Why is it difficult to restart the motor after it shuts down and it exhibits severe overheating?

Why is it difficult to restart the motor after it shuts down and it exhibits severe overheating?

Let Germana tell you from electrical and mechanical causes：

Electrical Causes:

1.Low Power Supply Voltage: The motor can operate normally within a ±10% fluctuation range of its rated voltage. However, if the voltage drops below 90% of the rated voltage, the motor will have difficulty starting and will overheat severely. Causes of low power supply voltage include abnormal grid voltage, overloaded transformers, long power line distances with insufficient cross-sectional areas, and more.

2.Phase Loss Operation: Phase loss is a major cause of motor winding burnout and should be given special attention. Installing a comprehensive motor protector can prevent the hazards of phase loss. There are many causes of phase loss, such as high-voltage phase loss in the transformer, internal breaks in the power lines, burnt switch terminals, poor contact of switch contacts, poor contact of contactor contacts, burnt motor terminals, and a single phase winding break in the motor.

3.Damaged Starting Capacitor in Single-Phase Motor: The starting capacitor is connected in series with the starting coil circuit. A decrease in capacitance will cause the motor to have insufficient starting power or be unable to start at all. When replacing, choose a capacitor with the same voltage and capacitance.

4.Inter-Turn Short Circuit in Motor Winding: This reduces the starting torque of the motor. There are two inspection methods: one is to measure the resistance with a bridge, where the phase with the lower resistance indicates a short circuit; the other is the three-phase current balance method, where a welding machine is used as the power source to pass low voltage, high current through the three-phase winding, with the phase having a higher current than the other two indicating a short circuit.

Mechanical Causes:

1.Mechanical Locking: This fault is easier to diagnose if the motor and machinery are not rigidly connected. If they are rigidly connected, it is more difficult to determine. The approach should be from easy to difficult, first checking for electrical causes and ruling them out before treating it as a locking issue.

2.Seized Motor Bearings: The main causes of seizure are lack of lubrication or the presence of impurities in the bearings. To prevent this fault, it is essential to adhere to regular inspection and maintenance schedules for the motor.

3.Unilateral Magnetic Pull in the Motor: This can be caused by severe bearing wear or misalignment of the end covers on both sides, resulting in uneven stator-rotor gaps. The magnetic field density is lower where the gap is larger and higher where the gap is smaller. Once powered on, the rotor is "pulled" to the area of higher magnetic field density and smaller gap, preventing the motor from starting. This fault can be diagnosed by visually inspecting the degree of bearing wear and end cover displacement. If these are not obvious, use a feeler gauge to check the stator-rotor gap.

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