US2458861A - Mercury vapor discharge vessel and connection arrangements for the same - Google Patents

Description

Jan. 11,1949. KQHLER 2,458,861

MERCURY VAPOR DISCHARGE VESSEL AND CONNECTION ARRANGEMENTS FOR THE SAME Filed March 26, 1947 Fi 9. Fig.2

fnrentar Alf/950M615? I Patented Jan. 11,1949

2,458,861 I optics;

ISCHABGEQVESSELANDQ MERCURY, VAPOR .1)

CONNECTION A m ANGEMENTSL. FUR. THE...

Alfredi Kohlerg. Neuchatel, Switzerland assignor .1. taSirceA-G.,zurichasfi itzsrlms A plicatibn Ma ch 26,

194i; Samar-No. 7 37;23

' lit Switzerland April t; 1946 sioaimsi. (01- 250-2115,),

' Mercury vapourdischarge vessels are i known especially as-i'ectifier'vessel'sg whereinthe mercury; vapour arc is i'gnitedwith the aid ot-asmag-netic field.

.Suoh vessels contain an axinu1ai =anode the annular surface of which is found parallert'oathe mercury level ofthe-oathode, several cathode plates consisting of metal surface pr which-lie parallel to the annular surfaces of the anodes, and a cathode consisting oiliq'uid mercury.- The anode annular surface andthe cathode =plates-are penetrated by a magnetic constant or alternating field, the cathode plates are connected conduct ing together and with the mercury cathode. These plates are designated hereinafter, metal cathodes, in contradistinction to the mercury cathode.

The magnetic field is produced by a solenoid coil or by-a permanent magnet oi suitableformi It cuts the metal cathode surfaces substantially vertically;

In order to keep the ignition voltage of such vessels as low as possible, the latter arefurnlshed with inert gas filling of a pressure ofat least-0.03 mercury column] The manner of operation of'these discharge vessels is the following: If a voltage is applied-be tween theanode and'the cathode, in such manner that the anode is positive as compared with the cathode, then there originates-firstly betWeenthe metal cathode and the anode; a glow discharge which ignites at about 300 volts. Whenthevo'ltage rises to 400500 volts, the glow current rises to about 10-20 milliamperes, whereby the glow discharge suddenly passes over" into the mercury vapour-arc. Therefore a cathode spot is ignited upon the surface of the mercury cathode. For this purposea magnetic field intensity-of 500 to 700 Gauss is required in'the centre of the'anode annular-surface. The ignition voltage rises with reduced magnetic field intensity,v against which an increase'of the same over and beyond these valuesusuallybrings about no substantial decrease of the ignition voltage.

' Hereinafter'that voltage is termed ignition voltage, which is present at the moment ofthe ignition of the arc betweenv the anodean'd the mercury cathode.v The glow'current, which flows previous to the ignition of the are between the anode: and the metal cathode, is termed hereinafter ionization current.

If an aiternatinavoltaga ssiapplied; betweenthe anode and the cathode, thenthe processofiignition is repeated in each cycle of the alternating voltage. I V

In order to obtain with such vessels,;.faul tless manner of operation-as rectifies, in the firstrplace various technical difficulties mustbe overcome. fi neeial aim i ni n vo tage; is not a e-b fluetuatese perm-anently.-. within. wide limits; also itirisesiwith' increasing temperature, therefore, rising, mercury-vapour, pressure, under. certain cireumstanceslto-2000:5and-morevolts:

since thexanodetand the: metal cathode. must lie very c'losetogether, particularly in the case :of high vapour pressures, the danger of backiignition is very great. In'particular, these back ignitions occur 'between the metal". cathode and the anode:-

The-present invention relates to several embodimentsof such vessels whichprevent the. diflicultiesamentioned, aswell as to an arrangement which i is. suitable. for controlling such. vessels. in simple manner. Finally, arrangements are proposed 'in-order to attain the production of the magnetic field with as low. aspossible an outlay.

In'Figs; 1 to 6, vessels in conformity with this invention are illustrated. Qne. embodiment is shown-yin Fig. 1-; l is the glass flask, 2 and 3are circular cathodeplates which are connected conducting by means of the holder 4. The plates 2 and S ar'eattached to the supply lead l2. 2, 3, 4 and I'Z to'gethe'r form the metal cathode. 5 is the annular anode which-is connected with its supply lead l through thedevioe 6; 8 is the mercury cathode and-l9 thesupply lead to the same. The axial: magnetic field is produced by the magnet coil- QiWh-ic-h maybe fed-with direct or alternating current. If the magnet coil is fed with alternating' current the phase position of the supply voltage as comparedwith that of the anode alternating' voltageis to be selected in such manner that the-coil flux at the ignition point attains approximately its maximum.

