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3.4 Power factor correction
Fig. 111. Lamp current (Il), lamp voltage (Vl) and mains voltage (Vm).
Vm
I
Vl
ϕ
This can be seen in Fig. 111, which is showing the lamp current Il, the lamp voltage Vl (both in phase with each other) and the sinus form of the mains voltage Vm.
The power factor of the circuit can be calculated by dividing the total wattage by the product of mains voltage and current. In formula:
P.F. = (Wl + Wb)/(Vm . Im) | (1) |
Without the parallel compensating capacitor the power factor of a
For the fundamentals of the voltages and current a
In any case the energy supply authority has to deliver an apparent power of Vm . Il to the system on which the distribution network must be based (cabling, transformers).
The energy meter only records the
Fig. 112. Example of a vector diagram showing lamp voltage and lamp current in phase.
Fig. 113. Uncompensated circuit with lamp current and mains voltage out of phase.
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Vm
Il Vl
For this reason, the supply authority demands compensation of the phase shift.
Where in general the ‘unadjusted’ power factor is about 0.50, it has to be compensated to a minimum of 0.85 or even 0.90.This is achieved by adding a capacitor across the mains. In contrast to an inductive
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