Cooling Tower Motor Maintenance Guide

Cooling tower motors mostly operate in humid, hot, dusty and even corrosive gas environments, and are subjected to frequent starts and stops, wide voltage fluctuations and sudden load transmission by belts or couplings. If there is a lack of system maintenance, they are prone to faults such as winding moisture, premature wear of bearings, corrosion of shaft extensions and overload burnout. To transform "post-event repair" into "predictive management", it is necessary to establish a four-level maintenance system with "daily inspection, weekly maintenance, monthly overhaul and annual major overhaul" as the main line, and adhere to the ten-point guideline of "cleanliness, dryness, tightness, lubrication and monitoring", so as to achieve the longest service life and the highest energy efficiency at the lowest cost. The following practices have been verified on-site over many years and can be referred to.

At the daily shift handover, conduct a quick physical examination through four methods: observing, listening, touching and smelling: check if the current exceeds the nameplate by ±5%, and check if the cable joints have changed color. Listen to whether the noise from the bearing is uniform. If there is a periodic "dada" metal impact, it is mostly a sign of cage damage. Feel the temperature rise of the casing. If it is more than 40℃ higher than the ambient temperature, the load must be immediately reduced or the cooling air duct inspected. Smelling for a burnt odor can help detect a local short circuit in the winding in advance. Simultaneously record the initial values of operating current, voltage and vibration to establish a baseline for subsequent trend analysis.

Every week when the machine is shut down, wipe the motor casing and the cooling fan cover to prevent willow catkins and dust from blocking the air passage. Measure the insulation resistance of the winding to ground with a 500V megohmmeter. If it is lower than 5MΩ, moisture drying or adding moisture-proof heating tapes is required. Check the torque of the bolts on the feet, junction box and end cover. Due to the large vibration of the cooling tower, the loosening of the bolts will aggravate the uneven air gap, causing current rise and vibration marks on the bearing track. For bearings with oiling nozzles, add lithium-based grease until the old grease is just squeezed out. Be sure not to add too much, as the increase in internal pressure may force the grease into the windings.

Every month, disassemble the rear end cover, pull out the rotor to check the rust condition of the shaft extension. If there are pitting spots, use fine sandpaper dipped in oil to grind them and apply epoxy iron red primer. Scan the cable nose and terminal block with an infrared thermal imager. If the temperature rise of the hot spot exceeds 15℃, re-crimping is required. For motors driven by belts, use a tensiometer to measure the deflection at the midpoint of the belt. A deflection of 15 to 20mm is ideal. If it is too tight, it will increase the bending moment of the shaft extension; if it is too loose, it will slip and generate heat. Clean the condensate water inside the junction box and install a breathable waterproof plug on the box cover to form a "breathing" seal, which can significantly reduce the accumulation of moisture.

Every 2,500 hours of operation or half a year, entrust the electrical repair workshop to carry out core-pulling maintenance: use dry compressed air to blow clean the dirt in the winding gaps, then spray with electronic cleaning agent, dry and then apply conformal coating. Before replacing the bearing, evenly heat the inner ring to 80℃ with an electromagnetic induction heater and then install it to avoid micro-cracking of the journal caused by cold knocking. After reassembly, three comparative tests of DC resistance, no-load current and vibration velocity should be conducted. If the deviation of any one of them exceeds ±3%, the cause needs to be identified. If the motor is out of service for a long time, it should be turned by hand at 180° and powered on for 5 minutes every two weeks to redistribute the lubricating oil film and prevent false Brinell indentations on the bearings.

During the annual major overhaul period, the motor is sent to a test station with CNAS qualification to complete 500V inter-turn impact, 1500V power frequency withstand voltage, and B-level temperature rise loading tests, and an authoritative life assessment report is obtained. Meanwhile, update the lubrication ledger. According to the ISO 4406 particle size standard, send the old grease for inspection. If the iron powder grade exceeds 18/16/13, it indicates that the bearing is close to fatigue spalling and spare parts should be prepared in advance. Finally, the maintenance data is entered into the CMMS system, and the three-year curves of insulation, vibration and current are displayed in trend charts, providing quantitative basis for technological transformation or energy efficiency benchmarking. As long as the above closed-loop management is adhered to, the cooling tower motor can be extended by another 30% on the basis of the designed service life, the failure rate can be reduced by 50%, and the comprehensive power-saving rate can be increased by 3% to 5%.