The so-called lack of phase three-phase motor running, that is, three-phase motor in the power phase open circuit or stator winding phase-phase operation. For example, one-phase fuse blown or poorly connected, circuit breakers , disconnectors, cable head and wire in one of the loose contact, and the motor stator winding phase disconnection, etc., may cause the motor phase-out operation. According to statistics, most of the accidents of burning three-phase asynchronous motor windings are caused by lack of phase operation. 1, three-phase motor running phase, if the load has not changed, that is, the two-phase winding to assume the original three-phase winding work, then the two-phase winding current will inevitably increase, causing the ammeter to rise or zero (if Just install the ammeter one phase is disconnected, the current indication is zero), the motor body temperature increases, increased vibration and abnormal sound, long time will burn out the motor coil. 2, three-phase motor phase loss when no-load, two-phase motor can drive long-term operation of the motor, but the current will increase to close to the rated value of the motor and the motor sound abnormalities. 3, three-phase motor lack of a phase power, because it can not produce rotational torque, which can not be started. Once the three-phase motor is found out of phase operation, immediately start the standby unit, quickly remove the fault motor, to inform the maintenance staff came to check the reasons and take countermeasures.