This practical guide shows you how to complete a signed, QR-verified AC Induction Motor & VFD Field Diagnostic Report certificate in OhmCert Module #29 and how to troubleshoot non-compliant readings on site.

1. Step-by-Step OhmCert UI Workflow

  1. Open Module #29: Navigate to AC Induction Motor & VFD Field Diagnostic Report from the Dashboard.
  2. Load a 1-Click Standard Annex Preset: Open the blue Standard Annex banner at the top and click a preset (such as "75 kW 400 V Industrial Pump / Compressor VFD Motor (Healthy)") to populate target limits automatically.
  3. Enter Your Field Measurements: Fill in the measured inputs (Motor Rated Voltage Class (IEEE 43 Table 2), Motor Nameplate Rated Mechanical Power Pn, Motor Nameplate Full-Load Current I_FLC, Measured Terminal Voltage U_L1-L2, Measured Terminal Voltage U_L2-L3, Measured Terminal Voltage U_L3-L1, Measured Motor Phase Current I_L1, Measured Motor Phase Current I_L2, Measured Motor Phase Current I_L3, Winding DC Resistance U1-U2 (or U-V), Winding DC Resistance V1-V2 (or V-W), Winding DC Resistance W1-W2 (or W-U), Temperature-Corrected Stator Insulation R_40C, Max Bearing Housing Temperature (DE / NDE), Measured VFD Shaft-to-Frame Peak Voltage (optional)). Blank inputs stay neutral PENDING.
  4. Complete the 12-Point Checklist: Grade each item, attach photos if needed, and export the SHA-256 signed PDF certificate.

2. Worked Numerical Field Case Study

Scenario: 75 kW 400 V Industrial Pump / Compressor VFD Motor (Healthy) (IEC 60034 / NEMA MG-1) — LV 75 kW IE3 motor with shaft grounding ring, balanced phases, and 450 MOhm R_40C..

  • Motor Rated Voltage Class (IEEE 43 Table 2): LV Motor (< 1 kV - Min 5 MOhm / Recommended >= 100 MOhm)
  • Motor Nameplate Rated Mechanical Power Pn: 75 kW
  • Motor Nameplate Full-Load Current I_FLC: 134 A
  • Measured Terminal Voltage U_L1-L2: 401 V
  • Measured Terminal Voltage U_L2-L3: 398 V
  • Measured Terminal Voltage U_L3-L1: 400 V
  • Measured Motor Phase Current I_L1: 112 A
  • Measured Motor Phase Current I_L2: 115 A
  • Measured Motor Phase Current I_L3: 113 A
  • Winding DC Resistance U1-U2 (or U-V): 42.4 mOhm
  • Winding DC Resistance V1-V2 (or V-W): 42.7 mOhm
  • Winding DC Resistance W1-W2 (or W-U): 42.5 mOhm
  • Temperature-Corrected Stator Insulation R_40C: 450 MOhm
  • Max Bearing Housing Temperature (DE / NDE): 64 degC
  • Measured VFD Shaft-to-Frame Peak Voltage (optional): 2.8 Vpk

3. Engineering Troubleshooting: Corrective Actions When a Reading Fails

  1. Redistribute single-phase loads or correct upstream loose transformer/breaker lugs to bring motor terminal voltage unbalance below 1.0%.
  2. Clean and re-torque star/delta terminal links if 4-wire DC winding resistance unbalance exceeds 2.0%.
  3. Install an AEGIS microfiber shaft grounding ring and/or ceramic-insulated NDE bearing whenever VFD shaft voltage exceeds 5 Vpk.

→ Try This Worked Example Live in Module #29 (Motor & VFD Diagnostics)