The glow discharge, which at times. precedes the cathode spot ignition, originates in thespace Wlthinthe: anode ring. 5 between the two metal cathode plates 2' and 3'. The ionization current flows from the anode 5 on to the metal cathode. Asshown in thefigure, thelower cathode plate 3 is equipped in its c.entre .w-ith a circular opening. This measure hasturned; out to beadvantageous in order to facilitate the ignition of the arc. The opening inutherplate itmakes a, connection between thedischarge space of the glow discharge andithe mercury; cathode. Instead of one circulair-shaped) opening, the plate 3 may be provided with, several small openings or may be constructed. as wire-grid;

For the perfectworking of the vessel, the distancehetween the lowestcathode plate 3 andthe surface of themercury cathode, is of paramount importance; When the tube is cold, therefore, withlow: mercury vapour pressure, the ignition takes place faultlessly-if this distance amounts to up to 40 mm. But in order to attain stable ignition voltage even with highvapour pressure, this distance'must amount toless-thanlO mm.

In order that the, ignition, Ofthearc may be possible, the metal cathode must be connected conducting with the mercury cathode. As mentioned, at high vapour pressures there is particular danger of back ignitions especially between One very eifective measure to make these back ignitions the metal cathodes and the anode.

non-prejudicial, consists in connecting the'metal cathodes system across a resistance with the mertrical output of a magnetic coil required for the production of the magnetic field, or the outlay on material for a permanent magnet, it is recomcury cathode. An eventual back ignition current between metal cathode and'anode is then' damped by this resistance and the back ignition is immediately extinguished after itsignition; In that the metal cathode and the mercury mended to take steps to concentrate the magnetic flux within the anode ring.

According to the present invention this is attained by the arrangement of guiding devices consisting of magnetic material within the tube as shown in Figs. 2, 3, 5, and 6.

Fig. 2 shows a vessel in which the magnetic Qneld is produced'by a permanent magnet, seen cathode are connected across a. resistance, the

ignition voltage of the vessel is somewhat raised since also the ionization current is reduced through this resistance and therefore a higher voltage is required in order to attain this.'

If the resistance between the metal cathode and the mercury cathode is made variable, then the possibility is oiiered, inrectifier operation, to control thedirect voltage within certain limits, by altering this resistance.

The ignition voltage rises when the resistance is increased and thereby the direct voltage falls, since the ignition voltage and the direct voltage are indirectly proportional within certain limits.

If use is made of this control possibility the metal cathode must be furnished with a separate supply lead as shown in Fig. l. The variable resistance is then arranged outside the vessel and connects the supply leads i2 and IS.

A further embodiment according to this invention is shown in Fig. 4. l is the glass flask, 9 the magnet coil, E9 the cathode supplylead, l is the anode supply lead, 8 the mercury cathode.

Here the anode consists of 4 rings of equal size 5, which are connected together and with the anode supply lead through the holder 6. The metal cathode consists of the three plates 3 perforated in the centre which are found between the anode rings 5 of the lowest plate H, which likewise is perforated in the centre and of the top solid plate 2. All five metal cathode plates are connected together by means of the holder 4, the entire metal cathode system is attached in the vessel by means of the holder I2.

As will be seen here, 4 discharge spaces are available for the ionization current. This measure has turned out to be most advantageous,

Also here the distance between the lowest I Through this resistance l5 flows likewise the ionization current. Since the latter is of the order of magnitude of about 10 ma. and only flows during a fraction of the cycle of the alternating current, the loss output in this resistance is very slight.

For slightly-loaded tubes, the connection between metal cathode and mercury cathode may be effected also by a metal pin,

at'the top in meridian section and at the bottom in section vertical to the axis of the vessel. The permanent magnet consists of the magnet steel .l3uwlth the pole-shoes ll which consists of soft iron. I is the glassiiask. The anode consists of thetwo rings .5, but the number selected may be as great as desired. These are connected togetherand with the anode supply lead 1, through the holder 6. Within the tube the magnetic flux of the permanent magnet is directed by the two guides I0 and H consisting of soft iron. The lower guide H is found in the cathode mercury 8, below the level or surface, and'is held by the cathode supply lead IS. The upper guide I 0 serves at the same time as upperm0st,, cathode plate. It is connected conducting with-the two annular perforated cathode plates Z-through the holder 4. The entire metal cathode is attachedto the holder [2 in the vessel.

Both guides l0 and H are supported against the glass wall of the flask through the medium or intermediate pieces l5 consisting of ceramic material. I

This measure is necessary, since the guides are pressed through the magnetic pull, against the glass wall.

The metal cathode is connected to the mercury cathode through the medium of the pin IS. The latter may consist of resistant material or of metal,

' Iialternating current is used for the production of the magnetic field, then the magnetic guides are not to be solid, in order to avoid eddy current losses. According to this invention, they arev made of metal strips as shown in Figs. 5 and 6. Figs 5 and 6 show at the top a meridian section through the vessel and at the bottom, a section vertical to the axis of the vessel. l is the glass flask, 9 the magnet coil, which is preferably supplied with alternating current, 5 is the anode ring. Also here as in Figs. 2, 3 and 4, several parallel anode rings may be provided.

