Time Delayed Derived Earth Fault Protection (51N); Figure 3.3.2-1 Logic Diagram: Derived Instantaneous Earth Fault Element - Siemens Argus 7SR21 Technical Manual

50N-n Inrush
Action
Off
Inhibit
&
81HBL2
AUTORECLOSE
79 P/F Inst Trips
= 50N-n
&
79 P/F Prot'n Trip n
= Delayed
50N-n Dir
Non-Dir
Forward
Reverse
67N Fwd
67N Rev
Figure 3.3.2-1
3.3.3

Time Delayed Derived Earth Fault Protection (51N)

Two time-delayed derived earth fault elements are provided in the 7SR21 relay. Four elements are provided in the
7SR22 relay e.g. giving the option of using two elements set to forward and two to reverse.
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 Delay (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 configured as an ANSI characteristic
an ANSI (DECAYING) reset. If ANSI (DECAYING) reset is selected for an IEC characteristic, the reset will be
instantaneous. 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.
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50N-n Element
Disabled
Enabled
Inhibit 50N-n
Inhibit 50N-n
&
50N-n Dir En
IL1
I
N
IL2
IL3
&
&
Logic Diagram: Derived Instantaneous Earth Fault Element
7SR210 & 7SR220 Description of Operation
50N-n
Setting
c
>
If directional elements are not present this block is
50N-n VTS Action
omitted and the '50N-n Dir En' signal is set TRUE.
Off
Non Dir
Inhibit
&
VT Fail
1
General Pickup
General Pickup
50N-n Delay
50N-n
50N-n
&
1
50N-n Dir En
&
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