Diskusjon:Impedans i jernbanenettet

Ifølge professor Hans Kristian Høidalen på NTNU er kravene til vern (i forhold til det som står i kap 1.1.4): Selectivity – Detect and isolate the faulty item only • Stability – Leave all healthy circuits intact • Sensitivity – Detect even the smallest fault • Speed – Minimize damage to components, surroundings and personnel. • Simple/inexpensive – Minimize the risk of wrong settings due to complications • Security – Dependable: Always trip when requested – Secure: Never trip when not supposed to