1. Analysis and treatment of common faults in electric motors

(1) After the timing is turned on, the motor cannot start, but there is a buzzing sound

Possible Causes:

(1) The power is not fully connected to a single-phase start;

(2) Motor overload;

(3) Jammed by the dragging machine;

(4) The rotor circuit of the wound motor is open and disconnected;

(5) The first end of the stator is connected wrongly, or there is a wire break or short circuit.

Treatment method: (1) Check the power cord, motor lead wire, fuse, switch contacts, find out the open circuit position, and eliminate it; (2) Start without load or half load after unloading; (3) Check for dragging Moving machinery, troubleshooting; (4) Check the connection of the contactors of the brushes, slip rings and starting resistance; (5) Re-determine the head and tail ends of the three-phase, and check whether the three-phase windings have bright wires and short circuits.

(2) The motor is difficult to start, and the speed is low after the rated load is applied.

Possible Causes:

(1) The power supply voltage is low;

(2) The original corner connection was wrongly connected to the star connection;

(3) The cage bar end of the squirrel cage rotor is disconnected, loose or broken.

Treatment methods: (1) Increase the voltage; (2) Check the nameplate wiring method and correct the stator winding wiring method; (3) Treat symptomatically after the inspection.

(3) After the motor is started, the heat exceeds the temperature rise standard or smoke

Possible Causes:

(1) The power supply voltage is too low, and the motor temperature rises too high under the rated load;

(2) The motor is poorly ventilated or the ambient humidity is too high;

(3) Motor overload or single-phase operation;

(4) The motor starts frequently or has too many forward and reverse rotations;

(5) The stator and rotor rub against each other.

Treatment method: (1) Measure the no-load and load voltage; (2) Check the motor fan and clean the air duct, strengthen ventilation to reduce the ambient temperature; (3) Check the current of each phase with a clamp-type ammeter, and treat it symptomatically; (4) Reduce The number of forward and reverse rotations of the motor, or replace the motor that is suitable for frequent starting and forward and reverse rotation; (5) Treatment after inspection.

(4) Low insulation resistance

Possible Causes:

(1) The winding is damp or dripped into the motor;

(2) There is dust and oil on the winding;

(3) The stator winding insulation is aging.

Treatment method: (1) Heat and dry the stator and rotor windings; (2) Use gasoline to scrub the winding ends and dry; (3) Check and restore the lead wire insulation or replace the insulated wire plate of the junction box; (4) General conditions Need to replace all windings.

(5) Electric motor housing:

Possible Causes:

(1) Insulation of motor lead wire or insulated wire board of junction box;

(2) The winding end touches the casing;

(3) The motor shell is not reliably grounded

Solution: (1) Restore the insulation of the motor lead wire or replace the insulation board of the junction box; (2) If the grounding phenomenon disappears after removing the end cover, you can install the end cover after adding insulation to the winding end; (3) Press grounding It is required to reliably ground the motor shell.

(6) The sound is abnormal when the motor is running

Possible Causes:

(1) The stator windings are connected incorrectly, partially short-circuited or grounded, resulting in unbalanced three-phase currents and causing noise;

(2) There is foreign body inside the bearing or serious lack of lubricating oil.

Treatment method: (1) Check separately and prescribe the right medicine; (2) After cleaning the bearing, change the new lubricant to 1/2-1/3 of the bearing chamber.

(7) Motor vibration

Possible Causes:

(1) The motor installation foundation is uneven;

(2) The motor rotor is unbalanced;

(3) Unbalance of belt pulley or coupling;

(4) The shaft head of the rotating shaft is bent or the belt pulley is eccentric;

(5) The motor fan is unbalanced.

Treatment method: (1) level the motor base, and fix it when the time is level; (2) the rotor is statically balanced or dynamically balanced; (3) the pulley or coupling is balanced; (4) the shaft is straightened, Align the belt pulley and insert a sleeve to load the vehicle; (5) Set the fan quietly.

