Protection plan for medium-voltage public distribution networks - Recent developments and electrotechnical additions

The principles behind the construction of a protection plan for a medium-voltage public distribution network are described in [D 4 811] . The following file [D 4 812] describes how to implement it, on the one hand by using very simple overcurrent protection devices, and on the other hand by showing the difficulties of detecting earth faults, particularly in the case of networks with compensated neutral.

The recent development of large-scale decentralized generation connected to medium-voltage grids has brought with it new constraints, particularly in terms of voltage and power flow. While the detection of ground faults is not affected, the detection of polyphase faults cannot always be satisfied with simple overcurrent protection: a directional criterion must sometimes be added. Fault location using fault passage indicators is a new element to be taken into account when constructing protection plans, as it facilitates network reconfiguration after one or more fault trips. It is useful to be familiar with the operating principles of all types of directional protection to identify their fields of application and their limits.