US2170446A - Electric discharge apparatus - Google Patents

Description

Aug. 22, 1939. M. A. EDWARDS 2,170,446

ELECTRIC DISCHARGE APPARATUS Filed MaICh 22, 1938 9 /e l5 Inve rwtor:

2a Martn A. Edwards 25cm/6,44 afg/refs. His Attorn ey.

Awill operate with Patented Aug. 22, 1939 ELECTRIC DISCHARGE APPARATUS Martin A. Edwards, Schenectady, N. Y., assignor to General New York Electric company, a corporation o! Application March 22, 1938, Serial N0. 197,526

lo'laims.

My invention relates to gaseous 'electric discharge devices and apparatus employed in operating the same from alternating current circuits particularly when the discharge devices are used for the purpose of giving light, namely as lamps, and when their construction is such that they require the application of a higher voltage for starting than for their subsequent operation.

One object of my invention is the provision of improved apparatus for such use which will provide the voltage `necessary to cause a discharge in the device to start and after starting has occurred will reduce automatically to the value required for the continued operation of the device thereafter. Another object of my invention is the provision of improved apparatus for such use whereby the amount of iiicker incidental to the circuit frequency is reduced to a low, if not imperceptible, value. A further object of my invention is the provision of such apparatus which high efliciency, will have a starting characteristic which is not injurious to the device, will provide a circuit which has a high degree of stability and one wherein the current supplied to the device is not critical to reasonable variations in the line voltage.

My invention the following description taken in. connection with the accompanying drawing and its scope will be pointed out in the appendedclaims.

Referring to the drawing, Fig. l is a combined circuit diagram and diagrammatic side elevation of one embodiment of my invention; Fig. 2 is a `simplified circuit diagram of the apparatus shown in Fig. l; Fig. 3 shows curves illustrating the performance of the device and the apparatus, and Fig. 4 is a circuit diagram showing a modification.

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 f or use where the devices 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 A 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 metal, 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. In the description to follow, therefore, I shall refer to the discharge devices as lamps.l It is well will be better understood from known that to start a. discharge in such a lamp by the application of a voltager to its electrodes a higher voltage must be employed than that required to maintain the discharge after it has been started.

In Fig. l, I have shown the electric discharge device or lamp at I provided at one end with the thermionic cathode 2 and at the other end with the two similar anodes 3 and 4 preferably separated by the insulating partition 5. If de- 10 sired, a well known form of separately heated cathode may be employed instead of the directly heated cathode as shown.

Before starting, the lamp has a high resistance and may require a voltage considerably higher 15 than that of the circuit from which it is supplied to start a discharge therein. A lamp, for example, that is adapted to operate on a 110 volt circuit may require the application of approximately 450 volts between its anode and cathode 20 to cause it to start. After it has started however the arc drop may be approximately only volts, but a voltage higher than that is required to maintain the discharge.

The lamp is supplied from the source 'I of single 25 phase alternating current which for example may be a 60 cycle, 110 volt lighting circuit through the unitary structure represented at 8 and comprising a combined high reactance transformer and reactor. 'Ihe core of the structure comprises 30 two E-shaped members 9 and I0 reversely arranged With respect to each other and with corresponding legs spaced from each other to form magnetic gaps. In the drawing these .gaps are shown for simplicity as air gaps but as the appa- 35 ratus is manufactured they comprise a suitable non-magnetic material against which the two members are clamped. Between the legs of the member I0 are magnetic shunts shown at II thereby increasing the flux leakage to provide a 40 higher leakage reactance.

On each of the outer legs of the core structure is a primary winding consisting of the coil I2, a main secondary winding consisting of the coil I3 plus the coil I2 thereby constituting an auto-v 45 transformer and a separate auxiliary secondary winding comprising tlie coil I4. The ends of the primary, thus composed of the two coils I2, are connected by the leads I5 and switch I 6 with the opposite sides of the source 'I. The opposite 50 ends of. the main secondary, composed of the two coils I2 and the two coils I3, connect withthe two anodes 3 and 4 and the mid-point thereof connects with the cathode 2. 'Ihe latter connection includes the conductor I1 and the auxil- 55 i Il are arranged adjacent lary secondary, made up of the two coils I4, the purpose of which is to supply heating current to the lamp cathodes.

As shown by the drawing the magnetic shunts the upper ends of the primary coils-and extend lbetween the outer legs of the 'core structure and the middle leg I8v thereof being spaced from those legs by magnetic gaps` which preferably comprise a suitable non-magnetic material.v It will beA seen that by this arrangement the amount of-leakage of the primary ux is greatly increased since the shunts provide a relatively low reluctance leakage path, with the result that the leakage reactance between the primary and the secondary is accordingly increased. The middle leg I8 also provides a return path for the uni-directional component of the flux in each of the two outer legs during the operation of the lamp, such a component being present by reason of the fact that since the lamp acts as a bi-phase rectifier the secondary current is unidirectional. By reason of the middle leg, moreover, I obtain Van exceptionally high reactance, hence a lowmutual reactance, between the two halves or coils of the secondary winding because of the magnetic shunt effect thereof, whereby they are virtually isolated from each other.

