Connection Mode of Distributed Equipotential Grounding Grid and Main Grounding Grid

Equipotential grounding grid is installed in areas where secondary equipment is concentrated, such as main control rooms and relay rooms. The connecting between equipotential grounding grid and main grounding grid is of great importance for secondary equipment. The requirements in relevant standards and regulations are accidentally vague in key points. By numerical calculations, we analyzed how the ways of distributed equipotential grounding grid and main grounding grid connection affect the voltage and current in secondary cables. By comprehensively considering the functions of the equipotential grounding grid, we put forward the connecting method of secondary and primary grounding grid, and took the measures to confine fault current in secondary cables. Research shows that, single-point connection, which can reduce the potential exerted on the secondary cables greatly, has a advantage compared with multipoint connection in the connection between equipotential grounding grid and main grounding gird. Installing drain wire can not only reduce the potential exerted on the secondary cables significantly, but also reduce the current flowing through the shielding layers of the cables. Though electric potential difference between different equipotential grounding grids in a substation can be eliminated by connecting them together with drain wire, and then connected to the main grounding grid at a single point, the method can also produce great potential difference between far-end of the equipotential grounding grid and main grounding grid. This will cause the problems such as primary equipment's insulation breakdown and high touch potential difference etc.