Motor Winding Burnt — Failure Analysis & Corrective ...

Symptoms Burnt smell/smoke; dark brown/black insulation Excessive current, trips breaker; IR 2% MCSA: Current spectrum for rotor/stator faults Thermography: Hot spot detection Possible Causes Overload: current > rated FLA — life halves per 10°C rise Phase imbalance >2%: negative-sequence currents Contamination: conductive dust/oil/moisture dV/dt spikes exceeding PDIV; cooling failure Single-phasing: motor runs on 2 phases, rapid overheat 5-Why Example Problem: Conveyor motor winding burnt after 1200h Why burnt? → Insulation carbonized > Class F 155°C limit Why overheat? → Current 115% of rated FLA Why overloaded? → Product weight 50→70 kg increased conveyor load Why undetected? → Current monitor had no alarm configured Why no alarm? → Commissioning checklist didn't require protection verification after load changes TRC: Insulation thermal degradation from sustained overload MRC: No motor sizing re-audit after product/process changes Fishbone (6M) Man: Operator bypassed tripping relay Machine: Conveyor bearing friction +30% without lubrication Method: No load change management process Material: Grinding dust contamination on winding Measurement: Current monitoring installed but alarm disabled Environment: Summer 45°C ambient reducing cooling efficiency D3 Containment Replace motor, verify <100% FLA; 100% check all conveyor motors Temporary forced-air cooling; reduce conveyor speed D5 Permanent Fix Motor relay: 95% FLA alarm, 105% trip; resize...