Siemens SIPROTEC 4 7UT6 Series Manual page 94

Functions
2.2 Differential Protection
[diff-stromdefinition-020926-rei, 1, en_GB]
Figure 2-20
•
Through-flowing current under undisturbed conditions or external fault:
flows into the protected zone, Ι
Ι
1
of signs, therefore Ι
moreover |Ι
= |Ι + Ι
Ι
diff 1
= |Ι | + |Ι
Ι
stab 1
No tripping effect (Ι
•
Internal short-circuit, e.g. fed with equal currents each side:
The following applies Ι
= |Ι + Ι
Ι
diff 1
= |Ι | + |Ι
Ι
stab 1
Tripping effect (Ι
•
Internal short-circuit, fed from one side only:
The following applies Ι
= |Ι + Ι
Ι
diff 1
= |Ι | + |Ι
Ι
stab 1
Tripping quantity (Ι
current.
This result shows that for internal fault Ι
with the slope 1 (45°) in the operation diagram (dash-dotted fault characteristic in
94
Definition of current direction
leaves the protected zone, i.e. is negative according tot he definition
2
= –Ι ;
2 1
| = |Ι |
2 1
| = |Ι – Ι | = 0
2 1 1
| = |Ι | + |Ι | = 2 · |Ι |
2 1 1 1
= 0); the stabilisation (Ι
diff
= Ι ; außerdem ist |Ι
2 1
| = |Ι + Ι | = 2 · |Ι |
2 1 1 1
| = |Ι | + |Ι | = 2 · |Ι |
2 1 1 1
) and restraint value (Ι
diff
= 0
2
| = |Ι + 0| = |Ι |
2 1 1
| = |Ι | + 0 = |Ι |
2 1 1
) and restraint value (Ι
diff
diff
) corresponds to double the through-flowing current.
stab
| = |Ι |
2 1
) are equal and correspond to the total fault.
stab
) are equal and correspond to the single-sided fault
stab
= Ι . Thus, the characteristic of internal faults is a straight line
stab
Figure 2-21).
SIPROTEC 4, 7UT6x, Manual
C53000-G1176-C230-5, Edition 09.2016