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Functions
76
The stabilizing quantity is derived from the arithmetical sum of the absolute values of
|I
| + |I
|. The following definitions apply:
1
2
The differential current
= |I
+ I
|
I
diff
1
2
and the stabilization or restraining current
= |I
| + |I
|
I
stab
1
2
is derived from the fundamental frequency current and produces the tripping effect
I
diff
quantity, I
counteracts this effect.
stab
To clarify the situation, three important operating conditions with ideal and matched
measurement qualities should be examined:
I
p
1
CT1
I
1
Figure 2-29
Definitions of Currents
1. Through flowing current through a healthy transformer or external fault:
reverses its direction, i.e. thus changes its sign, i.e. I
I
2
and consequently |I
= |I
+ I
| = |I
– I
I
diff
1
2
1
= |I
|+ |I
| = |I
| + |I
I
stab
1
2
1
No tripping effect (I
flowing current.
2. Internal short-circuit, e.g. fed with equal currents each side:
In this case I
= I
; and consequently |I
2
1
= |I
+ I
| = |I
+ I
I
diff
1
2
1
=|I
|+ |I
| = |I
| + |I
I
stab
1
2
1
Tripping effect (I
) and stabilizing (I
diff
the total fault.
3. Internal short-circuit, fed from one side only:
In this case I
= 0
2
= |I
+ I
| = |I
– 0| = |I
I
diff
1
2
1
=|I
|+ |I
| = |I
| + 0 = |I
I
stab
1
2
1
Tripping effect (I
) and stabilizing (I
diff
the fault current fed from one side.
Protected object
M
+ I
I
1
2
| = |I
|
2
1
| = 0
1
| = 2 ⋅ |I
|
1
1
); stabilization (I
) corresponds to twice the through
diff
stab
| = |I
2
| = 2 ⋅ |I
|
1
1
| = 2 ⋅ |I
|
1
1
) quantities are equal and correspond to
stab
|
1
|
1
) quantities are equal and correspond to
stab
I
p2
CT2
I
2
= –I
;
2
1
|
1
C53000-G1176-C149-3
7UM62 Manual
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