Analysis of the Reasons for the Phase Loss of Three-Phase Asynchronous Motors
The three-phase
Asynchronous Motor runs out of phase, and the case of burning the motor sometimes occurs.
The main reason is that the reverse sequence magnetic field generates a large braking torque after one-phase power failure, which reduces the output torque of the motor. When the applied load is constant, the slip rate increases, and the current in the stator winding increases compared with the normal operation. A lot of, resulting in copper consumption, increased iron consumption, and as a result, the motor temperature rises to burn the stator windings.
In the daily use process, it was found that most of the three-phase heterogeneous motor lacked phase operation caused by human inadvertent causing the main power circuit and starting the electric appliance.
Analysis of the specific situation of single-phase operation of the motor 1. When the power supply and load are star connections, the line voltage is equal to √3 times the phase voltage, and the line current is equal to the phase current; when the power supply or one phase of the load is disconnected, the current is proportional to the load on the motor. .
2. When the motor is connected to △, the line voltage is equal to the phase voltage, and the line current is equal to √3 times the phase current; If the external (power supply) is disconnected, the motor is actually connected in series with the two-phase winding, and then connected in parallel with the third phase and then connected to the two-phase uninterrupted power supply line. The line current is equal to the sum of the parallel paths, and the load is constant. The current of the two phases is unchanged, the current of the third phase in parallel increases by 0.5 times, and the line current of the full load is 1.7-2.0 times of the rated current.
3. When the motor is connected to △, if the internal phase of the motor is disconnected, the motor becomes V-shaped, the phase current and the line current are proportional to the motor load, and the two-phase current is increased by 1.5 times, and the current of one phase is increased to 1.5 times, the current of the other two-phase line is increased by about 0.9 times.
Analysis of the specific situation of power supply power shortage
It accounts for a certain proportion of the proportion of the motor that produces phase loss, which is represented by: circuit breaker and fuse.
1. Circuit breaker: Many times the operator of the equipment likes to use the circuit breaker as a switch to stop the operation.
Circuit breakers are non-regular electrical equipment. If the load is pulled, and the type of protection motor is wrong, it is easy to produce phase loss.
2. Fuse: Faulty fuse, due to frequent positive and negative reversal of the motor, causing single phase grounding of the main circuit of the motor.
Non-faulty fuse, fuse fuse capacity selection is too small, the installation is not reasonable.
3. Contactors: the selection is unreasonable and the installation is unreasonable.
4. Thermal relay: the matching is not matched, the installation is not up to standard, and the debugging is not in place.
5. Quality reasons for the motor itself
May 06, 2024
