US2020915A - Mercury arc rectifier - Google Patents

Description

Nov. 12, 1935. J. SLEPIAN EI'AL MERCURY ARC RECTIFIER Filed NOV. 25, 1932 2 Sheets5heet l I III lllll INVENTORS- Jase ab 5/0/40 [em RLudW/y.

ewwzm ATTORNEY Nov. 12, 1935. J. SLEPIAN ETAL 2,020,915

MERCURY ARC RECTIFIER Filed Nov. 25, 1932 2 Sheets-Sheet 2 JW 5%) I I W ATTORNEY Patented Nov. 12,,1935

UNITED STATES LIERCURY ARC RECTIFIER Joseph Slepian, Pittsburgh, and Leon B. Ludwig, burg, Pa., assignors to Westinghouse Electric & Manufacturing Company,

East

Pittsburgh, Pa., a corporation of Pennsylvania Application November 25, 1932, Serial No. 644,212

9Claims.

Our invention relates to vapor electric devices and particularly to make-alive circuits for such devices.

In our copending application Serial No. 626,866, we have disclosed a vapor electric device having a make-alive for establishing a cathode spot at the beginning of each active period in the rectifier.

In the operation of vapor electric devices having make-alives, considerable difficulty has been experienced in initiating the cathode spot. According to our invention, the cathode spot is initiated by means of a discharge initiated by the voltage in the anode circuit.

It is an object of our invention to provide a make-alive device which is substantially independent of the fluctuations of the cathode surface and in which the make-alive electrode is substantially separated from the cathode.

It is a further object of our invention to provide an intensified cathode spot initiating dis-'- charge initiated from the anode circuit.

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

Figure 1 is a schematic illustration of a rectifier embodying our invention.

Fig. 2 is a modification showing the use of fioating bodies for assisting in the cathode spot formation.

Fig. 3 is a similar illustration showing a highly cooled cathode for aiding the cathode spot formation.

Fig. 4 is a similar view of a further modification, and

Fig. 5 is amodification showing further means of initiating the cathode spot.

It has frequently been proposed to start an arc with cathode on the mercury pool of a mercury arc vessel, by means of a. discharge from an auxiliary electrode, this discharge being initiated by the application of sufllciently high voltage to the auxiliary electrode. It is usually overlooked however that such a discharge initiated in this way, generally takes the form of a glow, without the formation of an arc cathode spot on the mercury pool. While it is true that a glow to a mercury pool cathode has a certain degree of instability,

and that under its influence, a cathode spot may form spontaneously, nevertheless, it is our experience that such spontaneous formation of cathode spots are erratic and random in their occurrence, and do not occur with sufficient frequency to serve for the purposes of this invention without the; use of devices described herein for greatly increasing the probability of occurrence of the cathode spots. Without the use of such devices and means, cathodes of an arc may be struck to the mercury pool occasionally, but not regularly cycle after cycle as is contemplated in this invention.

We have found that the probability of formation of a cathode spot from a glow type of discharge to a mercury pool is greatly increased by 1 increasing the intensity of the discharge, and we have devised means for so increasing the intensity at local points on the mercury surface as to make certain that a cathode spot will be formed with negligible time delay. 15

In the modification according to Fig. 1 the vapor electric device comprises a mercury cathode I insulated by a suitable insulator 2 from a closely spaced anode 3. Insulated from both the anode 3 and the cathode l is an auxiliary electrode or 20 make-alive comprising a thermionic element 5 adapted to be connected to the cathode through a suitable transformer. While any suitable transformer may be used, it is preferable to use a special device such as a Tesla transformer 1 capable 25 of producing not only a-high potential but a high frequency as well. We have found that if an auxiliary high frequency discharge is inaugurated between an established cathode and the mercury, the probability of back-fire is so high when the 30 high frequency polarity reverses that a cathode spot will be formed with certainty on the mercury pool. Located between the anode and the transformer is a suitable unidirectional conductor or rectifier 8 for transmitting current to the pri- 35 mary of the transformer I only when proper potential is applied to the anode 3 as by the transformer 9. Preferably the auxiliary electrode is substantially enclosed in a. suitable shield l2.

