Causes and treatments of motor heating failure of positive and negative pressure thermoforming machine1. Cause analysis of motor heating failure
The heat generated by the motor during operation mainly comes from the heat generated by the friction between the mechanical structure, the electric heat generated by the current passing through the fixed (rotating) winding, the motor cooling system failure or the ventilation system blockage, iron loss during operation, copper loss to heat Heat accumulation caused by conversion and other reasons. Due to the complicated internal structure of the motor, there are more reasons for the overheating fault of the three-phase asynchronous motor, and the form of the fault is different. Therefore, it is necessary to conduct a detailed analysis and summary of the motor heating phenomenon and fault types in daily operation management.
1. Analysis of external causes
The change of operating environment is the main external cause of motor heating, such as: three-phase voltage imbalance, power supply voltage fluctuation, overload and overload operation, poor operating environment, etc.
1) Three-phase voltage unbalance
When there is a three-phase voltage imbalance in the motor power supply, a reverse sequence current and a reverse sequence magnetic field will be formed in the internal complex electromagnetic interaction environment, thereby forming a larger reverse sequence torque in the motor winding. Under the superimposition of the torque, the internal electromagnetic torque of the motor will decrease, which will cause the rotor speed of the motor to decrease. In the case of the same load capacity, in order to rebalance the motor system, the current of the motor must be increased. Increasing the heat generated by the internal windings of the motor will cause the motor to overheat and malfunction in severe cases. According to some engineering application statistics, when the three-phase voltage unbalance of the motor reaches about 5%, the current between the motor phases will exceed 25% of the rated current value, and the motor current value increases sharply with the increase of the voltage unbalance. Therefore, in order to ensure the safe and stable operation of the motor, it is necessary to strictly monitor the unbalance of the power supply voltage in daily management, and try to ensure that the motor runs under the three-phase balanced condition.
3) Overload and overload operation
Overload Overload operation is a common external cause of motor heating failure. In the entire motor system, if the mechanical system driven by the motor is jammed, the transmission mechanism is too tight, the lubrication system is damaged, and the load suddenly increases, etc., the motor can run in the low-efficiency working condition area, and overload and overload will occur. Unreasonable motor system design and selection may also cause the motor to appear "small horse-drawn cart". In this working condition, in order to ensure the balance between input and output, the motor system will reduce the motor speed, which will cause the internal current to increase, generate violent heat, and cause the motor to overheat.
1) Mechanical failure
When the motor bearing is not installed in place, there is eccentric jamming, the bearing lubrication system has no lubricating oil, too much oil, poor oil quality, improper oil sealing system, etc., and the motor end cover and the motor frame are out of alignment. All can cause problems such as increased friction between the bearings, distortion of the rotating shaft, and bore sweeping of the rotating shaft, which will cause the motor to generate intense heat and cause heating failure.
2) Stator (rotor) winding failure
Wrong connection of the three-phase windings of the motor, short circuits between turns or layers of the stator (rotor) windings, and single-phase grounding of the three-phase windings can cause the motor to overheat. When there is a virtual connection or virtual welding between the three-phase winding lead contacts of the motor, the contact resistance of the joint will be too large, and the severe heat at the winding joint will cause the motor to generate heat failure.
2, internal reasons
Internal mechanical structure failure, stator winding failure, rotor winding failure and insulation failure are the main internal causes of motor overheating failure.
3) Insulation failure
As the running time of the motor increases, the insulation of the laminated layer of the motor iron core will continue to age or be damaged under the combined influence of thermal and dynamic effects, which will cause the internal eddy current of the motor to increase, increase the iron loss surface of the motor, and generate intense heat at the iron core. . After the motor winding insulation is aging and damaged, the winding insulation effect will be greatly reduced, the leakage current will increase sharply, and more heat will be generated at the windings, which will cause serious heating failures in the motor.