(1) Description of Operation 7SR224
©2009 Siemens Protection Devices Limited Page 29 of 66
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 auto-reclose
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)
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