Question

Explain the concept of lagging and leading phase angle by waveform.

Answer 1

i) Leading phase angle :

 When two ac quantities of same frequency do not attain their respective zero or peak values simultaneously, then the quantities are said to be out-of-phase quantities. The quantity which attains the respective zero or peak value first, is called ‘Leading Quantity’.

 In the following first diagram, the voltage attains its zero or positive peak first and after an angle of  Φ, the current attains its respective zero or positive peak value, hence voltage is said to be leading the current by an angle of  Φ. Similarly, in the second diagram, the current is said to be leading the voltage by  Φ.

ii) Lagging phase angle:

 The quantity which attains the respective zero or peak value later, is called ‘Lagging Quantity’. In the following first diagram, the current attains its zero or positive peak later than the voltage after an angle of  Φ, hence current is said to be lagging the voltage by an angle of  Φ. Similarly, in the second diagram, the voltage is said to be lagging the current by  Φ.