Method of measuring transformer DC resistance

(1) Electric bridge method. Two types of bridges are commonly used: single-arm bridge (Wheatstone bridge) and double-arm bridge (Kelvin bridge). When the resistance is greater than 0.19Ω, a single-arm bridge is used, and when the resistance is less than 0.1Ω, a double-arm bridge is used. This method is gradually replaced by a transformer DC resistance tester.

(2) Voltage and current method. This method uses voltmeter and ammeter to measure, and the accuracy of the meter head is not less than 0.5. It should be noted that in order to ensure the accuracy of the measurement, the measuring point of the ammeter should be placed on the power side of the voltmeter when measuring small resistances, and the measuring point of the voltmeter should be placed on the power side of the ammeter when measuring large resistances.

(3) Use a dedicated transformer DC resistance tester to measure. Since the transformer is a large inductance device, it is both a resistive element and a capacitive device. In the DC circuit, the RCL circuit will have a transition process when it is closed and opened, and it takes a long time to reach a stable state, that is to say, it takes a long time to test a stable DC resistance value. The larger the capacity of the transformer, the longer the test will take. Only in this way can the accuracy of the test value be guaranteed.