US2565110A - Polyphase fluorescent lamp circuit - Google Patents

Description

All@ 2l, 1951 E. Q. ADAMS 2,565,110

POLYPHASE FLUORESCENT LAMP CIRCUIT Filed Oct. 13, 1949 {rm/@Whom ELLUt Q. Adams, b9 We Kwf I-Ii -ctatomeg Patented Aug. 21, 1951.

UNITED STATE-S PATENT OFFICE ration of :New York Application October 13, 1949, VSerial No. 121,214

5 Claims. 1

This invention relates generally to the operation of electric discharge devices of 'the type Vemploying ionizable mediums, such as the well known fluorescent lamps, and more particularly to polyphase starting and operating circuits therefor.

An object of my invention is to provide new and improved circuits for starting and operating electric discharge devices from a polyphase alternating voltage source.

Another object of my invention is 'to provide a polyphase operating circuit for a fluorescent lamp wherein resonant conditions between selected phases are utilized to start the lamp, and are subsequently eliminated as a result of phase changes caused by the discharge current flowing through the lamp during operation.

A feature of my invention is the possibility of operating fluorescent lamps in groups of three from a 6-phase circuit in such manner that, as soon as the lamps have started, circulating currents which had been used for heating -the filaments, are substantially balanced and eliminated as a result of the phase relations set up in the circuit. This feature permits avoidance of the necessity for switches, either of the glow or of the thermal type, for opening the lament heating circuits after the lamps have started in order to prevent unnecessary and destructive heating thereof.

A further feature of my invention is the possibility of operating the lamps in a group of three, with phase intervals, one from the other, displaced by 120, so that stroboscopic effects are vsubstantially eliminated.

Still another object of my invention is to provide various protective devices for use in conjunction with my circuit in order to prevent the maintenance of dangerously high voltages if some of the circuit elements should become defective.

For further objects and advantages and for a better understanding of my invention, attention is now directed to the following description and the accompanying drawings. The features of my invention believed to be novel will be more particularly pointed out in the appended claims.

In the drawings:

Fig. 1 is a schematic diagram illustrating the adaptation of a starting and operating circuit for a fiuorescent lamp, in accordance with my invention, to a six-phase alternating voltage source.

Fig. 2 is a vector diagram for the purpose of illustrating the phase and voltage relationships in the circuit of Fig. l.

Fig. `3 is a :schematic diagram of a starting and operating circuit similar `Ito that of Fig. 1 wherein Vcertain modifications have been made in `'order to accommodate -a `different type of fluorescent lamp.

Fig. '4 is a :schematic diagram of a similar circuit Tfurther modified by the addition 'of certain protective devices for lsafeguarding the circuit elements incase fthe 'lamp should become defectlve.

' As will shortly become apparent, my invention is applicable to any polyphase circuit containing an even number of phases in excess of four. However, for ease of explanation and understanding, 'It 'is most readily described with reference to a. six-'phase source. Such a source is readily obtained, through suitable 'transformer connections, from `a commercial three-phase supply. Thus, referring to Fig. l, there is shown a three-phase transformer :T consisting of a delta connected primary P, and of a star Vconnected secondary S, of which the windings are connected in common at their center points designated O. The input terminals of the primary P are adapted to be connected to a commercial three-phase supply. The secondary terminals have been brought out to points A, B, C, D, E, and F, all symmetrically disposed about the common point O in order to illustrate graphically the 6 phase relations of the voltages provided at those points.

In accordance with my invention, an electric discharge device or fluorescent lamp l may be operated in the position shown, or in either of the other positions illustrated in dotted lines. Lamp I comprises a sealed glass envelope 2 containing a mixture of rare gases .and a vaporizable metal such as, for instance, a small amount of mercury. Sealed into opposite ends of the lamp are a pair of therniionic electrodes 3 and 4. These may consist of coils of tungsten wire, preferably coated with an electron-emissive material such as oxides of alkaline earth metals, for instance, barium and strontium oxides. The interior surface of the lamp may, if desired, be coated with a iiuorescent material or a phosphor which, upon excitation by the short wave length radiation produced by a discharge in the lamp, generates a longer wave length radiation within the visible spectrum. One iilamentary end of electrode 3 is connected, by means of an inductor 5, to terminal A, and the other filamentary end is connected, by means of a capacitor 6, to terminal F. Similarly the lamentary ends of cathode 4 are connected, by means of an inductor 'I and a capacitor 8, to terminals D and C respectively. Inductors 5 and 'I, and capacitors 6 and 8, are selected to have substantially equal reactances at the frequency of the three-phase supply, which would normally be 60 cycles per second, so that each lamentary electrode is connected in a series resonant circuitL-M i f' '1 Referring to Fig. 2, the vector diagram therein illustrates the voltage and phase relationships in the circuit when a three-phase voltage is sup` plied at the terminals of transformer winding P. The vectors o-a through o-f represent the voltages, both in phase and magnitude, at'terminals A through F with respect to the common point O. Accordingly, the vector -f represents the voltage applied across the terminals- .of the resonant circuit of electrode 3. Since the reactance of inductor 5 is substantially equal and opposite in sign to that of capacitorv 6, the current therein is limited almost solely by theresistance of electrode 3 which, accordingly, heats up rapidly. In addition, the current flowing through inductor 5 and capacitor lI producesv voltage drops thereacross which may be represented by vectorsa--g and g-f respectively. These voltages addvectorially with the phase -voltages at terminals A and F respectively, to establish electrode 3 at a potential o-g fromthe common point O. Similarly, the large current flowing through electrode 4 raises `its temperature, and at the same time establishes it at a potential o-h with respect to the common point O. Thusthe voltage existing across the lamp from electrode 3 to electrode 4 is increased or boosted to the value g\-h,so that the discharge starts without diiculty.

