3.2 Electronic control gear (ECG). Osram HQI-E 150 W/NDL CL
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The parallel capacitor has no influence on lamp behavior.
GROUP COMPENSATION, where one joint fixed capacitor is allocated to simultaneously working inductive consumers, similar to individual correction (motors located close together, discharge lamps). Here again the strain on the leads is relieved, but only up to the point of distribution to the individual consumers. Under unfavorable conditions, resonance can be caused in two-phase grids.
the ballast curve. Because the capacitor for power factor correction is rated for a specifi c lamp and choke current, the power factor varies according to lamp current. For an extremely high lamp voltage, the choke current is so low that capacitive current exceeds the inductive current and the complete circuit becomes capacitive.
Under certain conditions, audio frequency central control systems have to be considered during installation.
In these cases, suitable audio frequency attenuation chokes are to be provided. This kind of system is still sometimes used for day/night circuits in street lighting, although directional radio systems are finding increasing use here.
CENTRAL COMPENSATION, where a number of capacitors are connected to a main or sub-distribution station. This is the normal procedure in large electrical systems with changing load. Here the capacitors are controlled by an electronic controller which constantly analyzes the demand for wattless power in the grid.
This controller switches the capacitors on or off to correct the current wattless power of the total load and thus reduce overall demand in the grid.
3.2 Electronic control gear (ECG)
Together with conventional ballasts, the use of electronic ballasts has meanwhile become widely accepted practice, particularly for interior lighting.
Capacitor for power factor correction values are stated for every lamp type in the Technical Information and can also be calculated using the following equation.
C
PFC
=
1
2
× π × f
S
× U 2
S
× U 2
S
× I 2
L
− P 2
W
−
(
P
W
× tan ϕ
K
)
Eq. 4.3
Electronic ballasts offer clear advantages compared to conventional ballasts. The main advantages include in particular simplified handling (e.g. lighter ballasts), lower energy consumption, a positive impact on lamp service life and light quality, and, last but not least, controlled and reliable shutdown of lamps at the end of the service life.
C
PFC
in F Capacitance of the capacitor for power factor correction
U
S
in V Rated supply voltage f
S in Hz Supply frequency
I
L
P
W in A Lamp rated current in W Total active power (lamp rated wattage plus choke loss wattage)
ϕ
K
Tolerable or desirable phase difference between the fundamental waves of the supply voltage and the supply current.
Basically, most of the technical information provided in this manual applies to both conventional ballasts and electronic ballasts. This refers for example to wiring requirements, wattage-reduced operation of MH lamps or instructions for luminaire design.
But in addition, there are also considerable differences between operation on an electronic or magnetic ballast.
The following section briefly explains the main differences and their effects.
But this only corrects the power factor for the fundamental wave. Phase difference remains for distortion, i.e. the harmonic waves, between current and voltage.
For this reason, the overall power factor can also only reach values between 0.95 and 0.98 in practice.
3.2.1 Structure and functioning of an electronic ballast
A higher level of harmonic waves can cause resonance effects and destroy the lamp. A power factor close to 1 is to be avoided as this can cause resonance between the choke and correction capacitor.
Electronic ballasts mainly consist of units with rectangular current and voltage. In principle, it is also possible to operate the lamps with high-frequency sinusoidal current similar to the fluorescent lamp. In any case, it is important to ensure that no acoustic resonances occur as these may result in arc instability
(lamp flicker) and in severe cases, lamp rupture.
While a discharge lamp is starting up, the power factor undergoes significant changes in value. After ignition, the lamp voltage is still very low with current higher than in steady state. This is why the power factor in this state is still low (inductive). While lamp voltage increases and the lamp current falls, the power factor increases to its nominal value of 0.85 – 0.9.
3.2.2 Service life and temperature
There is a significant difference between conventional and electronic ballasts particularly with regard to the service life and thermal behavior of the units.
As discharge lamps age, it is normal for lamp voltage to increase, causing the lamp current to fall according to
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