"Key Points of Transformer Core Grounding and Its Composition"

Transformer cores are primarily composed of silicon steel laminations during manufacturing. To a certain extent, to reduce eddy currents, there must be a specific insulation resistance between the laminations. However, due to the extremely large inter-lamination capacitance, they can be considered electrically conductive under alternating electric fields. Therefore, grounding the core at only one point is sufficient to clamp the potential of the entire stacked core laminations to ground potential.

If the transformer core or its metallic structural components are grounded at two or more points (multiple grounding), a closed loop will be formed between the grounding points. This loop links part of the magnetic flux, inducing an electromotive force and creating a circulating current. This leads to localized overheating and can even burn out the core.

Key Points for Transformer Core Grounding:

1. Install a separate grounding lead wire for the yoke structural clamp. If the core touches the upper clamp and causes a multiple-grounding fault, the ground current would flow only within the internal structure of the core and clamps, with no current flowing through the main core grounding wire. This could lead personnel to mistakenly assume that the core is free of faults. With this separate lead installed, any contact between the core and the clamp at any position will form a closed loop through the two external grounding leads, allowing the grounding current to be accurately detected externally.

2. Position the core grounding strap in the center of the yoke's cross-section. With this placement, regardless of the location of the insulating bolts on the yoke tie rods or the exact position of the fault point, the induced voltage in the loop will be limited to only one-quarter of the turn voltage. Consequently, the grounding current will be restricted to just a few amperes, which is significantly lower than when the grounding strap is placed in other locations.