Thèse de doctorat
Résumé : High Impedance Faults (HIFs) are undetectable by conventional protection technology under certain

conditions. These faults occur when an energized conductor makes undesired contact with a

quasi-insulating object, such as a tree or a road. This contact restricts the level of the fault current to a very low value, from a few mA up to 75A. In solidly grounded distribution networks where the value of the residual current under normal conditions is considerable, overcurrent devices do not protect against HIFs. However, such a protection is essential for guaranteeing public security, because of the possibility of reaching the fallen conductor and the risk of fire.