US2297257A - Alternating current discharge lamp - Google Patents

Description

Sept.'29, 1942. E. o. sElTZ EI'AL 2,297,257

ALTERNATING CURRENT DISCHARGE LAMP Filed Nov. 25, 1938 r I-ig.3

JYJTEH INPUT R -4 g I Y an uity 7 Capacity c C I C VWW" Patented Sept. 29 1942 Ernst Otto Seitz and Walter Lotz,'Hanau-on'-the- Main, Custodian Germany; vested in 'the Alien Property Application November 25, 1938, Serial No. 242,394

InG 9 Alternating current discharge lamps filled with as or vapor, particularly high pressure metal vapor lamps, for example, mercury vapor lamps having electrodes adapted to operate at mean-- descence, generally require, for stabilizing the.-

discharge, a current limiting device, which may consist of a non-inductive resistance, a choke coil or a condenser. For high pressure mercury vapor lamps a choke coil is generally used for limiting the current, as the power loss in the coil is small. Where-low cost is of greater concern than efliciency use is made also of a noninductive resistance. However, both of these means are defective in that the starting current is always considerably greaterthan the operating current. This is due to the fact that the initial terminal potential ci a high pressure metal vapor lamp is very low after ignition although when stable conditionsare reached,,thevoltage drop rises to about 100-150 volts or more. It is generally calculated that the starting current is about two or three times as great-as the operating current. For this reason high pressure metal vapor lamps must be operated in circuits which are safeguarded to a higher degree than'would be necessary in consideration of only the operating current. It is well known that this defect exerts an injurious influence'in many cases, for example, when the current rate-or cost is based only on the maximum current which can be taken from a power supply system and automatic circuit breakers disconnect the supply system when this current is'exceeded.

According to this invention these disadvantages are avoided by using stabilizing means-includinga condenser in connection with the high pressure metal vapor arc. It has been surprisingly discovered that when a condenseris used as an interposed apparatus in series with the lamp the I starting current is smaller than the operating lamp, a lamp operated with a condenser has a higher radiation efflciencythan one operated with a choke. This applies to the total light output efiiciency, but chiefly to the long wave and erythema producing ultra violet radiation. Thus, the same radiation efliciency can be attained at reduced load,v either by reducing the dimensions and thereby the cost of production, or, while retaining the same dimensions; reducing the specific ermany November 25, 1937 1 Claim. (01.176-124) I therewith the current consumption during continued operation. In addition, by the present invention, the defect, consisting in that powerful current surges can occur shortly after ignition, 5 with the choke operation, which surges are based on a rectifier action and are due to unequal heating of the two electrodes, is not present. With condenser operation this can not be manifested, as the condenser has an infinite resistance for direct current.

When a condenser is used the starting current is generally about below the operating current. Notwithstanding this however, the starting period is only a few minutes. It is hence practically the same as when operating with a choke coil or a resistance. When operating with a condenser the terminal voltage of a high pressure mercury lamp, wherein the mercury is completely vaporised during operation, is somewhat higher' I 29 than when operating the same lamp with a choke coil at the same load. In many types of lamps, however, the terminal voltage may increase to such a degree that the lamp is extinguished. Special consideration must be given this possibility, particularly with such types which'have,

shaped, or which operate with a high potential gradient as a result of having a vapor pressure 30 substantially exceeding 1 atmosphere. More stable operation can beprovided for such types of lamps also under all conditions if non-inductive resistance is connected in series with the condenser. By the use of this arrangement it is true that additional losses occur in the series apparatus which reduce the efllciency or output with respect to the load or power consumption as compared with pure condenser operation. Nevertheless, the efliciency is always greater than with 40 choke operation. This is due to the fact that when operating with only a condenser as current control element the efliciency is substantially greater than that obtainable with a choke. I

'In the accompanying drawing two preferred embodiments of the invention are represented:

Figure 1 is' a'diagrammatic showing of a lamp circuit in which a condenser is used.

Figure'la is an enlarged view of one end por-' tion of a. lamp partly in cross section,

Figure 2 is a view similar to Figure 1 of a difierent embodiment in which a resistance is used in'addition to the condenser in circuit with power consumption of the discharge tubes amiss asystem accordingtothe invention.

Figure 4 is a diagram of the radiation of a lamp -controlled according to the present invention.

Figs. 1 and 2 show two possibilities of condenser ably oxide electrodes heated from an extraneous source or, preferably, heated by the discharge.

It has been found that the stabilization of the arc can be effected by theuse of different values for the condenser and the resistance if a certain power consumption or load of the lamp is prescribed. Fig. 2 graphically shows the conditions or characteristics for an exemplary embodiment. In Fig. 3 it is assumed that the load or power consumption in the lamp is constant. This graph shows that there is co-ordinated with each capacity of the condenser a'certain predetermined resistance value R and also that the resistance must be increased with increasing capacity. Thus, a certain lamp, required to operate with a prescribed load, can be operated stably either,

with a capacity C1 and resistance R1 or with the When C2 is greater than C1, R2 Below a predetermined values C2, R2. is also greater than R1.

