The stabilizing voltage is calculated using the formula:
V
A
V
s
=
+
(
)
≈
25000
2000
15 75
1
209 37
.
.
.
Ω
Ω
GUID-8A00B448-8331-4455-8CDC-35E4E746C5C0 V1 EN
(Equation 93)
In this case, the requirement for the current transformer knee point voltage is fulfilled
because V
kn
> 2V
s
.
The magnetizing curve of the CT is assumed to be linear. The magnetizing current at the
stabilizing voltage can be estimated as:
I
V
V
I
m
s
kn
e
=
⋅
GUID-8B4549A4-1CFB-4983-B2F9-810409D699A5 V1 EN
(Equation 94)
I
V
V
mA
mA
m
=
⋅
≈
209 37
436
7
3 4
.
.
GUID-1C898845-A04C-43DC-AF34-FEB9AB66F2F0 V1 EN
(Equation 95)
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 96)
The sensitivity of the stabilizing resistor is calculated based on
.
R
V
A
S
=
≈
209 37
0 034
6160
.
.
Ω
GUID-A240913A-74ED-4A49-8746-182E0F53824F V1 EN
(Equation 97)
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 98)
The sensitivity of the protection is obtained as per
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 99)
The power of the stabilizing resistor is calculated:
1MAC059074-MB A
Section 4
Protection functions
615 series ANSI
563
Technical Manual
Summary of Contents for Relion 615 series
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