How is the measurement of winding resistance conducted?

When measuring winding resistance, both the bridge method and voltage drop method are employed. For resistance values exceeding 100, a single-arm bridge is utilized, while for values below 102, a double-arm bridge is employed. In the voltage drop method, a power source consisting of a 2-12V battery is used, and the connections of the voltmeter and ammeter are directly attached to the terminals of the winding under test. During the measurement process, it is essential to wait for the current to stabilize before connecting the voltmeter and, prior to cutting off the power supply, disconnect the voltmeter to obtain the measured resistance value (R = UfI).

To ensure measurement accuracy, the measurement of winding resistance should be carried out under conditions where the winding temperature (θ) is consistent with the ambient temperature. Additionally, the current passing through the winding should be less than 20% of the rated current to prevent errors caused by heating. The final measured value (R) should be converted to the reference temperature using the temperature conversion coefficient (K). For oil-immersed transformers, the reference temperature is 75°C, and for dry-type transformers, the average permissible temperature rise of the winding is increased by an additional 20°C above the insulation heat resistance class.

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