I. Reasons Why the three phase asynchronous motor cannot be started
1. The power is not connected.
2. Fuse blown;
3. Open circuit in the stator or rotor winding;
4. Grounding of the stator winding;
5. Phase-to-phase short circuit of the stator winding;
6. Incorrect wiring of the stator winding;
7. Overload or the transmission machinery being crushed;
8. The copper bars of the rotor are loose;
9. There is no lubricating oil in the bearing. The rotating shaft expands due to heat, which hinders its rotation within the bearing.
10. Incorrect or damaged wiring of control equipment;
11. The overcurrent relay was set too low.
12. The oil cup of the old-fashioned starting switch is short of oil.
13. Incorrect starting operation of the wound-rotor motor;
14. Improper configuration of rotor resistance for wound-rotor motors;
15. The bearing is damaged.
There are many factors that prevent the three-phase asynchronous motor from starting. A detailed analysis and careful inspection should be carried out based on the actual situation and symptoms. It is not advisable to force multiple starts. Especially when the motor makes abnormal sounds or overheats during starting, the power supply should be cut off immediately. The motor should be restarted only after the cause has been investigated and eliminated to prevent the fault from expanding.
Ii. Reasons for the Slow Rotational Speed of three phase asynchronous Motors when operating under load
The power supply voltage is too low.
2. Broken bars of the squirrel-cage rotor;
3. There are short-circuit points in the coil or coil group;
4. There are reversed connections in the coil or coil group.
5. Reverse connection of phase windings;
6. Overload;
7. One phase of the wound rotor is open-circuited;
8. Poor contact of the starting rheostat of the wound-rotor motor;
9. Poor contact between the brush and the slip ring.
Iii. Reasons for Abnormal Sounds during the Operation of three phase asynchronous Motors
1. The stator and rotor rub against each other;
2. Rotor fan blades touching the casing;
3. Wipe the rotor with insulating paper;
4. Lack of oil in the bearing;
5. Debris inside the three phase asynchronous motor;
6. There is a humming sound when the three-phase asynchronous motor operates in two phases.
Four. Reasons for the electrification of the three phase asynchronous motor housing
1. The power cord and the ground wire are mixed up.
2. The winding of the three-phase asynchronous motor gets damp and the insulation ages, reducing the insulation performance.
3. The lead wire touches the junction box shell.
4. Local winding insulation damage causes the wire to touch the casing.
5. Loose core punctures the wire;
6. Grounding wire malfunction;
7. The power strip is damaged or has excessive oil stains on its surface
V. Reasons for Excessive Sparks on the slip ring of the winding rotor
1. The surface of the slip ring is dirty.
2. The brush pressure is too low;
3. The brush is clamped inside the brush.
4. The brush deviates from the neutral line position.
Vi. Reasons for Excessive temperature rise or smoke Emission of Three-phase asynchronous motor
1. The power supply voltage is too high or too low;
2. Overload;
3. Three-phase asynchronous motor single-phase operation;
4. Grounding of the stator winding;
5. Damaged bearings or overly tight bearings;
6. Inter-turn or phase-to-phase short circuit of the stator winding;
7. Excessively high ambient temperature;
8. The air duct of the three-phase asynchronous motor is not smooth or the fan is damaged.
Vii. Reasons for the pointer Swing of the ammeter when the three phase asynchronous motor is running under no-load and load conditions
1. Broken bars of the squirrel-cage rotor;
2. One phase of the winding rotor is open-circuited;
3. Poor contact of the brushes in one phase of the wound-rotor motor;
4. The slip ring short-circuit device of the wound-rotor motor has poor contact.
Viii. Causes of Vibration in three phase asynchronous Motors
1. Rotor imbalance;
2. Shaft head bending;
3. Unbalanced belt pulley;
4. The shaft hole of the belt pulley is eccentric;
5. The anchor bolts for fixing the three phase asynchronous motor are loose;
6. The foundation for fixing the three-phase asynchronous motor is not solid or uneven.
Ix. Causes of Overheating of Bearings in three phase asynchronous Motors
1. Bearing damage;
2. Excessive or insufficient lubricating oil or poor oil quality;
3. The fit between the bearing and the shaft is too loose, moving within the inner circle or too tight.
4. The fit between the bearing and the end cover is too loose and runs around the periphery or too tight.
5. The oil ring of the sliding bearing is rolling or rotates slowly;
6. The end covers or bearing covers on both sides of the three phase asynchronous motor are not installed flat;
7. The belt is too tight;
8. The coupling was not installed properly.
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