Winding resistance testing reveals problems you cannot see from the outside: loose connections, deteriorating contacts, shorted turns and issues inside on-load tap changers (OLTCs). These faults increase heating, create imbalance and shorten transformer life.
Megger transformer ohmmeters deliver stable test currents up to 100 A, helping the core reach saturation quickly so measurements settle fast. With automated OLTC measurements and dynamic resistance recording, you can see transition issues and contact wear early—before they turn into failures.
Whether you’re commissioning a new transformer, checking for transport damage or carrying out routine maintenance, winding resistance testing gives you a clear picture of what’s happening inside the active part.
Winding resistance tests should be performed:
Many transformer issues cause a change in DC winding resistance, making this an essential diagnostic tool.
No. A ripple test measures how much current dips during a tap change and expresses it as a percentage. It gives a general indication of transition behaviour but not detailed timing or resistor values.
DRM, on the other hand, records current and/or voltage continuously during the tap change. This reveals:
DRM is a much richer diagnostic.
To get stable readings, the test current should be:
Most measurements fall comfortably between these limits. Too low a current leads to noisy, inconsistent values; too high a current risks temperature rise and inaccurate readings.
Winding resistance is measured by injecting DC into a transformer winding and recording the stabilised voltage and current. Key steps include:
Correct setup, saturation and demagnetisation are essential for repeatable results.
Megger’s winding resistance and OLTC diagnostic tools help you assess transformer condition confidently—whether you’re commissioning, troubleshooting or performing routine maintenance. Our experts can help you choose the right instrument for your test strategy.
Profundiza en las soluciones de medida de resistencia de transformadores con nuestras completas guías.
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Winding resistance testing hasn’t changed much in the last decade — but the demands on crews have.
