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I. Daily inspection and maintenance of the motor The motor consists of a stator frame, windings and insulating materials, a rotor, bearings at both ends, and end covers, making it relatively simple in structure. The causes of motor failures include: missing phase in the power supply, incorrect voltage or frequency ； Winding short circuit, open circuit, ground fault ； The bearing is not operating properly ； Internal and external dirt, poor heat dissipation (too thick a paint coating on the outside is also a cause of poor heat dissipation), as well as a faulty built-in cooling fan leading to inadequate ventilation ； Poor mechanical equipment ； Long-term high-load operation ； Environmental temperature, etc. Over 90% of the damages to ship motors are caused by inadequate routine inspections and insufficient maintenance on the part of management. By consistently paying close attention through visual inspection, listening, touching, testing, and taking action, the vast majority of failures can be prevented, thereby reducing the company’s costs related to spare parts and repairs, as well as any delays in shipping schedules. 1. Observation: During daily inspections, not only the motor operator but also the on-duty engineer and the person responsible for refueling should check how the motor is operating, as well as the level and fluctuations in current. They should also look for any signs of leakage or dripping water, as these can lead to reduced insulation of the motor and eventual damage to it. It is also necessary to check whether there are any objects around the motor that could affect its ventilation and heat dissipation conditions Check whether the fan cover, fan blades, and the exterior of the motor are too dirty and need cleaning It is necessary to ensure its cooling and heat dissipation effects. Whoever discovers the problem should address it promptly. 2. Listening: Carefully listen to whether there are any abnormalities in the operating sound of the motor. Since there is a lot of noise in the engine room during navigation, it is possible to use tools such as screwdrivers or listening rods to listen closely to both ends of the motor. By doing this regularly, it is not only possible to detect abnormal vibrations in the motor and its driven equipment, but also to determine the level of oil in the internal bearings. This allows for timely actions such as adding more bearing oil or replacing the bearings, thereby preventing the motor bearings from drying out due to lack of oil, which could lead to stalling, damage to the outer surfaces of the bearings, or even burning out of the bearings. Considering the difficulty of disassembling large motors to replace bearings, most manufacturers use open-type bearings. When filling them with oil using a grease gun, it is necessary to use specialized bearing oil (from -35°C to +140°C), and the plug screw on the other side should be removed in order to squeeze out the old oil. It prevents oil from being forced into the motor due to high pressure during refueling, and from splashing onto the stator during operation, which could affect the motor’s cooling capabilities. 3. Touch: Use the back of your hand to feel the temperature around the motor. When the bearing condition is good, the temperatures at both ends are generally lower than those of the middle winding section. If the temperatures at the bearings on both ends are high, the bearings should be inspected in conjunction with the sounds detected from them. If the overall temperature of the motor is high, it is necessary to examine the motor’s load, equipment, and ventilation in conjunction with the operating current, and take appropriate action. Based on the insulation class of the insulating material used in the motor, it is possible to determine the maximum temperature at which the winding insulation can remain functional over a long period of time while the motor is in operation; in other words, it determines the allowable temperature rise of the motor (the actual temperature of the motor minus the ambient temperature). The insulation class standards vary from country to country, but they are generally divided into the following categories: Y, A, E, B, F, H, and C. Among these, class Y allows the lowest temperature rise (45°C), while class C permits the highest temperature rise (over 135°C). Considering bearing oil and other materials, the temperature measured by a thermometer attached to the motor should preferably be kept below 85°C. Ship motors are mostly of Class E and B, while generators are mostly of Class B and F. 4. Testing: A: When the motor is not in operation, it is necessary to regularly use an insulation meter to measure the resistance between each phase and ground, as well as between phases. If poor insulation is detected, a desiccant lamp should be used to improve the insulation level, in order to prevent the windings from being damaged due to too low insulation levels (the recommended value is >1 megohm). For motors equipped with electric heating for moisture removal, do not turn off the heating switch casually unless under special circumstances. Special attention should be paid to the waterproofing, moisture protection, and drying of motors during dock repairs, in humid weather, and in winter. Before departure, arrival, and departure from the dock for repairs, the insulation of some important motors must be inspected. Special attention must be paid to water resistance in motors used in outdoor and humid environments. Motors that are suspected to be severely damp or have been exposed to water should be thoroughly inspected before use. Where possible, a canvas cover should be sewn on for protection, which can help to maintain the insulation of the motor. However, in hot weather or during prolonged continuous use, the canvas cover must be removed to prevent heat dissipation from being hindered, which could lead to the motor overheating and burning out. If it is found that the motor has been submerged in seawater, simply disassemble the motor, remove the rotor, rinse it repeatedly with hot fresh water at 60-70°C, dry it with compressed air, and then use a heating lamp to dry out