Electrical Engineering ⇒ Topic : Phase

Phase

Waves of alternating voltage and current are continuous. They do not stop after one cycle is completed but continue to repeat as long as the generator is operating. Consider an alternating voltage wave of time period T second as shown in Fig. (a). Note that the time is counted from the instant the voltage is zero. The maximum positive value (+ V_m) occurs at T/4 second cm π/2 radians. We say that phase of maximum positive value is T/4 second or π/2 radians. It means that as the fresh cycle starts, + V_m will occur at T/4 second or π/2 radians. Similarly,the phase of negative peak (-V_m) is 3T/4 second or 3π/2 radians.

Hence, phase of a particular value of an alternating quantity is the fractional of time period or cycle through which the quantity has advanced from the selected zero position of reference.

                                                     figure (a)