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Distance protection (ZM)
Distance protection (ZM)
Application
The ZM distance protection function provides fast and reliable protection for overhead lines and
power cables in all kinds of power networks. For each independent distance protection zone, full
scheme design provides continuous measurement of impedance separately in three independent
phase-to-phase measuring loops as well as in three independent phase-to-earth measuring loops.
Phase-to-phase distance protection is suitable as a basic protection function against two- and
three-phase faults in all kinds of networks, regardless of the treatment of the neutral point. Inde-
pendent setting of the reach in the reactive and the resistive direction for each zone separately,
makes it possible to create fast and selective short circuit protection in power systems.
Phase-to-earth distance protection serves as basic earth fault protection in networks with directly
or low impedance earthed networks. Together with the independent phase preference logic, it
also serves as selective protection function at cross-country faults in isolated or resonantly
earthed networks.
Independent reactive reach setting for phase-to-phase and for phase-to-earth measurement se-
cures high selectivity in networks with different protective relays used for short-circuit and
earth-fault protection.
Chapter 4
Line distance
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