About Power Factor

What Is Power Factor ?

All alternating current equipments (except those for lighting & resistance heating) draw an extra current from the supply, which remains 'idle' & cannot be converted into useful work. The ratio of the useful part of the current to the total current drawn from the supply can be defined as "Power Factor". Industrial equipment such as Induction Motors, Induction Furnaces, Welding Transformers draw excess current from the supply, than that the actual current required for the work done i.e. have low power factor which varies between 0.60 & 0.70. The remaining 0.30 to 0.40 is not convertable to useful power.

Thus Power Factor = ( kilowatt * 1000 ) / ( 3 * Volts * Amperes ) OR ( Average KW load ) / ( KVA Maximum Demand )

Disadvantages of Low Power Factor :

Supply tariff for industrial concerns include a penalty surcharge for low power factor. Thus low power factor results in extra electricity charges for the energy not utilized. Low power factor overloads cables, transformers, switchgears, etc. drawing greater current than required.

Due to low power factor, line losses increase & cause considerable voltage drop. Due to low power factor, larger captive generating sets, transmission & distribution equipment need to be installed. Under utilisation of Unutilized capacity from supply i.e., from 1000 KVA transformer only 600 KW can be drawn when power factor is 0.6 leaving 40 % or 400 KW unutilized.

Major advantages of Power Factor improvement with the help of Capacitors

Reduction in KVA demand & saving in Energy Bill	Capacitors reduce KVA demand, which in turn reduces the tariff levied by Electric Supply Company. Some undertakings also levy a penalty for low P. F. & grant incentive for higher P. F. Thus Capacitors behave as "Energy Savers".

Increase in System capacity	In addition to saving in power costs, an increase in system capacity is also achieved by Power Capacitors.

Improve Voltage	Excessive Voltage drops makes your Motors overheat. Low Voltage interferes with lighting & with proper operation of motor controls & instruments, Capacitors raise plant installation level. ( % Voltage Rise )=[ ( KVAR of Capacitors ) x { ( % Reactance of Transformer ) / ( KVA of Transformer ) } ]

Reduce Losses	Capacitors reduce system losses by reducing total current power flowing through the system.

Equipments which require Power Factor Improvement :

Induction Motors
Induction Furnace
Power Transformers
Welding Machines
Choke Coils
Discharge Lamps
Neon Signs
Magnetic Systems

Generally observed Power Factors in various Industries are as follows:

Industries	Power Factor
Textile	0.65 – 0.75
Chemicals	0.75 – 0.85
Machine Shops	0.4 – 0.65
Arc Welding Machines	0.35 – 0.4
Arc Furnaces	0.7 – 0.9
Induction Furnaces	0.15 – 0.4
Cement Plans	0.78 – 0.8
Clothing Factories	0.35 – 0.6
Cold Storages	0.7 – 0.8
Foundries	0.5 – 0.7
Plastic Molding shops	0.6 – 0.75
Rolling Mills	0.3 – 0.75

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