Main causes and troubleshooting methods for abnormal noise or vibration in YRKK high-voltage motors are as follows:

(1) Slight short-circuiting between stator and rotor windings causes uneven internal magnetic fields, resulting in abnormal humming. In such cases, measure the three-phase DC resistance of the motor windings using a bridge and compare the values. If the values differ significantly, further inspect the windings for short circuits, locate the short-circuit point, replace the shorted winding section, or re-insulate and reinsert it into the slots. For wound-rotor motors, keep the rotor stationary with its winding open-circuited; apply rated three-phase voltage to the stator winding and rapidly measure the open-circuit voltages across the three rotor phases, comparing them against nameplate values or among themselves to locate and rectify the short-circuit point.

　　(2) During motor startup, the starting current is very high. Severe grounding can cause noise and vibration during startup, but conditions may improve after startup completes. This occurs because winding-to-ground faults result in severely non-uniform magnetic fields. Use a megohmmeter to check whether windings are grounded.

　　(3) Upon sudden phase loss, the motor operates on single-phase or two-phase supply, with one-phase ammeter reading zero (for delta-connected motors, current readings are not zero, but the three-phase currents differ markedly). Immediately shut down the machine and locate the break point.

　　(4) Non-uniform air gap causes periodic humming and even motor vibration; severe cases produce rapid knocking sounds. At this time, inspect whether the fit between end shields and base, bearings and shaft, and end shields themselves is excessively loose; verify air-gap uniformity, bearing wear beyond allowable limits, shaft bending, uniform tightening of end-shield bolts, and any protruding sections on the core.

　　(5) Continuous or intermittent ringing noise originates from the bearings—possibly due to damaged ball (or roller) cages or ingress of sand particles. Inspect and clean the bearings; repair or replace as required.

　　(6) If mounting screws for the base or other components are loose, inspect and tighten them securely.

　　(7) If the drive system is unbalanced or the rotor is unbalanced, identify the root cause and eliminate it.

　　(8) Improper installation—such as misalignment with the load center or non-compliant foundation—must be corrected.

　　(9) If dust accumulates between the fan and fan guard or between the fan and end shield, immediately shut down and remove the dust.

　　(10) After pole-changing, improper slot combination may occur; adjust coil pitch accordingly. If resolution proves difficult, reduce the rotor outer diameter by approximately 0.5 mm.