一、 Analysis and Handling of Common Electrical Faults in Electric Motors
1、 After the timing is turned on, the motor cannot start, but there is a buzzing sound
Possible reasons:
(1) The power supply is not fully connected to single-phase starting;
(2) Motor overload;
(3) Being stuck by dragging machinery;
(4) The rotor circuit of the wound motor is open and disconnected;
(5) The head end position inside the stator is connected incorrectly, or there is a broken wire or short circuit.
Solution: (1) Check the power cord, motor lead out, fuse, and switch contacts, identify the open circuit position, and eliminate it; (2) Unload and start with no load or half load; (3) Check the dragged machinery and troubleshoot it; (4) Check the connection of the electric brush, slip ring, and starting resistor of each contactor; (5) Re evaluate the ends of the three phases and check if there are any visible wires or short circuits in the three-phase windings.2、 The motor has difficulty starting and the speed is low after adding the rated load.
Possible reasons:
(1) The power supply voltage is low;
(2) Originally, the corner connection was mistakenly connected to a star connection;
(3) The cage bar end of the squirrel cage rotor is welded off, loose or broken.
Solution: (1) Increase the voltage; (2) Check the wiring method of the nameplate and correct the wiring method of the stator winding; (3) After examination and targeted treatment.3、After the motor starts, it heats up beyond the temperature rise standard or emits smoke
Possible reasons:
(1) The power supply voltage is too low, causing excessive temperature rise of the motor under rated load;
(2) Poor ventilation of the electric motor or high environmental humidity;
(3) Motor overload or single-phase operation;
(4) Frequent starting or excessive forward and reverse rotation of the electric motor;
(5) The stator and rotor rub against each other.
Solution: (1) Measure the no-load and load voltages; (2) Check the motor fan and clean the ventilation duct, strengthen ventilation and reduce ambient temperature; (3) After checking the current of each phase with a clamp type ammeter, treat it accordingly; (4) Reduce the number of forward and reverse rotations of the motor, or replace it with a motor suitable for frequent starting and forward and reverse rotation; (5) Treatment of aunt’s symptoms after examination.4、 Low insulation resistance
Possible reasons:
(1) The winding becomes damp or water drips into the interior of the motor;
(2) Dust and oil stains on the winding;
(3) The insulation of the stator winding is aging.
Solution: (1) Heat and dry the stator and rotor windings; (2) Wipe the end of the winding with gasoline and dry it; (3) Check and restore the insulation of the outgoing line or replace the insulation wire board of the junction box; (4) Generally, it is necessary to replace all windings.5、 Electric motor casing is electrified:
Possible reasons:
(1) Insulation or junction box insulation wire board for motor lead wires;
(2) The end of the winding touches the casing;
(3) The motor casing is not reliably grounded
Solution: (1) Restore the insulation of the motor lead or replace the insulation board of the junction box; (2) If the grounding phenomenon disappears after removing the end cap, insulation can be added to the winding end before installing the end cap; (3) Ensure reliable grounding of the motor casing according to the grounding requirements.6、 Abnormal sound during motor operation
Possible reasons:
(1) Wrong connection of stator winding, local short circuit or grounding, causing three-phase current imbalance and noise;
(2) There are foreign objects or severe lack of lubricating oil inside the bearing.
Solution: (1) Check separately and prescribe the right medicine; (2) After cleaning the bearings, replace the lubricating oil with 1/2-1/3 of the bearing chamber.7、 Motor vibration
Possible reasons:
(1) The installation foundation of the electric motor is uneven;
(2) The rotor of the electric motor is unbalanced;
(3) Unbalanced pulley or coupling;
(4) Bending of the shaft head or eccentricity of the pulley;
(5) The electric motor fan is unbalanced.
Solution: (1) Flatten the motor base and fix it firmly after finding a level; (2) Static or dynamic balancing of rotor calibration; (3) Perform belt pulley or coupling balancing; (4) Straighten the shaft, align the pulley, and then insert the heavy-duty vehicle; (5) Calm down the fan.二、 Analysis and Handling of Common Mechanical Faults in Electric Motors
1、 Maintenance of stator and rotor iron core faults
The stator and rotor are both made of mutually insulated silicon steel sheets, which are the magnetic circuit parts of the electric motor. The damage and deformation of the stator and rotor iron cores are mainly caused by the following reasons.
