Electric Motor Fault by Source

Electric Motor Fault by Source

Source of Electric Motor Fault

• Age. It’s easy to blame motor failure on age, but the reality is that the unstoppable creep of time is responsible for fewer than 20% of motor failures. In fact, Cooper Bussmann says old age causes only 10% of electric motor failures.
• Bearing 51%.
• Winding 16%. We've put together a post on winding failure, with awesome photos courtesy of EASA, if you're looking for examples.
• External causes 16%. Tied with windings for almost 1 in 5 motor failures, external factors include temperature, contamination, poor maintenance, inappropriate mechanical loads and events such as flooding.
• Unknown. 1 in 10 failures are mysterious. Either no one bothered to determine why the failure occurred, so Bonnett and Yung didn’t have any data to work with, or the investigation failed to determine a cause.
• Rotor 5%.
• Shaft or coupling 2%. Shaft failure is the least common cause of motor failure. Physical damage, corrosion, improper installation and excessive loads are often the root cause.

Problem

• Transient voltage (“surges” or “spikes”)
  • Possible causes: Power factor correction capacitor banks; Adjacent loads turning on and off; Electrical storms; Power quality issues
  • Effect on motor: Degrades windings; Arcing; “Micro-jogging” from motor timing interruptions
  • Signs to look for: There may be no physical damage to motor; Excess heat ; Vibration; Noise
• Voltage imbalance
  • Possible causes: Power quality issues; Faulty circuits; High resistance connections
  • Effect on motor: Stress on each phase circuit; Insulation breakdown; Core losses
  • Signs to look for: Excessive heat; Vibration; Noise; Increased operating costs
• Current imbalance
  • Problems with leads, fuses, connections; Caused by either power supply or motor itself
  • Core losses; Torque pulsations
  • Excess heat; Vibration
• Vibration
  • Missing balance weights; Uneven mass in motor windings; Unbalanced magnetic field; Uneven mounting (“soft foot”); Shaft looseness; Shaft imbalance; Misalignment; Insufficient load
  • Bearing problems; Insulation breakdown; Broken shaft; Broken feet; Rotor damage
  • Vibration
• High operating temperature
  • Inadequate motor cooling; Wrong voltage supply; Buildup of dirt or debris in motor fins; Poor power quality; Voltage imbalance; Improper connections; Wrong motor for application
  • Reduces effectiveness of lubricants; Degrades windings
  • Motor is hot to touch; Hot spots in motor windings
• Harmonic distortion
  • Faulty power circuit; Power quality issues
  • Reduces motor efficiency; Insulation deterioration
  • Overheating; Vibration; Noise; Reduced torque; Bearing currents
• Motor overload
  • Excessive current draw; Insufficient torque
  • Damaged windings; Broken shaft; Damaged bearings
  • Overheating; Reduced torque
• Misalignment
  • Ineffective flexible coupling; Misalignment between motor drive shaft and load; Pipe strain; Uneven air gap; Bent or bowed shaft; Out-of-round rotor
  • Bearing problems; Excessive motor wear; Damage to shaft
  • Vibration of shaft; Vibration of load; High housing temperature close to bearings; High oil discharge temperature; Unusual oil leakage at bearing seals
• Moisture
  • Storing motor in a location without adequate climate control; Not using a totally enclosed fan cooled motor in a damp environment; Not positioning weep holes so water can drain from motor; Not keeping the temperature of the motor warmer than ambient air temperature
  • Corrosion of motor shaft, bearings and rotor; Insulation failure
  • Rust; Overheating
• Bearing current/shaft current
  • Leakage current from the armature windings (DC motors); Non-symmetrical magnetic fields; Induced voltage from a VFD
  • Bearing destruction
  • Noise; Overheating; Frosting of polished metal surfaces; Premature grease darkening