Power Factor Correction

     Discharge lamps (fluorescent lamps, halogen metal vapour lamps, mercury vapor lamps and sodium vapor lamps) require suitable chokes or leakage reactance transformers for ignition and also for current limitation during discharge.

     Due to their inductance, the power factor or cos ö, is depending on the type, between 0,5 and 0,7.

     Electricity companies therefore require that the wattless power (sin phi) from the chokes or transformers be suitably corrected to cos phi = 0,9.

     To improve the power factor, capacitors ideally designed for the widest range of operating climatic and thermal conditions, should be used.

     Capacitors can be for single lamps or group correction (parallel types), as well as for series use (where the choke and capacitor are in series).

     Because capacitors can retain their charge for a considerable time after they have been disconnected, international specifications stipulate the use of special discharge resistors to ensure that, one minute after disconnection, the voltage across the capacitor is reduced to less than 50V.

     These resistors are normally mounted across the winding of the capacitor or inside the pushwire connector.