What are the disadvantages of a low power factor?

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 “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/CosФ2 ….. Refer to Equation “I ∝1/CosФ”….… (1)

Thus, if Power factor =0.8, then losses on this power factor =1/CosФ2 =1/0.82 =1. 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 below0. lagging in Electric power bill. So you must improve Pf above0.. 

Disadvantages of operating and providing in Low power factor.

1. High inductive reactance load can cause much magnetic and core losses for inductive equipments.

2. With higher apparent power, total VA capacity of equipment will be lowered & limiting capacities like of the transformers.

3. In power generation, higher excitation with lower power factor give higher voltages than normally required.

4. Limiting entire system load capacity while decreased system true power.

Lets put it very very simple:

1) Power Factor = cosine of phase diff between current & voltage.

2) Ideally phase diif should be zero, so cos(phi) = cos(0) =1

3) Low pf, means current is projected downwards  or making delay in time with reference voltage axis. The more higher angle the current project upon reference voltage axis; the actual used current  or active part of current shall be decreasing. Thus we can say that for utilizing a certain value of current called active part of current, a higher current called apparent current is drawn form the line. A higher current shall have following disadvantages:

3A) For Consumer:  Meter shall run faster obviously. So higher tariff is applied. In addition to this, as per power factor deterioration, power distribution companies imposed penalty for running a low power factor load; as per Power Factor Tariff

3B) For Transmission Circuit:  Lines will be overloaded. & heated. There will be voltage dip in the line due to higher current (I X R = higher). Higher conductor size shall reduce IR drop & heating effect but Changing the conductor size is not a practical solution for the line. To maintain the same voltage profile or to counter for the incremental current, shunt capacitor banks or synchronous condenser are added to the line.

If still the voltage criterion is not met, line shall experience a dip in frequency at a more poor pf condition... At this stage the feeder  that corresponds to low power factor shall be thrown off or isolated for the safety of generation station. Otherwise Generator may stall due to excessive mmf forces at its stator.

Low Power factor has the following problems

1. Large Line Losses: Line Losses are directly proportional to the square of Current.

2. Greater Conductor Size and Cost: In case of Low Power Factor, current is increased and to transmit this high current, large size of conductor is required therefore cost of the conductor is also increased.

3. Poor Voltage Regulation and Large Voltage Drop: In case of Low Power factor, current will be increased, larger the current, more the voltage drop.  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 equipment i.e. Voltage regulators.

4. In case of low Power Factor, there would be large voltage drop and large line losses and this will cause the system or equipment 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.

5. Penalty from Electric Power Supply Company on Low Power factor: Most Electrical Power Supply Companies impose a penalty of power factor below0. lagging in Electric power bill. So the Power Factor must be improved above0.

there will be flow of exessive current which is dangerous for your wiring . and also the genating company. because they charge you for power KW not KVA  and low power factor is affecting their productivity comparativly .

The main disadvantage resides in excessive line currents due to higher apparent power consumption although the active power is the same. higher line currents impose over heat of transmission lines, transformers, and protection devices; in addition to over stresses and aging of these equipments, extra losses in transformers and transmission lines. 

finally, electrical companies charge extra fees for low power factor consumption !

it will increase the inductive load which will cause in the loss of power .