Motor inspections can proactively prevent equipment malfunctions and ensure stable and smooth production. Let's learn about the key points of motor inspection together.
Classification of motors
Motors are divided into two types: AC motors (see Figure 1) and DC motors (see Figure 2).
General inspection points for motors
Key points for visual inspection of motors
Key point 1: Is the motor speed normal? Are there any speed fluctuations or stalling phenomena? (This can be checked with a tachometer.)
Point 2: Check if the motor's anchor bolts are loose, if the foundation is intact, and if there are any debris around it.
Point 3: Check if the motor housing and coupling are intact, and whether the coupling screws are loose. Also check for debris or dirt on the motor body, and whether the ventilation slots are blocked.
Point 4: For air-cooled motors, check if the air pipes are unobstructed, if all connections are tight, if the valves on the pipes are in the correct position, and if natural ventilation is adequate. For water-cooled motors, check if the cooling water pipes are unobstructed, if there are any cooling water leaks, and if the cooling water temperature and flow rate are normal.
Important points to note:
Point 1: For synchronous motors, wound-rotor motors, etc., it is also necessary to check whether the contact between the brushes and the slip rings is good, whether there is commutation spark, and whether the color and shape of the spark are abnormal.
Point 2: Is the excitation system of the synchronous motor normal?
Point 3: Check whether the motor wiring and grounding wire connections are loose.
Special points:
Key Point 1: Check whether the current of the running motor exceeds the allowable value, whether it corresponds to the actual load, whether there are any sudden changes, whether the voltage is within the allowable range, and whether there is a phase loss.
Point 2: Check whether the temperature of each part of the motor exceeds the allowable value.
Point 3: Check if the bearing is overheating, if there is enough lubricating grease, if the oil level indicator shows the correct oil level, and if the oil ring rotates smoothly.
Point 4: Check if the motor is smoking or if the windings are discolored or showing signs of overheating.
Key points for auditory inspection of motors
Check if the motor is running normally, and whether there are any abnormal noises.
Key points for olfactory inspection of motors
Check for any unusual odors, burnt smells, or other abnormal phenomena.
Tactile Inspection Points of Motors
Key Point 1: Whether the vibration of the motor during operation is normal or abnormal can be judged by feeling it with your hand. If the vibration is large, use a vibration meter to measure it. (Generally, rolling or sliding bearings have a uniform sound and no obvious vibration when you feel the bearing. If the vibration is large, use a vibration meter to measure it. Generally, a vibration of less than 3.5 mm/s is considered good.)
Point 2: Is the temperature of the motor normal during operation? Is there any abnormal temperature rise? (If an embedded thermometer can be used, read its reading. If this type of thermometer cannot be installed, judge by feeling with your hand, or use a rod thermometer or infrared thermometer to measure.)
Point 3: The upper limit of the outer surface temperature of a bearing is generally when it is very hot (touched by hand for 3-4 seconds), that is, the upper limit of the rolling bearing temperature is generally 80℃.
Key points for motor inspection
Key Point 1: Ensure that the protective measures for transmission parts that are easily touched by inspectors are secure and reliable.
Point 2: When a motor has been out of use for three months or more, its insulation resistance should be measured before it is put back into operation. For motors with a rated voltage of 500V or higher, a 1000V or 2500V megohmmeter should be used.
Point 3: For motors that are supplied with cooling air from outdoors, the supply of cooling air should be stopped immediately after shutdown to prevent the motor from getting damp. For motors that have been shut down for more than 24 hours, the heater should be turned on to prevent the motor insulation resistance from decreasing.
Point 4: If the insulation resistance value of the windings of a running motor decreases by 50% or more compared with the previous value (converted to the same temperature), the cause should be investigated and a withstand voltage test should be performed if necessary.
Point 5: The core temperature should be measured with an alcohol thermometer. In the presence of a magnetic field, a mercury thermometer should not be used, as this may cause eddy current losses in the mercury and generate heat.
Point Six: For wound motor brushes and slip rings, check whether the copper braids of the brushes are intact, whether the contact is tight, and whether there is a short circuit or overheating with the casing. The brushes and brush holders should be free of dirt. If there is carbon buildup, clean it in time. The brushes should be replaced when they are worn to 2/3 of their original length.
Key Point 7: After on-site installation of the motor, the focus of the external condition inspection should be on the following: whether the external lead wires (phase sequence is correct and connection is reliable), grounding wire (reliable), thermometer, fan motor (rotation direction), cooling water pipe connection, valve status, and other electrical components' wiring and connection status are normal.
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