US2177704A - Arrangement for operating highpressure metal vapor discharge devices - Google Patents

Description

Oct. 31, 1939. v. J. FRANCIS 2,177,704

ARRANGEMENT FOR OPERATING HIGH-PRESSURE METAL VAPOR DISCHARGE DEVICES Fil ed Dec. 1, 1957 Mfirse M Kim/5 9 8 '9 INVENTOR Victor James Francis Patented Oct. 31, 1939 UNITED STATES ARRANGEMENT FOR OPERATING HIGH- PRESSURE METAL VAPOR DISCHARGE DE- VICES Victor James Francis, North Wembley, England,

assignor to GeneralElectric Company, a corporation of New York Application December 1, 1937, Serial No. 177,538

In Great'Britain Decemberli, 1936 3 Claims.

This invention relates to high-pressure metalvapor discharge devices ,(and particularly lamps). The term high-pressure implies here, as usually, that during full operation,,the coolest 5 part of the envelope, whose temperature sets an upper limit to the pressure of the metal vapor in the discharge space, is at a temperature greatly exceeding atmospheric.

It is well known that if, in such a device, the

10 discharge is extinguished by a fall of the voltage applied to the electrodes, it will not always start again when the voltage rises again to its normal value. If the fall of voltage lasts more than a small fraction of a second, a period must 18 elapse before the restoration of the discharge suflicient to allow'the temperature of the coolest part of the envelope, and therefore the vapor pressure of the metal, to fall to a value at which the starting potential of the discharge is less 20 than the applied voltage. This period is seldom less than a minute. Many devices have been suggested for overcoming this difliculty; the

object of the invention is to overcome it in a new and improved Way.

An obvious method of attaining it is to cool the envelope artificially so as to reduce greatly the cooling time, that is to say, the time that elapses between the extinction of the discharge and the attainment of a vapor pressure so low that the discharge can start when the normal applied voltage is restored. Indeed high-pressure metal-vapor discharge devices are known in which the envelope is cooled during operation by water circulation or like means; and it is known that in these devices the. aforesaid delay in'restarting is very much less than in uncooled devices. But continuous cooling imposes certain restrictions, often undesirable, on the operating characteristics of the device. Thus the applied voltage usually has to be higher than in uncooled devices of similar brightness, luminous V output, and efllciency, and the envelope usually deteriorates more rapidly, so that the life of the device, if it is a lamp, is short. Further a continuous supply of the cooling agent is required.

Again it has been proposed to reduce the cooling time by setting a fan into operation, as soon as the discharge is extinguished, which blows air over the device. But this method is very cumbrous and not very efiective; the reduction of cooling time is not great. Of course the fan could be replaced by water circulation, as in the aforesaid cooled devices, started when the discharge is extinguished; but this method again is cumbrous and usually involves considerable obstruction of the useful light, if the device is a lamp.

The invention rests on the realisation-of the fact that, in order to reduce the cooling time,

.it is not necessary to cool the whole envelope.

Since the limit to the vapor pressure is set by the temperature of the coolest spot on the envelope, it is necessary only to cool a small defined area of the envelope. Cooling means for this purpose 1 need not be cumbrous. Moreover, since only a 10 part of the envelope is cooled, the time required i'or the run up after the discharge restarts and the cooling is stopped, is less than it would be if the whole envelope were cooled.-

The proposal of the invention is therefore, roughly, to apply efficient artificial cooling to part only on the envelope as soon as the discharge is extinguished and to stop the cooling when the discharge starts again. But in order that the proposal should be practicable and useful, two conditions have to be fulfilled.

The first condition is that the device should be one having desirable operating characteristics, such as low operating voltage and long life, which cannot be obtained in a device whose envelope is cooled during full operation so efliciently that the said defect is absent.

The second condition is that the sudden application of cooling to the envelope should not crack it. This means that the material of which the envelope is composed must have a very low thermal expansion. It has been found that the condition can be fulfilled if the envelope is of quartz, but not if it is of glass having an expansion so great that thick tungsten wires can be sealed through it.

