The coup of car maintenance is 1. After electrifying, the motor can't rotate, but there is no abnormal sound, smell and smoke.
Cause of failure: ① The power supply is not connected (at least two phases are not connected); (2) Fuses are blown (at least two phases are blown); ③ The overcurrent relay is too small; (4) The wiring of the control equipment is wrong; Wait a minute.
Troubleshooting: ① Check the switch, fuse and junction box of the power supply circuit for breakpoints and repair them; (2) Check the fuse model and fuse reason, and replace it with a new fuse; ③ Adjust relay setting value to cooperate with motor; ④ Correct the wiring.
2. After electrifying, the motor does not turn, and then the fuse is blown.
Cause of failure: ① lack of one-phase power supply or one-phase stator coil connection; ② Short circuit between stator windings; ③ Stator winding grounding; (4) Wrong connection of stator winding; ⑤ The fuse section is too small; Wait a minute.
Troubleshooting: ① Check whether one phase of the circuit breaker is not closed or whether one phase of the power circuit is disconnected; Eliminate the reverse connection fault; (2) Find out the short circuit point and repair it; ③ Eliminate grounding; (4) Find out the wrong connection and correct it; ⑤ Replace the fuse.
3. There is no hum when the motor is started.
Causes of failure: ① stator and rotor windings are open (one phase is broken) or power supply is cut off in one phase; (2) The lead-out wires of the winding are wrongly connected at the beginning and the end, or the winding is internally connected reversely; (3) The contact of power supply circuit is loose, and the contact resistance increases; (4) The motor is overloaded or the rotor is stuck; ⑤ The power supply voltage is too low; ⑥ The small motor is assembled too tightly or there is too much grease in the bearing; ⑦ The bearing is stuck; Wait a minute.
Troubleshooting: ① Find the breakpoint and fix it; ② Check winding polarity; Jud whether that end of win is correct; (3) Tighten the loose wiring screws, judge whether each joint is false with a multimeter and repair it; (4) Load rejection or finding out and eliminating mechanical failure; (5) Check whether the specified delta is connected to y by mistake; Whether the voltage drop is too large due to the thin power conductor, correct it, 6 reassemble it to make it flexible; Replace qualified grease; ⑦ Repair the bearing.
4, the motor is difficult to start, rated load, the motor speed is lower than the rated speed.
Cause of failure: ① The power supply voltage is too low; ② △ Motor misconnection is y; ③ Cage rotor is welded or broken; ④ The local coils of stator and rotor are connected by mistake or reverse; ③ Too many turns are added when repairing the motor winding; ⑤ Motor overload; Wait a minute.
Troubleshooting: ① Measure the power supply voltage and try to improve it; ② Correct connection; (3) Check welding and breakpoints and repair them; (4) Find out the mistakes and correct them; ⑤ Restore the correct number of laps; ⑥ Reduce the load.
5. The no-load current of the motor is unbalanced, and the three phases are quite different.
Cause of failure: ① When rewinding, the number of turns of stator three-phase winding is unequal; (2) The winding ends are wrongly connected; ③ unbalanced power supply voltage; ④ Faults such as turn-to-turn short circuit and coil reverse connection exist in the winding; Wait a minute.
Troubleshooting: ① Rewinding the stator winding; ② Check and correct; (3) measure the power supply voltage, try to eliminate the imbalance; (4) suddenly eliminate the winding fault.
6, motor no-load, overload, ammeter pointer instability, swing.
Causes of failure: ① welding or fracture of cage rotor bars; ② Winding rotor fault (one-phase open circuit) or poor contact between brush and collector ring short circuit device; Wait a minute.
Troubleshooting: ① Find out the broken bars and repair or replace the rotor; ② Check the circuit around the rotor and repair it.
7. The no-load current of the motor is balanced, but the value is large.
Cause of failure: ① The number of turns of stator winding is reduced too much during repair; ② The power supply voltage is too high; ③ What is the wrong connection of Y-connected motor? ; (4) When the motor is assembled, the rotor is installed backwards, so that the stator core is dislocated and the effective length is shortened; ⑤ The air gap is too large or uneven; ⑥ When the old winding was dismantled in overhaul, the iron core was burned due to improper hot dismantling method.
