thus producing more positiveions and establishing a condition likely to lead to the formation of destructive arcs, commonly denoted by the expression are back, between the negatively charged anode and some other part of the device.

It is customary to surround the anodes of a vapor electric device with a shield or baffle for protecting them from the positive ions of the are when they are not trans.

mitting current. With this construction, trouble is encountered due to the presence of positive ions within the anode shield or baflie at the instant the anode polarity is changed from a positive to a negative value. In accordance with our invention, this difiiculty is avoided by the provision of means for attracting the positive ions away from the negatively charged anode and for intercepting the electrons emitted from the anode before they have had an appreciable efiect on the surrounding vapor.

Our invention will be better understood from the following description when considered in connection with the accompanyingdrawings and its scope will be pointed out in the appended claims. 1

Referring to the drawings, Fig. 1 shows a fragmentary sectional view of a mercury rectifier wherein my invention has been embodled' Frgs. 2 and 3 show various details thereof F1g. 4is a sector diagram showing the phase relation between the anode, shield and control electrode voltages; and Figs. 5 and 6 relate to a modified form of mercury rectifier.

Figs. 1, 2 and 3 show a mercury rectifier wherein current from a suitable source is transmltted through an are between an anode 1 and a cathode 2 which is located 1n a container 3 and is supported by an insulated wall portion 4 of this container. Chambers 5 and 6 are provided for circulatmg a cooling medium in contact with the container walls. It will be observed that an insulation member 7 is arranged to form a seal between the anode 1 and the cover of the container 3 upon which it is supported that a control electrode 8 and an anode shield 9 are supported by an insulator 10 extending between the anode and the tank cover, that a p1pe 11 is provided for applying a coolm medium to the anode 1, that the anode 1 is connected to a lead 12 through a primary winding 13 of an induction device comprising an adjustable core member 15 and a secondary winding 16, that control electrode 8 is connected to the anode 1 through a resistor 17 and the secondary winding 16, and that the shield 9 is insulated from the control electrode 8 by insulation member'IO and is connected to the control electrode 8 through an adjustable condenser 18 which is connected to the .s'ec= ondary circuit 16 in series with a resistor 19. It will be readily understood that, while onl one anode appears in the figure, the recti er will usually comprise either a palr of electrodes connected to the opposite terminals of a single phase source or a plurality of anodes connected to a polyphase source in any suitable manner.

With the connections illustrated, the phase relation between the voltages of the anode 1 and the control electrode 8 is dependent on the adjustment of the movable core member 15 of reactance device 14, and the phase relation between the voltages of control electrode 8 and shield 9 is determined by adjustment of condenser 18. Assuming the vectors 1', 8' and 9' of Fig. 4 to represent the voltages of anode 1, control electrode 8 and shield 9 respectively, it will be seen that the control electrode voltage leads both the anode and shield voltages and is somewhat larger than the anode voltage due to the fact that it is connected to the anode throu h the secondary winding 16 which raises t e control electrode voltage above that of the anode by an amount dependent on the mag-' nitude of the current transmitted through the anode.

The manner in which the phase relation between the anode, control electrode and shield voltages is utilized to prevent are back due to the resence of positive ions within the shield when the anode assumes a negative polarity will be explained on the assumption that transmission of current between the anode and cathode has ceased and the anode has just assumed a negative polarity. Under these conditions, the shield is charged to a negative value somewhat greater than that of the anode, the polarity of the control electrode is still positive and the positive ions are largely prevented from reaching the anode both due to the positively charged control electrode which repels them and to the comparatively large negatively charged surface of the shield which attracts them. Are back due to the residual positive ions is thus prevented.

As previously indicated, are back is also likely to be produced by the ionization of the surrounding vapor due to the emission of electrons from the negatively charged anode. This difiiculty is most ronounced when the anode is operated at a igh temperature and is charged to a comparatively high negative voltage. Referring to the vector diagram of Fig. 4, it will be noted that the control electrode assumes a negative potential soon after the polarity of the anode is changed from a ositive to a negative. The interval of time etween the changes in the polarities of the anode and control electrode may be controlled by the inductance device 14 and should be just suflicient to allow deionization of the vapor within the shield. With proper adjustment of the reactance device 14, a negative voltage is applied to the control electrode while the negative voltage of the anode is comparatively small and the emission of electrons from the anode is retarded in a manner to prevent ionization and are back. The control electrode thus performs the double function of protecting the anode from the positive ions during deionization and of preventing ionization of the vapor by electrons emitted from the anode when it is charged to a comparatively high negativevoltage.

