Power factor
is the ratio of true power (or active power KW) consumed by
a load to the apparent power (KVA - which is the product of
voltage and current) drawn by the load.
Before and after Power Factor Correction (PFC)
| S1 |
= apparent power
before PFC |
| S2 |
= apparent power
after PFC |
| P |
= active power |
| Q1 |
= reactive power
before PFC |
| Q2 |
= reactive power
after PFC |
| Qc |
= Q1-Q2 compensation
power of capacitor |
| j1 |
= phase angle before
PFC |
| j2 |
= phase angle after
PFC |
|
| Load
type |
Approximate
power factor
(half ...full load) |
| Electric
heater. |
1.0 |
| Incandescent
lamp (glow) |
1.0 |
| Induction
motor |
250
kW 0.8...0.9
<100kw 0.6...0.8 |
| Thyristor
drives |
0.7 |
| Arc
furnace |
0.6...0.8 |
| AC
arc or resistance welder |
0.5...0.6 |
| Fluorescent
lamp (hot cathode) |
0.5...0.6 |
| Mercury
arc lamp |
0.5 |
| Neon
tube lamp |
0.4...0.5 |
| Induction
furnace |
-.2...0.6 |
|
From the view point of both LT as well as HT industrial
consumers, to reduce losses, optimise ratings of equipment
and cables, reduce voltage drop, minimise expenditure on regulatory
equipment and also to minimise monthly electricity bills,
power factor of the order of 0.9 or higher is necessary.
Capacitors are connected in a circuit across the load (shunt)
to reduce the demand of reactive power and thereby increase
power factor of the whole electrical system.
Lastly, TNB levies a penalty
for low power factor, the following is an excerpt from the
TNB Tariff Book.
For all Tariffs, except Tariffs A and G, the consumer shall
use his best endeavours to obtain the highest Power Factor
possible in the operation of any of his electrical installations.
If the Average Power Factor in any month is found to be:
- Below 0.85 and up to 0.75 lagging, a supplementary charge
of one and one-half per cent (1½%) of the bill for that month
for each one-hundredth part (0.01) below 0.85 and up to 0.75
lagging Power Factor will be added to the bill for that month,
and
- Below 0.75 lagging, in addition to the charge payable under
subparagraph (A) above, a supplementary charge of three per
cent (3%) of the bill for that month for each one-hundredth
(0.01) part below 0.75 lagging Power Factor will be added
to the bill for that month.
Example: A Consumer has
a Power Factor at 0.60 and his consumption is RM4,800.00
| (a) |
0.85 - 0.75
= 1½% x 10 units lagging = 15% |
| (b) |
0.75 - 0.60 =
3% x 15 unit lagging = 45%
Total extra levied = 60% |
Therefore, his penalty
charge would be 60% of RM 4,800.00 which is RM 2,880.00
The total payable will hence be RM 7,680.00
|
