7SR224 Argus Description of Operation
3.4.3 Time Delayed Sensitive Earth Fault Protection (51SEF)
Four elements are provided 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.
For the directional elements 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
A binary or virtual input, or function key
79 SEF Inst Trips: 51SEF-n
When ‘delayed’ trips only are allowed in the autoreclose sequence
(
79 SEF Prot’n Trip n
=
Delayed
).
51SEF-n VTSAction: Inhibit
Operation of the VT Supervision function.
If the I
4
input is used for SEF, REF cannot be used.
Figure 3.4-3 Logic Diagram: SEF Time Delayed Element (51SEF)
©2010 Siemens Protection Devices Limited
Chapter 1 Page 28 of 70