1. Preparation and inspection before starting
(1) Check whether the grounding of the motor and starting equipment is reliable and complete, and whether the wiring is correct and good
(2) Check whether the rated voltage shown on the motor nameplate and whether the rated frequency matches the power supply voltage and frequency
(3) For newly installed or long-term disabled motors (disabled for more than three months), check the relative phase and phase insulation resistance values of the windings before starting. (Measured with a 1000 volt megohmmeter). The insulation resistance should be greater than 0.5 megohms. If it is below this value, the winding should be dried.
(4) For the wound rotor, check whether the brushes on the slip ring and the brush lifting device can work normally, and whether the pressure of the brushes can meet the requirements. The brush pressure is 1.5N / cm-2.5N / cm.
(5) Check that the rotor of the motor is flexible and reliable when the rotor rotates, and the oil in the sliding bearing reaches the specified oil level.
(6) Check whether the rated current of the fuse used by the motor meets the requirements.
(7) Check whether the fastening bolts and mounting bolts of the motor are firm and meet the requirements
If the above inspections are up to standard, you can start the motor. After the motor is started, run it for 30 seconds without load. Pay attention to observe the motor for abnormal conditions, noise, vibration, heat and other abnormal conditions. Measures should be taken. When the reasons are clear, the problem is solved Only then can run. When starting a wound motor, the starting rheostat should be connected to the rotor circuit. For a motor with a brush lifting mechanism, the brush should be lowered, the short-circuit device should be disconnected, the stator circuit switch should be closed, and the rheostat should be moved. When the motor is close to the rated speed, put on the brush and close the short-circuit device, and the motor is started.
2. Maintenance in operation
When the three-phase asynchronous motor is running, the staff on duty should check once every shift. The inspection items are as follows:
(1) Whether the current exceeds the allowable value and whether it has increased or decreased.
(2) The bearing should have no abnormal sound, the lubrication should be normal, the amount of oil should be sufficient, and the oil ring should be flexible.
(3) The running sound should be normal and there should be no abnormal odor.
(4) Whether the temperature of the housing and bearing is normal. It is normal if there is no hot feeling, otherwise it is overheating. The temperature of sliding bearings should not exceed 80 ° C, and the temperature of ball bearings should not exceed 100 ° C.
(5) Whether the vibration is normal and its standards should meet: speed 3000r / min, vibration not exceeding 0.06mm, speed 1500r / min, vibration not exceeding 0.10mm, speed 1000r / min, vibration not exceeding 0.13mm, speed 750r / min, The vibration does not exceed 0.16mm.
(6) Whether the cable head is leaking oil and the casing is grounded firmly.
(7) Inspection of brushes and slip rings of Rao line motors:
① Whether the brush on the slip ring sparks. If the spark is small, clean the brush. If the spark is large, it should be repaired.
② The pressure on the brush should be the minimum pressure to ensure that the brush does not ignite, and there is no shaking or jamming of the brush in the brush holder.
③ Whether the brush cord is complete, whether the contact is tight, whether there is a short circuit with the shell and overheating.
④ Brush edges should be free of wear.
3. Troubleshooting during operation
1. Failure at startup
When the circuit breaker or automatic switch is closed, the motor does not turn, only a humming sound is heard, or it cannot turn to full speed. The cause of this failure may be:
① One phase of the stator circuit is broken. For example, one phase of the low-voltage motor fuse is blown, or one phase of the high-voltage motor short-circuiter and the disconnector are in poor contact, which cannot form a three-phase rotating magnetic field.
② The rotor circuit is broken or the contact is poor, so that there is no current in the rotor winding or the current is reduced, so the motor does not rotate or rotates very slowly.
③ In the transmission machinery, there is a mechanical jam phenomenon. When it is serious, the motor does not rotate and there is an abnormal sound.
④ The voltage is too low to reduce the motor torque, making it difficult or impossible to start.
⑤ Motor stator and rotor iron core friction, which increases the load and makes rotation difficult.
When the operator finds the above-mentioned faults, for high-voltage motors, he should immediately open the motor's circuit breaker and disconnector and check its stator and rotor circuits.
2. Stator winding single-phase ground fault
The motor winding is eroded by various factors to reduce its insulation level. In addition, due to the long-term overload operation of the motor, the insulation of the winding will become brittle or fall off due to long-term overheating. This will cause single-phase grounding of the motor stator windings.
3. Failure of single-phase operation of three-phase motor
In the operation of a three-phase motor, if one-phase fuse burns out or has poor contact, disconnection of one phase of the disconnector, fuse, cable head and conductor, and disconnection of one phase of the stator winding will cause single-phase operation of the motor.
When the operator confirms that the motor is single-phase running based on the abnormal phenomenon generated by the motor, the power supply should be cut off to stop the operation. Measure the stator loop resistance value with a megohmmeter. If the resistance value is very large or infinite, it indicates that the phase is broken. Then check the fuses, circuit breakers, disconnectors, cable heads, and wiring connections in the stator circuit for good contact.