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 a few tens of ohms). Because the capacitance between the sheets is very large, it can be regarded as a pathway in the alternating electric field. The iron core is the main magnetic circuit part of a transformer. Generally, it is composed of hot rolled or cold rolled silicon steel sheets with high silicon content and coated with insulating paint. The core and the coil around it constitute a complete electromagnetic induction system. The power transmitted by the power transformer depends on the material and cross-sectional area of the iron core.

(1) Independently set an iron yoke clamp grounding lead wire. Because if the iron core encounters the upper clip to form a multi-point grounding fault, the grounding current is only in the inner activity of the iron core clip, the iron core grounding lead wire has no current flow, will cause the staff to mistake the iron core has no fault; After setting, no matter where the iron core meets the clip, it will form a loop through two external grounding leads, so that the external grounding current can be correctly detected.

(2) The iron core ground vane is placed in the middle of the iron yoke cross section. In this way, no matter where the yoke insulation bolt is and where the faulty ground point is, the maximum induced voltage of the loop is only 1/4 of the turn voltage, and the maximum ground current is only a few amperes or so, which is much smaller than when the core ground lug is placed in other directions.

(3) If the iron core ground lugs need to be placed in other directions because of inconvenient field devices, the insulation bolts and ground lugs of the iron yoke should also be placed diagonally, so as to avoid the occurrence of large current.