Gn 51N-n Follower DTL
Default setting: 0.00 s
This setting allows an additional time to be added to that achieved by the selected characteristic curve. It is
applied as a DTL time after the operate state from the curve is achieved. With this setting, the whole curve is
shifted linearly on the time axis by this additional definite time.
This is traditionally used with recloser systems only and otherwise is recommended to be left at the default
setting of 0 s.
Gn 51N-n Reset
Default setting: 00 s
The reset parameter is used to define whether the element pickup resets to 0 instantaneously when the
current falls below the setting or whether a reset curve characteristic or fixed DTL is applied. This operation is
significant during intermittent faults where an induction disc device would be partially rotated when the fault
current is re-applied.
Parameter Value Description
IEC/ANSI Decay
This selection applies a resetting curve to the element pickup to provide
emulation of an induction disc device. The standard IEC curve is applied if
the operating Char is an IEC Characteristic and the ANSI reset curve is
applied for an ANSI operating Char. Select this setting if the device is coor-
dinated with electromechanical devices or other devices which perform a
disc emulation reset.
00 s
Use this setting for an instantaneous reset of the element. When the current
falls below the setting the pickup will instantaneously reset completely and
subsequent increase in current above setting will restart the operation delay
from 0.
01 s – 60 s
The percentage operated state is retained when the current falls below the
setting for a period of the set delay. Subsequent increase in current to
above setting within the set delay will allow operation to resume from the
partially operated state instead of 0.
Gn 51N-n Inrush Action
Default Setting: Off
High levels of inrush currents into reactive components such as transformers when they are switched can
result in operation of elements. The inrush current can be detected by a high percentage of 2nd harmonic
current content by the 81HBL2 element. This can be configured to inhibit the element automatically by config-
uration of this setting.
Parameter Value
Description
Off
The earth fault element is not affected by operation of the 81HBL2 element.
Inhibit
The earth fault element is inhibited by operation of the 81HBL2 element
and automatically released when the 81HBL2 element resets.
Settings Example
The 51N-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 and ANSI/IEEE curves are supported. IDMTL characteristics are
defined as inverse because their tripping times are inversely proportional to the fault current being measured.
This makes them particularly suitable to grading studies where it is important that only the relay(s) closest to
the fault operate. Differentiation can be achieved with minimized operating times. Refer to 5.3 Time-Delayed
Overcurrent (51/51N) for more details.
Functions
3.5 51N Time-Delayed Earth Fault – Derived
Reyrolle, 7SR46 Device, Manual 53
C53000-G7040-C103-1, Edition 10.2022
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