POWER FACTOR CORRECTION
The power factor of a load is defined as the ratio of active power to apparent power, i.e. kW :
kVA and is referred to as cos
. The closer cos
is to unity, the less reactive power is drawn
from the supply.
For system with a low power factor the transmission of electric power in accordance with
existing standards results in higher expenses both for the supply distribution companies and the
consumer.
In general terms, as the power factor of a three phase system decreases, the current rises. The
heat dissipation in the system rises proportionately by a factor equivalent to the spare of the
current.
Types of Power Factor Correction :
- Single or Fixed PFC, compensating for the reactive power of individual inductive loads at the
point of connection so reducing the load in the connecting cables (typical for single,
permanently operated loads with a constant power)
- Group PFC, connecting on fixed capacitor to a group simultaneously operated inductive loads
(e.g. group of motors, discharge lamp)
- Bulk PFC, typical for large electrical systems with fluctuating load where it is common to
connect a number of capacitors to 3 main power distribution station or substation. The
capacitors are controlled by a microprocessor based relay which continuously monitors the
reactive power demand on the supply. The relay connects or disconnects the capacitors to
compensate for the actual reactive power of the total load and to reduce the overall demand of
the supply.