Negative Phase Sequence Indicator

The order in which the 3-phases attain their peak or maximum value and the three generated electrical voltages or currents rotate is called the phase sequence. Each voltage is separated from the next generated voltage by 120 degrees. The 3-phase has only two possible sequences ABC or ACB, positive and negative sequence respectively. In normal balanced condition, the 3-phase sequential order is positive i.e. ABC. In unbalanced condition, this sequence changed and turned into negative sequence components results the sequential order to change. Negative phase may cause damage to rotatory machines i.e. AC machines running on 3-phase. Negative phase sequence components create an opposite rotating magnetic field in the stator and induce voltages in the rotor. These induced voltages have a frequency that is double the system frequency.