Analysis of common failures of motors and solutions

Analysis of common failures of motors and solutions

As an important power provider that is indispensable in people's production and life, electric motors will generate serious heat during use, but many times do not know how to solve them. Any failure of the motor will affect production. , Electrical workers must master the basic knowledge about the safe operation of asynchronous motors and the handling methods of common faults, so as to discover and eliminate hidden dangers of motor accidents in time to ensure safe operation.

Common faults of motors are divided into two categories: mechanical faults and electrical faults. Electrical faults include: short circuit of stator and rotor windings, open circuits, and start-up equipment faults; mechanical faults include: excessive vibration, bearing overheating, friction between stator and rotor, and Abnormal noise, etc.

　　 One, the fault when the motor starts without load

　　 1. Phenomenon: no sound and no rotation

deal with:

　　① Use a multimeter to check the voltage at the motor terminal. If there is no voltage or only one-phase voltage, it means that the power supply is not connected or the power supply is faulty.

　　②If the three-phase voltage at the motor terminal is basically balanced, it indicates that there is a problem with the motor stator winding connection. The most likely reason is that the neutral point is not connected or the lead wire is not connected.

　　2. Phenomenon: After connecting the power, the motor only buzzes but does not rotate

　　 Treatment: The power must be disconnected immediately, and then carefully look for the cause

　　① For single-phase operation, first check the power supply to see if one phase of the power supply is broken, the fuse is blown in one phase, and the contactor is not in contact with one phase; then check the motor stator winding lead wire to see if one phase is not properly connected.

　　②Check if the machine is jammed. This kind of failure is easy to find when checking the motor before starting to see if the motor can rotate gently.

　　③The power supply voltage is too low or the motor with the ▲-shaped connection is technically connected into a Y shape and starts with a load. As long as the power supply voltage and motor wiring method are correct, it can be found.

　　 3. Phenomenon: When the motor is started after power on, the fuse will blow out quickly (or overcurrent protection action)

deal with:

　　① Check that the rated current of the fuse does not match the motor capacity.

　　②Check whether the motor of the Y-connection method is mistakenly connected to the ▲ shape.

　　③ There is a phase-to-phase short circuit or a short circuit to the ground between the motor power supply and the wiring terminal. Turn off the power switch, disassemble the motor terminal, and check it with a megohmmeter.

　　④The motor stator winding or lead wire is short-circuited or grounded.

　　 2. Abnormalities in motor operation

During the operation of the motor, there are often some abnormal operation phenomena, such as: motor vibration, motor overload, abnormal motor sound, temperature increase of bearing and wire circle, current increase and speed change, etc. These abnormalities will not cause the motor protection to operate. Tripping, but has affected the safe operation of the motor. Some important motors that run abnormally, if they are not handled in time, will not only cause the motor itself to malfunction, but also cause major accidents such as shutdowns and shutdowns.

　　 1. The motor runs under phase loss

　　 Phenomenon: The ammeter indicates an increase or zero; the temperature of the motor body increases, and the vibration increases, and the sound is abnormal.

　　 Treatment: The lack of phase operation of the motor is the operation mode of the three-phase motor when one phase of the circuit is disconnected due to some reason. First check whether the power supply lacks phase or the motor stator loop is faulty. One of the methods to prevent the motor from running under phase loss is to rely on the judgment of the attendant and deal with it promptly after discovery; the second is to install a phase loss protector in the motor circuit.

　　2, the motor body heats up

　　 Phenomenon: The body temperature and temperature rise of the motor during operation are significantly higher than those during normal operation, and the current increases.

deal with:

　　①Check whether there is friction or jamming on the mechanical load.

　　②Check whether the mechanical load increases. If so, reduce the load until the temperature stabilizes.

　　③ Check whether the motor ventilation system is faulty, and reduce the load at the same time.

　　④ Check whether the current of each phase of the motor is balanced, and judge whether the stator winding is faulty or the phase is missing.

　　3, the motor vibrates

　　①The motor is inconsistent with the attached mechanical center.

　　②The motor rotor is unbalanced.

　　③The motor bearing is damaged.

　　④The motor foundation is not strong enough or the anchor screws are loose.

　　⑤The motor runs under phase loss. If the motor vibration exceeds the allowable value range, the motor should be stopped immediately.

　　4, the motor sound is abnormal

　　①Mechanical reasons of the motor: the bearing sound is abnormal. If it is caused by lack of oil, it should be oiled immediately; if the bearing is damaged, it should stop running immediately.

　　②Electrical reasons: check whether the voltage and frequency are normal; check whether the three-phase stator current is balanced, and judge whether there is a wire break or an inter-turn short circuit inside the burning group.

　　 Three, motor burn-in

　　 The reasons for burn-in of three-phase asynchronous motors can be summarized as: load, power supply, motor insulation, and phase loss.

　　 1. Load (overload): Over-load operation causes the motor to heat up. Or the motor starts frequently, causing the motor to overheat. In this kind of burning, both ends of the stator and rotor inside the motor will burn black, and the black spots are relatively uniform (generally, the motor has a fixed operating power, called the rated power, in watts (W). In this case, if the actual power of the motor exceeds the rated power of the motor, this phenomenon is called motor overload).

　　2. Power supply: The voltage is too low and the load is under rated conditions, the current increases, and the motor is overheated. The power supply voltage is too high and the machine burns. Or the motor is running under phase loss. This kind of situation is relatively rare, and it is easy to judge, mainly because the circuit has burnt marks.

　　 3. Insulation: The internal insulation of the motor does not meet the standard, and there is a short circuit between turns. Or internal wiring is wrong. This kind of burn-in and overload burn-in are sometimes easy to confuse, the stator and rotor will also burn black, but there will be obvious burn marks in the short-circuit part, for example, sometimes there will be copper piping, and the winding will be severely burned.

　　 lack of phase burn machine:

　　 1. The motor is delta connection: only one phase winding will be burned, and the insulation damage of one phase winding to the ground can be measured with a megohmmeter (shake meter).

　　2. The motor is star-shaped (Y) connection: there are two-phase windings that will burn out. You can use a megohmmeter (shaking meter) to measure the insulation damage of the two-phase windings to the ground.