In order to ensure the accuracy and credibility of the measurement data as much as possible, the transformer DC resistance tester should follow the steps below to eliminate the interference when measuring the DC resistance, if there is an imbalance, so as to avoid unnecessary losses due to misjudgment.

1) First, check the test lead clamp, the elasticity and contact surface are good, the test lead is not broken, and the influence of the test lead and the test instrument is excluded.

2) Fully stand and discharge, eliminate the influence of residual charge or induced electric potential.

3) Switch the tap switch many times, if the unbalance rate is not significantly reduced, and the unbalance rate of the DC resistance of each gear is similar, the influence of poor contact of the tap switch can basically be eliminated.

4) Perform temperature conversion for comparison with the previous test.

5) According to the data in the factory and handover reports, determine whether the unbalance rate of DC resistance exceeds the standard due to the difference in lead resistance during manufacturing.

After completing these steps, if the DC resistance still exceeds the standard, the transformer may have the following defects:

① The winding connection is not tight or the welding quality is poor;

② Internal failure of tap changer;

③ The winding or lead wire is broken;

④ Short circuit between winding layers and turns.