the stator from both ends until the motor’s insulation returns to normal. The deviation of the resistance of the repaired motor’s three-phase windings from their average value should be less than 4%. Measurement of insulation resistance: Generally, insulation is measured only in the cold state (at room temperature); insulation in the hot state is measured after the device has been operating for half an hour. If there is a large difference between the insulation resistance in the hot state and that in the cold state, it indicates that the insulating paint on the windings has not fully dried. The insulation resistance of the windings with respect to the ground (i.e., the casing) and between the windings should not be lower than the value calculated using the following formula: Insulation Resistance (ΜΩ) = 3x Motor’s rated voltage (V) / (Motor’s rated power in KVA + 1000). Some motors have only three leads for their windings, making it impossible to measure the insulation between the windings; in such cases, the insulation resistance of these motors should generally be no less than 5 megohms. B: While the motor is running, its three-phase operating voltage and current can be measured to check if they are balanced. The voltages should be essentially equal, and the deviation of each phase current from the average value should not exceed 10%; if the difference in the phase currents measured with a clamp meter is too large, there may be an inter-turn short circuit. Sometimes it is necessary to disconnect the load in order to measure the no-load current; generally, for 2-pole motors this value is around 2800 rpm, which is 1/3 of Ie (the rated current) ； Approximately 1600 rpm at 4 poles, around 40% Ie ； 6 poles, about 900 rpm, 55% Ie. It varies depending on the number of poles and capacity. Also, be careful not to get the Y and Δ connections of the motor wrong; if the Y connection is mistakenly used in place of the Δ connection, the operating current will increase ； Conversely, it decreases. At the same time, issues such as incorrect wiring of the motor’s windings, a reduced number of winding turns, or an excessively large air gap between the stator and rotor in older motors (the normal range being 0.2–1.0 mm) can all lead to an increased no-load current in the motor. These factors can help us assess the condition of the motor. 5. Action: It is necessary not only to take timely remedial actions for the problems identified during inspections, but also to tighten screws and wiring on the motor according to the maintenance schedule, as well as to disassemble it for inspection and clean it for maintenance. Issues such as all 4 fixing screws on the motor end cover of the air-conditioning fan on the ship \"XX Hai\" coming loose, resulting in damage due to operation under abnormal conditions, and the fan blades of the boiler fan on the ship \"X Qiang\" falling off and causing jamming leading to damage, were caused by a lack of timely inspection and tightening ； On the vessel \"Kang X\", it was found that the bearings of the main sea water pump motor were defective and that the operating temperature was high; however, the bearings were not replaced in time, which led to the motor burning out. On the vessel \"X Qiang\", the open-type motor of the main oil pump failed due to a decrease in insulation resistance caused by humid weather, and the insulation was not improved through drying in a timely manner, resulting in breakdown – this was because maintenance actions were not taken despite the identification of the problems. Whether it is doing nothing or only looking without taking action, it will ultimately lead to failures or accidents. When disassembling a motor and replacing bearings, it is advisable to use imported bearings whenever possible; many domestic bearings are actually reconditioned used bearings, and their quality cannot be guaranteed. If it is found that the outer surface of the bearing does not fit tightly with the bearing seat in the end cover, that is, if the bearing shifts outward, measures such as scoring the inner ring of the bearing seat in the end cover, using copper shims, or installing copper sleeves should be taken depending on the severity of the issue. Be sure to align the center point; otherwise, it will get damaged again soon. Before putting it into operation, it is necessary to recheck the radial swing of the shaft’s extended end and the tightness of components such as the end cover, whether the rotor rotates smoothly, and whether the winding leads are connected correctly, among other things. There are also many electric motors; when the pumps connected to them start leaking, it is common for the engineers to apply pressure (to the packing gland) in order to stop the leak. Experienced engineers will first turn the shaft by hand to check how it rotates, adjust the tightening of the gland screws accordingly, and then start and stop the pump a few times to verify that the operating current is normal ； inexperienced new engineers only know how to tighten the seals and pay no attention to the motors associated with them; as a result, the motors experience excessive starting currents due to stall, and the thermal overload protection fails to activate in time, causing the windings to burn out. Furthermore, when maintaining, disassembling, and reassembling motor-driven mechanical equipment (pumps, oil pumps, etc.), it is also necessary to carefully check and adjust the axis lines of the motor and the driven machinery to ensure proper alignment; the coupling should rotate smoothly and effortlessly when turned by hand. Only by carrying out each step thoroughly, carefully, and meticulously can the equipment’s integrity rate be improved. II. Daily inspection and maintenance of the control system: The control system of the motor consists of switches, small transformers, fuses, main and auxiliary contactors, relays, as well as temperature and pressure sensing devices, making it relatively complex. Faults are diverse, and analysis and troubleshooting often require the help of control schematics. It is important to keep the inside and outside of the control box clean and dry at all times; there should be no water or oil stains. Regularly