ANALYSIS OF THE REASONS FOR THE LACK OF PHASE OPERATION OF THE MOTOR
After the IE2 SERIES THREE PHASE INDUCTION MOTOR is out of phase, the motor will run out of phase, which will burn the motor. If the motor is connected to a star, it can only be energized in two phases. If it is a corner connection, only one phase can be energized. There is a problem with the rotating magnetic field, the torque of the motor will drop, and the current will rise sharply until the overcurrent protection trips.
For the missing phase, because the circuit is broken and there is no current, the winding of that phase does not work and does not work.
Low-voltage and small-capacity motor circuits are generally equipped with fuses, thermal relays and AC contactors, which can protect the motor from short-circuit, overload, voltage loss and other faults. Function, the motor and often this fault is not found and eliminated in time and burns. In order to ensure the safe and reliable operation of the motor and prevent phase loss, it is necessary to understand the cause of the motor phase loss protector, prevent it in advance, find it in time, eliminate it in time, and prevent it from happening.
Phenomenon and Reasons of Motor Phase Loss Operation
The vibration increases, there is abnormal sound, the temperature rises, the speed drops, the current increases, and there is a strong humming sound when starting, which cannot be started.
②The contacts of the switch trigger are in poor contact. ③The wire connector is loose or a wire is broken.
④There is an open circuit in one phase winding.
3. Electromagnetism and torque relationship of motor phase loss operation
When the motor is running without phase, the rotating magnetic field of the stator is seriously unbalanced, and the stator will generate negative sequence current. The negative sequence magnetic field and the rotor will electromagnetically induce a potential of nearly 100HZ, which will cause the rotor current to increase sharply, which will cause serious heating of the rotor. The load capacity of the motor drops sharply, the motor will absorb a large amount of active power, resulting in a sharp increase in the stator current, and the heating will seriously increase the vibration of the motor due to the serious uneven magnetic field, thereby destroying the bearing and the frame, so the motor with a rated load running in phase loss will Stop immediately. If the protection does not act in time, the motor will be burned. Generally, the motor has phase loss protection.
In the absence of phase during operation, the magnetic field generated by the winding can also be divided into two rotating magnetic fields of equal size and opposite directions. However, the relative rotational speed between the rotating magnetic field opposite to the direction of the motor and the rotor is very large, and the induced electromotive force generated in the rotor and The frequency of the current is almost several times the frequency of the power supply, and the inductive reactance of the rotor is very large, so the active component of the current that determines the torque is very small, so the reverse torque is much smaller than the forward torque, so the motor can continue to run.
However, it should be noted that during operation, the air gap of the motor produces an elliptical rotating magnetic field with high three-phase harmonic components. Therefore, the running motor can still run after phase loss, but the magnetic field is distorted and harmful currents are generated. The composition increases dramatically, eventually causing the winding to burn out.
It is clearly stipulated that the motor cannot run when one phase is disconnected, because after the motor is disconnected, the stator coil will not generate a rotating magnetic field, but only a pulsating magnetic field, which will not drive the motor to rotate. However, due to inertia during operation, it will rotate, but due to the load Make the rotation of the motor gradually slow down. In addition, due to the slow rotation of the rotor, the magnetic field lines of the rotor will increase, and the stator current will gradually increase, which will burn the motor for a long time.
One-phase disconnection during motor operation cannot run for a long time, because after the motor is disconnected, the stator coil generates an elliptical magnetic field, which only generates pulsating magnetic potential. Due to the slow rotation of the rotor, the rotor cutting magnetic lines of force increase, and the stator current gradually increases, and the motor will be burned for a long time. . In addition, the negative sequence magnetic field will burn out the rotor!