When the grounding resistance is technically unreasonable, the grounding resistance of a large grounding short-circuit current system can be R ≤ 5 Ω. However, according to regulations, when a grounding fault occurs, the increase in grounding potential should not exceed 2kV for control, and the grounding resistance should be designed to be no more than 0.5 Ω and 5 Ω. In practice, people often believe that a ground resistance measurement value less than 0.5 Ω is qualified, and greater than 0.5 Ω is unqualified, without recognizing the underlying mechanism and ignoring the magnitude of short-circuit current, which is inappropriate.

The essence of grounding is to control the increase of ground potential at the fault point when a grounding short circuit occurs in a substation. Therefore, grounding is an important parameter of the main grid, but not the only parameter. With the continuous increase of power system capacity, the single-phase short-circuit current value is generally large. From the perspective of safe operation, regardless of the situation, the contact potential and step voltage of the grounding grid should be checked, and isolation measures should be taken to prevent high potential external introduction when necessary. When a grounding fault occurs in the system, the generated grounding short-circuit current flows into the system grounding neutral point through three pathways. ① Overhead ground wire tower system; ② Through the grounding of the equipment and the grounding system, it flows into the neutral point of the transformer in this station; ③ After entering the ground through the grounding network, it flows back to the neutral point of the system through the earth. The decisive factor in determining the grounding resistance of the grounding grid is only the short-circuit current entering the ground. Therefore, correctly considering and calculating the short-circuit current values of each part has a great impact on the rational design of the grounding grid.

For substations with effective grounding systems above 110kV, the overhead ground wires of the lines are directly connected to the substation's outgoing line structure. When a ground short circuit occurs, a large portion of the short-circuit current is diverted through the overhead ground wire system. When calculating, the diversion effect of this portion should be considered. When a grounding fault occurs, the total short-circuit current is constant. Increasing the shunt current of the overhead ground wire will correspondingly reduce the incoming short-circuit current. Therefore, reducing the impedance of the overhead ground wire is also an important aspect to consider in grounding design. The overhead ground wire adopts excellent conductors, and the correct use of the overhead ground wire system for diversion will make the design conditions of the grounding grid more favorable. According to analysis, the grounding short-circuit current is the total grounding short-circuit current minus the shunt of the overhead ground wire, and then minus the current flowing through the neutral point of the transformer. By calculating in this way, the actual value of the grounding short-circuit current is relatively small. According to the requirement of R ≤ 2000/I, the allowable value of the grounding resistance is relatively large. At this time, controlling according to the specified value makes the design easier to meet.