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3.2 Capacitors
To do things well, some aspects have to be considered:
-First of all, capacitors for discharge lamp circuits have to fulfil the requirements as specified in IEC publications 1048 and 1049.The use of PCB (chlorinated biphenyl) is forbidden.
-It is recommended that capacitors which have some approval marks, such as VDE, KEMA, DEMKO or ENEC be used.
-Normally every lamp circuit is compensated by its own capacitance. Only in some special cases group or central compensation for more lamp circuits can be a better solution.
-In case of failure of the parallel capacitor (open or
the lamp behaviour is not affected. Regular control of the mains currents and/or power factor (λ or cos ϕ) is advisable.
-In case of failure of the series capacitor the lamp behaviour is immediately affected.This type of capacitor must create an open circuit in case of failure, so that the lamp will be extinguished.
-The lifetime of capacitors depends on the capacitor voltage and capacitor case temperature.Therefore capacitors with the correct voltage marking (parallel 250 V with a maximum capacitance tolerance of +/- 10% or series 450 V with a maximum capacitance tolerance of +/- 4 %) and within the specified temperature range (normally - 25 ºC to + 85 or 100 ºC) should be used.
Used within the specifications, capacitors with the VDE marking will have a lifetime equal to that of ballasts: 30 000 hours or 10 years.
-If a specified parallel capacitance value occasionally is not available, the next higher value can be used, provided that the value is not more than 20 per cent above specification.
Two general types of capacitors are currently in use: the wet and the dry type.
Wet capacitors available today contain a
Dry,
Dry capacitors are more sensitive to voltage peaks than wet capacitors. In critical applications (mains supply containing peaks, frequent switching, high level of humidity or condensation) the wet capacitor is advisable.
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