I value of the capacity designated Co and with which a resistance R0 isco-ordinated, stable-operation is impossible.

this value C does the starting and operating current manifest the same relation as when operating with a choke or resistance. Co is the smallest value of the capacity in which, with a given lamp and a given load as well as frequency, stable operation is still possible. If a condenser with a capacity less than Co is selected, the discharge is unstable and must become extinguished. Finally, the power consumption is shown on Fig. 3. This increases in proportion to the loss in the auxiliary series resistance, as the power consumption in the lamp itself is assumed to be constant, and the slight losses in the condenser may be disregarded.

The critical values (00, R0) or (C, R) aredifierent with different types or lamps and at different loads. In cases in which operation with the condenser only is possible, if then Re is equal in order to render operation of an ordinary mercury lamp possible with an incandescent lamp as a -series apparatus. None .of these connections have given practical results, however, as their operation is not sumciently reliable. Therefore, if it is absolutely necessary to operate a mercury vapor lamp with incandescent lamps, for example to improve the color of the light, they have up to the present time been connected to the supply circuit independently of each other.

According .to the arrangement of the present invention it is also possible, with the use of condensers whose value lies between Co and C, to replace the resistance R by an incandescent lamp, as within this range the starting current is less than the operating current. The incandescent lamp can thus under no conditions be damaged by excessive current during starting. If the capacity of the condenser is equal to C, the incandescent lamp will burn with its normal brilliancy at all times since .the starting current is the same as the operating current.

As the power converted in the resistance R increases strongly between the capacity values represented by the points C0 and C (see Fig. 3) it is possible to select a point at which the desired relation between the power consumed by the high pressure lamp'to that consumed by the incandescent lamp is secured. In. the vicinity of the point Co, R is small and the power converted in the resistance or in the incandescent lamp is small, but it increases with increasing values of the capacity. It is possible to convert in the incandescent lamp up to double of the power which is converted in the metal vapor lamp.

With the combination of a mercury vapor lamp and a series incandescent lamp according to the arrangement of the invention, the mixed light furnishes light efilciencies substantially above the values obtainable when the two ,lamps are connected independently because, as previously stated, the vapor lamp when operated with a condenser, gives a greater output than when operated with a choke. Moreover, use may be made of ,a low voltage incandescent lamp the radiation efliciency of which, as known, is better than that of 220-volt incandescent lamps.

Also when used as a therapeutic ultraviolet radiator, good results are obtained by the consubstantially higher than one for 200 volts'and thus also emits more ultraviolet radiation.

The range between Co and C is thus of great practical'importance. The capacity of the condenser is generally selected within this range, in the endeavor, relative to low production cost, to employ the smallest possible condenser, particularly as in this range the outputs, with respect to net power consumption are in many cases the best and operation is carried out very advantageously in the vicinity of the point Co.

The advantages of condenser operation are .man'ifested to a particularly great degree when the mercury lamp is used as an ultraviolet radiator. (250-3l5 with equal energy conversion in the burner, is about greater than with choke operation, while the corresponding figures for the total light are about 20% and for the wave length 366; 70%. The arrangement is thus particularly suitable for use as an ultraviolet light radiator.

In explanation, the following table gives the The intensity in the erythematic range I to modify the lamp.

values for the condenser and resistance with diiferent types of lamps.

Type oi lamp A B B 0 Load in watts.-- 1i!) 200 250 680 Co In mi 19 27 36 63 37 7 8 0 22 M 52 78 67 83 22 6 The mercury lamps A, B and C are ordinary types, developed for chokeccil operation. The values given for the condenser .and resistance are for operation of these lamps on alternating 15 current of 220 volts, 50 cycles. Use may be'made of the ordinary types without it being necessary It is found that for lamps for operation on 220 volts A. C. 50 cycles, values of Co and C can 2 be calculated from the following equations Ce=l.30.B- :l5%

C'=0.9 8.B- i15% and where B is the load on the burner in. watts. The

values for Co and C are then obtained in microfarads. According to the invention the condenser should have a value preferably 'between '00 30 and C. a The values of the resistances can be calculated from the following equations for the same conditions 8760 (1:l;0.15) 3190 I Ohm and 7900 (1:l:0.15)- 3190 ohm A system for operating high pressure gasor vapor-filled alternating current discharge lamps having incandescent electrodes comprising an electric circuit, a high pressure, metal vaporillled electric discharge lam having its electrodes connected in said circuit, a condenser connected in said circuit, in series with said lamp for stabilizing the current flow in said circuit,

and a heat radiating non-inductive resistance element in the form of an incandescent lamp connected in series with said condenser and dis charge' lamp.

ERNST CTTO SEI'I'Z. WALTER LOTZ.

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