Siemens SIPROTEC 7SS523 V3.2 Manual page 349

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 ist established.
The following condition must be fulfilled in order to prevent bus zone tripping for an
external fault (see Figure A-1, page 333):
2 I sin ωT × k > I
scc max S
2 sin ωT × k > 1
S
Figure A-1 Short-circuit on a feeder with CT saturation
To determine the point in time T
must be considered.
Figure A-2 Current/time characteristic
If the CT is burdened with I
being equal to area B
ωTs
∫
I sin
( ⋅
scc max
i.e.
0
K (1 − cos ωT ) = 2
b S
If inequation (2) and equation (4) are combined, the result is the minimum selectable
stabilization factor k:
K
b
--------------------------- -
k
for K
>
4 K – 1
⋅
b
Basis for Selection of the Stabilization Factor k
(1) or
scc max
(2)
at which saturation occurs, the burdening factor K
S
= K I , it will saturate after time T
scc max b sat
.
π
∫
= I sin
ωt ) ( ⋅ ωt )
sat
(3)
0
(4)
> 2(5)
b
C53000-G1176-C182-1
I = I * K'
sat pn ssc
K = I / I
b scc max sat
7SS52 V4 Manual
b
, with area A
S
333