In the operation of our device, the thermionic 40 cathode 5 is normally insulated from the vaporizable electrode. Upon the application of proper potential to the anode, by the transformer 9, the auxiliary rectifier 8 carries current and energizes the make-alive transformer I which causes conduction of current between the vaporizable electrode l and the auxiliary thermionic cathode 5. The high frequency current impressed between the auxiliary cathode 5 and the vaporizable cathode I reverses so rapidly that the current path between the auxiliary electrode and the vaporizable electrode remains ionized while the high frequency potential passes through zero and builds up a positive potential on the auxiliary electrode. This positive potential between the auxiliary electrode and the mercury pool together with the momentary high positive ion current to the mercury pool causes current to flow to the mercury pool and establishes a cathode spot thereon. The main rectifying arc establishes itself to this cathode spot and effectively short circuits the auxiliary rectifier I and the makealive transformer I so that the make-alive arc is extinguished and only the current carrying arc remains in the device.

In themodification shown in Fig. 2, the thermionic auxiliary cathode 5 is replaced by a plain electrode. We have found that when certain bodies are floated on a mercury surface, in the presence of a glow or other back current discharge, the probability of the formation of a cathode spot is made very high. This may be explained as due to small patches on the float- 'ing bodies which become charged in the presence of the glow current, and later break down", yielding the arc cathode. Carborundum, quartz, glass, and various resistance materials are examples of the type of material used for the floating bodies. On the surface of the vaporizable cathode adjacent to the auxiliary cathode, we have placed a coating of resistance material such as carborundum H, a suitable barrier is provided for retaining the resistance material in the desired location. The barrier may be in the form of a water cooled coil submerged just below the mercury surface. It is desirable that this barrier should be coated with a refractory metal such as tungsten or molybdenum. In the operation of our device, according to this modification, the auxiliary rectifier 8 conducts upon the application of the proper polarity of potential to the anode 3 and energizes the primary of a suitable transformer 20. The secondary of the transformer 20 is then energized to impress a potential between the auxiliary electrode I5 and the vaporizable electrode The high potential causes a discharge probably in the form of a glow discharge between the auxiliary electrode and the vaporizable electrode. The presence of the high resistance material on the surface of the vaporizable electrode causes the glow discharge to concentrate and establish a cathode spot on the vaporizable electrode I. If desired, a suitable condenser 2| may be placed across the secondary terminals of the transformer 20. This condenser, upon the formation of a glow discharge, will be discharged in parallel with the transformer secondary and materially increase the current density in the discharge and materially assist in the formation of a cathode spot.

In the modification shown in Fig. 3, a suitable high frequency generator 25 has been inserted between the transformer 20 and the auxiliary electrode. Instead of using high resistance material on the vaporizable electrode, we prefer to strongly cool a portion 26 of the electrode adjacent to the auxiliary electrode. Cold bodies in a vacuum device, in particular cold mercury, we believe are usually contaminated by patches of relatively high dielectric strength on their surfaces. We have found that on the surface of cold mercury for example, oxides, nitrides, etc. are present, and that in the presence of a glow discharge, such patches become charged and later break down yielding a cathode spot. In any case, regardless of the theory, we have found that cold mercury readily forms an arc cathode under the influence of a glow or positive ion current arising from any source. Upon the application of suitable potential to the anode 3, the auxiliary rectifier I permits current flow through transformer 20 the secondary of which discharges through the high frequency generator and produces a high frequency discharge between the auxiliary electrode II and the vaporizable eleca trode i. The presence of the strongly cooled portion 26 of the vaporizable electrode, probably by inducing the formation of mercury oxides or nitrides at the mercury surface, causes a concentration of the glow discharge and a conse- 1o quent formation of a cathode spot. Obviously, the transformer and high-frequency generator could be replaced by a Tesla transformer where the relatively low frequency of the Tesla transformer interrupter is sufficiently high to cause II the formation of a cathode spot as often as is desired.

In the modification shown in Fig. 4, the auxiliary cathode is in the form of a thermionic cathode 30 which is connected to the vaporizable l0 electrode by a suitable resistance 3|. The shield i2 surrounding the auxiliary electrode 30 extends within very closely spaced relation with the vaporizable electrode Upon the anode 1 being energized with the proper potential, a ll discharge will take place between the anode and the auxiliary electrode 30. Thisv discharge will pass through the restricted space 33 between the shield l2 and the vaporizable electrode I, in effect pinching the are against the surface of 80 the vaporizable electrode. The resistance 3| between the auxiliary electrode and the vaporizable cathode causes a difference of potential between the arc and the surface of the vaporizable electrode adjacent to the arc. Because of the crowding of the arc next to the mercury surface, a very high density of ionization exists there, and under the influence of this difference of potential, a large positive ion current flows to the mercury which causes a current'to flow to the vaporizable 4o electrode and establishes a cathode spot thereon to which the current rectifying are immediately attaches and short circuits the resistance 3| between the auxiliary electrode and the vaporizable electrode. 5

In the modification according to Fig. 5, the auxiliary electrode is in the form of a tubular member 35 dipping into the mercury electrode and having at least a portion 36 adjacent to the mercury electrode of insulating material such as 50 quartz. A suitable nozzle 31 extends from the electrode and terminates in closely spaced relationship with the vaporizable electrode I. A heating element 38 supplied from a suitable power source 39 is connected in spaced relationship in 6|} said auxiliary electrode.

