Fault analysis and countermeasures of circulating water pump motor

A power plant is now equipped with four circulating water pump motors. At 23:06 on July 24, 2005, the operation found that the circulating pump A motor current suddenly rises from 191.1A to 204A (the switch chamber ammeter rises to 210A), the motor coil The temperature rises synchronously by about 3 °C, up to 110.3 °C, and the pump vibration is large. The company has formulated relevant emergency plans to maintain the pump operation. At 8:53 on August 20, the circulating current of the pump A is increased (194A-220A). The vibration of the in-situ inspection is intensified. The circulating water pump A and the circulating pump and the motor are transferred to the disintegration overhaul.

Maintenance process and treatment

First dismantling

On August 25th, the circulating water pump A motor was completely disassembled. The inspection was as follows: the oil at the bottom of the oiling chamber was seriously dirty, the labyrinth of the top cover of the lower oil chamber was partially worn, the stator core vent was blocked, and the stator winding end (slot) The gap between the mouth and the R angle is serious. The lower bearing: before the cleaning, the outer ring is slightly rubbed (running the outer ring), and there is local rust; the entire bearing body surface is thicker, the rafter track There are also attachments; after the bearing is cleaned, the surface of the tweezers is better, the measurement gap is qualified (0.36mm), the cage is flexible, and the upper bearing is inspected: there are burn marks on both ends of the groove at the bottom of the six guide tiles. There are also burn marks on the position of the corresponding rail of the guide bracket. Later, the burrs were removed with metallographic sandpaper.

The motor was overhauled according to the routine. After the assembly was completed, on September 21, the no-load test run: no-load current 109A, the vibration increased from the maximum 10 wire to 13.6 wire. Due to the large vibration and the rising trend of vibration, the motor is shut down for maintenance.

Second overhaul

On September 21, the inspection found that the wheel was not restored, and it was restored according to the original position. At the same time, the lower bearing was replaced. On September 30, the motor was put into operation again, and the abnormal sound still existed. Due to the time relationship, the motor is not used for the long-term operation of the pump.

Third overhaul

On October 9th, the circulating water pump A motor was running, the vibration was large, and the lower part had abnormal sound. The motor is again turned to overhaul. Disintegration found: the lubricating oil in the oiling chamber is dirty (there are burlap crumbs), the thrust pad is worn, and the thrust surface of the thrust head is scratched and streaked. The thrust head is sent to the fertilizer plant for processing and replacement of the thrust tile. After the motor is in place, the machine finds a positive distance and increases the distance between the wheels by 2 mm. The mechanical professional raises the pump side coupling by 2mm upwards. (Cause: The thrust head was not assembled in the last assembly. The thrust head was assembled in this reassembly, so this time the machine was looking for two couplings. The distance between the two is increased by 2mm).

On October 17, the gap measurement was carried out for each part of the motor's lower oil compartment: the clearance from the outer side of the oil cylinder to the lower bearing mounting ring was 0.60 mm, and the clearance from the inside of the oil cylinder to the shaft was 8.94 mm.

On October 19th, the motor no-load test run: no-load current 112.8A, the motor vibration is large, the lower part has abnormal sound (intermittent), stop running. On October 20th, the motor was again empty-tested: the top vibration was 0.11mm.

Motor for the fourth overhaul

After the company's leadership discussed and decided, the motor was dismantled again.

Use the feeler gauge to measure the clearance between the outer ring of the bearing and the insert: A, D (arc length 650mm) can be inserted with a 0.07mm feeler, and B, C (arc length 13.5mm) can be inserted with a 0.10mm feeler. . Initially, the bearing inner ring and the rotor journal have wear (gap). Pull out the rotor for further inspection:

The rotor was aligned at a machine factory: the rotor shaft was not found to be bent. When the bearing was ready to be removed, it was found that the lower bearing was very loose, and it was pushed out by hand. Another inspection revealed that the bearing mounting portion was worn out; the inner ring of the old bearing that was removed was also worn. Treatment: After the outer bearing bracket is rounded, the outer round is covered with 0.10mm stainless steel skin, welded by pulse welding, and then the burr is manually repaired. The final diameter is φ380+0.01～0.03mm, and the new lower bearing is replaced at the same time.
Measuring the size of the shaft head (the thrust head mating surface): the shaft diameter is φ220 mm. Since the thrust head is loosely coupled to the shaft, the new thrust head is replaced.

