US2431637A

US2431637A - Ingition device for electric discharge apparatus

Info

Publication number: US2431637A
Application number: US535892A
Authority: US
Inventors: Gaudenzi Arthur
Original assignee: BBC Brown Boveri France SA
Current assignee: BBC Brown Boveri AG Germany; BBC Brown Boveri France SA
Priority date: 1943-05-31
Filing date: 1944-05-16
Publication date: 1947-11-25
Anticipated expiration: 1964-11-25

Description

Nov. 25; 1947. A. GAUDENZIC IGNXTION DEVICE FOR ELECTRIC DISCHARGE APPARATUS Filed May 16, 1944 Patented Nov. 25, 1947 UNITED STATES IGNITION DEVICE FOR ELECTRIC DISCHARGE APPARATUS Arthur Gaudenzi,

12 Claims.

less power and in addition possess a number of other advantages. When back-arcing occurs the igniter can be disconnected and re-ignition prevented, whereupon the back-arc extinguishes. With this kind of igniter the magnitude of the rectified voltage can also be regulated. The single anode valve with a periodically operating igniter does not require a cathode insulator, so that the cathode can be galvanically connected with the casing. The cathode spots which occur after ignition originate for instance at the centre of the vessel and during a half wave never reach the wall of the vessel if the cathode diameter is greater than about 200 millimetres. This is due to the fact that the radius of action of the cathode spots is less than 100 mm. during /100 second.

Various kinds of periodically operating igniters are already known. The best known type is the semi-conductor igniter. It possess the disadvantage, however, that during the course of time its properties change and as a result ignition failures occur, until finally the igniter fails to operate at all. Although various improvements have been proposed and attempts have even been made to regenerate the igniter during service or whilst operation is interrupted, all these endeavours have failed to produce the desired results.

lhe present invention concerns an ignition device for electric discharge apparatus with fixed ignition anode and. liquid cathode, where the aforementioned disadvantages of the hitherto known periodically operating ignition devices are avoided. This is achieved according to the invention by forming a space over part of the cathode which is provided with a heating device, an ignition anode being arranged in this space in such a manner that the distance between this ignition anode and the cathode amounts to at least the free path of the electrons, so that a glow discharge is made possible at a considerably lower ignition voltage when main discharge space.

A special ignition space which is essentially separated from the main discharge space, so that a vapour density can be produced in the former whilst in the main discharge space the compared with the Wettingen, Switzerland, assignor to Aktiengesellschaft Brown,

Boveri &

Switzerland May 31, 1943 mercury in the main discharge chamber.

vapour density remains very low, can be achieved in various ways, a number of constructional examples of the invention being illustrated in diagrammatic form in Figs. 1-4 of the accompanying drawing, where each figure shows an ignition device in longitudinal section.

In Fig. 1 a sing1e-anode valve is shown, the main components of which are the metallic casing I, anode plate 2, anode bushing 3, main anode 5 and mercury cathode 5 which is not insulated from the casing. Main anode 4 has a control grid l arranged in front of it, this grid being fixed in an anode sleeve 5. An ignition anode 8 made of metal is mounted by means of the insulating tube 9 in the anode plate 2. This tube 9 which surrounds the ignition anode 3 dips with its lower funnel shaped end into the cathode mercury 5 and is provided with a number of uniformly distributed openings It which enable the mercury to flow into the ignition space and at the same time allow the cathode spots to wander out from the ignition An iron cap I2 is welded into the cathode plate H, this cap being enclosed concentrically by the insulating tube 9. On the atmospheric side a heating coil i3 is arranged inside cap l2 by means of which the mercury inside the tube 9 is heated, so that mercury vapour rises therein and completely fills the space up to the vapour density in the ignition space inside the insulating tube 9 thus becomes very high when compared with the vapour pressure in the main discharge space outside the insulating tube 9,

.- where corresponding to the low temperature there is only a very low residual gas pressure. The distance between the ignition anode 8 and the surface of the mercury cathode must be such that it is at least equal to the free path of the electrons.

If a voltage supply amounting to a few kilovolts is now connected to the terminal [4 of the ignition anode 8 and the cathode 5, a powerful glow discharge with small cathode spots on the mercury will occur in the ignition space inside the insulating tube 9. As soon as the main anode 4 is connected to a voltage of the same frequency an arc will be produced in the main discharge chamber. By means of the glow discharge in the ignition space it is thus possible to ignite the main discharge are periodically and very accurately. The glow igniter will operate even when in a dirty condition and is not subject to any changes. Inside tube 9 the current always remains small because as soon as the current exceeds 50 amperes the cathode spot splits up into space onto the cathode ignition anode 8. The

a large number of smaller spots of which several within a very short space of time wander out on to the cathode in the main discharge space, their rate of movement being very rapid.

