ABB RELION REX640 Technical Manual page 815

1MRS759142 F
4.3.8.8 Example calculations for high-impedance differential protection
The example shows the calculations for the
resistor value (R
Table 725: Protected generator values
Quantity
S
n
U
n
I
n
I
kmax
I
kmaxin
Table 726: Assumed CT data
Quantity
CT
R
in
U
kn
I
e
Figure 464: Example calculation for high-impedance differential protection (only one
phase is presented in detail)
The length of the secondary circuit loop is 200 m and the area of the cross-section
is 2.5 mm
REX640
Technical Manual
) and required knee point voltage (U
s
Value
8 MVA
6 kV
770 A
4620 A (6 × I
9.24 kA (12 × I
Value
1000/1 A
15.3 Ω
323 V
35 mA (at U
2
. Resistance at 75°C is 0.00865 Ω/m.
Operate value setting, stabilizing
) of the CTs.
kn
) out-of-zone fault
n
) in-zone fault
n
)
kn
Protection functions
815