ABB 615 series Technical Manual page 569

1MAC059074-MB A
615 series ANSI
Technical Manual
The stabilizing voltage is calculated using the formula:
25000 A
V 15 75 . 1 .
(
= Ω + Ω
s
2000
GUID-8A00B448-8331-4455-8CDC-35E4E746C5C0 V1 EN
In this case, the requirement for the current transformer knee point voltage is fulfilled
because V > 2V .
kn s
The magnetizing curve of the CT is assumed to be linear. The magnetizing current at the
stabilizing voltage can be estimated as:
V
s
I I
= ⋅
m e
V
kn
GUID-8B4549A4-1CFB-4983-B2F9-810409D699A5 V1 EN
209 37 . V
7 3 4 .
I mA mA
= ⋅ ≈
m
436 V
GUID-1C898845-A04C-43DC-AF34-FEB9AB66F2F0 V1 EN
To obtain adequate protection stability, the setting current I
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 sensitivity of the stabilizing resistor is calculated based on
209 37 . V
R 6160
= ≈ 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
35
I 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:
209 37 . V
)
≈
. A 0 A ) 140 A
⋅ + ≈
Section 4
Protection functions
must be at the minimum of
rs
Equation 97.
Equation 99, assuming I
(Equation 93)
(Equation 94)
(Equation 95)
(Equation 96)
(Equation 97)
(Equation 98)
= 0.
u
(Equation 99)
563