Square hole grounding grid and long hole grounding grid refer to the shape of horizontal grounding grid. For example, the grounding grids are all n=6(n is the number of balanced areas calculated), and the long-hole grounding grid only sets balanced areas in one direction (such as X axis) to form five grids. On the other hand, the square hole grounding grid is provided with pressure equalizing belts (such as X axis and Y axis) in two mutually perpendicular directions, forming a 5×5 mesh.