In such cases where very high anode voltages are employed it can happen that even when the ignition is interrupted the heated cathode portion inside the insulating tube 9 still produces such a high vapour density that an arc occurs between the main anode 4 and the cathodeportion in tube 9, this arc burning through the openings ID. This arc can, however, be easily prevented if a negative blocking voltage is applied to the control grid 1 at the same time as the ignition anode 8 is disconnected.

The ignition device according to the invention can be constructed in various difierent ways and is by no means confined to the constructional form shown in Fig. 1. The insulating tube surrounding the ignition anode can for instance be made in two parts, the lower part which dips into the cathode mercury being loosely connected to the upper part. Fig. 2 shows a modified form of the invention where there is no rigid connection between the insulating tube 9 surrounding the ignition anode 8 and the tube section l5 dipping into the mercury 5, The upper end l6 of tube portion I5 is in the form of a cone which fits into a corresponding funnel-shaped opening ll in tube 9, whereby both conical elements 5, I! are kept closed merely by the upward thrust exerted by the mercury. The gap in the cone is thus kept well closed without there being a rigid joint, so that both parts 9 and [5 can readily be mutually adjusted to a slight extent. Reference numeral It indicates the communicating openings in the lower tube portion l5 which enable the mercury and cathode spot to move about as required. The mercury inside the heating space is in this case heated directly by means of a heating rod l9 which is fixed inside a cap built into the cathode plate II and projecting into the cathode mercury. The heating current passes up the rod l9 and is conducted away by means of sleeve 2|. These elements are made of a material which is not affected by the mercury and has a high specific resistance, such as a chrome-nickel compound, whichcan be welded to the iron so as to form a vacuum-tight joint. In the example shown in the figure the cathode is also provided with a water-cooling system which is located in the double bottom 22.

Another modified constructional form of the invention is shown in Fig. 3. The insulating tube 9 which surrounds the ignition anode 8 does not dip into the cathode mercury 5 in this case, but is provided with a funnel-shaped extension located just over the surface of the mercury 5. Cap 28 which is built into the cathode plate H and contains a heating coil 21, is surrounded by a concentric cylinder 28 which extends beyond the surface of the mercury and is provided with slots 29. The are current of the main anode 4 can thus burn freely between the funnel-like extension 25 and the mercury inside cylinder 28. At the same time there will always be sufiicient vapor density in the ignition space inside tube 9 to enable ignition to be initiated at any time, on condition of course that the cathode heating coil 21 is in operation. With this arrangement the level of the mercury can fluctuate very considerably without the ignition being affected.

As a contrast to the arrangements already described where the ignition anode is fixed to the node plate, Fig. 4 shows a constructional form of submerged in the invention where the ignition anode is built into the cathode plate from the underside.

In Fig. 4 the ignition anode 30, which is surrounded by a concentric insulating tube 3| and provided with a current lead 32, is built into the cathode plate 33, the ignition device projecting into the mercury to such an extent that the glow discharge path between the ignition anode 30 and cathode 31 is at least equal to the free path of the electrons. Ignition anode 39 is covered by a hood 34 of ceramic material or metal which extends down to cathode plate 33 and thus encloses part of the cathode mercury. The mercury inside hood 34 is heated by a heating coil 35, and openings 36 are rovided in the hood to enable the mercury to circulate and to allow the cathode spot to wander out of the ignition space. As soon as the heating for the ignition is switched on the mercury inside hood 34 is heated and mercury vapour fills the space between anode 3c and mercury 3i. By this means the necessary ignition conditions are produced so that when a voltage is applied to the ignition anode 30 a glow discharge is started between this latter and cathode El, whereupon the main arc can ignite.

The ignition device according to the invention, of which only a few of the many possible constructional forms have been described, satisfies all the requirements which an igniter has to fulfill. Its construction is very simple and the materials required for same can readily be obtained and do not change during service. The power required to operate the igniter is very small. The mercury vapour which forms inside the ignition space only escapes to a very slight extent into the main discharge space. During pauses in the operation of the converter not much mercury vapour will condense on the anode. When adequate lateral heat insulation is provided very little heat will pass from the heating device beneath the ignition space to the main mass of the cathode mercury. During longer interruptions in service the heating power can be reduced or completely switched on. All parts which are touched by the cathode spot must be highly heatresistant, so that it is an advantage to make these elements of quartz or high quality glass.

