Three-phase motor open phase protection and current changes

One, foreword As is known to all, three-phase asynchronous motor for power fault phase operation and the number of fire alarming, its mostly because of the low voltage circuit breaker or disconnecting switch contact undesirable: ac contactor singeing, cannot be connected to reliable contact; Too long could fuse and fuse oxidation corrosion, is impacted by the starting current burn out, etc. General motor open phase running occurs: vibration increases, have abnormal sound, temperature, speed drops, electricalmotor1.blogspot.com current increase, lack of phase start have a strong "buzzing" sound, cannot be started. In order to protect the motor, according to the phase of possible fault point, add open phase protection set to three-phase motor circuit. In this paper, the author introduces three phase motor open phase protection circuit. 

Second, the motor phase specific situation analysis 1. Motor phase operation deficiency. Motor open phase running, the stator's rotating magnetic field serious imbalance, the rotor current rights, can cause the rotor severe fever, lacks when the motor load capacity fell sharply, since there is a serious inhomogeneous magnetic field, can make the machine shake seriously increase, thus bearing damage and stand, can still operate after the motor is running short of phase, only the distortion of magnetic field, the harmful composition of current increases sharply, eventually lead to the winding burn. Motor phase break specific provision can't run, because the motor stator coil after disconnection will not produce a rotating magnetic field, only pulse magnetic field is produced, not motor rotates, but due to the operation of the inertia, so will rotate, but due to the load ambassador motor rotating gradually slow magnet generator down. 2. Start motor phase. If the motor stop short of a phase, when the power switch, normally only happens "buzzing" sound and cannot start, this is because the motor ventilation with symmetrical three-phase alternating current will produce a rotating magnetic field in the stator core, but when the lack of a phase after the power supply, single-phase pulsating magnetic field is generated in the stator core, it can't make the start torque motor. Therefore, the power supply lacks when the motor can't start. 3. The motor is short of two phase. When lack of two-phase motor can't start at all, no running motor response, because the phase thread inside the motor winding cannot produce current loop, cannot produce magnetic field winding, no damage to the motor. 4. Lack of phase change of motor current. Normal starting or running, for balanced load three-phase motor, three phase current are equal in size, less than or equal to the rated value. Break after a phase, three phase current imbalance or too big. When starting phase: motor can't start, the winding current for 4 to 7 times the rated current. Calorific value for the normal temperature of 16 and 49 times, because of its exceed the permitted temperature rise quickly and makes the motor burn down. When full load running lack of phase, the motor is in a state of flow, the current more than rated current, electric opportunity from weakness to blocked, not more the phase line current is added, cause rapid burning motor. three phase induction motor When light load running lack of phase, not open phase winding current increase rapidly, make this phase winding burned due to temperature rise too high.