Power Factor Correction

It is the process of compensating for the lagging current by creating a leading current by connecting capacitors to the supply. A sufficient capacitance is connected so that the power factor is adjusted to be as close as possible to unity.

When dealing with direct current (DC) circuits, the power dissipated by the connected load is simply calculated as the product of the DC voltage times the DC current, that is V*I, given in watts (W). For a fixed resistive load, current is proportional to the applied voltage so the electrical power dissipated by the resistive load will be linear. But in an alternating current (AC) circuit the situation is slightly different as reactance affects the behavior of the circuit.

For an AC circuit, the power dissipated in watts at any instant in time is equal to the product of the volts and amperes at that exact same instant, this is because an AC voltage (and current) is sinusoidal so changes continuously in both magnitude and direction with time at a rate determined by the source frequency. The ratio of the real power absorbed by the load to the apparent power flowing in the circuit.

However, for an AC circuit containing an inductor, coil, or solenoid or some other form of inductive load, its inductive reactance (XL) creates a phase angle with the current lagging behind the voltage by 90o. Therefore there is both resistance (R) and inductive reactance (XL) both given in Ohms, with the combined effect called Impedance. Thus impedance, represented by the capital letter Z, is the resulting value given in Ohms due to the combined effect of a circuits resistance and reactance.

for example, Refer:"https://www.allaboutcircuits.com/textbook/alternating-current/chpt-11/practical-power-factor-correction/"

Effects Of Low Power Factor 

  • The current drawn is higher for low power factor.
  • copper losses (I2R losses) will also be high. This decreases the efficiency of the equipment.
  • Overheating of the equipment.
  • Low power factor causes higher load current. If the load current increases, the size of the conductor required will also increase. This will further increase the conductor cost.
  • For low power factor, current will be more and hence voltage drop will be increased. Hence, the voltage regulation at low power factor is poor.

Power Triangle

The relationship between real power P , reactive power Q and apparent power VI and the power angle is represented by Power triangle.


Lagging Power Factor

  • When current lags behind the voltage, the power factor of the circuit is called 'Lagging'
  • When the circuit is inductive, the pf is lagging.
  • The loads such as induction motors, coils, lamps, etc are inductive and have Lagging pf.

Leading Power Factor

  • When current leads the voltage (or voltage lags behind the current), the power factor of the circuit is called 'Leading'.
  • When the circuit is capacitive, the pf is leading.
  • Capacitive loads such as Synchronous condensers, capacitor banks etc draw leading current. Such circuits have leading power factor.

Unity Power Factor

  • Power factor is unity (i.e. 1) for ideal circuits.
  • When current and voltage are in phase, PF = 1
  • Power factor cannot be more than unity.
  • Practically, it should be as close to unity as possible.






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