Sensitive Earth Fault (SEF)
SEFs are low level earth faults < 80 A primary.
The SEF elements are driven by measured residual current. The residual current used for the SEF element is determined by measuring the current in the common connection between the three CT secondary currents on the PCOM board.
Residual current = A phase current + B phase current + C phase
current or
Ie= Ia+ Ib+ Ic
A SEF pickup occurs when the measured current ≥ the SEF setting current x the SEF pickup multiplier. A tripping time is calculated based on the magnitude of the fault current and the settings for the active trip and updated every sample.
Unless the fault resets, a protection trip will ensue.
SEF pickup, reset thresholds and multiplier settings are global that is they apply to all trips. Timing is determined by settings configured individually for Trips 1...4, Single Shot and Work Tag.
Configuration options for SEF protection are listed in the table below.
Table 36 SEF Protection Configuration Options
|
Phase O/C Configuration Settings |
Range/Options |
Resolution |
Default |
|---|---|---|---|
|
Global Settings |
|||
|
Setting Current |
10...1260 A |
1.0 A |
4 A |
|
Pickup Multiplier |
1.0...10.0 |
0.1 |
1.0 |
|
Reset Threshold Multiplier |
90...100% 10...100%(2) |
1.0% |
90% |
|
Per Trip Timing Settings |
|||
|
Curve Options |
|||
|
Inverse Time Curves |
3 x IEC255 Refer Appendix D 3 x IEEE Refer Appendix E 42 x TCC Refer Appendix F Up to 5 User Defined Curves |
Definite Time |
|
|
Other Curves |
Definite Time Instantaneous Only |
||
|
Inverse Time Curve Modifiers |
|||
|
Time Multiplier |
0.01...25.00 |
.01 |
1.00 |
|
Instantaneous Multiplier |
Off, 1.0...30.0 |
0.1 |
Off |
|
Minimum Time |
0.00...2.00 s |
0.01 s |
0.00 s |
|
Additional Time |
0.00...30.00 s |
0.01 s |
0.00 s |
|
Maximum Time(1) |
Off, 0.2...180.0 s |
0.1 s |
Off |
|
Other Curves |
|||
|
Definite Time |
0.01...100.00 s |
0.01 s |
1.00 s |
|
Definite Time Instantaneous Multiplier |
Off, 1.0...30.0 s |
0.1 s |
Off |
|
Instantaneous Only |
x 1.0...x 30.0 |
0.1 |
1.0 |
|
Instantaneous Minimum Time |
0.00...2.00 s |
0.01 s |
0.00 s |
| (1) This is a global setting unless Extended Minimum Time per Curve is On. | |||