Time Delayed Derived Earth Fault Protection (51N) - Siemens 7SR10 Argus Series Manual

3.2.3

Time Delayed Derived Earth Fault Protection (51N)

Two time delayed derived earth fault elements are provided in the 7SR1002/7SR1003 relay and four elements are
provided in the 7SR1004 relay.
51N-n Setting sets the pick-up current level.
A number of shaped characteristics are provided. An inverse definite minimum time (IDMT) characteristic is
selected from IEC and ANSI curves using 51N-n Char. A time multiplier is applied to the characteristic curves
using the 51N-n Time Mult setting. Alternatively, a definite time lag delay (DTL) can be chosen using 51N-n
Char. When definite time lag (DTL) is selected the time multiplier is not applied and the 51N-n Delay (DTL)
setting is used instead.
The 51N-n Reset setting can apply a definite time delayed reset, or when the operation is configured as an IEC
or ANSI or user characteristic if the reset is selected as IEC/ANSI (DECAYING) reset the associated reset curve
will be used. The reset mode is significant where the characteristic has reset before issuing a trip output – see
'Applications Guide'
A minimum operate time for the characteristic can be set using the 51N-n Min. Operate Time setting.
A fixed additional operate time can be added to the characteristic using the 51N-n Follower DTL setting.
Where directional elements are present the direction of operation can be set using 51N-n Dir. Control setting.
Directional logic is provided independently for each 51N-n element e.g. giving the option of using two elements
set to forward and two to reverse.
Operation of the time delayed earth fault elements can be inhibited from:
Inhibit 51N-n
79 E/F Inst Trips: 51N-n
51N-n Inrush Action: Block
51N-n VTSAction: Inhibit
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51N-1, 51N-2, (51N-3 & 51N-4 – 7SR1004)
A binary or virtual input.
When 'delayed' trips only are allowed in the auto-reclose sequence
(79 E/F Prot'n Trip n = Delayed).
Operation of the inrush current detector function.
Operation of the VT Supervision function.
7SR10 Description of Operation
Chapter 1 Page 32 of 77