The DC resistance of the transformer winding is measured by the voltage drop method or the bridge method. Although the measurement method is very simple, there are many factors that affect the accuracy of the measurement. In order to ensure the accuracy of the measurement, the safety of the equipment and personnel of the DC resistance tester speeds up the test process. The following points should be noted during the measurement:

(1) For transformers with voltage tap connections, measurements should be made at all tap positions.

(2) When the three-phase transformer has a neutral lead, the resistance of each phase winding should be measured. When there is no midpoint lead, the resistance between the lines can be measured, and then the resistance of each phase can be calculated.

(3) The measurement must be carried out under the condition that the winding temperature is stable and the difference between the winding temperature and the ambient temperature does not exceed 3°C. When the temperature is stable, the *oil temperature of the transformer can be used as the winding temperature.

(4) Due to the large inductance of the transformer, it takes a long time for the current to stabilize. In order to measure accurately, the meter must wait for the stability indication before reading, and measures should be taken to shorten the stabilization time if necessary.

(5) Considering that there are many factors that affect the accuracy of the transformer DC resistance measuring instrument, such as the accuracy level of the instrument, the test wiring method, the accuracy of temperature measurement, the state of the connection contact and the current stability, etc., it is necessary to review the measurement before proceeding. Measure, if in doubt, please re-measure to obtain accurate measurement results.

(6) When measuring, the non-test winding should be open, not short. When measuring low-voltage windings, high voltages are induced in the high-voltage windings when the power supply is turned on and off. Attention should be paid to personal safety.

(7) Due to the large inductance of the transformer, the self-induced electromotive force is very high when the power is turned on or off. Therefore, special attention should be paid to the operation sequence to prevent damage to the instrument; when turning on the power, please turn on the power circuit first, then turn on the voltmeter or galvanometer, and then turn off the power circuit