Key Points for Transformer Core Grounding

Install a separate grounding lead for the yoke clamps. If the core accidentally contacts the upper clamp and causes a multi-point grounding fault, the fault current will only circulate within the core and clamp assembly. Without a separate lead, no current will flow through the main core grounding lead, which may lead maintenance personnel to mistakenly believe that no fault exists. By installing a separate lead, any contact between the core and the clamp will form a loop through the two external grounding leads, allowing the grounding current to be accurately detected externally.

Position the core grounding shunt at the center of the yoke's cross-section. With this placement, regardless of the position of the insulating bolts on the yoke tie bands or the location of the fault grounding point, the maximum induced voltage in the loop will be only 1/4 of the turn voltage. Consequently, the maximum grounding current will be limited to just a few amperes, which is significantly lower than when the grounding shunt is placed in other positions.

If field installation constraints require the core grounding shunt to be placed in an alternative position, the insulating bolts of the yoke tie bands and the grounding shunt must be positioned diagonally opposite to each other to prevent the generation of excessive currents.