Considerations into the change of the distribution power system grounding

The grounding system became an important factor in the electrification of the large power systems in the early '20s, conditioning the choice of the system operation. In recent years, the energy service to the customers and the safety of the persons has become a major concern for the electric utilities. In some contingency cases, a fault can generate a ground potential rise compromising the service quality and the field team security. In this paper, we analyse a case of study, which is the 18 kV-distribution system of the Entreprises Electriques Fribourgeoises (EEF), a private utility in West Switzerland. A methodology is proposed to identify the unacceptable ground potential rise and to limit the customer interruptions. An optimisation, based on technical and legal matters, is then carried out to determine the appropriate improvement of the existing grounding system.