1. Analysis and treatment of common faults of electric motors

(I) when the time is switched on, the motor cannot start, but there is a buzz

Possible reasons:

(1) the power supply is not all connected to single-phase start;

(2) motor overload;

(3) stuck by the drag machine;

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

(5) the head end of the stator is misconnected, or broken or short circuit.

Processing methods :(1) check the contact points of power cord, motor lead, fuse and switch, find out the position of the break and rule out; (2) no-load or half-load starting after unloading; (3) check the machinery being dragged and remove the fault; (4) check the connection of the brushes, slip ring and start resistance contacts; (5) re-determine the head and tail of the three-phase winding, and check whether the three-phase winding has can line and short circuit.

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

Possible reasons:

(1) low power voltage;

(2) the original Angle connection is wrong star connection;

(3) the cage end of the cage rotor is unwelded, loose or broken.

Treatment :(1) increase voltage; (2) check the connection method of nameplate and correct the connection mode of stator winding; (3) after the examination and symptomatic treatment.

(3) the motor heats up beyond the temperature rise standard or smokes after starting

Possible reasons:

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

(2) bad ventilation or excessive humidity of the motor;

(3) motor overload or single-phase operation;

(4) too many times of starting or reversing of the motor;

(5) the stator and rotor are rubbed against each other.

Treatment method :(1) measure no-load and load voltage; (2) check the motor fan and clean the air duct, strengthen ventilation and reduce ring temperature; (3) after checking each phase current with the forced-type ammeter, symptomatic treatment was conducted; (4) reduce the number of positive and negative turns of the motor, or replace the motor suitable for frequent starting and positive and negative turns; (5) postoperative diagnosis and treatment.

Low insulation resistance

Possible reasons:

(1) the winding is wet or dripping into the motor;

(2) dust, oil and dirt on the winding;

(3) insulation aging of stator windings.

Treatment method :(1) heating and drying the stator and rotor windings; (2) wipe the winding end with gasoline to dry; (3) check and restore the outlet insulation or replace the insulation board of the junction box; (4) in general, all windings need to be replaced.

(v) electric motor enclosure:

Possible reasons:

(1) insulation board of electric motor lead wire or junction box;

(2) the end of the winding collision case;

(3) the motor enclosure has no reliable grounding

Treatment method :(1) restore the insulation of the power outlet wire or replace the insulation board of the junction box; (2) if the grounding phenomenon disappears after the end cover is removed, the end cover can be installed after insulation is added at the end of the winding; (3) the motor enclosure shall be reliably grounded as required.

(6) the motor does not sound properly when running

Possible reasons:

(1) wrong connection of stator windings, partial short circuit or grounding, resulting in unbalanced three-phase current and noise;

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

Treatment methods :(1) check separately, and take appropriate medicine; (2) after cleaning the bearing, replace the new oil with 1/2-1/3 of the bearing chamber.

Motor vibration

Possible reasons:

(1) the foundation of motor installation is uneven;

(2) imbalance of motor rotor;

(3) imbalance of belt pulley or coupling;

(4) bending of shaft head or eccentric belt pulley;

(5) imbalance of motor fan.

Treatment method :(1) make the motor base flat and fasten it when it is horizontal; (2) rotor static balance or dynamic balance; (3) adjust and balance the pulley or the coupling; (4) straightening and rotating shaft, and aligning the belt wheel to the rear insert heavy truck; (5) adjust the fan static.

Analysis and treatment of common faults of motor machinery

Troubleshooting of fixed and rotor iron cores

Both rotor and stator are made of insulating silicon steel, which is the magnetic circuit part of the motor. The damage and deformation of rotor core are mainly caused by the following reasons.

(1) excessive bearing wear or poor assembly will result in fixed and rotor phase abrasion, which will cause damage to the surface of the iron core and further cause short circuit between the silicon steel plates. The iron loss of the motor will increase and the temperature rise of the motor will be too high. At this time, tools such as fine file will be used to remove burrs, eliminate the short connection of the silicon steel plates, remove the short connection of the silicon steel plates, and then apply insulation paint after cleaning, and then heat and dry.

(2) excessive force is used to remove the old winding to make the inverted groove stretch outwards. At this point, small nose pliers, wood hammer and other tools are used to repair, so that the tooth slot reduction, and difficult to reset the gap between the silicon steel sheet add blue shell paper, plastic wood and other hard insulation materials.

(3) rust on the surface of the iron core caused by damp and other reasons. At this time, sandpaper should be used to clean it, and after cleaning, insulating paint should be applied.

(4) due to the grounding of the windings, high heat burns the core or tooth. Can use tools such as chisel or scraper to remove the melted product clean, coated with insulation qintong drying.

(5) the connection between the iron core and the machine seat is loose, and the original positioning screw can be tightened. If the locating screw fails, the locating screw can be re-drilled and tapped on the machine base.

Bearing failure maintenance

The rotating shaft rotates by bearing support, which is the heaviest part of load and the part that is easy to wear.

(1) fault inspection

Inspection during operation: when the rolling bearing is short of oil, you will hear a rumbling sound. When the bearing is mixed with sundries such as sand and soil or bearing parts are slightly worn, slight noise will be generated.

Down after unloading check: first examined the bearing rolling body, inner and outer steel ring to see if there is any breakage, rust, scar, etc., and then hold bearing inner ring with the hand, and makes the bearing straight, another hand push outside rims, if the bearing is good, the outer rims should turn to move smoothly, no vibration and obvious card lag phenomenon, in rotation after a halt outside rims no setback, otherwise the bearing cannot reoccupy. Hold the outer ring with your left hand, hold the inner ring with your right hand, and push hard in all directions.

(2) fault repair

The rust spots on the outer surface of the bearing can be wiped with no. 00 sandpaper and then put into the gasoline for cleaning; If the bearing is cracked, the inner and outer ring is broken or the bearing is excessively worn, the new bearing should be replaced. When replacing a new bearing, use the same bearing as the original model.

(3) shaft trouble maintenance

(1) axial bending

If the bending is not large, it can be repaired by grinding axle diameter and sliding ring. If the bending is more than 0.2mm, the shaft can be put under the pressure machine to correct the bending of the beat. After that, the shaft surface is machined and polished by the lathe. If the bending is too large, another axis should be replaced.

(2) journal wear

When the journal is not worn seriously, a layer of chromium can be plated on the journal before grinding to the required size; With more wear, surfacing can be carried out on the journal, and then cutting and polishing on the lathe; If the journal is too worn out, cut 2-3mm on the journal as well.

(3) axial crack or fracture

When the transverse crack depth of the shaft is no more than 10%-15% of the diameter of the shaft, and the longitudinal crack is no more than 10% of the shaft length, it can be remedied by surfacing welding method, and then refined to the required size. If the shaft crack is serious, a new shaft needs to be replaced.

(iv) maintenance of machine housing and end cover

Chassis and end cover if there is a crack should be welding repair if the bearing bore clearance is too large, cause bearing end cover with too loose, generally available to punch the bearing hole wall even hit MAO excitant, then bearing end cover, for motor power is bigger, also can adopt the method of set fill or plating finish the bearing size you need.