hello friends

ı try to make a phase failure relay for three phase main power there is a lot of phase failure relay on the bazaar but its not really effective because if one phase loss during motor running in that situation occur an regenerative effect in notor so the loss phase reproducing by motor and phase failure relay does not effect in this position
and whe ı mesure the phase angle by scop ı see that occur an phase shifting
so this is my question how can ı measure the phase angle for three phase