ABB RELION 620 Series Technical Manual page 590

Section 4
Protection functions
584
The stabilizing voltage is calculated using the formula:
25000 A
U 15 75 . 1
(
= Ω +
s
2000
GUID-3911986B-6B0A-4586-BDB7-E7F685E8FF0A 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-C334E82B-9844-4C41-A667-F66B9FF0D860 V2 EN
209 37 . V
I 7 mA 3 4 .
= ⋅ ≈
m
436
V
GUID-F0A8E0D4-C0FE-41CD-A0BA-C0A873F3A402 V2 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-9B9B81AE-DAA9-4D9A-823F-4D239D257E80 V2 EN
The resistance of the stabilizing resistor is calculated based on
209 37 .
V
6160
R
= ≈ Ω
S
0 034 . A
GUID-A240913A-74ED-4A49-8746-182E0F53824F 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-BC97F256-ECDD-432F-B8AE-74AB2769876F V1 EN
The sensitivity of the protection is obtained as per
I 2000 0 035 ( . A 10 0 0034
= ⋅ +
prim
GUID-357A9480-16D5-488E-B92C-A6C14FD3708B V2 EN
The power of the stabilizing resistor is calculated:
2
( 436 V )
P 32 W
≥ ≈
5900
Ω
GUID-28EF2E18-E1A9-4332-B39B-56D3C1141F70 V1 EN
. 209 37 . V
)
Ω ≈
mA
. A 0 A ) 140 A
⋅ + ≈
1MRS757644 F
(Equation 93)
(Equation 94)
(Equation 95)
must be at the minimum
rs
(Equation 96)
Equation 97.
(Equation 97)
(Equation 98)
Equation 99, assuming I
(Equation 99)
(Equation 100)
Technical Manual
= 0.
u
620 series