Hereinafter a device of the type specified will mean, a high-pressure metal-vapor electric discharge device which (a) is adapted to operate fully with an artificial cooling, that is to say, without cooling other than that produced by radiation, by conduction along leads and supports, and by contact with air, whose motion is due to convection and not to the action of a pump, (1)) when in the fully operative condition has desirable characteristics that are not possessed by any known lamp in which the envelope is subjected during operation to artificial cooling sufiicient to reduce greatly the cooling time, (c) has an envelope of vitreous material whose 5 thermal expansion is so small that some part of it can be cooled suddenly from the operating temperature to atmospheric temperature without cracking. But provision (0) must not be interpreted to imply that the cooling must necessarily be applied with full intensity immediately the discharge is extinguished and while the envelope is still at the full operating temperature. This would be diflicult to secure and, if it could be secured, might cause cracking, when a lapse of a few seconds after extinction would allow the envelope to cool so far that it would not crack. On the other hand the time elapsing between the extinction of the discharge and the possible full application of the cooling must be included in the reduced cooling time; this time must therefore be short compared with the natural cooling time.

According to the invention a device of the type specified comprises or is combined with means for increasing greatly the rate at which heat is abstracted from a predetermined, part, substantially less than the whole, of the envelope which means are controllable or controlled so as to reduce greatly the cooling time of the device. The means arecontrollable when the times at which the said rate is increased or restored to its normal value are under the control of an operator; they are controlled when the said times are determined automatically in accordance with the state of the device and/or the applied voltage, for example, when, as described below, they are controlled by a voltageor current relay.

The preferred means is a chamber applied or sealed to the exterior of the envelope and sharing one wall with it through which a cooling fluid (preferably a liquid and more particularly water) can be passed or into which a cooling fluid can be introduced. But in special circumstances other means might be suitable, though they would probably be less eflicient, for example a massive or water cooled metal body brought into close thermal contact with the envelope. It is not necessary that the part of the enverope to which the cooling is applied should include the spot that is coolest in operation, but of course it is permissible.

The invention is of particular utility in connection with lamps in which the discharge takes place in a roughly spherical quartz envelope between central electrodes separated by a distance less than the radius of the envelope.

In the drawing accompanying and forming part of this specification embodiments of the invention are illustrated, in which Fig. l is an axial sectional through the lamp,

Fig. 2 is a schematic representation of the lamp, a cooling system therefor and a circuit for the lamp and for controlling the-cooling system,

Fig. 3 is similar to Fig. 2 and illustrates another circuit for the lamp and the cooling system.

Referring to Fig. 1 of the drawing, I is the quartz envelope, having extensions 2, 3 through which are introduced the leads 4, 5 carrying the starting electrodes 6, I and the main electrodes 6', 1 associated with them; the electrodes 6', I are 3 mm. apart. The controllable means accord-v ing to the invention is a tube having a flattened central portion 8 and two ends 9 of circular section, sealed to the main envelope I, so that the bottom l0 of this envelope forms the upper surface of the flattened portion. The thickness of the quartz forming this bottom, and intervening between the interior of the envelope l and the interior of the tube 8 is 3 to 4 mm. The lamp operates on a 240 volts A. C. supply with about 60 volts between the electrodes; it then consumes 250 watts and the brightness of the discharge column, viewed perpendicular to the plane of the drawing (this direction is that in which the useful light is emitted) is some 20,000 candles per sq. cm.

The normal cooling time in such a lamp is some 3 minutes. If a stream of water is started through the tube 8 as soon as the discharge stops, the cooling time is reduced to 20 seconds: if the tube is merely filled with water, but no stream passed, the cooling time is reduced to one minute.

Lamps of this kind are often continuously attended, for example when they are sources 01 light in cinema projectors. There is then no need to control the means automatically. If the lamp goes out, the operator immediately starts a stream of water into or through the cooling chamber, for example by pressure of a rubber reservoir of water attached to one end 01' it. He thus ensures that the lamp starts with the least possible delay after the voltage is restored. As soon as the discharge starts again, he empties the chamber, so that there is no appreciable delay in the lamp running up again.

