ABB RELION 611 Series Applications Manual page 68

Section 4
Requirements for measurement transformers
62
The VDR is recommended when the peak voltage û ≥ 2kV, which is the insulation
level for which the protection relay is tested.
The maximum fault current in case of a fault inside the zone is considered to be 12.6
kA in primary, CT is of 1250/5 A (ratio n = 240), knee point voltage is 81 V and the
stabilizing resistor is 330 Ohms.
12600 A
U 330
= × Ω =
max
240
GUID-83BA854A-8BF2-4E60-A6F7-90E79458B6E5 V1 EN
∧
u 2 2 81 17325 81
(
= × × −
GUID-9BA35770-2458-4CE0-9E06-5D56CAA21B57 V1 EN
As the peak voltage û is 3.2 kV, VDR must be used. If the R
avoided. However, the value of R
voltage of the protection relay. Thus, either a higher setting should be used or the
stabilizing voltage should be lowered.
As the peak voltage û = 3.2 kV, VDR must be used. If the R
avoided.
The value of R depends on the protection relay operating current and the stabilizing
s
voltage. Therefore, either a higher setting in the protection relay or a lower stabilizing
voltage must be used.
17325 V
3 34 . kV
)
≈
depends on the operation current and stabilizing
s
1MRS757455 E
(Equation 9)
(Equation 10)
is smaller, VDR could be
s
is smaller, VDR can be
s
REB611
Application Manual