US2170447A - Electric discharge apparatus - Google Patents

Description

Aug. 22, 1.939. M. A. EDWARDS ELECTRIC DISCHARGE AEPARATUS I Filed March 22, 1938 Inventor:

Martin A. Edwards,

His Attorney.

Patented Au 22, 1939 UNITED STATES anaemic mscnaacn maaa'rus Martin A. Edwards, Schenectady, N. Y., alsigncr to General ElectricOompany, a orp ration of New York Application March 22, 1938, sci-nu No. 191.5%:

11 Claims. (01. rte-124) m invention relates to gaseous electric discharge devices and apparatus for operating the same from alternating current circuits. It relates particularly to electric discharge devices which require the application of a higher voltage for starting them than for the subsequent operation thereof. Certain forms of apparatus of this character which have been constructed heretofore and which have included capacitors for obtaining the required higher starting voltage have not been entirely satisfactory for various reasons; the cathodes of the devices often have been damaged by the high current peaksproduced by the capacitors employed, and the apparatus has not had as good operating characteristics as desired.

One object of my invention is the provision of improved. apparatus of the above mentioned character which employs simple means including capacitors by which the desired starting voltage may be obtained without danger of damage to the cathodes. Another object is the provision of improved apparatus of this character which will operate with high efliciency and good stability which will not be critical to reasonable variations in line voltage and whose construction will be simple and inexpensive to manufacture.

My invention will be betterunderstood from the following description taken in connection with the'accompanying drawing and its scope will be pointed out in the appended claims.

Referring to the drawing, Fig. 1 is a circuit diagram illustrating one embodiment of my invention in which an electric discharge device is em-- ployed having non-thermionic electrodes; Fig. 2 is a circuit diagram illustrating a modification thereof; Figs. 3 and 4 are circuit diagrams showing modifications in which the discharge device is provided with thermionic electrodes, and Fig. 5 is a circuit diagram illustrating a further modiflcation wherein two discharge devices are connected in series, each device being provided with thermionic electrodes.

While my invention is applicable to apparatus employing various forms of electric gas discharge devices it is of particular interest and has been especially developed for use in connection with low pressure discharge devices which are employed to give light. A preferred form of such device is a lamp of the positive column type comprising a tubular envelope having electrodes at its ends and containing a gaseous atmosphere such as a few millimeters of a rare gas, for example argon, and a small quantity of a vaporizable meta! such as" mercury. Preferably the envelope is coated internally with a suitable fluorescent material in order that the electric discharge, which in itself may be scarcely visible, shall produce the desired high degree of illumination. The coating may also contain a suitable material to cause the lamp to continue to give light during the intervals of current reversal therein. In the description to follow, therefore, I shall refer to the discharge devices as lamps. It is well known that to start a discharge in such a lamp by the application of a voltage to its electrodes a higher voltage must be employed than that required to maintain the discharge after it has been started.

Referring to Fig. 1, I have shown the electric discharge device or lamp at i, the same being provided at its ends with the thermionic electrodes 2 and 3 which are heated by the discharge which takes place between them rather than being previously heated to an electron emitting temperature as, for example, by passing 8. current through them. Before starting, the lamp has a high resistance and may require a voltage considerably higher than that of the circuit from which it issupplied to start a discharge therein.. A 'lampfor example that is adapted to operate on a 115 volt circuit may require the application of approximately 300 volts between its electrodes to cause it to start. After it has started however,-the arc drop will be approximately only volts but a voltage somewhat greater than that is required to maintain the discharge. This required voltage 'has been found to be of the order of the v times the voltage of the arc .drop. In the circults now to be described the diiference between v the voltage of the source of supply and the arc drop voltage is absorbed by the ballast employed.

The lamp is shown connected withthe source of supply 6 of alternating current which, for example, may be a 60 cycle, volt lighting circuit by the connections 4 and 5.- These connections include ballast'devices comprising the reactor or choke coil 1 which, for example, may have an inductance of 1.2 henries and the capacitor 8 which, for example, may have a capacitance of 3 mid., the reactor and capacitor being arranged in series with the lamp. Connected across the lamp is a second reactor or choke coil 9 which, for example, may have an inductance of 1.4 henries. Energization of the lamp circuit may be controlled by any suitable switch'such a switch being illustrated by way of example at It.

When the switch It is closed to energize the lamp, thereactor i, the capacitor 8 and the reactor 9 constitute a circuit which is in a condition of partial resonance, that is, the inductance and the capacitance of the circuit are not such that the circuit is tuned or inexact resonance at the frequency of the source of supply but rather is only partly tuned or, in other words, is operated oil-the resonance peak. As a result of that condition the voltage across the reactor 9 and hence the voltage applied to the electrodes of the lamp is raised considerably above that'of the supply circuit and is suficient to cause a discharge to start in the lamp. As soon as the discharge starts the reactor 9 is substantially short circuited by the lamp inasmuch as the impedance of the lamp is materiallyless than that of this reactor. The lamp continues tooperate therefore on the circuit comprising substantially only the reactor 5 and capacitor 8, and inasmuch as the reactance provided by the capacitor predominates over the reactance produced by the reactor 1 the lamp, in effect, operates with capacitative ballast; hence the apparatus draws a leading current from the supply circuit 6. If desired, the reactor 9 may be constructed to saturate before the discharge in the lamp starts but I prefer it shall not saturate.

