You can use pic16f87x seri microcontroller. This mcu has ADC inputs.
Uses 2 or 3 current transformer for monitoring to motor phases current.
Use 3 small transformator for monitoring 3 fhase line voltage.
1. Any phase current exceed the maximum level system must be stops. 2. Any phase voltage is lost system must stop.
3. Any phase voltage dropt the minumum level system must be stop.