Burning out of motors is a common problem, especially those used on ships. If the motor is burnt, there will be a preliminary appearance: the motor shell is hot, there is smoke, and there is a burnt smell. We also need to measure whether the three-phase resistance of the motor is balanced, and to measure the insulation resistance of the stator winding to the ground. If the three-phase is unbalanced and the insulation to ground is zero, it can be judged that the motor has been burned out.

　　1. Overload burned

　　The typical feature is that the overall overheating of the stator winding causes a serious color change. This is a gradual process, and you can make a preliminary judgment by observing the color of the motor winding during daily maintenance.

　　The main reasons for motor overload are as follows:

　　(1) The motor bearing is damaged or jammed; the axis is not centered; the installation is eccentric; the trimming diameter and number of turns of the stator are incorrect; the wiring method is wrong; the rotor bar is broken; and the power of the dragged load does not match.

　　(2) Practical experience and instructions show that the efficiency of the motor is the maximum at 85% of the rated power. Once the motor current is greater than about 85% of the rated current, it will cause great concern, which indicates that there is a problem with the load or the motor.

　　(3) Undervoltage or overvoltage of the power supply will also cause damage to the motor to a certain extent.

　　2. Burning due to lack of phase

　　The main reasons for the lack of phase of the power supply include the lack of phase of the main power supply entering the control box, the burning of the main contactor contacts, the fracture of the terminal, the falling off of the terminal sheath, and the open circuit of the winding connection.

　　Preventive measures include regular inspection of the contact status of the main contactor, polishing or replacement, testing the contacts; tightening the wiring; testing the overload protection relay function, the setting value generally does not exceed 1.25 times the rated current.

　　3. Short-circuit between turns and phase-to-phase of the stator winding are burnt out

　　Turn-to-turn shorts and inter-phase shorts are generally caused by damage to the insulation, weak insulation, and heat caused by long-term overload, which leads to aging of the insulator, and finally insulation failure. The characteristic is that the winding is partially broken, the winding enameled wire is broken, and the port is melted and rounded.

　　4. Other reasons for burning

　　(1) The starting current of the motor is generally 5-7 times or even 10 times the rated current. The time interval between two starts and the number of starts within a certain period of time are strictly limited, and the motor cannot be started frequently.

　　(2) The start-up time is too long.

　　(3) Phenomena such as looseness between turns and cracks in the insulation have accelerated the aging speed of the insulator.

　　(4) The load does not match the motor, and the motor output power is insufficient

　　(5) When the motor is repaired, the insulation level of the enameled wire is reduced, the number of turns is reduced or increased, and the wire diameter is wrong, which can easily cause the motor to overheat and burn.

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