In one situation, the power cord needs to be checked. First, check the motor wiring and fuses to see if there is any damage to the wiring.
The second scenario involves unloading the motor and starting it under no-load or half-load conditions.
The third possibility is that the problem is caused by a malfunction of the towed equipment. Unload the towed equipment and look for the fault in the towed equipment.
The fourth step is to check the engagement status of each contactor, including the brushes, slip rings, and starting resistor.
In the fifth case, the start and end points of the three phases need to be re-determined, and it needs to be checked whether there are any open circuits or short circuits in the three-phase windings.
Measuring the motor terminals reveals a severe overload if the three-phase voltage is balanced and at the rated value. The inspection process involves first removing the load. If the motor's speed and sound are normal, it indicates an overload or a mechanical fault in the load. If it still doesn't turn, manually rotate the motor shaft. If it's very tight or impossible to turn, measure the three-phase current. If the three-phase current is balanced but higher than the rated value, the motor's mechanical parts may be stuck, such as insufficient lubrication of the motor shaft, rusted or severely damaged bearings, an overly tilted end cover or oil cap, or rotor rubbing against the inner bore (also called stator rubbing). If rotating the motor shaft by hand to a certain angle feels difficult or a periodic "chattering" sound is heard, it indicates stator rubbing.
The reasons are as follows:
(1) The clearance between the inner and outer rings of the bearing is too large, and the bearing needs to be replaced;
(2) The bearing bore is too large, and long-term wear causes the inner diameter to become too large. Emergency measures include electroplating a layer of metal or adding a sleeve, or punching small dots on the inner wall of the bearing chamber;
(3) Shaft bending and end cap stop wear.
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