Several factors can affect the accuracy of winding resistance measurements:
Temperature: Resistance measurements are temperature-sensitive. Winding resistance varies with temperature, so measurements should be corrected to a standard temperature (usually 20°C) or measured at a consistent temperature.
Test Current Stability: Fluctuations in the DC current supplied by the tester can cause inaccurate measurements. A stable, constant current is essential for reliable results.
Contact Resistance: Poor or inconsistent contact between test leads and the winding terminals can introduce extra resistance, skewing the measurements.
Lead Resistance: The resistance of the test leads themselves can add to the measured value. This is usually minimized through a 4-wire (Kelvin) measurement setup to negate the effect of lead resistance.
Magnetic Field Effects: The presence of strong electromagnetic fields near the transformer or motor can interfere with measurement readings, particularly in high-current environments.
Inductive Effects: The winding inductance can cause delays in reaching a stable resistance reading. For accurate results, it's important to wait for the current to stabilize and the inductive effects to dissipate.
Winding Saturation: High test currents can saturate the magnetic core of the transformer or motor, affecting the measurement accuracy. Selecting an appropriate test current is crucial.
Winding Configuration: Differences in the connection of winding taps, especially in transformers with tap changers, can result in varying resistance values across different taps.
By controlling these factors and following proper testing procedures, the accuracy of winding resistance measurements can be significantly improved.
Nov 06,2024
