This guide details static mechanical performance testing, routine inspections, and visual checks for squirrel-cage three-phase induction motors, covering key standards and best practices.
1. Shaft Extension Radial Runout
• Requirement: ≤ 0.05mm (small electric motors) or ≤ 0.1mm (medium/large motors).
• Method: Measure using a dial indicator; ensure no ovality or axial movement.
2. Bearing Clearance & Lubrication
• Clearance: Radial clearance must comply with ISO 5753 (e.g., 0.01–0.03mm for deep-groove ball bearings).
• Lubrication: Grease fill: 1/3–2/3 of bearing cavity. Avoid overfilling to prevent overheating.
3. Air Gap Uniformity
• Standard: Deviation ≤ ±10% of design value (e.g., ≤ ±0.05mm for a 0.5mm design gap).
• Method: Use feeler gauges at symmetric stator points; average multiple readings.
4. Rotor Bar & End Ring Integrity
• Requirement: No cracks, broken welds, or looseness; short-circuit ring resistance deviation ≤ ±5%.
• Method: Visual inspection + acoustic check (tapping test). Use IR thermography for hotspots if needed.
1. Insulation Resistance Test
• Standard:
♦ ≤380V motors: ≥1MΩ (cold, min. 0.5MΩ).
♦ High-voltage motors: ≥1MΩ/kV.
• Tool: 500V/1000V megger; test winding-to-ground & phase-to-phase for 1 minute.
2. Dielectric Strength Test
• Voltage: 1890V AC (1s) for 690V motors; 2200V for 1000V motors.
• Pass Criteria: No breakdown/arcing; no significant post-test insulation drop.
3. Protective Conductor Continuity
• Standard: Ground resistance ≤0.1Ω at 10A for 5s.
• Tool: Ground tester; verify junction box-to-frame continuity.
1. Frame & Structure
• Check for cracks, deformation, rust. Verify end cover/frame sealing.
• Ensure fan runs quietly; vents unblocked; fins dust-free.
2. Junction Box & Wiring
• Terminals: No oxidation/looseness. Wiring: Intact insulation, clear labels.
• Verify seal gasket integrity to prevent moisture ingress.
3. Fasteners & Guards
• Bolts/nuts torqued to spec (e.g., 20–25N·m for M8). Confirm lock washers present.
• Guards securely mounted; no exposed rotating parts.
1. Key Standards (GB 14711-2013)
• Clearance: ≥1.5mm (≤750V).
• Creepage Distance: ≥2.5mm (Pollution Degree II, CTI ≥400).
2. Correction Factors
• Pollution Level: Increase distances by 20% for Degree III (dusty).
• Altitude: Increase clearance 10–20% per 1000m >2000m.
• Material CTI: Double creepage for CTI <175; prioritize CTI ≥600 materials (e.g., polyimide).
3. Measurement
• Use calipers/laser distance meters for shortest air path (clearance) and surface path (creepage).
• Note: PCB solder mask invalidates creepage distance; evaluate based on actual insulation.
1. Common Causes
• Non-standard processes (e.g., missing bearing seals, wrong bolts).
• Incomplete inspection (e.g., skipped terminal checks).
• Poor design (e.g., inadequate stator lead space).
2. Prevention
• SOPs: Use visual work instructions + dual-operator verification.
• Poka-Yoke: Asymmetric connectors/color-coded terminals.
• Automation: Real-time monitoring via torque sensors/vision systems.
Critical Focus Areas:
► Static Performance: Shaft runout, bearing clearance, air gap.
► Routine Tests: Insulation, dielectric strength, ground continuity.
► Visual Checks: Structural integrity and sealing.
► Safety Spacing: Voltage-specific creepage/clearance with environmental adjustments.
Pro Tip: Standardized workflows and error-proofing reduce assembly defects, boosting motor reliability.
