What Is The Lead And Lag Of Voltage And Current

Because Sin [_t] will appear after derivation or integration, the phenomenon of waveform leading and lagging can be observed when the inductance and capacitance of sinusoidal wave are connected with_t. It is not easy to understand directly from the static function diagram, but it is better to make animation.            The figure below is inductance. It shows voltage in red and current in blue. If connected with the ideal DC voltmeter and ammeter, it can be observed that the change of voltage is ahead of the current, and the change of current lags behind the voltage. As time increases, the ordinate axis and time origin move to the left along with the waveform.

If the waveform is drawn on the right side of the vector graph, this is the following animation, but the right side of the abscissa is the waveform that existed in the past, pointing to the past, is - _t. Although the waveform is reversed, the change of voltage is still ahead of that of current, and the change of current is still lagging behind that of voltage. The time origin moves to the right along with the waveform. The ordinate axis in the function diagram does not intersect with the abscissa at the origin, and the time represented by the intersection point is increasing. If you don't pay attention to it, the judgment of leading and lagging is easy to make mistakes.

It is best to understand the concept of lead-lag by phasor diagram. It is not intuitive and error-prone to observe from measured data or from static waveform. The figure below is capacitive. Voltage changes lag behind current, and current changes ahead of voltage. The right side of the coordinate system is the future, and the left side is the past.

When the abscissa is -_t, the change of capacitor voltage is still lagging behind the current, and the change of current is still ahead of the voltage. Because the left side of this coordinate system is the future, while the right side is the past.