In Industrial electrical system, Major load is resistive and inductive. Resistive loads are for heating application. In case of resistive Load
V= I X R or Power (KW) = V X I
Indicative loads are induction motors, induction furnaces, transformers etc, Inductive load requires two kind of powers:-
- Active Power ( working power) KW
- Reactive Power (Create and maintain electric field) KVAR
Active power and reactive power are 90 deg apart vectorically in pure inductive circuit.ie Reactive power KW is lagging active power KVAR
The Ratio of KW to KVA is called as power Factor.
Power factor is usually less than or equal to unity. Theoretically when power factor is unity maximum power can be supplied. However when power factor is low electrical distribution system is stressed for capacity.
Power factor can be improved by adding Capacitors, Capacitor reduces reactive power thus reduces total power generation as shown below.
With the use of 600 KVAR capacitor KVA load is reduced from 1383 to 1054, providing additional capacity in distribution system along with lower demand charges.
Advantages of Power factor improvement:-
- I2R losses get reduced as current will reduced. Reduced KWH in distribution system
- Reactive power will get reduced thus reduction in total power.
- Voltage improvement at user end.
- A higher power factor will help in utilizing the full capacity of electrical system.
- Penalty of lower pf can be avoided from utility power supply.
- Utility power supply companies provide Pf rebate for maintaining higher pf.
- Improved performance of motor with higher pf.
- Investment on transformer, cable, switchgear etc will get reduced as current will get reduced with improved pf.
Selection of Capacitor:-
KW Multipliers table for Determining Capacitor Kilovars
Eg : Total KW-input of load from watt meter reading 100 KW at a power factor of .6. The capacitive KVAR necessary to raise the power factor to .99 is found by multiplying the 100 KW by the factor found in the table (.840). Then 100 KW x 1.192 = 1192 KVAR capacitor is required.