The three-phase resistance is unbalanced or there is not much difference between the measured value and the design value (factory test value). Generally speaking, the following main reasons are as follows:

1. The lead rod in the transformer bushing is in poor contact with the inner lead, and the connecting bolts between the lead rod and the inner lead of the bushing are not tight after many on-site inspections, which causes the joint to heat up.

2. The decomposition switch can contact bad society. Due to the unclean interior of the tap switch system, the electroplating fall off, and the insufficient management of the spring working pressure, the resistance of individual taps is too large and the three-phase resistance is unbalanced.

3. The low-voltage winding of the large-capacity transformer adopts double-spiral or quad-spiral, resulting in unbalanced resistance between the windings of each phase.

4. Poor welding work. Due to poor quality control of the lead wire and winding welding technology, the resistance at the student contact is too large, or one or several strands of the multi-strand parallel winding are not welded, resulting in a high resistance.

5. Wrong measurement system wiring and experimental research methods.

The error measurement wiring and test methods that cause resistance imbalance are usually:

1. The charging time management is not enough, and the measured value is read when the current is not stable.

2. The measurement wiring and the transformer wiring are not in the right position, that is, the voltage lead is located outside the current lead or the same position as the current lead, so that the resistance at the contact is included in the measurement value.

3. When measuring and studying a certain winding, the other windings of the enterprise were not disconnected from the grounding body, which caused unstable charging system.