ABB RELION 620 Series Technical Manual page 603

1MRS757644 F
4.3.6.7
620 series
Technical Manual
A
12600
U
330
= ⋅ Ω =
max
240
GUID-5CFBCB0D-AD77-40FE-BAAE-ADB7F4433814 V1 EN
˘
u
2 2 81 17325 81
( )
= ⋅ ⋅ −
GUID-36CB9591-47BB-4FFD-A6B0-2088AF2B9C18 V1 EN
As the peak voltage ȗ = 3.2 kV, VDR must be used. In some cases, VDR can be
avoided if R is smaller. The value of R
s
current and stabilizing voltage. Thus, a higher setting in the protection relay must be
used or the stabilizing voltage lowered.
Flux-balancing principle
When the function block is used with the flux-balancing principle, there are no extra
requirements for the measuring devices. The core-balance transformers used in an
ordinary overcurrent protection are adequate here as well.
Example calculations for high-impedance differential protection
The example shows the calculations for the Operate value setting, stabilizing resistor
value (R ) and required knee point voltage (U
s
Table 530: Protected generator values
Quantity
S
n
U
n
I
n
I
kmax
I
kmaxin
Table 531: Assumed CT data
Quantity
CT
R
in
U
kn
I
e
V
17325
. kV
3 34
≈
depends on the protection relay operation
s
) of the CTs.
kn
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
Section 4
Protection functions
(Equation 113)
(Equation 114)
) out-of-zone fault
n
) in-zone fault
n
)
kn
597