What are the two main reasons for motor difficulty in restarting after shutdown and heat generation?
Recently, many customers have been asking: what causes difficulty in restarting a motor after shutdown and the occurrence of overheating? Today, we will provide some answers.
Actually, there are two main reasons for this situation:
1. Electrical Reasons
1. The power supply voltage is too low. The motor can operate normally when the power supply voltage fluctuates within ±10% of the rated voltage. If it falls below 10% of the rated voltage, the motor will struggle to start and overheat severely. Abnormal grid voltage, transformer overload, excessively long power line distance, and insufficient cross-sectional area can all cause the power supply voltage to drop.
2. Motor phase loss operation: Phase loss is the primary cause of motor winding burnout, requiring special attention. A comprehensive motor protector can be installed to prevent the hazards of phase loss. The causes of phase loss are numerous, including high-voltage phase loss in transformers, internal power line breaks, burned switch terminal posts, poor switch contact connections, poor contactor contact connections, burned motor terminal posts, and single-phase winding breaks in motors.
3. The starting capacitor of the single-phase motor is damaged. The starting capacitor is connected in series in the starting coil circuit. A decrease in capacitance can cause weak motor startup or failure to start. When replacing, select a capacitor with the same voltage and capacitance.
4. There is an inter-turn short circuit in the motor winding, which reduces the starting torque of the motor. There are two inspection methods: one is to measure the resistance with a bridge, and the phase with lower resistance is the shorted phase; the other is the three-phase current balance method: using a welding machine as the power source, apply low voltage and high current to the three-phase windings, and the phase with current exceeding the other two is the shorted phase.
II. Mechanical Reasons
1. Mechanical stall: If the motor and machinery are not rigidly connected, this fault is relatively easy to diagnose. However, if they are rigidly connected, it is more difficult to determine. A step-by-step approach can be adopted, starting with checking for electrical causes. After ruling out electrical issues, proceed with stall troubleshooting.
2. Motor bearings seizing, primarily due to lack of lubrication or foreign matter ingress. To prevent this fault, it is essential to adhere to the regular inspection and maintenance regime for motors.
3. Unilateral magnetic pull of the motor is caused by severe bearing wear and misalignment of the two end covers, resulting in significant uneven air gaps between the stator and rotor. In areas with larger gaps, the magnetic field density is lower, while in areas with smaller gaps, the magnetic field density is higher. When the motor is powered on, the rotor becomes "stuck" in the area with smaller gaps and higher magnetic field density, preventing the motor from starting. To diagnose this fault, visually inspect the degree of bearing wear and end cover displacement. If the symptoms are not obvious, use a feeler gauge to measure the stator-rotor clearance.
