This arrangement used to detect the phase sequence/rotation of a three-phase power system. by connecting the three phase system to a unbalanced reactive loads with two equal resistive loads and one capacitor (connected the third phase) that has a reactance equal to each resistance at the system frequency (60Hz).
Three-phase system has only two possible phase sequences (1-2-3 or 3-2-1) corresponds to the two possible way of rotating the shaft of the alternator (CCW or CW).
Phase rotation can be changed by:
1. reverse the alternator rotation
2. swap any two of the three wires (as can be simulated here by toggling the two SPDT switches at the same time).
If the phase sequence was 1-2-3, then the upper resistive load will have a lower voltage drop 48.1V and the bottom resistive load will have a higher voltage drop 180V. However, if the phase sequence was 3-2-1, then the voltage drops will be reversed.
** use SPST switch before toggling the phase, to prevent source short circuiting.
