When cleaning: Dust, oil, grit, and moisture may appear. Oil can attack insulating varnish, and an oil-soaked motor can burn out.

When moisture is present: Humidity on iron and copper can lead to oxidation, resulting in increased heating and resistance, and eventual failure.

When tightness occurs: High speed movements cause wear and imbalance of moving parts, leading to vibrations.

When there’s stressing of bearings and races: Repeated stressing results in bearing failure and fatigue of the metal. The higher the load, the higher the stress, and the shorter time until the bearing fails.

When windings are experiencing operating interruptions/failure: Causes usually include insulation deterioration, accumulation of dust and dirt, and obstruction of ventilation.

When stator windings are malfunctioning: Traced to causes like moisture, worn bearings, overloading, failing insulation, and operating single phase.

Cleaning: Check for dust, oil, grit, and moisture and ensure they’re not present; otherwise, thoroughly clean the motor and apply a fresh coating of insulating varnish.

Moisture: Maintain dry conditions at all times; keep humidity to a minimum, and maintain low moisture levels like oil from building up. Use space heaters if needed.

Tightness: During the overhaul of motors, mechanical measurements of bearing journals and bearing housings are recommended.

Bearings failure: Periodic replacement of bearings is vital for a good maintenance program.

Windings: Windings should be regularly inspected for obstruction of ventilation, accumulated dust and dirt, and insulation deterioration.

Stator windings: Periodic cleaning, oven drying, and varnishing to be carried out to fill all air spaces caused by drying and shrinkage will maintain a solid winding and provide an effective seal against moisture.

There are numerous reasons (but not limited to) that cause stator winding failure, and they include:

• High partial discharge (PD) levels leading to rapid ageing of the stator winding insulation system.
• Electric stress control coating resulting in issues like coating deterioration and bar abrasion.
• Loose coils in the slot causing load cycling and sheer stressed between the coils and stator core.
• Vibration sparking that inflicts damage on coil insulation, may result in failure in 5 years.
• Endwinding PD may slowly erode the groundwall insulation and even result in phase-to-phase stator failure.
• Inadequate support of coils in the endwinding area, resulting in white powder and fretting issues that’ll cause a high risk of a ground fault.

Premature stator winding insulation issues

Have an adequate purchase technical specification. Possible suggestions (but not limited to) include:

• Stators rated more than 6 kV should undergo a ‘black-out’ test and partial discharge test.
• Groundwall insulation system is required to pass a voltage endurance type test just like the ones mentioned in IEEE 1043 and IEEE 1553.

Rotor winding failure

Have a detailed technical specification that comprises the crucial aspects of the rotor winding design. Relying on standard specifications like API 546 is insufficient as it doesn’t include all the required details for a reliable salient pole rotor winding design.

Furthermore, it’s also key for the manufacturer to have an adequate quality assurance problem that covers component manufacture, design verification, rotor winding assembly, and final testing of the assembled motor.