2. Analysis and treatment of common faults in motor machinery

(1) Troubleshooting of stator and rotor cores

The stator and rotor are made of mutually insulated silicon steel sheets, which are the magnetic circuit parts of the motor. The damage and deformation of the stator and rotor cores are mainly caused by the following reasons.

(1) Excessive wear of the bearing or poor assembly will cause the stator and rotor to rub together, damage the surface of the iron core, and cause a short circuit between the silicon steel sheets, increase the iron loss of the motor, and make the motor temperature rise too high. At this time, use fine files and other tools to remove Burr, eliminate the short circuit of silicon steel sheet, clean it, apply insulating paint, and heat and dry.

(2) Excessive force was used when removing the old winding, so that the inverted slot was slanted and opened. At this time, use small-nose pliers, wooden hammers and other tools to trim, to reset the alveolar, and add hard insulating materials such as green shell paper and bakelite between the silicon steel sheets with gaps that are not easy to reset.

(3) The surface of the iron core is corroded due to moisture and other reasons. At this time, it needs to be polished with sandpaper, and then coated with insulating paint.

(4) The iron core or teeth are burnt due to high heat generated by the grounding of the winding. Use tools such as chisels or scrapers to remove the fused deposits and coat them with insulation and dry them.

(5) The combination between the iron core and the base is loose, and the original positioning screws can be tightened. If the positioning screw fails, re-drill and tap the positioning hole on the machine base, and tighten the positioning screw.

(2) Overhaul of bearing failure

The rotating shaft is supported by the bearing to rotate. It is the part of the load and the part that is easy to wear.

(1) Failure inspection

In-service inspection: When the rolling bearing is short of oil, you will hear the sound of rustling. If you hear the discontinuous stalking sound, the bearing steel ring may be broken. When the bearing is mixed with debris such as sand or the bearing parts are slightly worn, a slight noise will be produced.

Check after disassembly: first check whether the bearing rolling elements, inner and outer steel rings are damaged, rusted, scars, etc., then pinch the inner ring of the bearing with your hand, and make the bearing level, and push the outer steel ring with the other hand, if the bearing is good , The outer steel ring should rotate smoothly, there is no vibration and obvious blocking phenomenon during the rotation, and the outer steel ring does not retreat after stopping, otherwise the bearing can no longer be used. Hold the outer ring with your left hand, pinch the inner steel ring with your right hand, and push hard in all directions. If you feel loose when pushing, it means serious wear.

(2) Troubleshooting

The rust spots on the outer surface of the bearing can be wiped off with No. 00 sandpaper and then cleaned in gasoline; or when the bearing is cracked, the inner and outer rings are broken, or the bearing is excessively worn, replace the bearing with a new one. When replacing a new bearing, use the same bearing as the original model.

(3) Overhaul of shaft failure

(1) Shaft bending

If the bend is not large, it can be repaired by polishing the shaft diameter and slip ring; if the bend exceeds 0.2mm, the shaft can be placed under a press, and the bend can be pressure-corrected, and the corrected shaft surface can be cut with a lathe Polished; if the bending is too large, a new shaft is required.

(2) Axle neck wear

When the journal wear is not large, a layer of chromium can be plated on the journal and then ground to the required size; when the journal is worn out, surfacing welding can be carried out on the journal, and then cut and polished on the lathe; if the journal is worn When it is large, turn 2-3mm on the journal, then turn a sleeve on the journal while it is hot, and then turn to the required size.

(3) Shaft crack or fracture

When the horizontal crack depth of the shaft does not exceed the shaft diameter, and the longitudinal crack does not exceed the shaft length, it can be remedied by the surfacing method, and then refined to the required size. If the crack of the shaft is serious, a new shaft needs to be replaced.

(4) Overhaul of the case and end cover

If there are cracks in the casing and end cover, they should be repaired by surfacing welding. If the bearing boring gap is too large and the bearing end cover fits too loosely, usually a punch can be used to make the bearing hole wall evenly irritating, and then the bearing Into the end cover, for the larger power motor, the size required by the bearing can also be processed by inlay or electroplating.