Questions about phase loss in three-phase motors? ?

In the delta connection, current flows between phases; if one phase is missing, for example phase C, then only the winding between A and B carries current, while there is no current in the A-C and B-C connections due to the absence of phase C； In the star connection, there is current between the phase and neutral; if one phase is missing, no current flows through that winding, while the other two phases will experience overcurrent and get damaged.

The star and delta shapes are: Y, △; the conclusion can be drawn from the diagram above.

#The analysis on the 1st floor is correct; when one phase is missing, operation with two phases cannot generate a rotating magnetic field, but it does produce a pulsating magnetic field. Therefore, the motor will generate a lot of noise, and the circuit impedance drops sharply; if the power supply is not disconnected in time, the motor will be damaged. Also, just as the fire at a city gate can affect nearby areas, this can also lead to the burning of phases without any current flow!

　　For a three-phase asynchronous motor connected in a delta configuration, if one phase of the power supply to the motor is missing – for example, phase C – then the internal circuit of the motor will result in the A-C and C-B windings being connected in series, with these two series combinations being connected in parallel to the A-B winding. The voltage applied across this circuit is the line voltage (380 volts). Since the phase sequences of the power supplies feeding these parallel circuits are the same, no rotating magnetic field is generated, and as a result the motor rotor will lock up； At this point, since the rotor has stopped, there is no induced back electromotive force, and the current generated in the motor windings is essentially the motor’s starting current. Such a high current can destroy the motor windings in a short time. Due to the relatively high series impedance of the A-C and C-B windings, the current will be relatively low ； When the winding between A and B burns out first, a ground short circuit occurs; the air switch in the motor’s power supply circuit trips instantly due to the short-circuit current, as a result of which the A-C and C-B windings may not suffer any damage. However, if the air switch is not selected properly and causes delayed tripping, the A-C and C-B phase windings may also be damaged. 　　In the star-delta connection configuration, the winding of the missing phase will certainly have no current flow. However, due to the presence of a neutral point, the two-phase currents flowing through the remaining two windings still create a non-circular rotating magnetic field when the motor is in operation, allowing the motor to keep running. With the load remaining constant, an increase in the load on the two-phase windings leads to an increase in current; prolonged operation can cause these windings to burn out due to overload. If the mechanical load is at no load or light load during a phase loss in the power supply, the motor current will not exceed its limits, and burning out of the motor will not occur.

It is mainly about determining which phases have current flowing through them, as well as the magnitude of that current.

Question: The explanation given by Haiyou on the second floor is incorrect. \"The triangular connection involves current flowing between phases; if one phase is missing, for example phase C, then only the winding between A and B will have current flow, while there will be no current in the A-C and B-C connections due to the absence of phase C.\"； That statement is incorrect! The explanation from Haiyou on the fifth floor is the correct one. For a three-phase asynchronous motor connected in a delta configuration, if one phase of the power supply to the motor is missing – for example, phase C – the internal circuit of the motor will still result in the A-C and C-B windings being connected in series, with these two series combinations then connected in parallel to the A-B winding. The voltage applied across this setup is the line voltage (380 volts). Since the phases of the power supply to the two parallel circuits are the same, no rotating magnetic field is generated, and as a result the motor rotor will lock up ； At this point, since the rotor has stopped, there is no induced back electromotive force, and the current generated in the motor windings is essentially the motor’s starting current. Such a high current can destroy the motor windings in a short time. Due to the relatively high series impedance of the A-C and C-B windings, the current will be relatively low ； When the winding between A and B burns out first, a ground short circuit occurs; the air switch in the motor’s power supply circuit trips instantly due to the short-circuit current, as a result of which the A-C and C-B windings may not suffer any damage.

It is determined by the wiring method. Triangle connection: Only one phase winding will burn out; with phase A missing, the windings between phases B and C get damaged. Star connection: Two phase windings will burn out. Phase A is missing, and the B and C windings have burned out.

Agree with the view on the fifth floor; I’ve learned it