As soon as the discharge hasy started, the current flowing through the lamp causes voltages L -g, g--f to come more nearly into` phase, so that in such case, four lamps might be utilized in a combination with the discharge current established at 90 phase intervals. However, as a matter of commercial practice, it is believed that the six-phase system which is readily obtained from a standard three-phase supply is the most practical.

4 Referring to Fig. 3, there is shown a discharge circuit wherein similar reference characters refer tol similar elements as in Fig. l, and which is adapted to be connected, in the same manner, to opposite and adjacent terminals of a six-phase supply. In this particular circuit, the lamentary ends of electrodes 3 and 4 are short circuited together and connected to the junction points of similar pairs of equal inductors I I, I2 and I3, I4. Moreover, device I is provided with va starting electrode or stripe I5 which is connected at one end to electrode 3. Inductor II is connected to terminal A, and inductor I 2 is connected to terminal F through a capacitor I6. Similarly, inductor I3 is connected to terminal C through a capacitor Il and inductor I4 is connected directly to terminal D.

The lamp utilized herein is of the so-called instant-start variety, wherein electrode heating current is not utilized, but the heating conse-l quent upon high voltage emission is relied upon to bring the electrodes up to a temperature capable of providing suicient electron emission to ionize the lamp and start the arc therein. With this variety of lamp, starting occurs in the same way as with the lamp shown in Fig. l except that y the feature of supplying heating current to the the large starting voltage across the lamp4 elec- U trodes is eliminated. If the normal voltage'drop across the lamp is equal to what might be referred to as the delta voltage of secondary winding v3, the voltage drop across the lamp is reduced to g-h, and for such acombination no heating current whatsoever ilows through electrodes 3 and 4 except the dischargetcurrent which flows in substantially equal amounts in opposite directions from the midpoint of .the 4electrode. lament. Where the normal voltagedrop across the lamp is less than the delta voltage of the transformer, the voltage across the lamp may, for instance, be represented by g f-h. .In such case suiicient reactive current circulates through inductor` 5 and capacitor 6 to provide the voltage drQp `7.-y". Where the required voltage'drop across the lamp is greater than the deltanvoltage, the reactive currents ilow in an opposite direction' and generate the small boosting voltage necessary to maintain the discharge through thelamp.

It will be apparent that lamps 9 and I0, which have been illustrated in dotted outline, ,willoper ate in an identical fashion and, when connected symmetrically as shown, will serve substantially to eliminate reactive volt amperes in the combination. Moreover, thervoltages supplied to the three lamps in thecombination are at 120 phase intervals', so thata substantially constant luminous intensity is obtained from the combination and stroboscopic effects, areeliminated.

While I have shown lamp Land its associated circuit connected across adjacent and opposite terminals vof a six-phase supply, it will be apparent that my. invention Iis not in any way limited to this particular combination, For instance,- an eight-phase supply may readily be utilized and electrodes is not utilized, and the resonantvoltages provided by the circulating currents are alone utilized for starting.

In this circuit, the inductors are selected to have substantially equal reactances at the operating frequency and the capacitors are selected to have double the reactance of any one of the inductors. Accordingly, the circuits are still resonant at the operating frequency, but, since the reactance of the capacitor is twice what it was before, smaller size capacitors may be employed and this may be economically advantageous under certain circumstances. Moreover, the life of the fluorescent lamp appears to be lengthened when inductive ballasts are provided in series with the electrodes and the voltage source,` rather than exclusively capacitive ballasts, and this circuit fulfills this requirement. Referring to Fig. 4, wherein like reference l characters denote corresponding elements as in the preceding` figures, there is provided a protective device for short circuiting capacitors I5 and II in case of failure of thelamp to start, for some reason or other. It will be apparent q that if the lamp should fail to start, a large current would continue to ow through the lilamentary electrodes 3 and 4 and large resonant voltages would be created across the circuit elements. This might cause dangerous heating of the circuit elements and possibly bring about their destruction. This occurrence could be safeguarded against by fusing each of the electrode circuits A-F and C-D. Another means of safeguarding the circuit might be to insert a thermal switch with a Alockout feature in series with each.