To assist one in the understanding of the several flux paths which the above described structure provides, I have represented the alternating flux at any instant by dash lines and thev unidirectional ux by dotv and dash lines. In order to cause the magnetization of the core by the primary to have a linear characteristic and also to limit the voltage produced in the secondary by` the condition of partial resonance obtained at the time of starting, which condition will be-described later, I provide a magnetic gap in reach of the outer legs. I also provide a gap in the middle leg I8 so as to prevent saturation therein due to the this leg when the that it results in obtaining a long commutating angle between the currents supplied to the two anodes and consequently a long conducting time for each anode. Oscillograph records made with apparatus such as disclosed herein show that each anode carries current for approximately 230 degrees so that a large overlap of the anode currents occurs at the beginning and end of each half cycle. With such a large overlap of anode currents the ripple-in the total unidirectional or cathode current through vthe lamp is reduced to a low value and the amount of flicker in the light emitted by the lamp is very small, if not imperceptible. This is illustrated by the curves of Fig. 3. In that iigureI have represented at 20 and 2l the wave form of the currents in the anodes 3 and 4 respectively plotted against electrical degrees. This illustrates the large overlap of the anode currents resulting from the above described structure. At 22 I have shown thecathode current which, it will be observed, has but a small amount of ripple therein; this results in the lamp producing light which is substantially without fiicker.

It is well known that a high reactance transformer produces a low power factor but that the power factor may be improved by the use of a capacitor across the primary or across another Winding closely coupled therewith. A capacitor so used, however, is objectionable because of the andere current harmonics of large magnitude which. it draws from the line when lamps of the varc discharge 4type are being operated by the apparatus and,y because the high current peaks due to such I harmonics are found trodes of the lamp if allowed to continue for any appreciable length of time. With apparatus such as thatv disclosed by this application should a capacitor be connected directly across the secondary for the purpose of improving the power factor it would be objectionable not only for the reasons mentioned above but for the additional reason that it would decrease the angle of commutation thereby ofE-setting to a certain extent the good effect of the high reactance of the sec-A ondary. In the arrangement which I have devised I employ the capacitor 24 acrossthe secondary for improving the power factor-and I overcome the objections noted aboveby connecting in series therewith the reactor'or choke coil 25-V the reactance of which is materially less than that of the capacitor. 'Ihe inductive reatance supplied by the reactor is suiclent to dissipate or smooth out the objectional high current peaks originating in the capacitor while the combinato be injurious-to the elec- I tion of capacitor and reactor is sufficiently capacitatively reactive to effect the desired power factor correction. i

The capacitor 24 and the reactor 25 thus bridged across the secondary performs the additional function of raising the= voltage applied between the cathode and the anodes of the lamp. This is because the relative amounts of capacitative and inductive reactance in the closed circuit including those. membersand the leakage reactance between the primari/ and lits secondary is such that a condition of partial resonanceexists therein. A condition of actual or complete resonance is not desired, the natural resonance frequency of the circuit being somewhat higher than the supplied frequency.l For example, if the sup-- plied frequency is 60 cycles per second the ',natural resonance frequency 'of the circuit maybe 65 cycles. For stability reasons it is desirable that f 1 the operating frequency shall be on the low frequencyside ofthe resonance. curve;

The reactor 25 may have any desired core providedsit is not the same as the transformer core,

in other words, is not 'in the path of the transformerux. It may, however, be of a form that constitutes an ranged adjacent'to a part of the transformer core" which part therebyserves to'complete its lmagnetic circuit. Such 'a core construction is shown by the E-shaped member 26 separated from the transformer core by the magnetic gaps 21.

Inasmuch as the voltage applied between the 450 incomplete-magnetic circuit in it- Vself but, for purposes-of-economy, may bear-v cathode and eitheranode, namely the voltage of I' one-half of the secondary plus that obtained by the above described bridge circuit, is not sufcient to cause a discharge to start in the lamp,

I have providedmeanslnow to be described for applying a higher voltagel'between the cathode and one anode to cause the discharge to start. In connection therewith I employ a time delay means whereby the high starting voltage is not applied to the lamp electrodes until the cathode has had time to become heated to the desired degree. For obtaining the higher starting voltage I connect the capacitor 28 across onehalf (the left half as shown in Figs. 1 and 2) of the secondary, this capacitor being of such a value i that it forms therewith a circuit in partial resonance. The connection of the capacitor Yincludes the electro-magnetic switch 29 which is biased to closed position by the spring 30 and which has a small armature 3| arranged opposite the gap 32 in the middle leg I8. The capacitor connection also includes the time delay apparatus to insure the heating of the cathode to the desired temperature before the starting voltage is applied. As an example of such apparatus I have shown a well known form comprising a thermal switch having the bi-metallic blade 34 and the resistance heater 35 adjacent thereto and in shunt therewith, the blade being constructed to short circuit the heater when heated thereby.

