US2382012A - Fluorescent lamp circuits - Google Patents

Description

' Aug. 14, 1945. R. w. KEISER 2,382,012

FLUORESCENT LAMP CIRCUITS Filed Dec. 4, 1941 Patented Aug. 14, 1945 I ZSSZMZ 2332,4112 FLUORESCENT the puncture Russell W. Keiser, Atlanta,- Ga., assignor to Boucher and Kaiser Company, Atlanta, Ga.-, a

partnership Application December 4; 1941, Serial No. 421,700

' (Cl. sis-282) 7 Claims.

This invention relates to reactances and more particularly to plural reactances intended primarily for the division of and limitation of current from a single source for application to a plurality of negative resistances.

It is a general object of the present invention to provide novel and improved forms of plural reactances and novel and improved circuit combinations using the same.

More particularly it is an object of the invention to provide a plurality of reactance coils arranged on a common core together with means for providing flux interlinkage between the several coils.

An important object of the invention resides in the provision of a plurality of reactance coils on a common core so that in normal operation each acts on one portion of a divided electric circuit to control the current flow therein entirely independently of the-other; but under certain abnormal conditions the flow of current in one coil induces a current in the other'which is superimposed on that normally impressed on this second coil to increase its potential.

A further important object 01 the invention consists in the provision of circuits for fluorescent lamps adapted to divide the current froma single source for independent operation of a plurality of lamps, for regulating the current flow to each of the same, and for supplying operating current at normal lamp potential with a minimum'of loss.

Yet another object of the invention consists in the provision of a dual reactor for use with fluorescent lamps to adapt the same for starting by ionic bombardment at higher voltage and operation at normal voltage, the whole control being entirely automatic and inherent in the reactances.

As an important feature of the invention may be mentioned the construction ofthe reactor to provide for the division of alternating current into two componentsv either equal or unequal for the operation of electrical apparatus having negative load characteristics.

Another feature of the invention relates to the construction of the reactance to provide independent operation of each lamp of a plurality so 1 that the failure of one-will not prevent the op-' panying drawing and following specification wherein are disclosed several exemplary embodiments of the invention with the understanding that various modifications and combinations of the same may be made such as fall within the scope of the appended claims without departtion;

Figure 2 is a schematic showing of the structural features of the type of reactance suitable for the circuit of Figure 1;

Figure 3 is a view similar to Figure 2 showing a shell type core;

Figure 4 is a diagram similar to Figure 1 illustrating the use of iiuorescentlamps, a dual inductance, and a step-up auto transformer for providing operating voltages suiiiciently high for cold starting;

Figure 5 is a view similar to Figure 4 but illustrating the use of the conventional automatic starters in conjunction with the fluorescent lamps;

Figure 6 is a view illustrating the use of a plurality of dual reactances for the operation of a number of negative resistances; and

Figure 7 illustrates schematically the arrangement of a, multi-reactor.

In the operation of negative resistance loads from alternating current sources some means must be provided for restricting the flow of current to an amount which is not harmful to the apparatus constituting this resistance. By a negative resistance is meant one in which the voltage drop continually decreases in value with increased flow of current. An excellent example of a negative resistance and one which will be used, illustratively only, hereinafter in this specification is the so-called fluorescent lamp now popularlvused for lighting purposes and comprising an elongated evacuated glass tube, the inner walls of which are coated with some material adapted to fluoresce when activated by an ionized gas. A-quantity of suitable gas is incorporated within the tube along with some metallic vapor if necessarmand each end of the tube is provided with at least one electrode.

The conventional fluorescent lamp has, instead of a. single electrode at each end of the tube, a filament thereat adapted to be temporarily heated to provide the necessary ionization for a break-down of the cold resistance of the tube by extinguished when the arc strikes through the tube and the lamp is in normal operation. 'The automatic equipment for the purpose is extremely V unreliable and constitutes the source of. perhaps 90% of the difficulties experienced with fluorescent lamps.

In accordance with the present invention means is provided to eliminate this automatic starting equipment cooperating with the filaments and to start the lamps by ionic bombardment resulting from a sufiiciently high potential applied between the terminals at the opposite ends of the lamps.' Since the lamp in operation under all conditions requires some current "limiting means, convenient use is made of this re- 4 quirement to provide for automatic ionic bombardment starting and current control by the arrangement of a suitable reactance in the circuit between the lamp and-the source of alternating current.