Troubleshooting: ① Rewind the stator winding to restore the correct number of turns; ② Try to restore the rated voltage; Change 3 to y; ④ reassembly; ③ Replace the rotor with a new one or adjust the air gap; ⑤ Repair the iron core or recalculate the winding, and appropriately increase the number of turns.
Common faults of asynchronous motors and their solutions 1, mechanical faults
The air gap between stator and rotor of asynchronous motor is very small, and the bore is swept due to bearing damage and shaft bending, which makes the core temperature rise sharply, resulting in winding grounding, turn-to-turn short circuit, phase-to-phase short circuit and motor burning. In severe cases, the stator core is reversed, dislocated, the rotating shaft is worn, and the end cover is scrapped.
(1) The main causes of bearing damage are as follows: ① improper assembly (too loose or too tight) between bearing and journal or end cover, such as uneven tapping of bearing inner ring during cold installation, resulting in shaft wear, resulting in reduction or loss of interference between bearing inner ring and bearing, and the phenomenon of inner ring escaping, and uneven tapping of end cover when installing motor end cover, resulting in the phenomenon of outer ring escaping. (2) The bearing cavity is not clean or the oil quality is not good, and it contains impurities. The bearing is short of oil due to untimely refueling. ③ If the bearing clearance is too large or too small, the bearing will be replaced and reworked. After the motor is nested, the interference is too large or the ellipse is too large, which will cause the bearing ball oil gap to be too small or uneven, and lead to the increase of friction when the bearing is running. ④ Bearing damage caused by mixing of different oils and fats. ⑤ The connector between the motor and the load is not calibrated or the belt is too tight. ⑥ The bearing itself has quality problems, so be sure to check it carefully before installation.
Troubleshooting methods: ① Generally, when loading and unloading bearings, the bearings should be heated to 80℃ ~ 100℃, such as bearing heater or oil boiling. When assembling the bearing, tap the inner ring of the bearing with a steel pipe with an inner diameter slightly larger than the diameter of the motor shaft to ensure the assembly quality of the bearing. ② Before assembly, carefully clean the bearing hole and replace the clean grease. It is not easy to add too much oil, which is generally about 1/2 ~ 1/3 of the volume of the inner ring of the bearing box, otherwise the bearing will overheat. (3) Re-nesting and machining the motor and replacing the new bearing. 4) Recalibrate the motor and load coupling to adjust the belt tension.
When the motor works normally, the fuselage should be stable and the sound should be low and even. The vibration of the motor should be distinguished whether it is caused by the motor itself, improper installation of the rotating device, or transmitted by the mechanical load end, and then eliminated according to the specific situation. Vibration can cause noise and extra load.
(2) The main causes of vibration failure of the motor itself are: ① The gap between worn bearings is too large and the air gap is uneven. ② The rotor is uneven and the rotating shaft is bent. ③ The core is deformed or loose, and the center of the coupling (pulley) is not corrected. ④ The fan is unbalanced, and the motor anchor screw is loose. ⑤ Open welding or short circuit of cage rotor. The winding rotor is open.
Troubleshooting methods: ① Replace and adjust the air gap when necessary for bearing maintenance to make it even. ② Correct rotor balance and shaft. (3) Correct the overlapping cores and recalibrate them to meet the requirements. (4) overhaul the fan, correct the balance, and tighten the anchor screws. ⑤ Repair the rotor winding.
2. Common electrical faults
Common electrical faults include unbalanced three-wire current, turn-to-turn short circuit of stator winding, and open-phase operation. Among them, the proportion of motor burning due to lack of phase operation is the largest. The imbalance of three-phase current will not only generate extra heat for the motor, but also cause the imbalance of three-phase rotating magnetic field to make the motor make a deep sound, and the fuselage will also vibrate.
