US2225757A - Mercury arc converter - Google Patents

Description

Dec. 24, 1940.

H. T. RAM SAY MERCURY ARC CONVERTER Filed May 23, 1939 FIG? FlCaJ INVENTOR ///v/?Y 7mm Emmy Attorney Patented Dec; 24, 1940 MERCURY ARC CONVERTER.

Henry Thomas Ramsay, Pinner, England, assignor to The General Electric Company Limited,

London, England Application May'23, 1939, Serial No. z75,204 In Great Britain May 26, 1938 Claims.

This invention relates to mercury arc converters of the type having liquid cathodes and wherein means are provided whereby the point in each cycle of the A. C. input at which the arc 5 starts can be controlled by an electrical signal which induces the formation of a cathode spot. The said liquid will be termed hereinafter mercury; but it is to be understood that mercury may also be replaced by its known substitutes, e. g.

1 various amalgams.

The object of my invention is to provide converters of this type having improved said means, the main improvement being in durability and certainty of operation.

According to my invention a converter of the type specified comprises means for causing a stream of mercury to issue from an orifice within the envelope of the converter, normally as a continuous jet impinging on an electrode, and comprises or is adapted to be associated with means for causing an electric current to flow along the said jet and means for breaking the said jet under the influence of an electric signal.

The means for lcausing an electric current to flow along the jet maynalso constitute the means for breaking the jet under the influence of an electric signal; thus the electric signal may consist of a large impulsive current passed through the jet which isbroken before the impulse terminates.

' If a suflicient current is passing through the jet and the jet is broken, an arc will start in the gap or gaps formed; if the voltage between the said electrode and the source is suillcient, the are will eventually terminate on the said electrode. The said electrode is preferably the cathode or a porous tungsten block partially immersed in the cathode and providing in known manner a fixed surface saturated with the mercury. Then a 40 cathode spot will be formed on the cathode and,

if the voltage between cathode and anode is sufficient, the main discharge will start. But the said electrode might be an electrode so near the cathode that an are formed between the parts of the broken jet transfers itself to the cathode; but

no advantage of this alternative is known.

The jet may be broken by simply passing a sufficient current through it; thus I have found that if, for example, the diameter of the jet is some 0.3 mm., a current of 25 amp. will be sufficient to break it. The breaking may be due to the pinch effect, but is more probably due to a disturbance originating at the orifice on the application of the electric signal. But other means 5:, of breaking the jet may be adopted. Thus the jet may be permanently subjected to a transverse magnetic fleld and broken by the lateral force due to a current through it; the current caused to flow along the jet may then be the electrical sig nal. Conversely, a constant current may be 5 passed along it, and a transverse magnetic field established at the appropriate point in the cycle. Other methods will occur to those skilled in the art.

I am aware that it has been proposed to ignite 10 a mercury arc converter (but not necessarily so as to control the starting of the arc in each cycle) by means of a "mercury bridge broken by the pinch effect? but I am not aware that it has been proposed to do so when the bridge is a ll jet. I am aware also that it has been proposed to use mercury jets in various ways to control the ignition of a mercury arc converter; but I am not aware that it has been proposed to do so when the jet flows continuously except when the main discharge is being started, and is broken under the influence of an electric signal when carrying current.

The speed of the jet must be such that the jet is renewed in the interval between successive in- 25 terruptions. If the frequency of the A. C, is 50 cycles, if the jet is interrupted only once per cycle, if the length of the jet is 1 cm. and its diameter 0.3 mm., this condition can be obtained if the head driving the jet is at most a few cm. of 0 mercury.

The supply of mercury in the source may be renewed, in steel tank converters, by mercury condensing on the upper part of the tank and led into a container constituting the source. But a pump may be provided, for example the known 3-phase pump operating by eddy-currents or a piston pump operating similarly to the wellknown petrol pump of an automobile. If D. C. is required to be passed through the jet, the imped- 40 ance of the pumping circuit may be made sufliciently large by including in it a suflicient length of narrow glass tubing.

Four embodiments of the invention will now be described, by way of example, with reference to 45 Figures 1, 2, 3 and 4 of the accompanying drawing, of which Figure 1 shows a section through a steel tank converter in accordance with the invention in which mercury is supplied from the cathode pool to a reservoir within the tank by 50 evaporation and condensation and Figures 2, 3

and 4 show steel tank converters in which the mercury .issuing in the jet is pumped from the cathode p001.

In Figures 1 and 2 the jet is adapted to be .66

broken under the influence of an impulsive current passed through the jet, and in Figures 3 and 4 the jet is adapted to be broken under the influence of a magnetic field.

6 In all the figures I is the steel envelope, 2 the anode within it, 3 the cathode poolat the bottom. Mercury flows through the tube 1 and issues from the orifice 8 in the jet 9. Between the anode 2 and cathode 3 is connected the main circuit which is supplied with alternating current from an A. C. source I4 through a transformer I 5 and comprises a D. C. load I5. I6 is the source of electric signals which is connected across the primary I of a transformer having a secondary I2.

In Figure l, 4 is a channel on the envelope I collecting mercury condensing on the upper part and a tube through which the condensed mercury drips into a container 6. The container 6 is supported from the wall by an insulating member II and is connected to the cathode through the aforesaid secondary I2. Impulsive electric signals from the source l8 are applied to the primary l0 and cause a suflicient current to pass through the jet to break it whilst the current is still passing; the breaking of the current then starts an are which produces a cathode spot and initiates the discharge between the anode 2 and cathode 3.

In Figure 2 the mercury for the jet is pumped into the tube I from the cathode 3 by means of a tube I1. communicating with the cathode, and a pump I8.

