The purpose of daily maintenance inspection of motors is to detect equipment abnormalities as early as possible, so as to facilitate timely treatment and avoid aggravation of accidents. Maintenance staff can detect abnormalities based on the action of the relay protection device and the transmitted signal, or they can judge based on their own experience.
The main methods are divided into look, touch, listen and smell
1. Look - appearance inspection, the following abnormal phenomena can be found only by naked eyes
(1) Whether the external fasteners of the motor are loose, whether the parts are damaged, and whether there is oil stain or corrosion on the surface of the equipment.
(2) Whether the contact points and connections of the motor have discoloration, burn marks, smoke marks and other undesirable phenomena. These phenomena occur due to abnormal conditions such as local overheating of the motor, poor conductor contact or winding burnout.
(3) Whether the instrument indication is normal. If the voltmeter has no indication or is abnormal, it indicates that the power supply voltage is unbalanced, the fuse is blown, the rotor three-phase resistance is unbalanced, single-phase operation, poor conductor contact, etc. If the ammeter indicates too much, it means that the motor is overloaded, the bearing is faulty, the winding turns are short-circuited, etc.; the motor stops, the reasons are: power failure, single-phase operation, low voltage, too small motor torque, excessive load, excessive voltage drop, bearing burnout, mechanical jamming, etc.
2. Touch - Touch the surface of the casing with your hand to find that the motor temperature is too high and the vibration phenomenon
① Unbalanced mechanical load
② Looseness of each fastening component
③ Insufficient motor foundation strength
④ Improper coupling connection
⑤ Uneven air gap or mixed with debris
⑥ Unbalanced voltage
⑦ Single-phase operation
⑧ Winding failure
⑨ Bearing failure, etc.
Causes of excessive motor temperature:
① Machine overload
② Cooling air duct blockage
③ Single-phase operation
④ Inter-turn short circuit
⑤ Voltage is too high or too low
⑥ Three-phase voltage is unbalanced
⑦ Poor acceleration characteristics make the starting time too long
⑧ Stator and rotor rub against each other
⑨ Poor contact of the starter
⑩ Frequent starting and braking or reverse braking
⑪ Excessive inlet air temperature
⑫ Mechanical jamming, etc. When estimating the temperature by touching the surface of the motor with your hand, it is subjective because everyone's senses are different, so it should be determined by experience.
3. Listening - Use a stethoscope to hear various noises of the motor
Noises include electromagnetic noise, ventilation noise, mechanical friction noise, bearing noise, etc., so as to determine the cause of the motor failure.
The mechanical reasons for the high noise are:
① Bearing failure
② Mechanical imbalance
③ Loose fastening screws
④ The coupling connection does not meet the requirements
⑤ Stator and rotor cores rub against each other, etc.;
The electrical reasons are:
① Voltage imbalance
② Single-phase operation
③ Winding has short circuit or breakdown failure
④ Poor starting performance
⑤ Poor acceleration performance, etc.
4. Smell - Burning and odor can be detected by smell
The reasons for this phenomenon are:
① Motor overheating
② Winding burnout
③ Single-phase operation
④ Winding failure
⑤ Bearing failure, etc.
Routine maintenance inspections of motors can be divided into daily inspections, monthly or regular inspections, and annual inspections.
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