When the switch I6 is first closed to energize the lamp and the controlling apparatus therefor, a discharge does not immediately start in the lamp since the voltage applied thereto is not sufficient. Heating of the cathode, however, im-

mediately starts. The switch 29 remains in closed position since before the discharge in the lamp starts there is substantially no flux in the middle leg of the transformery and the switch 34 being cool is open. Because of the resistance of the heater 35, the current flow through the capacitor 28 is not suilicient to produce a starting voltage between the cathode and the anode 4 to which the capacitor is connected. However, by the time that the cathode has reached the required temperature the switch 34 will have been bent down by the heat received from its heater shes to snort circuit the heater. That being done,l the circuit including the capacitor 28 and that half of the secondary to which it is connected immediately comes intov partial resonance and the resulting high voltage across the capacitor is applied between the cathode 2 and anode 4. With the starting of a discharge in the lamp between those electrodes, the other anode 3 also comes into action. The uni-directional flux now passing through the middle leg of the core attracts the armature 3l toward the gap 32and opens the switch 29. It will be seen that the operation of this switchopens the circuit of the capacitor 28 which will be held open as long as the lamp continues in operation. As the switch 34 cools it will open the short circuit around the heater 35 in readiness for a subsequent starting of the lamp.

In the modified form of my invention illustrated by the circuit diagram comprising Fig. 4, the apparatus is substantially the same as that shown by Figs. 1 and 2 except that the lamp is provided with the non-thermionic cathode 38: hence, no secondary coils are needed for cathode heating and the cathode connects directly with the mid-point of the'secondary. Moreover, since the cathode is not initially heated, it is unnecessary to provide any means for delaying the application of the starting voltage. The operation of the apparatus represented by Fig. 4 otherwise is like that already described above-in connection with Figs. 1 and 2.

I have chosen the particular embodiment described above as illustrative of my invention and it will be apparent that various other modifications may be made without departing from the spirit and scope of my invention which modifications I am 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, an electric discharge device having a cathode and a plurality of anodes, a transformer having spaced points of its secondary connected each with one of said anodes and an intermediate point-thereof connected with La transformer having the ends of its said cathode, means for applying a starting voltage between said cathode and one of said anodes, said transformer being constructed to provide a path for the uni-directional flux resulting from the operation of said device, and means responsive to said ux for rendering said starting means inoperative.

latter path for rendering said means inoperative.

3. In combination, an electric discharge device having a cathode and a plurality of anodes, secondary connected each with one of said anodesand having an intermediate point thereof connected with said cathode, a capacitor connected between one end of said secondary and said intermediate point for producing a starting voltage for said device, said transformer being constructed to provide an alternating ux path anda uni-directional flux v path, and means responsive to the flux in the latter path for opening said capacitor connection.

4. In combination, an electric discharge device having a. cathode and a plurality of anodes, a transformer having a core structure comprising three legs, a secondary winding on two of said legs, the ends of the winding being connected each with one of said anodes and an intermediate point thereof being connected with said cathode, means for applying a starting voltage to said device,`and means responsive to the flux in the third leg of said core structure for controlling said means. i

5. In combination, an electric discharge lamp having a cathode at one end and a plurality of anodes at the other end, a transformer core having two outer legs and an intermediate leg traversed by an air gap, primary and secondary coils on each of said outer legs, the secondary coils being connected each with said cathode and with one of said anodes, a capacitor connected across one of said secondary coils to provide a starting voltage for said lamp, a switch in circuit with said capacitor and .means responsive to the flux in said air gap for controlling said switch.y

6. In combination, an electric discharge device having a cathode and a plurality of anodes, a high leakage reactance transformer having spaced points of its secondary connected with said anodes and an intermediate point thereof connected with said cathode, a capacitor connected to improve the power factor and means associated therewith for preventing the eifect of said capacitor of diminishing the overlap of the anode currents.

7. In combination, an electric discharge device -having a cathode and a plurality of anodes, a transformer having spaced points of its secondary connected with said anodes and an intermediate point thereof connected with said cathode, said transformer having means providing a high leakage reactance between the parts of said secondary divided by said intermediate point and a capacitor and a reactor connected in series in a normally closed circuit across said the path of flux o! the'transformer.

8. Inl combination, an electric discharge det vice having a cathode and a plurality of anodes, a

transformer having spaced points of its secondary connected with said anodes and an intermediate point thereofconnected with said cathode, a capacitatlve connection comprising a capacitor and a reactor across 'said secondary and forming therewith a normally closed circuit whose resonance frequency is higher than the applied frequency, said reactor being arranged to operate independently of the flux of said transformer.

,9. In apparatus for controlling electric dis*- charge devices, a transformer comprising a'core having a central leg and two outer legs all connected together at their ends, each of saidouter legs having thereon a coil forming a part of the primary winding and a coil at the side of said including a plurality of E-shapedV members arranged withtheir legs toward each other, a magnetic shunt arranged between the center leg of one member and each of the outer legs thereof, a coil on each outer leg of said oneV member be- 'tween one of said shunts and the yoke portion of the member, and coils on the outer legs of said members between said shunts and the yoke portion of the other of said members.

A. EDWARDS.

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