Power factor play an
important role in AC circuits and power dissipation depends on this factor. For
instant, we know that;

Power in a Three Phase
AC Circuit = P = √3 V x I CosФ

And Current in a Three Phase AC Circuits = I = P / (3 V x
CosФ)

I ∝1 /CosФ….…
(1)

Also,

Power in a Single Phase
AC Circuits = P = V x I CosФ

And Current in a Three
phase AC Circuits = I = P / (V x CosФ)

I ∝ 1/CosФ………
(2)

It is clear from both equations
(1) an (2) that
Current “I” is inversely proportional to CosФ i.e. Power
Factor. In other words, When Power Factor increases, Current Decreases, and
when Power Factor decreases, Current Increases.

Now, In case of Low Power Factor, Current will be increased,
and this high current will cause to the following disadvantages.

**1.) Large Line Losses (Copper Losses):**

We know that Line Losses is directly proportional to the
squire of Current “I

^{2}”
Power Loss = I

^{2}xR i.e., the larger the current, the greater the line losses i.e. I>>Line Losses
In other words,

Power Loss = I

^{2}xR = 1/CosФ^{2 }….. Refer to Equation “I ∝ 1/CosФ”….… (1)
Thus, if Power factor = 0.8, then losses on this power
factor =1/CosФ

^{2}= 1/ 0.8^{2 }= 1.56 times will be greater than losses on Unity power factor.**2.) Large kVA rating and Size of Electrical Equipments:**

As we know that almost all Electrical Machinery
(Transformer, Alternator, Switchgears etc) rated in kVA. But, it is clear from
the following formula that Power factor is inversely proportional to the kVA
i.e.

Therefore, The Lower the Power factor, the larger the kVA
rating of Machines also, the larger the kVA rating of Machines, The larger the
Size of Machines and The Larger the size of Machines, The Larger the Cost of
machines.

**3.) Greater Conductor Size and Cost:**

In case of low power factor, current will be increased,
thus, to transmit this high current, we need the larger size of conductor. Also,
the cost of large size of conductor will be increased.

**4.**

**)**Poor Voltage Regulation and Large Voltage Drop:
Voltage Drop = V = IZ.

Now in case of Low Power factor, Current will be increased.
So the Larger the current, the Larger the Voltage Drop.

Also Voltage Regulation = V.R = (V

_{No Load}– V_{Full Load})/ V_{Full Load}
In case of Low Power Factor (lagging Power factor) there
would be large voltage drop which cause low voltage regulation. Therefore,
keeping Voltage drop in the particular limit, we need to install Extra
regulation equipments i.e. Voltage regulators.

**5.**

**)**Low Efficiency:
In case of low Power Factor, there would be large voltage
drop and large line losses and this will cause the system or equipments
efficiency too low. For instant, due to low power factor, there would be large
line losses; therefore, alternator needs high excitation, thus, generation
efficiency would be low.

Electrical Power supply Company imposes a penalty of power factor below 0.95 lagging in Electric power bill. So you must improve Pf above 0.95.

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**6.) Penalty from Electric Power Supply Company on Low Power factor**Electrical Power supply Company imposes a penalty of power factor below 0.95 lagging in Electric power bill. So you must improve Pf above 0.95.

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