ABB REF615 F - Setting Examples

4.3.4.8 Setting examples
Example 1
n
n2
m
u
s
GUID-AB960DE4-4DD2-4312-9921-0D6E7CD001AA V1 EN
Figure 236: Restricted earth-fault protection of a transformer
The data for the protected power transformer are:
S
n
= 20 MVA
U
2n
= 11 kV
The longest distance of the secondary circuit is 50 m (the whole loop is 100 m) and
the area of the cross section is 10 mm
2
.
I
n
= S
n
/ (√3 · U
n
) = 1050 A
I
kmax
= 12 · I
n
= 12600 A
In this example, the CT type is IHBF 12, the core size is 35 percent, the primary
current is 1200 A and the secondary current is 5 A.
R
in
= 0.26 Ω (value given by the manufacturer).
U
k
= 40 V (value given by the manufacturer).
I
e
= 0.055 A (value given by the manufacturer).
R
m
= 1.81 Ω/km · 2 · 0.05 km = 0.181 Ω ≈ 0.18 Ω
1YHT530004D05 D Section 4
Protection functions
615 series 441
Technical Manual