__Definition__**:-**

Power factor is the ratio between the KW and the KVA
drawn by an electrical load where the KW is the actual load power and the KVA
is the apparent load power.

Simply, it is a measure of how efficiently the load
current is being converted into useful work output and more particularly is a
good indicator of the effect of the load current on the efficiency of the
supply system.

**Consider this:**

When you buy fuel for a vehicle, the manufacturer
makes in it in litres, the pump dispenses it in litres and you pay for it in
litres. Rs/litre – simple!

When you buy potatoes, the supplier bags them in
kilos the shop sells them in kilos and you pay for them in kilos. Rs/kg –
simple!

When you buy electricity, the “manufacturer”
(electricity generator) makes KVA (kilo volt amperes) and you pay for it in KWh
(kilowatt hours) or maybe on your bill (Units) – not so simple! Maybe we all
should have KVA meters to make life simple. So what is the kilowatt hour (or
unit) we get on our bills? Simply, 1000 watts of electricity being used for 1
hour.

**Example:**10 x 100 watt lamps x 1 hour=1000 watts/hr divided by 1000=1kWh – simple!

Now here comes the problem: In an alternating
current (AC) electrical supply, a mysterious thing called “Power Factor” comes
into play. Power Factor is simply the measure of the efficiency of the power
being used, so, a power factor of 1 would mean 100% of the supply is being used
efficiently. A power factor of 0.5 means the use of the power is very
inefficient or wasteful.

**What causes Power Factor to change?**

In the real world of industry and commerce, a power
factor of 1 is not obtainable because equipment such as electric motors,
welding sets, fluorescent and high bay lighting creates what is called an
“inductive load” which in turn causes the amps in the supply to lag the volts.
The resulting lag is called Power Factor.

For a 3 phase power supply: KVA, which the
electricity generator makes=Line Volts x Amps x 1.73÷ 1000. This is converted
to kilowatts KW by the formula: Line Volts x Amps x 1.73 ÷ 1000 x Power
Factor=KW (V x A x 1.73÷ 1000 x pf) or KVA x pf=KW (N.B. 1.73 is the square
root of 3) so as the power factor worsens from say 0.98 to 0.5, the generator
has to supply more KVA for each kW you are using.

For example, a large electric motor will typically
have a Power Factor of about 0.85 at full load. If we have a hypothetical
electric motor rated at 100kW, then ignoring the inherent inefficiency of the
motor, when running at full load the electricity supplier would have to supply
100÷0.85=118KVA to provide the 100KW to run the motor.

Or
put the other way they would be supplying 18% more electricity than they are
charging you for. If the same motor was operating “off load” at say 50kW or
being used on a cyclic duty then the power factor may go as low as 0.5. In this
case the supplier would have to supply “double” the KVA to match the 50kW duty
point. (50÷0.5=100kVA)

How this power is wasted can be shown graphically
since in 3 phase power supplies "power" can be represented and
measured as a triangle. ACTIVE Power is the base line and is the “real” usable power
measured and paid for in KW. REACTIVE power is the vertical or that part of the
supply which causes the inductive load. The reactive power in is measured in
KVAR (kilo volt-amperes reactive). APPARENT Power is the hypotenuse. This is
the component the electricity generator must supply and it is the resultant of
the other two components, measured in KVA. Mathematically the power can be
calculated by Pythagoras or trigonometry whereby Power Factor is expressed as
COS Ø (The angle between Apparent Power and Active power)

But
we want a simple explanation so consider a barge being pulled by a horse:

Since
the horse cannot walk on water its pulling effort is reduced by the “angle” of
the two ropes. If the horse could walk on water then the angle Ø would be zero
and COS Ø=1. Meaning all the horse power is being used to pull the load.

However the relative position of the horse influences
the power. As the horse gets closer to the barge, angle Ø

_{1}increases and power is wasted, but, as the horse is positioned further away, then angle Ø_{2}gets closer to zero and less power is wasted
So, by improving Power Factor (reducing the angle),
the reactive power component is reduced, what does it do to my electricity
bill?

As stated above in a 3 phase power supply, KW
consumed is 3 phase VOLTS x AMPS x 1.73 x Power Factor. The Electricity Company
supply you VOLTS x AMPS and they have to supply extra to make up for the loss
caused by poor Power Factor. When the power factor falls below a set figure,
the electricity supply companies charge a premium on the KW being consumed, or,
charge for the whole supply as KVA by adding reactive power charges (KVAR) to
the bill.

**How does Power Factor Correction work?**

By installing suitably sized switched capacitors
into the power distribution circuit, the Power Factor is improved and the value
becomes nearer to 1 thus minimizing wasted energy, improving the efficiency of
a plant, liberating more KW from the available supply and saving you money! The
purchase cost of the installation is usually repaid in less than 1 year’s
electricity savings.

----------------------------------------------------------------------------

Article By

-----------------

**Mr.D.Narasimha Rao,**

M.Tech , Assistant Professor

EEE Departement

LAQSHYA Institute of Technology & Sciences

## No comments:

## Post a Comment