2.2 Phase Sequence Detection and Phase Reversal
The three phases of a three-phase power supply, usually designated as L1, L2 and L3, attain their respective peak voltages periodically one after the other in a particular sequence, and this is referred to as a phase sequence.
The phase reversal occurs when any two phases of a three-phase supply are interchanged from the normal sequence. The phase-reversal fault occurs as a result of mistakes made during equipment installation and commissioning or maintenance.
The phase-reversal fault can be detected by monitoring the phase sequence of the three-phase power supply.
The correct phase sequence is required for driving the load properly in the three-phase AC system. It ensures that the load works as desired. When the phase sequence of the three-phases AC supply is incorrect, the connected three-phase loads may operate in the opposite direction or result in an unintended operation of the load, thus damaging the system installation.
Three possibilities exist while forming the phase sequence of the three phase supply:
- Positive phase sequence
- Negative or reversed phase sequence
- Zero phase sequence
The phase sequence of the three-phase supply can be monitored by measuring the phase-shift among the three sinusoidal signals, in units of time.