Siemens Reyrolle 7SR45 Argus Device Manual page 96

Applications
5.3 Time-Delayed Overcurrent (51/51G/51N)
[dw_IEC-NI-curve_with_min-op-time-setting-appl, 1, en_US]
Figure 5-5
To increase sensitivity, dedicated ground fault elements are used. There must be a little or no current flowing
to earth in a healthy system, so that relays can give far lower pickup levels than relays which detect excess
current (> load current) in each phase conductor. Such dedicated earth-fault relays are important where the
fault path to ground is a high-impedance (such as in highly arid areas). Such dedicated ground fault relays are
important where the system uses high values of earthing resistor/reactance and the fault current detected in
the phase conductors is limited.
96
IEC NI Curve with Minimum Operate Time Setting Applied
Reyrolle, 7SR45, Device Manual
C53000-G7040-C101-2, Edition 09.2020