ABB RELION REX640 Technical Manual page 738

Section 4
Protection functions
732
The setting current I should be at the minimum of the sum of the magnetizing
rs
currents of all connected CTs to obtain adequate protection stability.
I 2 8 5 . mA 17 mA
= ⋅ ≈
rs
GUID-C367812A-85D1-43B4-8BA5-10CABC70BE53 V1 EN
The resistance of the stabilizing resistor is calculated based on
78 7 . V
R 4629
= ≈ Ω
s
A
0 017 .
GUID-C972850F-5DB8-42BB-9660-D24D4ADA506A V1 EN
The calculated value 4629 Ω is the maximum value for the stabilizing resistor. If this
value is not available, the next available value downwards should be chosen and the
protection relay setting current is to be tuned according to the selected resistor. For
example in this case the resistance value 3900 Ω is used.
78 7 . V
I 20 mA
= ≈
rs
3900 V
GUID-09CE46EA-859C-42E3-A266-B4D45C9A845E V1 EN
The sensitivity of the protection is obtained as per
zero.
I A
1000 0 020 . 2 0 0085
(
= ⋅ + ⋅
prim
GUID-1F1BBF6E-069C-4B58-A285-2FF0A84BF9BD V1 EN
The power of the stabilizing resistor is calculated as follows.
2
V
323
( )
P 27 W
≥ ≈
3900
Ω
GUID-74634182-4053-46DF-9E46-B73D8406AA72 V1 EN
Based on Equation 172
checked.
12 770 A
⋅
U 3900
(
= ⋅
max
1000
GUID-98B8F78B-3D75-4FA4-A707-2EE3D08E5EB6 V1 EN
˘
u 2 2 323 V 36200 V
(
= ⋅ ⋅
GUID-ABCF21A8-F7FF-4908-8C66-49C5CFBD1CAF V1 EN
The voltage dependent resistor, one for each phase, is needed in this case because the
voltage during the fault is much higher than 2 kV.
The leakage current through the varistor at the stabilizing voltage can be available
from the varistor manual, assuming that to be approximately 2 mA at stabilizing
voltage.
Iu ≈ 0 002 . A
GUID-40D4DB06-058B-43BA-BF44-8B347179590D V1 EN
A A A
. 0 37
)
+ ≈
and Equation 173, the need for voltage dependent resistor is
15 3 . 1 73 . 0 10 .
Ω + Ω + Ω +
323 V 9 6 . kV
)
− ≈
1MRS759142 C
Equation 168.
Equation 170, assuming I
36 2 . kV
)
Ω ≈
Technical Manual
(Equation 180)
(Equation 181)
(Equation 182)
to be
u
(Equation 183)
(Equation 184)
(Equation 185)
(Equation 186)
(Equation 187)
REX640