Setting Examples - ABB RELION REX640 Technical Manual

Section 4
Protection functions
4.3.5.9
682

Setting examples

Example 1
n
n2
GUID-5E04A1BA-CEC9-4B4D-97C8-F20ABBACCBC9 V1 EN
Figure 377: Restricted earth-fault protection of a transformer
The data for the protected power transformer are:
S = 20 MVA
n
U = 11 kV
2n
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
I = S / (√3 · U ) = 1050 A
n n n
I = 12 · I = 12600 A
kmax n
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 = 0.26 Ω (value given by the manufacturer).
in
U = 40 V (value given by the manufacturer).
k
I = 0.055 A (value given by the manufacturer).
e
R = 1.81 Ω/km · 2 · 0.05 km = 0.181 Ω ≈ 0.18 Ω
m
m
u
s
2
.
1MRS759142 C
REX640
Technical Manual