use a small fan to blow away dust from the various components, terminals, and wiring within the box, or use a brush dipped in electrical cleaner to clean them, so as to prevent issues with the operation or insulation of contacts and relays. For a control box equipped with a dehumidification resistor, it is generally not advisable to turn off the heating switch casually. The enclosure should also be kept properly grounded to prevent electric shock. Regularly check the wiring inside the box and the tightness of the screws to prevent them from loosening. Check whether components such as switches, contactors, and relays are damaged or burned, and verify that the operating status of each component as well as its start, stop, and interlock functions are normal. It is necessary to maintain good engagement between the moving and stationary contacts of the contactor to ensure proper contact, thereby preventing the motor from operating with an incomplete phase supply and getting damaged as a result of poor contact. If the contact surface is in good condition and only discolored, it can be wiped with coarse cloth; do not easily polish off the heat-resistant alloy layer on the surface, as this will shorten the life of the contact ； If the surface of the contact is severely abraded, it can be smoothed out using sandpaper numbered “0”. The moving and stationary contacts should maintain line contact or surface contact, rather than point contact. To check the quality of the contact, a piece of paper can be placed between the moving and stationary contacts; if it is not held tightly when they come together, it indicates that the contacts or springs need to be adjusted or replaced. This aspect requires attention. In mild cases, poor contact can result in high contact resistance (current), which means an increased load and thus triggers the overload protection relay to trip; in severe cases, it can cause the motor to operate with a missing phase, leading to its damage. In one instance, operation with a missing phase occurred due to a jammed spring in the main contactor inside the control box; as a result, 3 oil distribution motor units were damaged within 10 months. When replacing relay contacts, attention should be paid to the operating voltage of the electromagnetic coil to avoid using the wrong one and damaging the coil. Generally, there are 24V, 110V, and 220V. For time relays, in addition to paying attention to the coil voltage requirements, it is also necessary to understand the time adjustment units (hours, minutes, seconds) and range of the time relay. For motors started using the star-delta (Y-△) method (with a transition delay of about 5 seconds), it is necessary to check whether their transition start is proceeding normally. Typically, manufacturers impose strict regulations on the starting frequency of motors (i.e., the number of starts per minute), and warning labels are provided on the start control box to remind users to prevent the motor from being damaged due to frequent starting. This also helps to avoid overheating and damage to certain electrical components within the start control box, such as start reactors. Therefore, for motor control systems with frequent start-stop operations or high current levels, the inspection and maintenance cycle should be shortened. Items such as kilo-grams, anchor winches, cable winches, auxiliary blowers for the main engine, main air compressors, and boiler water pumps all require close attention. It is necessary to regularly check the protection function of the thermal overload relay (this can be done by adjusting the small red marker next to it); the set operating value should not exceed the rated current value indicated on the motor’s nameplate, to ensure that it can provide proper overload protection. In short, as long as the mechanical and electrical staff enhance their sense of responsibility, carry out regular inspections and maintenance as required, and are able to address any abnormalities in the equipment’s noise, temperature rise, operating current, and insulation in a timely manner, our level of electrical management will surely reach a new height, providing an additional layer of safety for the operation of the fleet. Maintenance Procedures for Equipment Motors 1. Purpose: To ensure the reliable, economical, and long-term operation of motors in order to meet the requirements of continuous coating production, it is necessary to carry out maintenance on these motors. 2. Scope of application: Maintenance technicians, supervisors, and team leaders. 3. Daily maintenance (by maintenance personnel) 3.1 Keep the motors clean and prevent substances such as oil and water from entering their interior. 3.2 Check whether the bolts of the motor’s wiring terminals and the bolts used to secure the motor base are loose. 3.3 Check the rotation of the motor fan blades. 3.4 Check whether the motor housing is noticeably hot, and whether there is any oil leakage from the bearings at both ends. 3.5 Pay attention to checking whether the motor produces any abnormal noises, vibrations, or unusual odors during operation. 4. Regular maintenance: For motors that are operating properly, machine mechanics and electrical technicians must carry out maintenance on them once a year. 4.1 Remove dust or debris inside the motor (be careful not to damage the motor windings). 4.2 Check whether the motor rotor is flexible, and replace worn parts (bearings, etc.). 4.3 Check the insulation resistance of the motor windings to ground; if the insulation resistance is below 0.5 MΩ, the motor must be dried. 4.4 Replace the lubricating grease. 4.5 Check whether the no-load current is within the specified range. 5. Precautions 5.1 During maintenance, attention should be paid to electrical safety and mechanical transmission safety; illegal operations are strictly prohibited. 5.2 When installing motors that have been repaired or replaced, care should be taken to ensure that the wiring method is the same as that indicated on the nameplate, and it is also important to verify that the rotation direction of the motor matches the actual direction. 5.3 After installation, start the motor briefly and pay attention to whether it operates normally.