This circuit is for synchronizing 2, 3 phase, alternators.
The lamps in the center are all that is necessary to confirm proper phase rotation, frequency, and amplitude.
The lamps under the voltmeters are just to check if all 3 sources are correctly sequenced.
The SPDT beside the alternators is to switch between phase-check and synchronize mode.
The relay is for switching between the 3-Dark and 2-Bright method.
The phase is buggy when cheging frequencies, so reset all phase rotations to 0°, 120°, and 240° after adjusting frequency.
--3 Dark Method--
If the alternators are synchronous, 3 lamps will be dark
If the frequency is off, the lights will fade on and fade off
If the voltage is off, the lamps will be illuminated to some degree
If the phase rotation is off, the lamps will be lit.
--2 Bright 1 Dark Method--
If the alternators are synchronous, 2 lamps will be bright and the last will be dark
If the frequency is off, the lamps will alternate between 1 bright and 2 bright
If the voltage is off, 2 lamps will be bright and the third will be illuminated to some degree
If the phase rotation is off 2 adjacent lamps will be bright