I. have found that when a capacitor is em-- results are apparent in the electrodes of the lamp. 1 In the modified form of my invention illustrated by Fig. 2 the reactor i2, which for example may have a. value of 2.6 henries is arranged to shunt both the lamp i and the reactor i3 whose reactance may be 2.6 henries. In series with the lamp is the capacitor it whose capacitance may for example be 3 mid. In this case when the switch ill is closed to start the lamp thecircuit including the capacitor M and the reactor 52 is-in partial resonance; hence the voltage across the reactor i2 is raised sufliciently to cause a discharge to start in the lamp. As soonas this occurs the reactor l2 becomes shunted by the lamp and the reactor i2. Since the lamp current now passes in series through the capacitor and the reactor i3 and since the reactance of the capacitor predominates .over that of the reactor IS the lamp operates with capacitative ballast and hence draws a leading current from thesource 6 as in Fig. 1. The reactor i3 also serves to absorb and smooth, out the high current peaks produced by the capacitor thereby saving the lamp cathodes from damage.

In the modification shown by Fig. 3 the electrodes i5 and it are initially heated to an electron emitting temperature by passing a current through them. In this case I also employ in series with the lamp the reactor ii whose inductance, for example, may be 1.2 henries and the capacitor l8 whose capacitance may, for example be 3 mid. Connected across the lamp is the reactor !9 whose'inductance, for example, may be 1.2 henries, the reactor in this case however being arranged in series with the electrodes 65 and i6 whereby before the lamp starts the resonance 'spot formed thereon.

current that passes the reactor I! also traverses the two electrodes and heats them.

. start therein. It having started, the reactor it is substantially short circuited by the lamp and the electrodes are kept hot chiefly by the cathode The lamp then operates with capacitative ballast and the electrodes are protected by the reactor l6 from current peaks originating in the capacitor.

That form of my invention illustrated by Fig. 4 also has initially heated electrodes and the circuit is similar to that shown in Figs. 1 and 3 except that instead of employing a reactor to shunt the lamp, I employ a split core transformer, that is, a transformer having an air gap in its magnetic circuit, whose primary 20 shunts the lamp and whose two secondaries 22 and 23 are connected to supply heating current to the lamp electrodes. In this case the series reactor 24 may have an inductance, for example of 1.2 henries. the capacitor 25 may have a capacitance for example of 3 mfd. and the primary 20 may have an inductance of 1.4 henries. As in the forms of my invention previously described, the primary 20, before the lamp starts, forms with the reactor 24 and the capacitor 25 a circuit in partial resonance whereby a sufficiently high voltage is ap-. plied to the electrodes of the lamp to start a discharge therein and a heating current proportional to the resonance current is supplied to the electrodes. During the subsequent operation of .the lamp the voltage across the primary 20 of the transformer is insufllcient to produce an appreciable heating current in the two secondary windings thereof but the lamp electrodes are maintained at an electron emitting heat by the cathode spot formed thereon.

The modification illustrated by Fig. 5 is similar to that of Fig. 3 except that two lamps i and i' are shown in series, each lamp being shunted by a. separate reactor l9 and iii. In this case the series reactor H1 and capacitor l8 may, for example, have the same values as the corresponding parts of Fig. 3. Reactors i9 and I9 however, each mayhave an inductance, for example of 0.7 henries. In this modification reactors I9 and 59 together with reactor I l and capacitor i8 form the circuit in partial resonance, otherwise the operation of this modification is similar to that shown by ,Fig. 3, hence a further description thereof seems to be unnecessary. While in Figs. 1 and 2 I have not shown any means for initially heating the electrodes, it will be understood that the electrodes may be heated if desired at starting by supplying current thereto from any suitable source.

I have chosen the particular embodiments described above as illustrative of my invention and it will be apparent that other modifications may be made without departing from the spirit and scope of my invention which modifications I aim to cover by the appended claims.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. In combination, a source of alternating current supply, a circuit comprising a capacitor and a reactor connected across said source, an electric discharge device having a starting voltage higher than said source connected to receive the 3. In combination, a source of alternating cur-' rent supply, an electric discharge device connected to be supplied therefrom, a capacitor and a reactor arranged in series in said connection and a reactor connected across said discharge device.

4. In combination, a source of alternating current supply, an electric discharge device connected to be supplied therefrom, capacitative ballast for said device in said connection, means in said con-' thermionic electrodes, a ballast capacitor and a reactor connected in series between said source.

and said device and a second reactor connected between said electrodes and forming a series circuit therewith.

7. In combination, a source of alternating current supply, an electric discharge device having thermionic electrodes, means connecting said source with said electrodes including a ballast capacitor and a smoothing reactor arranged in series, a transformer having a primary connected across said device and a plurality of secondaries and means for supplying current from said secondaries to said electrodes to heat the same.

v8. In combination, a source of alternating current supply, a circuit connected to be supplied therefrom having capacitative and inductive elements arranged in series and 'an electric discharge device in shunt relation to one of said elements, the inductive reactance in said circuit being materially less than the capacitative reactance therein whereby a condition of resonance does not occur and excessive current flow in the circuit is avoided.

9. In combination, a source of alternating current supply, an electric discharge device having a starting voltage higher than the voltage of said source, means including a ballast capacitor connecting said device across said source, a reactor cooperating with said capacitor for raising the voltage supplied to the device from said source and. a reactor in circuit with said device for smoothing out current peaks arising in said capacitor.

10. In'combination, a source of alternating current supply, a circuit connected to be supplied therefrom including a-capacitor and a reactor, an electric discharge device having a starting voltage higher than the voltage of said source connected to receive the voltage across said reactor, the amount of capacitance in the circuit being more than that required to produce a condition of resonance therein and means in circuit

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