Philips Electromagnetic Lamp Indoor Furnishings User Manual


 
This can be seen in Fig. 111, which is showing the lamp current I
l
, the
lamp voltage V
l
(both in phase with each other) and the sinus form of
the mains voltage V
m
.
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. = ( W
l
+ W
b
)/(V
m
.I
m
) (1)
Without the parallel compensating capacitor the power factor of a
gas-discharge circuit is approx. 0.5.
For the fundamentals of the voltages and current a so-called vector
diagram can be made (see Fig. 112). Lamp voltage and lamp current
are in phase and the voltage across the ballast is leading 90 electrical
degrees to the current.The vectorial sum of lamp voltage and ballast
voltage gives the mains voltage. Now we see that cos ϕ = V
l
/V
m
, which
is less accurate than (1).
In any case the energy supply authority has to deliver an apparent
power of V
m
.I
l
to the system on which the distribution network must
be based (cabling, transformers).
The energy meter only records the in-phase component V
m
.I
l
cos ϕ,
so the supply authority does not get paid for the so-called ‘blind’ part:
I
l
sin ϕ .V
m
(Fig. 113).
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
5
120
Fig. 111. Lamp current (I
l
), lamp voltage (V
l
)
and mains voltage (V
m
).
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.
3.4 Power factor correction
V
m
V
l
I
ϕ
V
b
1.1 V
m
V
m
0.9 V
m
V
l
I
l
ϕ
V
b
V
m
V
l
I
l
I
l
sin j
I
l
cos ϕ
ϕ