(1) The main reasons for the three-phase current imbalance fault are as follows: ① The number of turns of the stator three-phase winding is not equal when rewinding. (2) The winding end is wrong. ③ The power supply voltage is unbalanced. (4) The winding has turn-to-turn short circuit and coil reverse connection. Troubleshooting methods: ① Rewind the stator winding. ② Check and correct. ③ Measure the power supply voltage and try to eliminate the imbalance. (4) eliminate winding fault. When a three-phase motor is short of one phase, if it is in a stopped state, it will stall because the combined torque is zero, and the stall current is 3% of the normal current. 464 times ~ 6. 062 times. So in this case, turning on the power for a long time or turning on the power frequently for many times will burn out the motor. When the running motor is out of phase, if the load torque is small, it can still run, with only a slight speed drop and abnormal noise. Running for too long under heavy load will burn out the motor winding.
(2) The main reasons for the failure of open-phase operation: ① Fuse blown. (2) The fault fuse is caused by the single-phase grounding or interphase short circuit of the main circuit of the motor, so it is necessary to select the motor suitable for the surrounding environment and the correctly installed low-voltage electrical appliances and circuits, and check and maintain them regularly. In the main circuit, the reasons for the lack of phase operation are as follows: ① The static and moving contacts of the contactor are worn and the contact is seriously poor. (2) harsh environment and contact oxidation.
Maintenance of motor winding grounding fault 1, fault phenomenon
The shell is charged, the control circuit is out of control, and the winding is short-circuited and heated, which leads to the motor not operating normally.
2. the reason
The winding is damp, which reduces the insulation resistance; Long-term overload operation of motor; Harmful gas corrosion; Metal foreign bodies invade the winding and damage the insulation; When rewinding the stator winding, the insulation is damaged and touches the iron core; The winding end contacts the base of the end cover; Friction between stator and rotor leads to insulation burn; Lead insulation damage and shell collision; Overvoltage (such as lightning strike) leads to insulation breakdown.
3. Inspection method
(1) observation method. Visually inspect the insulation of winding ends and slots, and observe whether there are any signs of damage and blackening, and if there are any, it is the grounding point.
(2) Multimeter inspection method. Check with a low-resistance multimeter. If the reading is small, it will be grounded.
(3) Megger method. According to different grades, different megohmmeters are selected to measure the insulation resistance of each group of resistors. If the reading is zero, it means that the winding is grounded. However, it is necessary to judge the motor insulation from damp or accidental breakdown by experience. Generally speaking, where is the pointer? 0? When it swings irregularly, it can be considered as having a certain resistance value.
(4) Test lamp method. If the test light is on, it means that the winding is grounded. If sparks or smoke are found somewhere, it is the winding grounding fault point. If the light is dimmed, there is a ground fault in the insulation. If the light is off, but sparks appear when the test bar is grounded, it means that the winding has not yet broken down, but it is seriously wet. Hardwood can also be struck at the edge of the shell, hitting a place, indicating that the current is off, and that place is the grounding point.
(5) Current burn-through method. When a voltage regulating transformer is connected to the power supply, the grounding point will heat up rapidly, and the place where insulation smokes is the grounding point. It is especially important to note that the small motor should not exceed twice the rated current for less than half a minute; The large motor is 20%-50% of the rated current or gradually increase the current, and the power will be cut off as soon as the grounding point smokes.
(6) Grouping elimination method. For the grounding point in the core wire and serious combustion, the burning copper wire fuses with the core wire. The method adopted is to divide the grounded one-phase winding into two halves, and so on, and finally find out the grounding point.
In addition, there are high voltage test method, magnetic needle exploration method and power frequency vibration method. I won't introduce it here.
4. Processing method
(1) If the winding is grounded due to moisture, it should be dried first and cooled to 60? When the temperature is about 70℃, it is poured with insulating paint and then dried.
(2) When the winding end insulation is damaged, re-insulate it on the ground, paint it, and then dry it.
(3) When the winding grounding point is in the slot, the winding should be rewound or some winding elements should be replaced.
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