The setting depends on the required sensitivity of the protection and the type of
system earthing. In high impedance earthed systems, the residual voltage can be at
maximum rated phase-to-phase voltage, which should correspond to 200%.
In solidly earthed systems, this value depends on the ratio Z0/Z1. The required
setting to detect high resistive earth faults must be based on network calculations.
Typically it shall be lesser than 100%.
tn
: time delay of step n, given in s. The setting is highly dependent on the
protection application. The time delay must be co-ordinated with other automated
actions in the system.
1MRK 506 375-UEN A Section 9
Voltage protection
Railway application RER670 2.2 IEC 203
Application manual
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