Basis for Selection of the Stabilization Factor k
341
7SS52 V4 Manual
C53000-G1176-C182-3
A.2
Basis for Selection of the Stabilization Factor k
In a first step, the relationship between the point (in time) at which saturation occurs
and the stabilization factor is established.
The following condition must be fulfilled in order to prevent bus zone tripping for an
external fault (see Figure A-1, page 341):
2 I
scc max
sin
ω
T
S
×
k
>
I
scc max
(1) or
2 sin
ω
T
S
×
k
>
1
(2)
Figure A-1 Short-circuit on a feeder with CT saturation
To determine the point in time T
S
at which saturation occurs, the burdening factor K
b
must be considered.
Figure A-2 Current/time characteristic
If the CT is burdened with I
scc max
=
K
b
I
sat
, it will saturate after time T
S
, with area A
being equal to area B
.
K
b
(1
−
cos
ω
T
S
)
=
2
(4)
If inequation (2) and equation (4) are combined, the result is the minimum selectable
stabilization factor k:
for K
b
>
2(5)
I
sat
=
I
pn
* K’
ssc
K
b
= I
scc max
/ I
sat
i.e.
(3)
I
scc max
ω
t
sin
⋅
(
)
0
ω
Ts
∫
I
sat
ω
t
sin
⋅
(
)
0
π
∫
=
k
K
b
4
K
b
1
–
⋅
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