ABB Relion 611 Series, Technical Manual

Page: 229 / 536

The stabilizing voltage is calculated using the formula:
U
A
V
s
= +
( )
≈
25000
2000
15 75 1 209 37 . . .
Ω Ω
GUID-3911986B-6B0A-4586-BDB7-E7F685E8FF0A V1 EN
(Equation 13)
In this case, the requirement for the current transformer knee point voltage is fulfilled
because U
kn
> 2U
s
.
The magnetizing curve of the CT is assumed to be linear. The magnetizing current at
the stabilizing voltage can be estimated as:
I
U
U
I
m
s
kn
e
= ⋅
GUID-C334E82B-9844-4C41-A667-F66B9FF0D860 V2 EN
(Equation 14)
I
V
V
mA mA
m
= ⋅ ≈
209 37
436
7 3 4
.
.
GUID-F0A8E0D4-C0FE-41CD-A0BA-C0A873F3A402 V2 EN
(Equation 15)
To obtain adequate protection stability, the setting current I
rs
must be at the minimum
of the sum of magnetizing currents of all connected CTs.
I mA mA
rs
= ⋅ ≈
10 3 4 34 .
GUID-9B9B81AE-DAA9-4D9A-823F-4D239D257E80 V2 EN
(Equation 16)
The resistance of the stabilizing resistor is calculated based on Equation 17 .
R
V
A
S
= ≈
209 37
0 034
6160
.
.
Ω
GUID-A240913A-74ED-4A49-8746-182E0F53824F V1 EN
(Equation 17)
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.
I
V
mA
rs
= ≈
209 37
5900
35
.
Ω
GUID-BC97F256-ECDD-432F-B8AE-74AB2769876F V1 EN
(Equation 18)
The sensitivity of the protection is obtained as per Equation 19 , assuming I
u
= 0.
I A A A A
prim
= ⋅ + ⋅ + ≈
2000 0 035 10 0 0034 0 140 ( . . )
GUID-357A9480-16D5-488E-B92C-A6C14FD3708B V2 EN
(Equation 19)
The power of the stabilizing resistor is calculated:
P
V
W
≥ ≈
( ) 436
5900
32
2
Ω
GUID-28EF2E18-E1A9-4332-B39B-56D3C1141F70 V1 EN
(Equation 20)
1MRS757454 D
Section 4
Protection functions
611 series 223
Technical Manual