Time Delayed Sensitive Earth Fault Protection (51Sef); Figure 3.4-3 Logic Diagram: Sef Time Delayed Element (51Sef) - Siemens 7SR224 Technical Manual

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
79 SEF Inst Trips: 51SEF-n
51SEF-n VTSAction: Inhibit
If the I input is used for SEF, REF cannot be used.
4

Figure 3.4-3 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 autoreclose sequence
(79 SEF Prot'n Trip n = Delayed).
Operation of the VT Supervision function.
7SR224 Argus Description of Operation
Chapter 1 Page 28 of 70