Common causes of errors in winding resistance measurements include:
Temperature Variability: Transformer windings are sensitive to temperature changes, as resistance values in copper and aluminum windings increase with temperature. Accurate testing requires recording the temperature and adjusting resistance values to a reference temperature, typically 20°C. Without this adjustment, the actual resistance value can differ significantly from readings taken at different temperatures, leading to misdiagnosis.
Loose or Contaminated Contact Connections: Connections between the test leads and the transformer terminals need to be secure and clean. Any looseness, oxidation, or dirt at the contact points increases contact resistance, which can distort measurement results. Regularly cleaning connections and ensuring a tight fit reduces these potential inaccuracies.
Residual Magnetism in Transformer Core: Magnetic properties in the core, especially from recent operations or high current flow, can introduce residual magnetism. This affects current flow within the windings during testing, leading to inconsistent resistance values. Demagnetizing the transformer core or allowing it to stabilize after shutdown can help mitigate this.
Inadequate Stabilization or Settling Time: When current is first applied, the initial readings might be unstable until the current reaches a steady state throughout the windings. Taking readings too soon after applying current can capture these transient values, leading to inaccurate results. Allowing time for full current stabilization in the winding is essential for precise measurements.
Environmental Factors: High humidity, dust, and temperature fluctuations in the testing environment can impact the winding resistance tester’s performance and transformer conditions, especially if these factors introduce moisture into the windings or affect instrument calibration. Testing in a controlled environment can help reduce these influences.
Tester Calibration and Instrument Quality: Regularly calibrated testers are crucial for accurate readings. Lower-quality or uncalibrated testers might introduce their own error margin, especially with fluctuating test currents or less sensitive components. High-quality, well-maintained instruments with recent calibration documentation help to ensure measurement accuracy.
Addressing these factors improves reliability in winding resistance measurements, supporting better identification of potential transformer faults like internal winding damage, poor connections, and insulation issues
Nov 06,2024