10 and II are the twoguides for the magnetic fiux, which bring about a concentration of the flux within the anode ring. They consist of strips of magnetic sheet-metal distanced from each other and held together by the pins I8.

The lower guide H is found in the cathode mercury 8 under. the level of the same and is attached to the cathode supply lead IS.

The upper body l0 serves at the same time as top cathode plate. It is fixed to the holder l2 and connected with the lower perforated cathode plate 3 by the holder 4. The pin I6 which again may be constructed as resistance, connects the metal cathode and the mercury cathode.

Electrode arrangements as described here consisting of an'ode rings, metal cathode plates and magnetic field, may likewise be used as ignition device and control device in mercury vapour discharge vessels with one or more main anodes. Themain anodes in this case are built into the vessel in the usual arrangement of mercury 5 vapour vessels. The ignition system consisting of the metal electrodes according to this invention and of the magnetic field, is then arranged directly over the level of the mercury cathode of the vessel and serves for the ignition of the cathode spot as well as eventually, for the control of the instant of the ignition insofar as it is a matter of a vessel with only one main anode. The anode ring of the ignition system then carries only a small current of about 0.1 amp, which is sufficient to ignite the cathode spot, whilst the main current of the vessel is conducted through the main anodes. The control of the instant of time of the ignition is brought about, in that the phase position of the voltage of the ignition anode or the phase position of the supply voltage of the magnet is displaced as compared with that of the voltage of the main anode. Thereby the instant of time of the ignition of the main anode within the positive halfwave of the main anode voltage, is displaced in the same way as this can be attained by means of control grids in known manner.

Having now particularly described and ascertained the nature of my said invention and in what manner the same is to be performed, I declare that what I claim is:

1. A mercury vapour discharge device, comprising in a Vessel a mercury cathode, an annular anode in a plane parallel to the mercury surface, cathode plates on both sides of said anode and parallel thereto, the cathode plate nearer to the mercury level being at a distance less than 10 mm. therefrom and a magnet so positioned with respect to said elements that the field of it passes through said cathode plates at right angles with their surface.

2. A mercury vapour discharge device, comprising in a vessel a mercury cathode, an annular anode in a plane parallel to the mercury surface, cathode plates on both sides of said anode and parallel thereto, the cathode plate nearer to the mercury level being at a distance less than 10 mm, therefrom and an electromagnet so positioned with respect to said elements that the field of it passes through said cathode plates at right angles with their surface.

3. A mercury vapour discharge device, comprising in a vessel a mercury cathode, a plurality of anular anodes in planes paralled to the mercury surface, cathode plates alternated with said anodes and parallel thereto, the cathode plate nearer to the mercury level being at a distance less than 10 mm. therefrom and a magnet so positioned with respect to said elements that the field of it passes through said cathode plates at right angles with their surface.

4. A mercury vapour discharge device, comprising in a vessel a mercury cathode, an annular anode in a plane parallel to the mercury surface,

*cathode plates on both sides of said anode and parallel thereto, the cathode plate nearer to the mercury level being at a distance less than 10 mm. therefrom, and a magnet so positioned with respect to said elements, that the field of it passes through said cathode plates at right angles with their surface, a set of strips of magnetic metal extended in the direction of the magnetic flux being provided on each side of the anode.

5. A mercury vapour discharge device comprising in a vessel a mercury cathode, an annular anode in a plane parallel to the mercury surface, cathode plates on both sides of said anode and parallel thereto, the cathode plate nearer to the mercury level being at a distance less than 10 mm. therefrom, and a magnet so positioned with respect to said elements, that the field of it passes through said cathode plates at right angles with their surface, the mercury cathode and the cathode plates being connected through a resistor. 1

6. A mercury vapour discharge device comprising in a vessel a mercury cathode, an annular anode in a plane parallel to the mercury surface, cathode plates on both sides of said anode and parallel thereto, the cathode plate nearer to the mercury level being at a distance less than 10 mm. therefrom, and a magnet so positioned with respect to said elements that the field of it passes through said cathode plates at right angles with their surface, the mercury cathode and the cathode plates being connected through a resistor placed inside the vessel.

'7. A mercury vapour discharge device comprising in a vessel a mercury cathode, a plurality of annular anodes in planes parallel to the mercury surface, centrally perforated cathode plates alternated with said anodes and parallel thereto. the cathode plate nearer to the mercury level being at a distance less than 10 mm. therefrom, and a magnet so positioned with respect to said elements that the field of it passes through said cathode plates at right angles with their surface.

8. A mercury vapour discharge device comprising in a vessel a mercury cathode, an annular anode in a plane parallel to the mercury surface, cathode plates on both sides of said anode and parallel thereto, the cathode plate nearer to the mercury level being at a distance less than 10 mm. therefrom, and a magnet so positioned with respect to said elements that the field of it passes through said cathode plates at right angles with their surface, the mercury cathode and the cathode plates being connected through a variable resistor.

ALFRED KOHLER.

No references cited.

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