Phase

In voltage and current, when there are two or more waveforms with matching periods, the numerical value indicating the temporal displacement of the starting point of each waveform is called the phase, and its unit is expressed as an angle (degrees or radians). In AC voltage, phase is important, and when operating generators in parallel, not only the voltage waveforms but also their phases must completely match. When the phases completely match, it is called being in phase. In three-phase AC voltage, the phase of each voltage waveform is shifted by 120 degrees (2/3π rad) relative to each other.