We have found that the probability of the formation of a cathode spot from a glow type of discharge is greatly increased by increasing the pressure of the gas at the region near the cathode. N This is probably because the current density at the cathode of a glow varies as the square of the density of the gas in which the glow is playing. Consequently, we have devised means for causing high local vapor pressures of the mercury which 05 will be sufllcient so that a glow formed by the application of sufficient voltage will certainly change to an arc with negligible time delay.

In operation, the heating element 18 is supplied with current to produce a high vapor pres- 70 sure in the auxiliary electrode 35 which is discharged through the nozzle 31 and against the mercury surface. when proper potential is applied to the anode 3 the transformer 20 is energized and a discharge takes place between the 7 nozzle 81' and the mercury surface. The high vapor density in the vicinity of the nozzle causes a highly concentrated discharge which results in the formation of a cathode spot on the mercury surface. I

While we have shown and described specific embodiments of our invention, it is apparent that changes and modifications can be made therein without departing from the spirit and scope of our invention. We desire, therefore, that only such limitations shall be imposed as are embodied in the accompanying claims or as may be necessitated by the prior art.

We claim as our invention:

1. A vapor electric device comprising an anode, a cathode, an auxiliary electrode spaced from both the anode and cathode, a transformer having a primary and secondary winding, the primary being connected between the anode and cathode,

means in series with the transformer primary for permitting current flow in the primary only during the prevalence of a predetermined polarity of potential between said anode and said cathode, the secondary being connected between the cathode and the auxiliary electrode.

2. In a vapor electric device comprising an anode and a cathode, a make-alive comprising an auxiliary thermionic cathode, a shield about the thermionic cathode, a source of high frequency current having terminals connected to said thermionic cathode and the main cathode and means connected to the anode for actuating the source of high frequency current.

3. An electrical translating device comprising a container, a main cathode and an anode in said tainer, said electrode being spaced from the main cathode and anode, an alternating current system connected to said anode, a direct current system connected to said cathode, an external circuit between said cathode and said anode, an external circuit between said cathode and said auxiliary rent carrying are between said anode and cathode for each conducting half cycle.-

4. An electrical device comprising a container, a main cathode and anode in said container, an electrode in said, container,

3 circuit between said cathode and said auxiliary electrode, a high frequency transformer connected between said external circuits for initiating a current carrying are between said anode and cathode, and valve means in said first mena timed circuit for controlling said' high frequency transformer in response to the polarity of the anode potential.

5. In a vapor electric device having a main cathode and an anode, an auxiliary thermionic 1o cathode, a high frequency generator connected to said main cathode and to said auxiliary cathode, and a unidirectional conductor connected between the anode and the high frequency generator for actuating the generator only when potential of a predetermined polarity is applied to the anode.

6. In a vapor electric device having a main cathode and an anode, an auxiliary thermionic cathode, a high frequency gene'rator connected to said main cathode and to said auxiliary cathode, means for supplying current to the high frequency generator and a unidirectional conductor for controlling the fiow of current to the high frequency generator.

7. A vapor-electric device comprising an evacuated container, 9. vaporizing cathode therein, an anode closely spaced from said cathode, an auxiliary electrode in said container, means for creating a high vapor pressure in the vicinity of said auxiliary electrode and means for supplying potential to said auxiliary electrode only when said anode is positive with respect to said anode.

8. A vapor electric device comprising a chamber, an anode and a cathode in spaced relation in said chamber, an auxiliary electrode spaced from said anode and said cathode and means for applying potential to said auxiliary electrode for initiating an electrical discharge between said auxiliary electrode and said cathode and means 40. for causing the formation of a cathode spot on said cathode said means consisting of means for producing a high vapor density at some local point of the cathode surf 9. Avapor electric converter comprising a pair as of main electrodes, an ignition transformer the primary of which is connected across said main electrodes, an auxiliary electrode in said con- LION n. 'wnwm: is

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