KW is Working Power
(also called Actual Power or Active Power or Real Power).
It
is the power that actually powers the equipment and performs useful
work.
KVAR is
Reactive Power.
It
is the power that magnetic equipment (transformer, motor and relay) needs to
produce the magnetizing flux.
KVA is Apparent Power.
It is the vectorial
summation of KVAR and KW.
Power
factor is an important measurement in electrical AC systems because
- an overall power factor less than 1 indicates that the electricity supplier need to provide more generating capacity than actually required.
- the current waveform distortion that contributes to reduced power factor is caused by voltage waveform distortion and overheating in the neutral cables due to yhe generation of harmonics in three-phase systems.
Reactive
power (KVAR) required by inductive loads increases the amount of apparent power
(KVA) in our distribution system . This increase in reactive and apparent power
results in a larger angle (measured between KW and KVA). We know that, as angle
increases, cosine of that angle (or
power factor) decreases.
So,
inductive loads (with large KVAR) result in low power factor.
Effect Of Loads:
- With a purely resistive load current and voltage changes polarity in step and the power factor will be 1. Electrical energy flows in a single direction across the network in each cycle.
- Inductive loads - transformers, motors and wound coils - consumes reactive power with current waveform lagging the voltage.
- Capacitive loads - capacitor banks or buried cables - generates reactive power with current phase leading the voltage.
Inductive
and capacitive loads stores energy in magnetic or electric fields in the
devices during parts of the AC cycles. The energy is returned back to the power
source during the rest of the cycles.
DISADVANTAGE OF LOW
PF.:
Increased
Power Supply:
We
know that inductive loads, which require reactive power, caused our low power
factor. This increase in required reactive power (KVAR) causes an increase in
required apparent power (KVA), which is what the power plants are supplying. So,
low power factor causes the power plants to have to increase its generation and
transmission capacity in order to handle this extra demand. By lowering our
power factor,we use less KVAR. This results in less KW, which increases savings
of power generation.
Other harmful effects are:
Increases
heating losses in the transformers and distribution equipments.
Reduce
plant life.
Unstabilise
voltage levels.
Increase power losses.
Decrease
energy efficiency.