Although the ignition device according to the invention has only been described in connection with single anode-converters it can of course also be used with multi-anode converters. The ignition device can also be used in a known manner for the purpose of regulating the voltage when the required phase displacement between the ignition and main anode voltage occurs. Furthermore by switching-off the ignition when back-arcing occurs, it is possible to cause the back-arcing current to become extinguished.

I claim:

1. Electric discharge apparatus comprising, in combination, a main anode, a cooperating liquid cathode, an ignition anode spaced from said cathode a distance at least equal to the free path of the electrons, means providing a restricted space around said ignition anode, heating means said liquid cathode and arranged and adapted to vaporize a portion thereof, and means for directing the vapor into said restricted space whereby a glow discharge results between said ignition anode and said cathode on application thereto of predetermined voltage to initiate current flow between said main anode and said cathode.

2. Electric discharge apparatus comprising, in combination, a main anode, a cooperating liquid cathode, an ignition anode spaced from said cathode a distance at least equal to the free path of the electrons, means providing a restricted space around said ignition anode, heating means disposed entirely underneath the surface of said liquid cathode and arranged and adapted to vaporize a portion thereof, and means for directing the vapor into said restricted space whereby a .glow discharge results between said ignition anode and said cathode on application thereto of predetermined voltage to initiate current flow between said main anode and said cathode.

3. Electric discharge apparatus comprising, in combination, a main anode, a cooperating liquid cathode, an ignition anode spaced from said cathode a distance at least equal to the free path of the electrons, means providing a restricted space around said ignition anode, heating means disposed externally of said liquid cathode in heat transfer relation with the oathode to vaporize a portion thereof, and means for directing the vapor into said restricted space whereby a glow discharge results between said ignition anode and said cathode on application thereto of predetermined voltage to initiate current flow between said main anode and said cathode.

4. Electric discharge apparatus comprising, in combination, a closed container, a main anode mounted on said container, a cooperating mercury cathode carried by said container, an ignition anode carried by said container and spaced from said cathode a distance at least equal to the free paths of the electrons, closure means within said container providing a restricted space around said ignition anode, and heating means disposed externally of said cathode in heat transfer relation therewith to heat the portion of said mercury in closest proximity to said ignition electrode, whereby a glow discharge is caused therebetween on application thereto of predetermined voltage to initiate current flow between said main anode and said cathode.

5. Discharge apparatus as in claim 4, wherein said closure means comprises a tube the lower end of which dips into the mercury heated by said heating means and which is apertured to permit flow of mercury to the ignition space and emergence of the cathode spot therefrom.

6. Discharge apparatus as in claim 4, wherein said closure means comprises two tube sections loosely connected together the lower of which dips into the mercury heated by said heating means, is pressed against the upper section by the upward thrust of the mercury, and is apertured to permit entrance of the mercury and exit of the cathode spot.

7. Discharge apparatus as in claim 4, wherein said closure means comprises a tube the lower end of which is provided with a funnel-shaped extension which dips into the mercury heated by said heating means for directing the vapor toward said ignition anode and is apertured to permit entrance of the mercury and exit of the cathode spot.

8. Discharge apparatus as in claim 4, wherein said heating means is located in a metallic cap opening to the atmospheric side of said container.

9. Discharge apparatus as in claim 4, wherein said heating means is located in a metallic cap opening to the atmospheric side of said container and is surrounded by a cylindrical tube element enclosing part of said mercury, extending beyond the surface thereof and being slotted to permit entrance of the mercury and exit of the cathode spot.

10. Discharge apparatus as in claim 4, wherein said ignition anode is located in a tube projecting into said container through said cathode and said closure means includes said tube and a hood dis-- posed over the open upper end of said tube.

11. Discharge apparatus as in claim 4, wherein said heating means comprises a heating rod extending from the atmospheric side of said container into heat conductive relation to said cathode.

l2. Discharge apparatus as in claim 4, wherein said heating means comprises a space heater.

ARTHUR GAUDENZI.

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

UNITED STATES PATENTS Number Name Date 2,242,786 Kingdon et al May 20, 1941 1,032,914 Kruh July 16, 1912- 1,652,921 Wimberger Dec. 13, 1927 2,179,929 Hansell Nov. 14, 1939 FOREIGN PATENTS Number Country Date 360,342 Great Britain Nov. 5, 1931 474,565 Great Britain Nov. 3, 193'? 118,103 Switzerland Dec. 31, 1925 272,958 Great Britain Apr. 12, 1928