Transformer Winding Resistance Test Report

Transformer winding resistance testing is a foundational commissioning and maintenance measurement — it verifies tap changer contact integrity, detects high-resistance connections or turn-to-turn faults, and establishes a baseline for trend analysis over the transformer's service life. Getting the measurement right requires the correct test configuration for the winding arrangement, temperature correction applied consistently, and phase balance evaluation against meaningful acceptance criteria. This tool addresses all three. A three-step Configuration Wizard guides setup: Step 1 selects phase configuration (3-phase or single-phase), Step 2 selects winding configuration using IEC designations (Delta-Wye Dyn, Wye-Delta Ynd, Delta-Delta Dd, Wye-Wye Yyn), and Step 3 specifies the number of tap positions (1–33). Configuration presets provide one-click setup for the four common transformer vector groups. Custom groups can be added for non-standard or split-winding configurations. Measurement units are selectable as microhms (μΩ) or ohms (Ω). The record captures job and site information, standard and acceptance threshold basis (project/manufacturer, NETA ATS-2025, NETA MTS-2023, or custom), nameplate data including insulating medium (mineral oil, FR3, dry/air) and winding material (copper or aluminum), test instrument and calibration information, test current and validation data, and ambient and winding temperature for correction. Temperature correction follows IEEE C57 using the 234.5 constant for copper (225 for aluminum) and corrects measurements to a user-selected reference temperature of 75°C or 20°C. Phase balance analysis evaluates measurements using either maximum deviation from average or maximum pairwise percentage difference methods. The Trend Comparison section imports prior test data from JSON (factory or previous field test) and computes deviation to highlight resistance increases indicative of deterioration. A Test Procedure Checklist and Comments/Deficiencies/Exceptions section complete the record. Data saves to localStorage, exports and imports as JSON, and prints to PDF.

Example data — not a real field report

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• 01Configure the winding resistance test matrix for any transformer vector group (Dyn, Ynd, Dd, Yyn) using the wizard or presets, specifying the correct number of tap positions
• 02Record winding resistance measurements in μΩ or Ω for HV and LV windings across all tap positions and phases
• 03Apply IEEE C57 temperature correction using the 234.5 constant (copper) or 225 (aluminum) to normalize measurements to a 75°C or 20°C reference temperature
• 04Evaluate phase balance using maximum deviation from average or pairwise percentage difference methods and identify readings that exceed acceptance thresholds
• 05Import prior test data (factory acceptance test or previous field measurement) from JSON and compute deviation to identify resistance increases indicative of tap changer or winding deterioration
• 06Complete the test procedure checklist, document deficiencies or exceptions, export the record to JSON for trending, and print the formatted report

Record readings across taps and phases and evaluate consistency.

No sign-in required. Progress is saved on this device.

• —Not a design document, stamped calculation, or approval record.
• —Not a substitute for engineering analysis by a licensed professional.
• —Not an accredited test report — it is a NETA-aligned educational field workflow, and acceptance decisions stay with the responsible test organization.
• —Not connected to live equipment and not a safety device.