August 8, 2016

What are the disadvantages of Low Power Factor?

Low Power Factor Disadvantages:

In AC circuits, power consumed depends on the power factor. Thus the power factor plays an important role in AC circuits. 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)

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 cause the following disadvantages:

1.) Large Line Losses (Copper Losses):
We know that Line Losses is directly proportional to the squire of Current “I2
Power Loss = I2xR i.e., the larger the current, the greater the line losses i.e. I>>Line Losses
In other words,  
Power Loss = I2xR = 1/CosФ….. Refer to Equation “I ∝ 1/CosФ”….… (1)
Thus, if Power factor = 0.8, then losses on this power factor =1/CosФ2 = 1/ 0.8= 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.
CosФ = kW / kVA

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 = (VNo Load – VFull Load)/ VFull 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. 

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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