There are two ways of transformer core grounding, namely direct grounding and casing lead grounding. Direct grounding involves putting one end of the tinned copper sheet between the yoke laminators. When the yoke is pressed, it becomes a dead end, and the other end is bolted to the yoke clamps, because normally the yoke clamps are in direct contact with the fuel tank, which is grounded. In the case of hanging cover (hanging core), it can be disassembled at any time to measure the insulation of the core.

The lead grounding of bushing is required to measure the medium loss Angle of coil for large power transformer with electricity. The iron yoke clamp is insulated from the oil tank. After connecting the iron core to the yoke clamp with copper sheet, the lead is led out from the small insulating bushing installed at the bottom of the oil tank and then grounded outside the oil tank. At this point, the core part of the power transformer is insulated from the tank.

Transformer core grounding reason: when the power transformer is in normal operation, the iron core must have a little reliable grounding. If there is no grounding, the suspension voltage of the iron core to the ground will cause the intermittent breakdown and discharge of the iron core to the ground, and the possibility of forming the suspension potential of the iron core is eliminated after the iron core is grounded. However, when the core is grounded at more than two points, the uneven potential between the cores will form a circulation between the ground points, and cause the multi-point grounding heating fault of the core.

The ground fault of the iron core of the transformer will cause the local overheating of the iron core. In serious cases, the local temperature rise of the iron core will increase, light gas action, and even the trip accident of heavy gas action will be caused. The short-circuit fault between the iron chips caused by the burnt partial iron core increases the iron loss and seriously affects the performance and normal operation of the transformer, so that it is necessary to replace the iron core silicon steel sheet for repair. So transformers do not allow multi-point grounding and only one point grounding.