The reason of the motor temperature is too high?
1. Excessive load
If the drive belt is too tight and the shaft is not flexible, the motor may be overloaded for a long time.At this time, mechanical maintenance personnel should be asked to properly relax the belt, disassemble the machine to check the flexibility of the rotating shaft of mechanical equipment, and try to adjust the load, so as to keep the motor running at rated load.
2. Poor working environment
Such as motor in the sunlight, more than 40 ℃, environment temperature or in a poorly ventilated environment conditions, will cause the motor temperature rise that high.Simple awning can be used for shade or blower, fan blower, should pay attention to remove the motor itself ventilation duct oil and dust, in order to improve the cooling conditions.
3. The power supply voltage is too high or too low
The motor can keep the rated power constant when the power supply voltage is in the range of -5% -- + 10%.If the power supply voltage exceeds 10% of the rated voltage, it will cause a sharp increase in the flux density of the core, which will increase the iron loss and lead to overheating of the motor.The specific inspection method is to use ac voltmeter to measure bus voltage or motor terminal voltage, if the reason for the grid voltage, should be reported to the power supply department to solve;If the voltage drop of the circuit is too large, the conductor with a larger sectional area should be replaced and the distance between the motor and the power supply should be shortened.
4. Power supply is off
If the power supply is out of phase and the motor runs in a single phase, the winding of the motor will be heated sharply and burn down in a short time.Therefore, it is necessary to check the fuse and switch status of the motor before measuring the front line with a multimeter.
5. cage type rotor guide bar fracture, open welding or rotor guide bar cross-sectional area is too small
To increase the loss and heat, the rotor temperature can be measured after the shutdown, find out the cause of failure and troubleshoot.
6. The motor starts frequently or has too many positive and negative turns
If the motor starts frequently or the positive and negative rotation times are too many, the starting times should be limited and the overheating protection or the motor suitable for production requirements should be properly selected.
7. Three-phase voltage is seriously unbalanced
Short circuit between stator windings and grounding of stator windings shall be checked.
8. Poor lubrication of bearings or clamps
Check whether the temperature of bearing chamber is higher than other parts;Check whether the grease is too low or dry.
9. The ventilation system fails
Is due to the wind road blockage or heat sink dust accumulation too much, oil scale is too thick and affect heat dissipation.
10. The rotor is connected with the stator core to generate continuous metal impact sound
Will cause local temperature rise is too high, should pull out the heart to check, find out the cause of failure for troubleshooting.
The axial wind rotates in the opposite direction
The motor that USES axial flow fan, if fan rotates direction is opposite, also can cause motor overheat.
12. Transmission device malfunction (friction or jamming)
Cause the motor over current heating, even make the motor stuck does not cause a sharp rise in the motor temperature, winding is soon burnt out.
13. rewound motor due to changes in winding parameters
The three-phase no-load current of the motor can be measured. If the three-phase no-load current is greater than the rated value, it indicates that the number of turns is insufficient and the number of turns should be increased.
14. external wiring errors, connection motor misconnection ya connection
Although it can be started and run with load, the higher the load current is, the higher the rated current will cause heat.Recommend ya connection motor misconnection into train connection, no-load can exceed the rated current and can not run.
Motor fault current measurement criteria
The measurement criteria are as follows: the difference between any phase current value and the average three-phase current value shall not be more than 10%.
Normal operation of the motor, in the condition of power supply voltage balance, its three-phase current is basically balanced.In the operation of asynchronous motor, if ammeter or clamp ammeter is used to measure the serious imbalance of three-phase current, it may be caused by the following reasons.
1. For some reason, the three-phase voltage is out of balance, and thus the three-phase current is out of balance.If the power supply is out of phase or the one-phase contact is bad, the motor is out of phase operation. For the star-connected motor, the current in the other two-phase windings rises sharply, while for the triangular connected motor, the current in the one-phase windings rises sharply.A long time, the winding will burn down, this situation is the most harmful.According to statistics, such faults account for more than 50% of motor burn-down accidents.
2. A branch circuit in the three-phase winding is broken, which results in inconsistent three-phase impedance and unbalanced three-phase current.3. Motor windings occur inter-turn or grounding short circuit fault, if the fault is serious, circuit breaker and other over-current devices will trip, not serious, often will not trip, at this time the three-phase current imbalance.Latent short circuit fault winding current is very large, causing additional heating winding, a little longer time, the fault will further expand.Once the fault is found, the machine should be stopped immediately for maintenance.
4. In the process of motor maintenance (such as rewind motor stator winding), due to a mistake that the first phase, result in the following the formation of highly uniform rotating magnetic field caused by the phase current is very big, difficulty in starting at the same time, the noise big abnormal phenomenon, the author himself in after overhaul of the commissioning process of an electric motor just met once.
5. If the pointer of the three-phase ammeter is oscillating periodically in the operation of the squirrel cage motor, especially for the motor with frequent start and stop or positive and negative rotation, the possibility of broken bar of the squirrel cage rotor should be considered.