Basic elements of the protection plan
Plan de protection des réseaux de distribution publique à moyenne tension

The appearance of a fault on a network will cause variations in its characteristic electrical quantities, and even in certain other associated physical quantities. By monitoring and analyzing these quantities, protection systems are able to detect the presence of a fault and take action.

Polyphase faults will generate a very significant increase in phase currents, making them relatively easy to detect. Ground faults are characterized by current "leakage", which can be detected by one of three methods:

• residual current monitoring (i.e. the sum of the three phase currents), well suited to large systems such as MV feeders;

• direct detection of a current flowing between an isolated system and earth, well suited to small-scale...