1. Problem description and scope
Overheating in industrial electric motors is one of the most critical failures that compromises the useful life of the windings, the lubrication system and, finally, the mechanical integrity of the motor. This phenomenon is classified as a high severity anomaly that requires immediate intervention to prevent catastrophic failures. This manual addresses the systematic diagnosis of squirrel cage induction motors, common in pumping, ventilation and industrial transportation applications.
2. Safety precautions
WARNING: Failure to follow safety protocols can result in serious injury or death.
- It is mandatory to apply Lockout Tagout (LOTO) procedures before performing any physical inspection, opening terminal boxes or measuring inside the motor.
- Wear appropriate personal protective equipment (PPE): dielectric gloves, safety glasses, antistatic footwear, and arc flash resistant clothing per NFPA 70E.
- Be cautious with energy stored in capacitors or inertial mechanical loads.
3. Diagnostic tools required
| Tool | Specification/Model | Rank | Purpose |
|---|---|---|---|
| thermal imaging camera | Min resolution 320x240, -20°C to 600°C | -20°C to 600°C | Detection of hot spots in casing and connections |
| True-RMS Multimeter | CAT IV 600V / CAT III 1000V | Accuracy 0.05% | Voltage and current measurement |
| vibration analyzer | Piezoelectric accelerometer | 10Hz to 10kHz | Bearing and misalignment diagnosis |
| Current clamp | True-RMS, min. 1000A | 10mA to 1000A | Current imbalance analysis |
4. Initial checklist
| Observation | Action | Registration |
|---|---|---|
| Environmental conditions | Check room temperature and ventilation | °C |
| engine load | Compare measured current vs. nominal plate | Amps |
| Alarm history | Check thermal relays and PLC registers | Events |
| Cleaning | Inspect obstructions in air inlets | visual |
5. Systematic diagnostic flow
The diagnosis follows a logic of exclusion:
- External Thermal Analysis: IF casing temperature > 85°C, THEN perform thermography on bearings and connections. IF hot connections -> Cause: Loose connection. IF hot bearings -> Cause: Mechanical failure.
- Electrical Analysis: IF balanced but high temperatures -> Measure current per phase. IF imbalance > 2% -> Cause: Supply or winding problem.
- Mechanical Analysis: Normal electrical IF -> Check vibrations. IF high vibration (RMS > 4.5 mm/s) -> Cause: Misalignment or mechanical imbalance.
6. Failure cause matrix
| Symptom | Probable causes (Ranking) | Test | Expected result |
|---|---|---|---|
| Total overheating (winding) | 1. Overload, 2. Voltage imbalance | Measure current phase by phase | Rated current ±2% |
| Heating in the bearing area | 1. Lack of lubrication, 2. Misalignment | Vibration analysis | Standard spectrum profile |
| Hot terminal connection | 1. Loose terminal, 2. Corrosion | Visual inspection/thermography | Same at room temperature |
7. Root Cause Analysis (RCA)
Insulation degradation: Excessive heat accelerates the aging of insulating materials (class F/H). Every 10°C above the nominal limit reduces motor life by half.
Voltage imbalance: An imbalance of just 3% in the phases causes an 18% increase in the winding temperature due to reverse sequence currents.
8. Step-by-step resolution procedures
- Correct current imbalance: Check connections in terminal box. Tighten to specified torque (e.g. M8: 20 Nm).
- Mechanical alignment: Use laser aligner. Maximum angular misalignment tolerance < 0.5 mrad.
- Ventilation cleaning: Clean deflectors and air inlets. Eliminate waste that impedes thermal flow.
9. Preventive measures
| Cause | Strategy | Monitoring | Interval |
|---|---|---|---|
| Obstruction | Periodic cleaning | Visual inspection | Monthly |
| Overload | Load adjustment/PLC | Current monitoring | Continuous |
| Wear | Preventive lubrication | Vibration analysis | Quarterly |
10. Spare parts and components
| Description | Specification | When to replace | UNITEC Category |
|---|---|---|---|
| Bearings | SKF/NSK C3 series | Every 20,000 hrs | Mechanics |
| fan | Polyamide material | If it has cracks | Ventilation |
| Coupling | flexible type | When detecting recurrent misalignment | Transmission |
To purchase certified spare parts, consult our catalog at: https://www.unitecd.com/e-catalog/
11. References
- UNE-EN 60034-1: Rotating electric machines.
- IEC 60085: Thermal classification of insulating materials.
- OEM maintenance manuals corresponding to the engine manufacturer.
