When the transformer is operating normally, there is an electric field between the live winding and the oil tank, and the iron core and other metal components are in the electric field. The capacitance is unevenly distributed, the field strength is different, and the iron core cannot be connected, then charging and discharging will occur, which will damage the solid insulation and oil insulation strength. The iron core must have a point of reliable connection.

The iron core is composed of silicon steel sheets. In order to reduce eddy current, there is a certain insulation resistance between the sheets (usually only a few ohms to tens of ohms). The capacitance between the sheets is very large, which can be regarded as a path in the alternating electric field. Only one point of connection in the iron core can clamp the potential of the entire stack of iron core sheets.

When the iron core or its metal components are connected at two or more points (multiple points), a closed circuit will be formed between the contacts, which will chain some magnetic flux, induce electromotive force, and form a loop, causing partial overheating and burning the iron core.

The transformer iron core can be connected normally only if it is connected at one point. That is, the iron core must be connected, and it must be connected at one point. Core failure is mainly caused by two factors: one is the short circuit caused by poor construction technology, and the other is the multi-point connection caused by accessories and external factors.

After monitoring finds that the transformer has a multi-point connection fault, the transformer can be shut down and should be shut down in time to completely eliminate the multi-point connection fault after exiting. To eliminate this kind of fault, the multi-point connection type and factors should take corresponding maintenance measures.