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Difference between Leading and Lagging Power Factor
In electrical engineering, the power factor of an AC system is the expression of energy efficiency. The power factor (PF) is defined as the ratio of active power (measured in Watts) to the apparent power (measured in VA).
The power factor expresses the ratio of true power which is used in an AC circuit to the total power delivered to the circuit. Mathematically, the power factor can be expressed using the following formula −
$$\mathrm{Power \: factor \, \mathrm{=}\,\frac{Active \: power}{Apparent \: power}}$$
There are two major terms are associated with the power factor of an AC circuit viz. Lagging and Leading. These two terms show the relation between the current and voltage in the circuit.
What is Leading Power Factor?
In an AC system, when load current leads (or advances in phase) the supply voltage, then the load is said to have a leading power factor. In practice, the capacitive loads cause a leading power factor, i.e. a leading power factor signifies that the load is capacitive as the load will deliver reactive power.
The leading power factor can also be described as the load current that attains its peak value upto 90° ahead of the voltage. A leading power factor also means that the same voltage across the load terminals can be maintained with a lower internal induced voltage. An inductive load is used to correct the leading power factor.
What is Lagging Power Factor?
When the load current lags behind the supply voltage, then the load is said to have lagging power factor. In other words, power factor of the load is said to be lagging if the current waveform is behind the voltage waveform.
The lagging power factor of the load signifies that the load is inductive and it will consume the reactive power. The lagging power factor can also be described as the load current that attains its peak value upto 90° later of the voltage. In order to correct the lagging power factor capacitive loads are employed.
Difference between Lagging and Leading Power Factor
The following table shows the key differences between the lagging power factor and leading power factor.
| Parameter | Lagging Power Factor | Leading Power Factor |
|---|---|---|
| Definition | For a given load, if the load current lags behind the voltage, then the power factor of the load is called lagging power factor. | For a given load, if the load current leads or advances in phase the voltage, then the load power factor is called leading power factor. |
| Nature of Load | The lagging power in an AC electric circuit is caused by the inductive loads such as induction motors, etc. | In an AC electric circuit, the capacitive loads cause a leading power factor. |
| Power factor value | The value of lagging power exists between -1 and 0. Here, the "-ve" sign have significance in case of digital meters only. | The value of leading power factor exists between 0 and 1. |
| Power factor angle | For lagging power factor, the phase angle of current is negative with respect to the phase angle of voltage. | In case of leading power factor, the phase angle of current is positive with respect to the phase angle of voltage. |
| Reactive power component | For lagging power factor, the reactive component is negative. | The reactive power component is positive for a load of leading power factor. |
| Reactive power absorption | When the power factor of the load is lagging, then it absorbs lagging reactive power or we can say it delivers leading reactive power. | When the load have leading power factor, then it absorbs leading reactive power (or delivers lagging reactive power). |
| Power factor correction | A poor lagging power factor can be improved by adding a capacitive load in the circuit. | A poor leading power factor can be corrected by adding an inductive load in the circuit. |
| Examples of loads | The loads of lagging power factor are inductive loads such as inductors, transformers, electromagnetic relays, induction motors, etc. | The capacitive loads have leading power factor, the common examples are overexcited synchronous motor, capacitors, radio circuits, etc. |
Conclusion
The key difference between the leading power factor and the lagging power factor is that, for the leading power factor, the current is advanced in phase with respect to the voltage; while for the lagging power factor, the current lags behind the voltage.
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