Figure 3.5-3 Logic Diagram: Sef Time Delayed Element (51Sef) - Siemens 7SR21 Manual

3.5.3 Time Delayed Sensitive Earth Fault Protection (51SEF)
Two time delayed sensitive 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.
51SEF-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 51SEF-n Char. A time multiplier is applied to the characteristic curves
using the 51SEF-n Time Mult setting. Alternatively, a definite time lag (DTL) can be chosen using 51SEF-n Char.
When DTL is selected the time multiplier is not applied and the 51SEF-n Delay (DTL) setting is used instead.
The 51SEF-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 51SEF-n Min. Operate Time setting.
A fixed additional operate time can be added to the characteristic using 51SEF-n Follower DTL setting.
Where directional elements are present the direction of operation can be set using 51SEF-n Dir. Control setting.
Directional logic is provided independently for each 51SEF-n element.
Operation of the time delayed earth fault elements can be inhibited from:
Inhibit 51SEF-n
79 SEF Inst Trips: 51SEF-n
51SEF-n VTSAction: Inhibit
51SEF-n Element
Disabled
Enabled
AUTORECLOSE
79 P/F Inst Trips
= 51SEF-n
&
79 P/F Prot'n Trip n
= Delayed
51SEF-n Dir Control
Non-Dir
Forward
Reverse
67SEF Fwd
67SEF Rev

Figure 3.5-3 Logic Diagram: SEF Time Delayed Element (51SEF)

©2010 Siemens Protection Devices Limited
A binary or virtual input, or function key
When 'delayed' trips only are allowed in the auto-reclose sequence
(79 SEF Prot'n Trip n = Delayed).
Operation of the VT Supervision function (7SR22).
Inhibit 51SEF-n
&
51SEF-n Dir En
I
4
I
5
51SEF-n VTS Action
Off
Non-Dir
Inhibit
VT Fail
&
1
&
7SR21 & 7SR22 Argus Description of Operation
51SEF-n Setting
51SEF-n Charact
51SEF-n Time Mult
51SEF-n Delay (DTL)
51SEF-n Min Operate Time
51SEF-n Follower DTL
51SEF-n Reset
c
Pickup
(7SR21)
(7SR22)
(I )
SEF
If directional elements are not present this block is
omitted and the '51SEF-n Dir En' signal is set TRUE.
&
&
General Pickup
trip
51SEF-n
&
1
51SEF-n Dir En
Chapter 1 Page 37 of 71