The DC resistance tester under UHV power can help many power workers conduct various power tests more conveniently.

By measuring the DC resistance of the transformer winding and bushing, the welding quality of the internal wire joints of the winding, the welding quality of the leads and winding joints, the tap position of the voltage tap changer and the contact between the leads and bushing, the correctness of the parallel branch connection, whether the current carrying part of the transformer is short circuited, and whether the winding is short circuited can be checked; In addition, in transformer short-circuit testing and temperature rise testing, in order to provide accurate winding resistance, it is also necessary to measure DC resistance. Therefore, the measurement of winding DC resistance is the main item of transformer testing. The handover testing standards are mandatory items;

The voltage drop method or bridge method is used to measure the DC resistance of transformer windings. Although the measurement method is simple, there are many factors that affect the measurement accuracy. It is necessary to choose appropriate instruments and measure according to relevant regulations to obtain more accurate results. Ensure the accuracy of measurements, the safety of measuring equipment and personnel, and accelerate the testing process. The precautions during measurement are as follows:

1) For transformers with voltage taps, measurements should be taken at all tap positions.

2) When a three-phase transformer has a neutral wire lead out, the resistance of each phase winding should be measured; When there is no neutral wire, the resistance between the wires can be measured and the phase resistance can be calculated.

3) The measurement must be carried out when the winding temperature is stable, and the temperature difference between the winding and the environment should not exceed 3 ℃. When the temperature is stable, the upper oil temperature of the transformer can generally be used as the winding temperature, and the measurement results can be recorded.

4) Due to the large inductance of the transformer, it takes a longer time for the current to stabilize. In order to measure accurately, it is necessary to wait for the instrument indication to stabilize before reading. Take measures to shorten the stabilization time when necessary.

5) Considering that there are many factors that affect the accuracy of DC resistance measurement, such as the accuracy level of the instrument, testing wiring method, temperature measurement accuracy, connection contact state, and current stability, it is necessary to recheck after measurement. If you have any questions, please retest to obtain accurate measurement results.

6) During measurement, all untested windings should be open circuited and not short circuited. When measuring the low-voltage winding, a high voltage will be induced in the high-voltage winding at the moment of power switching, so personal safety should be taken into account.

7) Due to the large inductance of transformers, the self induced electromotive force is very high at the moment of power on or off. Therefore, in order to prevent damage to the instrument, special attention should be paid to the operation sequence. When connecting the power supply, first connect the power circuit, then connect the voltmeter or ammeter, and finally disconnect the power circuit.

8) When measuring resistance values, the influence of leads should be corrected.

9) In order to compare with the factory value or previous measurement values, the DC resistance value measured at any temperature should be converted to the same temperature.