Fig. 5 is a diagrammatic showing of a system wherein current supplied from a suitable alternating current source is transmitted to a direct current circuit 20 through a polyphase transformer 21 comprising secondary windings 22, 23 and 24. a rectifier comprising anode 25 and cathode 26, an interphase transformer 27 of well known construction, and a reactor 28 which is provided for smoothin out pulsations in the current of the circu1t20. It will of course be understood that, while only one anode 25 has been illustrated, the rectifier will comprise a lurality of anodes each connected to a di erent secondary terminal of the transformer. A spiral grid or control electrode 32 is interposed between the anode 25 and cathode 26 and is connected to the anode through the resistor 17 and a phase control device 28 supplied with current from the left hand part of the secondary winding 22 through a otential transformer 29. As indicated by Fig, 6, the active surface of the anode 25 is located within a funnel-shaped bafile to which it is connected through a resistor 31. The resistor 31 corresponds to the resistor 19 of Fig. 1 and may be connected between the anode and shield either independently of the phase control device or in series therewith as previously explained.

The form of anode shield illustrated by Fig. 6 has the advantage that it radiates heat away from the anode to the cool wall of the container and allows the vapor surrounding the anode to readily expand toward the container wall thus preventing excessive rise in temperature and va or-pressure around the anode. The operation of the modification shown by Figs 5 and 6 will be apparent in vieZv of the previous discussion of Figs. 1 to The embodiments of the invention illustrated and described herein have been selected for the purpose of clearly setting forth the principles involved. It will be apparent;

however, that the invention is susceptible 0 being modified to meet the different conditions encountered in its use and we therefore aim to cover by the appended claims all modifications within the true spirit and scope of our invention.

What we claim as new and desire to secure by Letters Patent of the United States, 1s.:-- 1. The method of operating a vapor electric device comprising a control electrode inter osed between an anode and an anode shiel which comprises changing the polarity of said shield and anode, and thereafter changing the polarity of said control electrode.

2. The method of operating a vapor electric device comprising a control electrode interposed between an anode and an anode shield, which comprises successively changit is charged. to a negative polarity, a control electrode interposed between said shield and anode, means for applying voltages to said shield and control electrode, and means for controlling the relation between the voltage of said anode and the voltages of said shield and control electrode.

4. A vapor electric device wherein current is transmitted through an are between a cathode and an anode alternately charged to positive and negative polarities, comprising an arc shield for protecting said anode when it is charged to a negative polarity, a control electrode interposed between said shield and anode, means for applying voltages to said shield and control electrode, and means for controlling the phase relation between the voltages of said shield and control electrode.

5. A vapor electric device comprising an external anode, an anode shield insulated from said anode, and a control electrode interposed between said anode and shield and insulated therefrom.

6. A vapor electric device comprising an external anode, an anode shield insulated from said anode, a control electrode interposed between said anode and shield and insulated therefrom, and means for applying a cooling medium to the external surface of said anode.

A vapor electric device comprising an external anode, an anode shield insulated from said anode, a control electrode interposed between said anode and shield and insulated therefrom, and means for applying potentials of predetermined magnitude and phase relation to said anode, control electrode and shield.

8. The method of operating a vapor elec-'.

during deionization of the vapor enclosed within said shield.

9. The method of operating a vapor electric device comprising a control-electrode interposed between an anode and an anode sh eld, which comprises applying a negative potential to said anode, applying a positive potential at said control electrode during deionization 01 the vapor within said shield, and changing the polarity of said control electrode at a predetermined time after said anode has been charged to a negative poten: tial.

In witness whereof, we have hereunto set our hands.

LEWIS T. ROBINSON. CAMILLE A. SABBAH.

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