Professional knowledge | Common after-sales problems of motors

According to Mr. Wang, who has been engaged in motor after-sales service for 20 years, the common faults caused by motor quality are as follows: 1. Motor bearing failure (31%~51.3%), motor turn short circuit burning (6.3%~19.7%), motor core rubbing burning (6.8%~18.97%), bearing failure burning (1.6%~7.4%), and phase short circuit burning (1.6%~6%)

Other issues include electromagnetic noise, motor heating, motor vibration noise, motor off-axis, motor bearing chamber looseness, stator looseness, loose outgoing line, broken motor oil seal, lack of bottom hole drilling, missing bamboo stick, burnt balance pad, motor to ground, thin bearing platform, thin motor shaft, missing holes in motor flange, incorrect motor keyway, rotor error, stator error, motor bearing misalignment, outgoing box misalignment, incorrect standard parts, nameplate mismatch with reality, burnt spring pad inside the motor, etc.

As an excellent after-sales service personnel, it is necessary to have a certain understanding of the causes of common motor faults, and strive to find the cause of the fault in a timely and accurate manner when handling after-sales work, repair the motor as soon as possible, and minimize customer losses to the greatest extent possible.

There are mainly the following types:

(1) Bearing damage;

(2) Excessive or insufficient lubricating oil or poor oil quality;

(3) The fit between the bearing and the shaft is too loose, causing the inner circle to become loose or too tight;

(4) The fit between the bearing and the end cap is too loose, causing the outer circle to become loose or too tight;

(5) The belt is too tight;

(6) The coupling is not installed properly.

Example 1: A three-phase asynchronous motor with vibration, noise, and severe overheating during operation, while the power supply voltage is normal and the bearings and shaft are intact. If both the mechanical part and the power supply voltage are normal, then the fault is mostly a short circuit in the winding.

Example 2: A three-phase stepper motor can start without load, but the current increases and the three-phase currents are different in magnitude. The motor vibrates, produces noise, and quickly heats up, resulting in a significant decrease in starting torque. If the load cannot be started at all, the fuse will immediately burn out as soon as the power is turned on. Based on the above phenomenon, it can be determined that there is also a serious short circuit fault in the stator winding.

Common winding short circuit faults include inter turn short circuit (i.e. inter turn short circuit between coils within one phase winding or adjacent coils); Short circuit of pole phase group (i.e. short circuit of two lead wires of one pole phase winding); Inter phase short circuit (i.e. short circuit between windings of different phases).

The main causes of winding short circuit are:

(1) The motor operates under overload for a long time, and the current in the winding is too high for a long time, causing the insulation to age and become brittle, losing its insulation function, or cracking and falling off due to vibration.

(2) The insulation of the winding became damp and was directly connected to the power supply without drying, causing insulation breakdown due to power supply voltage.

(3) The insulation of the connecting wires or lead wires between the coil groups of the stator winding is poor or damaged due to breakdown, or one or several coils are short circuited due to carelessness during wiring.

(4) Due to careless wire embedding operation, the insulation on the outer layer of the electromagnetic wire was scraped or the lead wire was soldered, causing high temperature and touching the end cap, resulting in a short circuit.

(5) Due to careless assembly operation, the outer insulation layer of the electromagnetic wire was damaged, resulting in a short circuit.

(6) The insulation between the phases at the end of the winding or in the slot of the double-layer winding is not properly padded, or it is damaged due to breakdown.

(7) The winding end is too long and touches the end cover, causing a short circuit.

(8) There are spring pads and balance pads inside the motor, forming a turn to turn short circuit.