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"t
" is the setting [50/51SEF1.t_Op], the time setting of the SEF1 protection;
SEF1
[50/51SEF1.En] is the logic setting of the stage 1 sensitive earth fault protection;
[50/51SEF1.En1] is the binary signal for enabling the stage 1 sensitive earth fault protection;
[50/51SEF1.Blk] is the binary signal for blocking the stage 1 sensitive earth fault protection;
"50/51SEF1.Dir" denotes the status of the directional element for the stage 1 sensitive earth
fault protection, see Section 3.6.3 for more details about the directional element.
3.6.2 IDMT Sensitive Earth Fault Protection
The stage 4 sensitive earth fault protection also can be used as inverse definite minimum time
(IDMT) sensitive earth fault protection. It has the same inverse time characteristic with the IDMT
overcurrent protection (see Section 3.3.2), and the setting [50/51SEF4.Opt_Curve] can be used to
select the expected curve.
The logic diagram of the IDMT sensitive earth fault protection is shown as below. The sensitive
earth fault current block is a level detector that detects whether the current magnitude is above
the threshold.
I
> [50/51G4.3I0_Set]
01
50/51G4.Dir
50/51G4.HmBlk
[50/51G4.En]
[50/51G4.En1]
[50/51G4.Opt_Curve] = 0
[50/51G4.Blk]
Figure 3.6-2 Logic diagram of the IDMT sensitive earth fault protection
Where:
[50/51SEF4.3I0_Set] is the current setting of the stage 4 sensitive earth fault protection;
[50/51SEF4.En] is the logic setting of the stage 4 sensitive earth fault protection;
[50/51SEF4.En1] is the binary signal for enabling the stage 4 sensitive earth fault protection;
[50/51SEF4.Blk] is the binary signal for blocking the stage 4 sensitive earth fault protection;
[50/51SEF4.Opt_Curve] is the setting for selecting the inverse time characteristic curve ;
"50/51SEF4.Dir" denotes the status of the directional element for the stage 4 sensitive earth
fault protection, see Section 3.6.3 for more details about the directional element.
3.6.3 Directional Element for Sensitive Earth Fault Protection
The residual voltage is used to polarize the directional element for the SEF protection. With earth
fault protection, the polarizing signal is required to be a representative of the earth fault condition.
As residual voltage is generated during earth fault conditions, this quantity is commonly used to
polarize directional elements. The residual voltage is also derived from the 3-phase voltage input,
which are same with the directional element for the zero sequence overcurrent protection.
PCS-9611 Feeder Relay
&
IDMT
&
Date: 2014-04-08
3 Operation Theory
[50/51G4.St]
[50/51G4.Op]
3-29
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