Measuring DC resistance is an important item in transformer test. Through measurement, the conductive circuit of the equipment can be checked for defects such as poor contact, poor welding, coil failure and wiring error. In the actual measurement of medium and small power supply transformers, the DC bridge method is mostly used. When the resistance value of the tested coil is more than 1 ohm, it is generally measured with a single arm bridge, and when the resistance value is less than 1 ohm, it is measured with a double arm bridge. When using double arm bridge for wiring, the potential pile head of the bridge shall be close to the measured resistance, and the current pile head shall be connected to the potential pile head. Before measurement, the resistance value of the coil to be measured shall be estimated first, the bridge multiplying button shall be placed at an appropriate position, the non measured coil shall be short circuited and grounded, the power switch shall be turned on for charging, the galvanometer switch shall be pressed after sufficient power is supplied, and the measuring arm shall be adjusted rapidly to make the galvanometer pointer move towards the zero line in the middle of the galvanometer scale for fine adjustment, and the resistance value shall be recorded when the pointer stops at the zero position stably, Measured coil resistance=multiplying factor × Measure the resistance of the arm. After the measurement, open the galvanometer button first, and then release the power switch.
matters needing attention:
During measurement, in addition to strictly complying with electrical safety regulations and equipment test regulations, special attention shall be paid to:
1) When the coil temperature is stable, the temperature difference between the upper and lower parts of the transformer oil tank shall not exceed 3 ℃;
2) As the transformer coil has inductance, the charging current during measurement is not very stable, so it must be counted after the current is stable. If nece