Siemens SIPROTEC 7UT613 series Manual page 106

2 Functions
106
I
= |I | + |I |
stab 1 2
The current sum definition is extended for more than 2 measurement locations, e.g.
for 4 measuring locations (figure 2-18 or 2-19), therefore:
I + I + I
= |I +I |
diff 1 2 3 4
I
= |I | + |I | + |I | + |I
stab 1 2 3
I
is derived from the fundamental frequency current and produces the tripping effect
diff
quantity, I
counteracts this effect.
stab
To clarify the situation, three important operating conditions with ideal and matched
measurement quantities are considered.
Figure 2-20 Definition of current direction
1. Through-flowing current under undisturbed conditions or external fault:
I flows into the protected zone, I
1
cording tot he definition of signs, therefore I
moreover |I | = |I |
2 1
I + I – I
= |I | = |I
diff 1 2 1
I
= |I | + |I | = |I
stab 1 2 1
No tripping effect (I
through-flowing current.
2. Internal short-circuit, e.g. fed with equal currents each side:
The following appliesI
I + I + I
= |I | = |I
diff 1 2 1
I
= |I | + |I | = |I
stab 1 2 1
Tripping effect (I ) and restraint value (I
diff
fault.
3. Internal short-circuit, fed from one side only:
The following applies I
I + I
= |I | = |I + 0| = |I
diff 1 2 1
I
= |I | + |I | = |I
stab 1 2 1
Tripping quantity (I
the single-sided fault current.
This result shows that for internal fault I
faults is a straight line with the slope 1 (45°) in the operation diagram (dash-dotted fault
characteristic in figure 2-21).
|
4
leaves the protected zone, i.e. is negative ac-
2
| = 0
1
| + |I | = 2 · |I |
1 1
= 0); the stabilisation (I
diff
= I
; moreover |I | = |I
2 1 2
| = 2 · |I |
1 1
| + |I | = 2 · |I |
1 1
stab
= 0
2
|
1
| + 0 = |I |
1
) and stabilising quantity (I
diff
= I
diff stab
= –I ;
2 1
) corresponds to double the
stab
|
1
) are equal and correspond to the total
) are equal and correspond to
stab
. Thus, the characteristic of internal
7UT613/63x Manual
C53000-G1176-C160-2