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 will flow only within the internal structure of the core and clamps. Without this separate lead, no current would flow through the main core grounding wire, potentially leading 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 maximum induced voltage in the loop will be limited to only one-quarter of the turn voltage. Consequently, the maximum grounding current will be restricted to just a few amperes, which is significantly lower than when the grounding strap is placed in other locations.

(3) If site installation constraints require placing the core grounding strap in an alternative location, the insulating bolts of the yoke tie rods and the grounding strap should be positioned diagonally opposite to each other. This arrangement helps prevent the generation of excessive circulating currents.