Effects of High Fault Currents on Ground Grid Design

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Due to increased load demands and reduced incentives to build new transmission lines, energy companies are increasing power flows on the existing transmission assets, which will increase the fault current levels (for both three-phase and phase-to-ground faults) throughout the power system. New generation sources to be added at the transmission and distribution network will increase fault current intensities. It is crucial for the users of industrial facilities to be aware of increased ground-fault current magnitude at the service entrance and of the actual condition of the grid. The protection that ground grids provide against step and touch potentials is only good up to the expected level and duration of ground-fault currents, as originally communicated by the electric utility in the design phase. In addition, thermal and mechanical stresses to the customer's ground grid and ground grid connections can increase the grid's resistance to ground and, at the same time, fault potentials. In order to prevent these problems from occurring, a ground grid assessment, utilizing field and utility updated data, should be carried out on a regular basis. This paper will illustrate a European Committee for Electrotechnical Standardization (CENELEC) approach to ground grid design, aimed to maximize the electrical safety under ground fault. In addition, case studies will be included, showing how high fault currents have damaged ground grids and what repairs are possible.