But if the lamp is not continuously attended, the means may be controlled automatically as shown'in Figs. 2 and 3' of the drawing. Thus a voltage relay l I (Fig. 2) across the lamp or 9. current relay I 2 (Fig. 3) in series with it may be used. It is to be noted that they operate rather differently. The current relay l2 will turn the cooling means on when the current through the lamp falls below some value and turns it off when it rises again above that value, subject to the usual backlash. The cooling will therefore start immediately the discharge is extinguished, even if the supply voltage becomes zero; but it will continue as long as the lamp is extinguished and thus may continue long after the lamp is cold. It may be therefore desirable, in order to conserve cooling water, to provide subsidiary means l3, automatic or manual, to turn ofi the cooling when the lamp is intentionally switched ofl.

The voltage relay ll will turn on the cooling when the voltage across the lamp rises above some limit (above the operating voltage) and turn it off when the voltage falls below that limit. The cooling will therefore be turned off automatically when the lamp is switched oif intentionally; nc subsidiary means will be required. 0n the other hand, if the discharge is extinguished accidentally by the supply voltage falling below the operating voltage (e. g. to zero), the cooling will not begin until the voltage rises again above the said limits. Accordingly the delay in starting may sometimes be slightly longer than if a current relay is used. namely when the interval between the reduction of the voltage and its restoration is an appreciable fraction, but not nearly the whole of the natural cooling time. The difference cannot ever be very great and in the two limiting cases it is zero, namely when the drop in voltage endures only just long enough to extinguish the discharge, so that the delay in restarting is simply the cooling time, and when it endures longer than the natural cooling time, so that the delay in restarting is due wholly to the delay in restoring the voltage and cannot be reduced by any means ex--' cept the provision of an alternative source. Butin yiew of these facts, in interpreting the appended claims, it must be understood that the means, if automatically controlled, need not reduce the cooling time in all circumstances; it is suflicient if they reduce it in the circumstances in which reduction is most urgent, namely whenthe normal applied voltage is restored immediately after the extinction of the discharge.

In view of Patent Specification No. 470,770,

published after the date of this application, I declare that I exclude from the scope of my claims a high-pressure mercury-vapor electric discharge device adapted to be operated so that the discharge is potentially unstable (as defined in the said specification), wherein the line joining the electrodes has on one side of it refractory solid matter and on another side of it a transparent portion of the envelope, the distance between the said refractory matter and the said transparent portion being such that when the discharge is driven towards the refractory matter by forces perpendicular to its length, so as to lie stably adjacent to it, the column is substantially further from the transparent portion than from the refractory solid matter, whereby the transparent portion undergoes substantially no obscuration during life owing to the heat developed in the discharge column, and wherein the said refractory solid matter is a part of the envelope artificially cooled on its exterior surface.

I claim:

1. In combination, a gaseous electric discharge device of the high vapor pressure type comprising a container, electrodes sealed therein, a vaporizable material therein, a current source to supply sufiicient electrical energy to said device to vaporize said material and cooling means for said container, said cooling means being out of contact with said container during the starting and operation of the device and in contact with said container when current flow through said device is interrupted, to rapidly reduce the vapor pressure to facilitate restarting of said .device on temporary failure of said current source.

2. In combination, a gaseous electric discharge device of the high vapor pressure type comprising a container, electrodes sealed therein, a vaporizable material therein, a current source to supply sufficient electrical energy to said device to vaporize said material and cooling means for a said container, said cooling means being out of contact with said container during the starting and operation of the device and in contact with a limited part of the surface of said container when current flow through said device is interrupted to rapidly reduce the vapor pressure to facilitate restarting oi! said device on temporary failure of said current source.

3. In combination, a gaseous electric discharge device of the high vapor pressure type comprising a container, electrodessealed therein, a vaporizable material therein, a current source to supply suflicient electrical energy to said device to vaporize said material, cooling means for said container and means responsive to changes in the electrical phenomena between said electrodes for controlling said cooling means, said cooling means being out 01' contact with said container during the starting and operation of the device and in contact with said container when current flow through said device is interrupted to rapidly reduce the vapor pressure to facilitate restarting of said device on temporary failure 01 said current source.

VICTOR JAMES FRANCIS.

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