Austin Bonnett
EASA Education and Technology Consultant
Gallatin, MO
In the paper "The Most Unlucky Things That Can Happen To A Customer’s Motor," presented at the EASA Convention 2004, Austin Bonnett explores the common causes of motor failures and provides insights into how these failures can be predicted, prevented, and repaired. The paper emphasizes the importance of understanding the root causes of motor failures, which are often predictable, repeatable, and preventable.
Bonnett outlines a methodology for identifying the root causes of motor failures, which includes examining the failure mode, failure pattern, appearance, application, and maintenance history. He stresses the importance of recording critical data and measuring results to benchmark performance and make necessary upgrades or revisions.
The paper identifies the most common sources of motor problems, including issues with bearings, stators, rotor cores, shafts, misalignment, and other factors. Bearing problems are often caused by improper lubrication, contamination, and excessive vibration and shock. Improper lubrication can result from using too much or too little lubricant, incompatibility of lubricants, or using the wrong type of lubricant. Contamination can occur due to moisture, foreign materials, and corrosion, leading to bearing damage. Excessive vibration and shock can be caused by rotor unbalance, coupling unbalance, system unbalance, sudden stops or loading, and environmental influences.
Stator problems are typically related to thermal overload, severe electrical abnormalities, and contamination of the insulation system. Thermal overload can result from horsepower overload, excessive ambient temperatures, load cycling, too many starts, or failure to accelerate. Electrical abnormalities include overvoltage, undervoltage, unbalanced voltage, single phasing, transients, and partial discharge. Contamination of the insulation system can be caused by moisture, condensation, abrasion, and foreign materials.
Rotor core failures are often due to poor geometry, out of balance, defective or damaged squirrel cages, and improper joining of bars to end rings. Common shaft failures include metal fatigue, rotational bending, torsional bending, extreme temperatures, residual stress, and environmental factors. Misalignment issues can arise from problems with the motor, coupling, driven equipment, mounting base, and other factors.
Bonnett also discusses other frequent causes of motor failures, such as misapplication, misuse, inappropriate repairs, alteration of the cooling system, hazardous terminal boxes, and coupling failures. He emphasizes the importance of proper maintenance and monitoring to prevent these failures and ensure reliable motor operation.
Key Points Covered:
- Root cause methodology for identifying motor failures
- Common sources of motor problems, including bearings, stators, rotor cores, shafts, and misalignment
- Causes of bearing problems, such as improper lubrication, contamination, and excessive vibration and shock
- Stator problems related to thermal overload, electrical abnormalities, and contamination
- Rotor core failures due to poor geometry, defective squirrel cages, and improper joining of bars to end rings
- Common shaft failures, including metal fatigue, rotational bending, torsional bending, and residual stress
- Misalignment issues and other frequent causes of motor failures
Key Takeaways:
- Motor failures are often predictable, repeatable, and preventable.
- Understanding the root causes of motor failures is essential for effective troubleshooting and repair.
- Proper lubrication, contamination prevention, and vibration control are crucial for bearing health.
- Thermal overload, electrical abnormalities, and contamination are common causes of stator problems.
- Rotor core failures can result from poor geometry, defective squirrel cages, and improper joining of bars to end rings.
- Shaft failures are often due to metal fatigue, rotational bending, torsional bending, and residual stress.
- Misalignment and other factors can lead to motor failures, emphasizing the importance of proper maintenance and monitoring.
To read the full technical paper and view the slides, download the PDF below.
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