In the normal operation of fluorescent lamps there occurs a certain amount of flicker at the.

frequency of the alternating current because of. the absence of any metal or solid material for holding heat during the passage of the current through the zero point. A single lamp is therefore often unsatisfactory because of the stroboscopic effects obtained in the presence of rotating or moving parts operating from the same source of current and hence in synchronism in multi ples or sub-multiples of the current frequency. The lamps are therefore almost always operated in pairs with some means to provide current ad- "vance for one of the tubes to break up these diificulties by having the lamps extinguished at difierent times in the current cycle. 'The current to these lamps normally lags the voltage providing a relatively low power factor. The device of the present inventiontherefore incorporates means for operating at least two lamps and includes means for dividing the current from a single alternating current source into two equal or unequal parts feeding several lamps. Conventional power factor correction may be used for one. lamp of the pair.

The invention is illustrated in several embodiments which are only illustrative of structures and systemsincorporating the-same. Referring particularly to Figure 1 there is depicted schemined quantity of winding but providing a cer tain interlinkage of flux between the magnetic circuits of the two windings so that under stipu-- therein.

lated conditions the reactances do not actentirely independently.

- The reactance of each winding I4. or IE .is the sum of its direct current resistanceand its in? ductance and in the circuit illustrated acts to limit the quantity of current which can flow ary resistance in whichth voltage drop increases in proportion to the current in the resistance in' accordance with the recognized formula E=RI.

A negative resistance if directly connected across asource of current of unlimited capacity will bedestroyed because of this peculiar property. -A

reactance such as illustrated in Figure 1 serves to-prevent-this and can be proportioned to pro-' vide any desired potential drop across the negative resistance and hence the requisite'current Whenthe negativeresistances of Figure 1 are fluorescent lamps they are commonly of like capacity whenoperated in pairs so that the two 7 parts of the reactance are identical, but this is not a requirement for proper operation of the dual reactances of thefpresent invention.

From a structural standpoint the dual'react-,

ances are constructed as schematically illustrated in Figure 2; where the straight ,core portion ll is of rectangular cross section-and formsonly a portion of the whole core which is completedby the E-shaped section l8 having the central arm l9 longer than the end'arms 20 and 2| so that it ings l5 and I6 as shown, while air gaps 23 and 24 are provided between the-arms- 20 and 2| and the ends of the core bar l'l. This construction and the disposition of the coils provides for two substantially closed magnetic paths one for each coil, eachof Which'paths hastherein a small-air gap. The two paths have a common portion in-the central arm IS SO that there .is an interlinkage of magnetic flux resulting from the currentspassing through the two windings. In the event that current passes through but one winding, as sometimes happens, particularly'when two fluorescent lamps are operated together and one starts before the other, these air gaps serve to force a portion of the flux from the coil carrying substantially normal current through the companion magnetic cir-, cult to provide an-induced' potential in the com panion winding. The purpose of this will appear in a subsequent descriptionof the manner of operating the reactor for starting and lighting fluor-' escent lamps. v

In Figure 3 a dual reactance is shown with a so-called shell type of core as often used in transformers. with the so-called core type of Figure 2 are'thc same as in connection with alternating current transformers. The structural difference involves only the addition of a second E-shaped member l8 to the straight core portion opposite the first one to provide more complete iron'paths for the magnetic flux so that there is less leakagev through the air except in, the purposely provided air gaps.

Figure 4 illustrates a circuit involving two fluorescent lamps 30 and 3| adapted to be operated from a commercial source of alternating current 33. Since these sources are usually of one of the well-known potentials 110, 220, or 440 volts and since the lamps operate on different potentials from these in accordance with their length and/or The advantages of this as'cornpa'redv diameter, it is conventional to provide some form of transformer to step up the voltage to that required by the lamp or the lamp and its ballast. The voltage may be lower in some cases by ballast resistances or the like. A step-up auto transformer 35 is illustrated, and since it is of conventional construction and operation needs no description here. In this arrangement the source of current 33 plus the transformer-35 becomes the source of total voltage supply for the lamps and reactors and may be substituted for the source shown at I! in Figure 1.