(1) Excessive wear or poor assembly of bearings can cause friction between the stator and rotor, resulting in damage to the surface of the iron core and causing short circuits between the silicon steel sheets. This can increase the iron loss of the motor and cause excessive temperature rise. In this case, tools such as fine files should be used to remove burrs, eliminate short circuits in the silicon steel sheets, clean them thoroughly, apply insulation paint, and heat dry them.
(2) Excessive force was applied when dismantling the old winding, causing the reverse slot to tilt and open outward. At this time, tools such as pliers and wooden hammers should be used to repair and reset the tooth grooves. Hard insulation materials such as green shell paper and plywood should be added between the silicon steel sheets with gaps that are difficult to reset.
(3) Due to moisture and other reasons, the surface of the iron core may rust. In this case, sandpaper should be used to polish it clean, and after cleaning, insulation paint should be applied.
(4) Due to high heat generated by winding grounding, the iron core or teeth are burned out. Use tools such as chisels or scrapers to remove the accumulated material, apply insulation and dry it.
(5) The connection between the iron core and the machine base is loose, and the original positioning screws can be tightened. If the positioning screw fails, the positioning hole can be re drilled and tapped on the machine base, and the positioning screw can be tightened.2、Bearing fault maintenance
The rotating shaft is supported by bearings and is a part of the load, as well as a component that is prone to wear and tear. (1) Fault inspection
During operation inspection: When the rolling bearing is short of oil, you will hear a rustling sound. If you hear a discontinuous stem sound, it may be due to the rupture of the bearing steel ring. When there is sand or other debris mixed in the bearing or when the bearing parts have slight wear, a slight noise will be produced.
After disassembly inspection: First, check whether the bearing rolling elements, inner and outer steel rings are damaged, corroded, scarred, etc. Then, pinch the inner ring of the bearing with your hand and flatten the bearing. Use your other hand to push the outer steel ring with force. If the bearing is in good condition, the outer steel ring should rotate smoothly without vibration or obvious jamming during rotation. If the outer steel ring does not reverse after stopping, it means that the bearing can no longer be used. Grasp the outer ring with your left hand and the inner steel ring with your right hand, pushing it in all directions with force. If you feel loose when pushing, it indicates severe wear and tear.
(2) Fault repair
The rust spots on the outer surface of the bearing can be wiped off with 00 grit sandpaper, and then cleaned in gasoline; When the bearing has cracks, broken inner and outer rings, or excessive wear, a new bearing should be replaced. When replacing a new bearing, choose the same type of bearing as the original one.3、 Maintenance of shaft malfunction
(1) Axis bending
If the bending is not significant, it can be repaired by polishing the shaft diameter and slip ring; If the bending exceeds 0.2mm, the shaft can be placed under a press machine, and pressure correction can be applied at the bending point. The surface of the corrected shaft can be cut and polished with a lathe; If the bending is too large, a new shaft needs to be replaced.
(2) Neck wear
When the wear on the shaft neck is not significant, a layer of chromium can be plated on the shaft neck and then ground to the required size; When there is a lot of wear, welding can be carried out on the journal, and then cut and polished on the lathe; If the journal wear is too large, also sharpen 2-3mm on the journal, then turn a sleeve while it is hot and fit it on the journal, and then turn it to the required size.
(3) Shaft crack or fracture
When the transverse crack depth of the shaft does not exceed the shaft diameter and the longitudinal crack does not exceed the shaft length, the welding method can be used to remedy it, and then precision machined to the required size. If the cracks on the shaft are severe, a new shaft needs to be replaced.4、 Maintenance of the casing and end cover
If there are cracks in the casing and end cover, welding repair should be carried out. If the clearance between the bearing holes is too large, causing the fit of the bearing end cover to be too loose, a punch can generally be used to evenly punch the wall of the bearing hole with rough stimulation, and then the bearing can be driven into the end cover. For high-power motors, the required size of the bearing can also be processed by inlaying or electroplating.
