Features of operation of fluorescent lamps


Principle of operation of fluorescent lamps

The fluorescent lamp represents the glass tube in which end faces electrodes are sealed. The fluorescent lamps of low pressure used to lighting of residential buildings have coiled-coil or trispiralny electrodes from the tungsten provoyoloka on which the layer of active agent (oxide) possessing low work function at the temperature about 900 - 950 °C is applied.

Схема включения люминесцентной лампы

Scheme of turning on of the fluorescent lamp.

 The small koliyochestvo of mercury creating at the normal temperature the neznachitelyyony pressure of its saturating vapors and inert gas with the partial pressure of several hundred pascals (millimeters of the mercury stolyob) are entered into tubes with the pumped-out air. Inert gas facilitates ignition of lamps and reduces the raspyyoleniye of oxide of electrodes. The electric arc in vapors of mercury has high performance of transformation of electrical energy to ultra-violet radiation which is outside the viyodimy part of the range. The layer of the phosphor transforming the ulyyotrafioletovy part of radiation to visible is applied on the internal surface of the tube ravnomeryono on all length.

Схема устройства люминесцентной лампы

Scheme of the device of the fluorescent lamp.

Combination of two specified factors: the mercury-vapor discharge and transformation of ultra-violet radiation in the layer of the lyuminofoyor - provides high light return of fluorescent lamps. The luminous flux of fluorescent lamps of the same power and the design depends on brand of the applied phosphor and the tekhnoyologiya of its drawing. The industry releases fluorescent lamps of five types on the chromaticity of the radiation (LD, LDTs, LHB, LB and LTB) having different value of the luminous flux. In the tab. of 1 priyovedena of value of the luminous flux of fluorescent lamps мощно­стью 20, 40 and 65 W depending on phosphor brand.

Table 1 of Value of the luminous flux of fluorescent lamps after 100 h burning, lm

Lamp type

 Luminous flux

 Lamp type  Luminous flux  Lamp type  Luminous flux
LDTS 20-4

820

LDTS 40-4 2100 LDTS 65-4 3050
LD 20-4

920

LD 40-4 2340 LD 65-4 3570
LHB 20-4

935

LHB 40-4 2600 LHB 65-4 3820
LTB 20-4

975

LTB 40-4 2580 LTB 65-4 3980

From tab. 1 it is visible that lamps like LB have the greatest luminous flux. Because special requirements to the tsvetopereyodacha in lighting installations of all-house rooms it does not predjyoyavlyatsya, recommended to use LB or LTB fluorescent lamps.

Схема включения люминесцентной лампы

Figure 1. Scheme of turning on of the fluorescent lamp.

Fluorescent lamps differ from glow lamps in the fact that their inclusion in network requires use of puskoreguliruyushchy devices. The last is caused by the falling volt-ampere characteristic of the discharge through gases of fluorescent lamps, in koyotory with reduction of tension on the lamp current, prokhoyodyashchy through it increases. At direct connection of lyuminestsentyony lamps in network any short-term undervoltage priyovodit to the avalanche increase of current through the lamp and to the peregoyoraniye of its electrodes. Therefore the basic purpose of puskoreguliruyushchy devices consists in stabilization of the current proceeding through the lamp at admissible fluctuations of mains voltage. Except the lamp current stabiyolization, puskoreguliruyushchy devices perform one more function - create conditions for reliable ignition of the lamp.

As the elements stabilizing discharge parameters apply throttles (inductive ballast) and consistently connected throttles and the condenser (inductance-capacitor ballast). Schemes of single-tube starter puskoreguliruyushchy devices with inductive and reactance-capacitiest ballast are provided on fig. 1.

Feature of these schemes are the nizyoky value of electrical power factor and considerable size of the poyotreblyaemy wattless current. Increase in the wattless current vyzyyovat the current overload of network, increases power losses in it and can be the reason of operations of devices of protection. Therefore in houses it is reasonable to apply one - and two-lamp lamps with high power factor (with kompensirovanyony puskoreguliruyushchy UBK or ABK devices).

Povyyosheniye of electrical power factor in single-tube lamps with inyoduktivny ballast is reached by inclusion parallel to entrance clips of the lamp of the compensating Sn condenser (in fig. 1a it is shown by the dotted line). Because of the nonsinusoidal form of current of the lamp it is almost impossible to increase electrical power factor to unit. Reactive power of the upper harmonics of current of the lamp remains noncompensated, and electrical power factor always to the menyyosha 1.

Схема изменения тока люминесцентной лампы

Figure 2. Scheme of change of current of the fluorescent lamp.

For single-tube lamps the extreme size of the koefyofitsiyent of power is in limits 0,92 - 0,94. In dvukhlampoyovy lamps reactive power compensation is reached at inclusion of one lamp with inductive, and another - with the reactance-capacitiest ballast. The maximum size of electrical power factor in two-lamp lamps reaches 0,98.

In fig. 2 and static volt-ampere harakteriyostik (i.e. dependence between current and tension, sootvetstvuyuyoshchy in each point to the set electric mode of the eleyoment) the fluorescent lamp, inductive ballast and their summaryony characteristic are shown at series connection of the lamp and the balyolast, in fig. 21, respectively, volt-ampere harakteristiyok of the lamp, the reactance-capacitiest ballast and total.

Let points of A and A1 correspond to points of stable work of the lamp with ballast with the rated voltage of Un network. Current of the lamyopa and ballast in this case will be equal to I лн, and tension on the lamyopa of Uln is defined on the lamp volt-ampere characteristic in points of C and C1. At increase in mains voltage otun to U2 of the point of stable work of the lamp with ballast move sootvetstvenyono to points of B and B1. Current of the lamp increases to I l2, and tension on it decreases to Ul2 (respectively tochkid id1). Apparently from drawings, change of current of the lamp at the reactance-capacitiest balyolast will be much less, than at inductive. Specific change of current of the lamp and parameters of ballast resistance zayovisit from type of the lamp, ballast and value of tension of the power line.

Changes of current and power of the fluorescent lamp, in the zavisiyomost from tension of the power line, are defined by expressions:

for Il lamp current : Il. N =? (U: Un – 1) + 1, for the power of lamp Rl: Rl. N =? (U: Un – 1) + 1,

where? and ? - instability coefficients on the power and current of the lamp respectively, Rl. N and Il. N - the power and current of the lamp with the rated voltage of Un network respectively.

For fluorescent lamps extreme value of coefficients? and? makes 2. It means that at voltage variation of network for 10% current and power of the lamp have to change no more than for 20%.

Reduction of service life of fluorescent lamps at the povysheyoniya of mains voltage is defined by two factors: the cathode breakdown due to increase in its temperature caused by growth of current of the lamp, and the cathode breakdown at the expense of the intensive bombardiyorovka its positively ionized atoms at increase of instantaneous values of current of the lamp.

For the fluorescent lamps working in the starter scheme of inclusion it is established that increase in current by 1% reduces service life of cathodes by 1,5%. Thus, koleyobaniye of mains voltage influence key parameters of fluorescent lamps much less, than parameters of lamps of the nakaliyovaniye.

Service life of the fluorescent lamps working in starter and starterless schemes of inclusion at fluctuation of mains voltage does not decrease by +10%. Thanks to big service life and stability of the luminous flux of fluorescent lamps annual eksyopluatatsionny charges on lighting installations with these it is much less lampayoma, than on installations with glow lamps.

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