The arrangement of Figure 3 is generally similar to that of Figure 2, but the envelope I contains in addition a permanent magnet l9 supported from the wall of the tank by a member 20 and arranged with its pole pieces close to the jet. When current is passed through the jet by means of signals applied from the source IS, the jet is 40 broken under the influence of the transverse force arising from the presence of the magnetic field.

In Figure 4 the pole pieces of an electro-magnet 2| are sealed through the lower part of the en- (5 velope I and arranged about the jet 9; the exciting windings 22 of the magnet are connected in series with the secondary I2 so that the electric signals from the source l6 produce transient magnetic fields between the pole pieces. A D. C. cur- 50 rent is passed through the jet by means of a D. C. source 23 so that at each signal from the source IS the resulting magnetic field produces a lateral force on the jet which sufiices to break it and thereby initiate the main anode-cathode dis- 65 charge.

I claim:

1. In a mercury arc converter of the type wherein a discharge occurs within a discharge envelope along an arc from an anode to a mercury pool cathode. means for initiating said discharge, said means comprising means for causing a stream of mercury to issue from an orifice as a continuous jet impinging on an electrode within the discharge envelope, means for causing an electric current to flow along said jet and means for breaking said jet under the influence of an electric signal while the jet current is flowing.

2. In a mercury arc converter of the type wherein a discharge occurs within a discharge envelope along an are from an anode to a mercury pool cathode, means for initiating said discharge, said means comprising means for causing a stream of mercury to issue from an orifice as a continuous jet impinging on an electrode within the 76 discharge envelope, means for causing an electric current to flow along said jet and means for breaking said jet while said jet current is flowing under the influence of an electric signal during successive cycles of the alternating current rectified by said converter so as to initiate a said discharge in each of said cycles.

3. In a mercury arc converter of the type wherein a discharge occurs within a discharge envelope along an arc from an anode to a mercury pool cathode, means for initiating said discharge, said means comprising means for causing a stream of merucry to issue from an orifice as a continuous jet impinging on an electrode within the discharge envelope, and means for passing a large impulsive current through said jet during successive cycles of the alternating current rectified by said converter so as to break said jet while said impulsive jet current is flowing and thereby initiate the discharge between the said anode and said cathode of said device in each of said cycles.

4. In a mercury arc converter of the type wherein a discharge occurs within a discharge envelope along an are from an anode to a mercury pool cathode, means for initiating said discharge, said means comprising means for causing a stream of mercury to issue from an orifice as a continuous jet impinging on an electrode within the discharge envelope, means for passing an electric current through said jet and means for establishing a magnetic field transverse to the said jet during successive cycles of the alternating current rectified by said converted so as to break said jet, while said jet current is flowing, and thereby initiate a said discharge in each of said cycles.

5. In a mercury arc converter of the type wherein a discharge occurs within a discharge envelope along an are from an anode to a mercury pool cathode, means for initiating said discharge, said means comprising means for causing a stream of mercury to issue from an orifice as a continuous jet impinging on an electrode within the discharge envelope, means for establishing a constant magnetic field transverse to said jet and means for passing an electric current through said jet during successive cycles of the alternating current rectified by said converter so as to break the said jet, while said jet current is flowing, and thereby initiate a said discharge in each of said cycles.

6. In a mercury arc converter of the type wherein a discharge occurs within a discharge envelope along an are from an anode to a mercury pool cathode, means for initiating said discharge, said means comprising pumping means for pumping mercury from said cathode and causing it to issue from an orifice as a continuous jet impinging on an electrode within the discharge envelope, means for causing an electric current to flow along the said jet and means for breaking said jet while said jet current is flowing under the influence of an electric signal during successive cycles of the alternating current rectified by said converter so as to initiate a said discharge in each of said cycles.

'7. In a mercury arc converter of the type wherein a discharge occurs within a discharge envelope along an are from an anode to a mercury pool cathode, means for initiating said discharge, said means comprising a reservoir containing mercury and communicating with an orifice from which a stream of mercury issues under the influence of gravity in the form of a continuous jet impinging on an electrode and falling into the cathode pool, means for leading mercury evaporated trom the cathode pool and condensed on the upper part of the said discharge envelope in operation into the said reservoir, means for causing an electric current to flow along said jet and means for breaking said jet, while said jet current is flowing, under the influence of an electric signal during successive cycles of the alternating current rectified by said converter so as to initiate a said discharge in each of said cycles.

8. In a mercury arc converter of the type wherein a discharge occurs along an are from an anode to a mercury pool cathode, means for initiating said discharge, said means comprising means for causing a stream of mercury to issue from an orifice in the form of a continuous jet falling into said cathode pool, means for causing an electric current to flow along said jet and means for breaking said jet, while said jet current is flowing, under the influence of an electric signal during successive cycles of the alternating current rectified by said converter so as to initiate a said discharge in each of said cycles.

9. In a mercury arc converter of the type wherein a discharge occurs at regular temporal intervals along an arc from an anode to a mercury pool cathode, means for initiating said discharge at each or said intervals, said means comprising an orifice, means for causing a jet of mercury to issue continuously from said orifice, means for causing an electric current to flow along said jet and means for breaking said jet at each of said intervals while said jet current is flowing.

10. In a mercury arc converter of the type wherein a discharge occurs at regular temporal intervals along an arc from an anode to a mercury pool cathode, means for initiating said discharge at each of said intervals, said means comprising an orifice spaced apart from said cathode pool, means for causing a jet of mercury to issue continuously from said orifice and impinge said cathode pool, means for causing an auxiliary electric current to flow along said jet and means for breaking said jet at each of said intervals while said jet current is flowing.

HENRY THOMAS RAMSAY.

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