The dual reactance of the present invention is illustrated at 38 and is of the form of Figure 2 -but may be as shown in Figure 3 or as later described. One end of each of the windings is connected at 39 to the output from the transformer while the wire connecting the two lamps together is associated at 4| with the opposite end of the source of -supply. The remaining ends of the reactance coils are connected respectively by wires 42 and 43 with the outside ends of the two lamps, a suitable condenser 45 being inserted in one but not both of these lines. In normal operation of a fluorescent lamp the power factor is reduced by the lag in current. This condenser 45 as is well known serves to cause a leading current and improves the power factor in the circuit of the lamp with which it is associated, whereby the two lamps operate out of phase to eliminate the sti'obcscopic eii'ects earlier referred to.

The lamps will b seen to be connected by only a single wire at each end, the filaments being used only as terminals, if present. as in lamps now available.

The voltage supplied from the source is such that in the absence of current flow in the reactance coils the potential across each of the lamps is substantially higher than the normal operating voltage of the same, but since the lamps are cold when the switch 48 is first closed there is no rush of current. The relatively high potential existing between the terminals at the two ends of the lamp results in an ionic bombardment of the same thereby slightly heating them and causing the emission of electrons which break down the high resistance path throughout the length of the tube and allow what may be considered an arc to strike through the same which provides the source of activation for the fluorescent material with which the inside of the tube is coated. Now the lamp becomes a negative resistance but at the same time it draws substantial current, which, flowing in the coils of the reactor, produces a voltage drop across the same which will increase with any tendency to increased current. The current is thereby stabilized to a value determined by the characteristics built into the reactor which must be adjusted for each size of lamp in accordance with its desired potential and current.

The above method of cold starting fluorescent lamps does away with the trouble-making starters referred to in'the early portion of this specificatio'n and it will be seen that starting is effected merely by closing the switch supplying current to the lamps, the operation being entirely automatic and inherent in the structure of the reactor. Such lamps, however, either because of age, initial high resistance, or other characteristics, do not start so readily as others, perhaps requiring a slightly higher voltage for starting. One of the important features of the reactor of the present invention is that it assists in starting lamps which are normally difllcult to place in rmeratinn fnr thn nnaratimr current. flnwimr through the winding of the reactor of the easy starting lamp acts bymutual induction, because of the interlinked magnetic flux of the two core sections, to build up a voltage in the winding of the companion reactance which is superimposed on the voltage existing across the same from the source and therefore the sum of these two voltages is available for starting, ensuring a quick and ready start of even the most refractory lamp. The air gaps in the interlinked magnetic circuits come into play in this operation of starting one lamp after the other has been started, for if the active and energized coil had a 100% complete iron magnetic circuit there would be no tendency to magnetize the circuit of the other winding, but with this air gap in its circuit the flux tends to follow the line of least resistance and some of its travels in the interlinked magnetic circuit thereby energizing the second coil to provide the additional starting voltage.

It will be noted that there is substantially no current required in the starting operation 50 that the reactance does not reduce the available potential except by its low direct current resistance. Therefore, the lamp which may be burning does not haveits voltage reduced below the critical value and does not tend to be extinguished by the operation of starting the other lamp. The critical value of voltage is that necessaryto keep the lamp in operation under normal conditions.

In normal operation the reactors act substantially independently and serve only to provide the necessary current limiting facilities such as are required in the operation of all fluorescent lamps. A reactance is superior to a ballast resistance since there is less current loss in the same by heating. If one lamp should go out because of some defect preventing it from operating, the other lamp can carry on with its normal potential and current supplied with the assistance of its portion of the reactance.

In case it is not desired to make use of the cold starting. characteristics of the reactance of the present invention the circuit may be wired as shown in Figure 5 which is substantially identical with Figure 4 except for the addition of the starting switches SS each arranged in a circuit; between opposite terminals of each of the lamps 50 and SI. When these switches are momentarily closed a circuit is completed through the filament windings at both ends of the lamps to heat the same and provide the necessary electron emission for starting. This starting current is provided through the reactances which serve to limit it to a usable amount. Note that under these conditions the high potential available for starting in accordance with the circuit of Figure 4 is not available because of the current flow in the inductances which produces a voltage drop across the same. The reactor in this case serves only as a current divider and limiter.