In accordance with my invention, I prefer to utilize anotherv means which has the addedadvantage-ofsimplicity and economy and which does not require any resetting after operating.

'I'he protective element consists of a varistor I8 and a thermistor I9 connected in a parallel with capacitor I6, both elements being included in a container 20 (shown in dotted outline) in order to maintain them in thermal contact. Varistor I8 is composed of a material whose resistance decreases rapidly with an increase in the applied potential; thermistor I9 is composed of a material Whose resistance decreases rapidly with a rise in temperature. With the combination shown, if lamp I fails to start and a large current should continue to flow through the electrode circuits, the large voltage developed across capacitor IG causes a substantial current to flow through varistor I8. Accordingly, varistor I8 heats up and in turn causes thermistor I9 to heat up and its resistance to decrease to the point Where capacitor I6 is effectively short -circuited. From then on, the current through thermistor I9 is sufiicient to maintain it at a high temperature and short circuit capacitor I6 so that resonance is effectively destroyed in circuit A-F. A similar device 2l may be connected in circuit C-D to operate as a protective element therein.

While certain specific embodiments have been shown and described, it Will, of course, be understood that various modifications may be made without departing from the invention. Thus, as has been mentioned before, various polyphase sources may be utilized instead of the six-phase supply which has been described. Likewise, it need hardly be mentioned that other circuit elements capable of performing the same electrical functions may be substituted for those shown. The circuit is adaptable to the operation of large numbers of lamps in parallel and these may be combined, as to their starting circuits, so that all the starting elements need not be duplicated in each individual lamp. The appended 4claims are, therefore, intended to cover any such modifications coming Within the true spirit and scope of the invention.

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

l. Apparatus for starting and operating an electric discharge device of the type including a pair of thermionic electrodes, comprising said device, a polyphase source of alternating voltage of predetermined frequency containing an even number of phase terminals not less than four, first and second pairs of reactive circuit elements respectively connecting said electrodes to diametrically opposite pairs of adjacent phase terminals, one of said elements in each pair of elements being substantially equal in magnitude but opposite in sign to the other in order to constitute a resonant circuit at said frequency.

2. Apparatus for starting and operating an electric discharge device of the type including a pair of thermionic electrodes, comprising said device, a six-phase source of alternating voltage of predetermined frequency, first and second pairs of reactive circuit elements respectively connecting said electrodes to diametrically opposite pairs of adjacent phase terminals, one of said elements in each pair of elements being substantially equal in magnitude but opposite in sign to the other in order to constitute a resonant circuit at said frequency.

3. Apparatus for starting and operating ari electric discharge device of the type including a pair of thermionic electrodes, comprising said device, a polyphase source of alternating voltage of predetermined frequency containing an even number of phase terminals not less than four, i'irst and second pairs of reactive circuit elements respectively connecting said electrodes to diametrically opposite pairs of adjacent phase terminals, one of said elements in each pair of elements being substantially equal in magnitude but opposite in sign to the other in order to constitute a resonant circuit at said frequency, the reactances of said elements being selected in proportion to the voltage required for starting a discharge within said device and occurring as a result of the iiow of current through said resonant circuit from adjacent phase terminals.

4. Apparatus for starting and operating an electric discharge device of the type including a pair of thermionic electrodes, comprising said device, a polyphase source of alternating voltage of predetermined frequency containing an even number of phase terminals not less than four, first and second pairs of reactances respectively connecting said electrodes to diametrically opposite pairs of adjacent phase terminals, the reactances in each -pair being substantially equal in magnitude, but one being inductive and the other capacitive in order tc constitute a resonant circuit at said frequency for augmenting the voltage across said electrodes at starting as a result of the flow of current within said circuit from adjacent phase terminals, said current serving `simultaneously to heat said electrodes.

5. A circuit for operating and starting a iluorescent lamp of the type comprising a pair of filamentary thermionic electrodes, comprising said lamp, a polyphase source of alternating voltage of predetermined frequency containing an even number of phase terminals not less than four, a circuit for one of said electrodes including an inductive reactance connecting one end thereof to a first phase terminal and a capacitive reactance of substantially equal magnitude connecting the other end thereof to a second phase terminal adjacent said first one, a similar circuit for the other of said electrodes including an inductive reactance and a capacitive reactance of equal magnitude connecting the ends thereof to a third and to a fourth phase terminal adjacent to each other and diametrically opposite to said first and second phase terminals, said circuits serving simultaneously to heat said electrodes and to increase the voltage applied between them at starting.

ELLIOT Q. ADAMS.

REFERENCES CITED The following references are of record in the iile of this patent:

UNITED STATES PATENTS Number Name Date 2,265,323 Spanner Dec. 9, 1941 2,298,935 Freeman Oct. 13, 19424 2,354,654 Abbott Aug. 1, 1944

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