phase

In terms of voltage and current, when there are two or more waveforms with matching periods, the numerical value indicating the time difference between the starting points of each waveform is called the phase, and it is expressed in units of angle (degrees or radians). In alternating current voltage, phase is important, and when operating generators in parallel, it is necessary for not only the voltage waveforms but also their phases to be perfectly aligned. Complete phase alignment is called being in-phase. In three-phase alternating current voltage, the phase of each voltage waveform has a positional relationship shifted by 120 degrees (2/3π rad).