The motor of a power plant is equipped with a motor power of 220 kW and a voltage of 6 kV. The shaft end of the motor shaft is a 2322E Cylindrical Roller Bearing, and the non-shaft end is a 6322 Deep Groove Ball Bearing. When the motor was operated in 2019, the bearing temperature at the shaft end rose sharply, and the bearing oil cap was discolored, accompanied by smoke of burnt smell. After the on-duty personnel stopped checking, it was found that the motor shaft extended end bearing burned out and locked with the motor rotor.
1. Accident investigation
After the accident, the maintenance personnel conducted a physical examination of the motor and found that:
1) The bearing end of the motor shaft is burned, the bearing frame and the roller are worn out seriously, and the outer ring of the bearing turns blue.
2) The bearing chamber has obvious wear marks and is accompanied by deep cracks;
3) The rotor shaft is combined with the inner and outer oil caps, and there are many deep wear marks;
4) The inner and outer oil caps of the motor shaft extension end bearing are burnt.
After the disintegration inspection, the maintenance record of the motor was also checked, and it was found that the motor had replaced the bearings at both ends two years ago. When the bearing was replaced, it was found that there was a problem with the tolerance of the motor shaft end bearing and the bearing chamber, and the bearing was slightly rounded, but it was not treated. After the replacement of the bearing, the motor was replenished only once in February 2004, and there was no maintenance record.
2, the cause analysis
1) The maintenance personnel did not deal with the defects of the outer circle of the bearing, which caused the bearing to heat up and burn after long-term operation.
2) The maintenance personnel failed to timely refuel the motor.
According to regulations, the motor's supplementary refueling cycle is 2000h; the time to clean the bearings and replace the grease is 1 year. However, in the course of more than 2 years of operation, only one refueling was added and no grease was replaced. Due to the harsh operating environment and long-term operation of the motor, the quality of the oil deteriorates and the bearing lacks oil, causing the bearing to burn.
3) When the motor bearing is refueled, it is just in winter, the temperature is lower, and the hardness of the lubricating oil is increased. Due to improper operation of the refueling method, the grease cannot fully enter the inside of the bearing, and the lubrication is not good, resulting in bearing burning.
4) After discovering that the motor has a fever, the operating personnel did not use the local accident button to stop the faulty equipment in an emergency. Instead, they reported to the leader first and then stopped the equipment, which extended the accident handling time and caused the accident to expand.
3. Preventive measures and countermeasures
1) Replace the bearing at both ends of the motor, the bearing chamber of the shaft end and the inner and outer oil caps, and repair the worn rotor shaft of the motor.
2) Formulate the “Regulations on the Maintenance of Motor Bearings for Oil Bearings”, and re-clarify and emphasize the supplementary fueling and overhaul cycle of motor bearings.
3) Organize maintenance personnel to further study motor maintenance procedures and improve business skills. Strengthen the organization and management of equipment maintenance. At the same time, it is required that when the operating equipment is refueled in winter, the motor bearing oil cap should be properly heated so that the new grease can fully enter the bearing interior.
4) In the operation and management of the equipment, it is required to strengthen the operation monitoring of the equipment with abnormality (heating, abnormal sound, vibration), and timely stop the equipment maintenance.
