Time-Delayed Overcurrent (51/51G/51N) - Siemens Reyrolle 7SR45 Argus Device Manual

5.3

Time-Delayed Overcurrent (51/51G/51N)

The 51-n characteristic element provides a number of time/current operate characteristics. The element can be
defined as either an Inverse Definite Minimum Time Lag (IDMTL) or Definite Time Lag (DTL) characteristic. If
an IDMTL characteristic is required, then IEC, ANSI/IEEE, and a number of manufacturer-specific curves are
supported.
The IDMTL characteristics are defined as Inverse because the tripping times are inversely proportional to the
fault current being measured. This is suitable for grading studies and important in operating the relay which is
close to the fault. Discrimination can be achieved with minimized operating time.
To optimize the grading capability of the relay extra time multiplier, Follower DTL or Minimum operate time
settings can be applied.
[dw_IEC-NI-curve_with_time-muliplier_followe-DTL, 1, en_US]
Figure 5-4
Reyrolle, 7SR45, Device Manual
C53000-G7040-C101-2, Edition 09.2020
IEC NI Curve with Time Multiplier and Follower DTL Applied

5.3 Time-Delayed Overcurrent (51/51G/51N)

Applications
95