The inner cap bearing insert sleeve was measured with an inner diameter micrometer and the lower end cap bearing insert was found to be large and elliptical in diameter. The lower frame and end cover are processed according to the standard fit size.

On November 15th, the overall assembly began, and the assembly process was carried out in accordance with the standard requirements.

On November 22, no-load test run: no-load current increased from 111A to 117A. The upper vibration is at most 0.11 mm, which is not ideal. The level and stator clearance are re-examined and the values ​​change.

On November 24th, the stator and rotor clearances were re-adjusted to pass. The parallel rotor (90 degrees per disk) measures the stator and rotor gaps respectively, and the values ​​are basically unchanged. The motor is again in no-load test run: no-load current 116.1A, vibration condition: about 0.05~0.07mm before half an hour ago, and stable when the vibration increases up to 0.10~0.12mm after half an hour.

On November 26, the motor vibration was re-tested at night, and the vibration value was slightly reduced between 0.08 and 0.10 mm.

At present, the motor vibration value is 0.04~0.06mm, which meets the standard (≤0.20mm), and the motor can operate normally.

Cause Analysis

The motor has been repaired four times to eliminate the defects of the motor, the burn marks on the surface of the thrust tile (replace a new set of thrust tiles), the inner and outer rings of the lower bearing are worn (processed), the lower frame and the bearing are poorly matched (processed), and the thrust Poor fit between the head and the shaft (replacement of the thrust head and key), deformation of the flange surface on the stator body (with gasket treatment), deformation of the lower bearing mounting ring of the rotor, wear and deviation (processed), loosening of the end cap positioning pin ( The pin has been processed and machined according to the actual size), and the inner and outer rings of the lower oil chamber are worn (treated). The reasons for the analysis are:

a. The main cause of the motor failure is the long-time faulty water pump operation. The motor runs from the fault phenomenon of the water pump to the maintenance and repair, and the overload operation and the large vibration operation in the past one month.

b. The main reason for the abnormal sound after the motor is repaired is that the inner and outer rings of the oil are worn and deformed, and the lower bearing runs the inner ring.

c. The main cause of damage to the thrust tile is the large vibration of the motor.

d. The main cause of damage to the thrust head is also caused by large motor vibration.

e. The reason for repeated overhaul is that the equipment failure is underestimated, the existing defects are not comprehensively inspected, the maintenance technology is not adequately prepared, and the maintenance process control and supervision are not in place. The inspection was not careful and lacked maintenance experience. During the assembly process, it is not strictly in accordance with the process requirements, and the assembly is not in place. Several inspections have found that the process defects left by the previous inspections hinder the search for the cause of the real defects, and directly lead to the repair and detour, delaying the troubleshooting time. When the second bearing was replaced and the lower bearing was replaced, the inspection did not close the quality. The lower bearing assembly size is loose, but the operator did not find it in time, and missed the best opportunity to find the cause of the failure. The person in charge of the work has changed too much, and the handover process has not been clearly explained, so that the person in charge of the work at the back has insufficient understanding of the overhaul, resulting in missing items for inspection and overhaul.

Preventive measures

a. Revise the maintenance documents and arrange for the maintenance of equipment with hidden dangers to be different from the applicable inspection documents for routine inspection overhaul.

b. The faulty equipment maintenance should be comprehensively analyzed and understood, and the accident prediction and technical preparation should be fully prepared.

c. The technical personnel should supervise the position during the overhaul and do a good job in the process control.