Figure 6 shows the combination of three dual reactors 60, iii, and 62 used to divide current from the single source 63 into four branches for operating the four negative resistances 64, 65, 66 and 81, each pair of which is supplied in the manner above described by one of the dual reactances 60 or 62. The current is divided to supply these twodual reactances by the single dual reactance 6| connected to one end of the source, the other end being conne'cted to the lower terminals of the four resistances.

The pair of dual reactances 60, 62 may be.

' Letters Patent is:

prises two of the units of Figure 3 with the central core member in the form of two E's arranged back to back. 7

I In the several structural arrangements of the reactors it will be appreciated that the core forms may be of different shape and arrangement and that the air gaps need not be provided-in the 'manner illustrated. For instance, in Figure 2 the end air gaps maybe substituted by tight magnetic joints and a single central air gap provided between H and i9. The effect will not be substantially difierent.

It will be appereciated that reactors may be constructed to divide current from a single source into any desired number of circuits by suitably arranging reactance coils on a common core as illustrated in several of the figures of the drawing.

Furthermore the reactors may be constructedwith unbalanced windings, i. e., more turns on one section of a two section reactor (for instance) than on the other. Such a reactor has two uses, first with a power factor correcting condenser which is used in conjunction with the reactor .operable fluorescent lamps and a single source of alternating current at a potential higher than the operating potential of either lamp, of a dual reactance and current divider comprising an iron core having two substantially closed magnetic circuits, each provided with an air gap, a portion of said core being common to both circuits, 9.

pair of coils, each connected between said source and one lamp, each coil being mounted on said core in operable relation to one Of said magnetic circuits, and wound in a direction to receive mutual induction'from' the other coil to augment the potential therein.

4. The methodof starting and operating a pair of fluorescent lamps comprising, dividing a source of current into two parts, each having a, potential suflicierrt for starting normal lamps from the cold state, applying said potentials to said lamps,

causing the increased current flow resulting from the starting of one lamps to induce a potential,

' and adding said potential to that of the other section of fewer turns, and second, to provide the proper current distribution to two lamps of unlike capacity such as one watt and one 40 watt lamp.

Having thus described the invention, what is claimed as new and desired to be secured by I 1. The combination with a plurality of lamps adapted for starting by ionic bombardment at high voltage and subsequent normal operation at a lower voltage and a single source of alternating current at said high voltage, of a multiple reactor including a coil connected between each lamp and said source, an iron core common to said coils,

part to increase the potential applied to the other lamp.

5. The method of starting and operating a pair of fluorescent lamps comprising, dividing a source of current into two parts, each having a potential suflicient for starting normal lamps from the cold state, applying said potentials to said lamps,

causing the increased current flow resulting from the starting of one lamp to induce a potential, adding said potential to that of the other part to increase the potential applied to the other lamp,

and. counteracting said induced potential when said second lamp starts.

at least one air gap in said core, said coils and core being so associated that upon the starting of one lamp, a voltage is induced in the coils of the other and unlighted lamps and added to that of the'source to ensure their starting. 4

2. The combination with two fluorescent lamps constructed for cold starting and normal current operation of the same and a, single sourceof cur-'- desired amount, saidcoils and magnetic circuits being so related that when one lamp starts 'the voltage applied to the other is greater than that of the source.

3. The combination with a pair of separately 6. The method of starting and operating a pair of fluorescent lamps having different cold resistances comprising, dividing a source of current into two parts, each having a potential suflicient -to start'the lamp of lower resistance, applying said potentials simultaneously each to one of said lamps, automatically limiting the voltage applied to a lamp after starting, inductively associating said divided circuits to cause the increased current flow in the one supplying a lighted lamp to increase the potential applied to the other to start the same.

, 7. The method of starting and operating a pair of fluorescent lamps having different cold resistances comprising, dividing a source of current into two parts, each having a potential sufllcient to start the lamp of lower resistance, applying said potentials simultaneously each to one of said lamps, automatically limitin the voltage applied to a. lamp after starting, magnetically associating said divided circuits to cause the increased current flow in the one supplying a lighted lamp to increase the potential applied to the other to start the same, and automatically terminating the association of the said circuits when both lamps are lighted.

I RUSSELL W. KEISER.

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