ABB RELION REX640 Technical Manual page 704

Section 4
Protection functions
698
The stabilizing voltage is calculated using the formula:
25000 A
U 15 75 .
(
= ⋅ Ω +
s
2000
GUID-52310FE0-8E97-458B-B3DF-84E20C9892DA V1 EN
In this case, the requirement for the current transformer knee point voltage is fulfilled
because U > 2U .
kn s
The magnetizing curve of the CT is assumed to be linear. The magnetizing current at
the stabilizing voltage can be estimated as:
U
s
I I
= ⋅
m e
U
kn
GUID-C7A61C61-DC76-4FA8-8B5B-683E628CC869 V1 EN
209 37 . V
I 7 mA 3 4 .
= ⋅ ≈
m
436 V
GUID-7C9BA18A-81C0-4C7C-8A26-B0B041266179 V1 EN
To obtain adequate protection stability, the setting current I
of the sum of magnetizing currents of all connected CTs.
I 10 3 4 . mA 34 mA
= ⋅ ≈
rs
GUID-E85DABB9-663A-4123-8B63-C4341DAD8120 V1 EN
The resistance of the stabilizing resistor is calculated based on
209 37 . V
R 6160
= ≈ Ω
S
A
0 034 .
GUID-AA018C8F-AA1F-4C55-A6EC-42E9C3678E23 V1 EN
The calculated value is the maximum value for the stabilizing resistor. If the value is
not available, the next available value below should be selected and the protection
relay setting current is tuned according to the selected resistor. For example, in this
case, the resistance value 5900 Ω is used.
209 37 . V
I 35 mA
= ≈
rs
5900
Ω
GUID-C9054420-634C-46DC-921A-9DE38ED5E76A V1 EN
The sensitivity of the protection is obtained as per
I 2000 0 035 ( . A 10 0 0034
= ⋅ +
prim
GUID-D3D6624E-7038-485E-BC89-1A7C995813A6 V1 EN
The power of the stabilizing resistor is calculated:
2
V
( 436 )
P W
32
≥ ≈
5900
Ω
GUID-8FDA9EC7-3231-4D2F-85EC-F03E52A2D6F3 V1 EN
1 . 209 37 . V
)
Ω ≈
mA
. A 0 A ) 140 A
⋅ + ≈
1MRS759142 C
(Equation 141)
(Equation 142)
(Equation 143)
must be at the minimum
rs
(Equation 144)
Equation 145.
(Equation 145)
(Equation 146)
Equation 147, assuming I
(Equation 147)
(Equation 148)
Technical Manual
= 0.
u
REX640