scope:

This part of IEC 62689 defines the minimum requirements (therefore performances) and consequent classification and tests (with the exception of functional and communication ones) for fault passage indicators (FPIs) and distribution substation units (DSUs) (including their current and/or voltage sensors), which are, respectively, a device or a device/combination of devices and/or functions able to detect faults and provide indications about their localization

By localization of the fault is meant the fault position with respect to the FPI/DSU installation point on the network (upstream or downstream from the FPI/DSU's location) or the direction of the fault current flowing through the FPI/DSU itself. The fault localization may be obtained

• directly from the FPI/DSU, or

• from a central system using information from more FPIs or DSUs, considering the features and the operating conditions of the electric system where the FPIs/DSUs are installed.

In this part of IEC 62689, the FPI/DSU classification is specified in detail, in accordance with the first "core" classification defined in IEC 62689-2, which is explicitly focused on the description of electric phenomena and electric system response during faults, considering the most widely diffused distribution system architecture and fault typologies.

Thus, IEC 62689-2 is mainly focused on helping users in the correct choice of FPIs/DSUs, whereas IEC 62689-1, IEC 62689-3 and IEC 62689-4 are mainly focused on FPI/DSU requirements, communication and testing procedures, respectively.