A thermal power plant is equipped with a motor with a 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. In 2004, when the motor was in operation, the temperature of the bearing at the shaft end was sharply increased, the bearing oil cap was discolored, and the smoke of the burnt smell was accompanied. After the operation of the on-duty personnel stopped the inspection, it was found that the motor shaft extension end bearing burned and was 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 partially;
(2) The bearing chamber has obvious signs of wear 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 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 the regulations, the refueling cycle of this motor is 2 000 h; the period of cleaning the bearings and replacing the grease is 1 year. However, in the operation of more than 2 years, only the refueling was added once, and the grease was not replaced. Due to the poor operating environment of the motor and the long-term operation, the oil quality is deteriorated and the bearing is short of 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 bearings at both ends of the motor, the bearing end of the shaft end and the inner and outer oil caps, and repair the worn motor rotor shaft.
(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.
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 partially;
(2) The bearing chamber has obvious signs of wear 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 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 the regulations, the refueling cycle of this motor is 2 000 h; the period of cleaning the bearings and replacing the grease is 1 year. However, in the operation of more than 2 years, only the refueling was added once, and the grease was not replaced. Due to the poor operating environment of the motor and the long-term operation, the oil quality is deteriorated and the bearing is short of 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 bearings at both ends of the motor, the bearing end of the shaft end and the inner and outer oil caps, and repair the worn motor rotor shaft.
(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.
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