REG 316*4 1MRB520049-Uen / Rev. F ABB Switzerland Ltd
3-133
Note:
Because of the voltage drop of the v.t’s, the voltage does not
reach 520 V at the full E/F current, but only 360 V. The setting of
the protection must therefore be modified as follows:
Overvoltage setting
005
360
520
0 034..= (3.4 % U
N
instead of 5 % U
N
)
Example 5
U
GN
= 27 kV; U
HV
= 400 kV; C
12
= 3 x 10
-9
F; x = 314 1/s
HV system solidly grounded
I
E
= 15 A
U
U
V
n
GN
1
3
27000
3
15600
== =
R
U
U
e
n
nmin
³
´
æ
è
ç
ö
ø
÷
=´ ´
-
27000
315
3
15600
27 10
2
2
6
2
2
R
U
U
e
n
nmax
.
£
´
´´´ ´
æ
è
ç
ö
ø
÷
=´ ´
-
-
005 27
6 314 3 10
400
6
3
15600
132 10
9
2
2
6
2
2
I
e
= 250 A (chosen)
UV
n2
15600
15
3 300
260
=
´
=
The resistor R
e
is chosen according to R
emin
:
R
e
= 27 ´ 10
-6
´ 260
2
= 1.825 W
R
e
I
e
= 1.825 ´ 300 = 547 V
3 U
2n
= 3 ´ 260 = 780 V
S =
3 ´ 260 ´ 300 = 135 ´ 10
3
VA
The specification and the modification of the protection setting is
similar to Example 4.
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