ABB REF615 Applications Manual page 186

Section 5
Protection functions
180
The value reduced to the 10 kV voltage level is X
The setting can now be calculated:
X
U 0 67 1 0 67 . .
( )
= + −
1 G
'
X
kB
GUID-E8CE42AB-E53C-478E-B907-828FFBB19CAC V1 EN
0 0013 .
0 67 0 33 . .
+
0 0044 0 0013 . .
+
GUID-BBBBB39E-B1D2-49A4-948E-130672A0DBDA V1 EN
The actual setting should be slightly, for example, 10 percent higher than the value
calculated to allow some margin for the fault resistance and other factors that increases
U value:
1
Voltage start value 1.1 × 0.83 = 0.91
In the examples, it is assumed that the generator is connected to the
10 kV network without a power transformer in between. If there is
such a transformer, the same setting principles are still followed. The
short circuit reactance of the transformer has to be added to the
transient reactance of the generator if the voltage is measured at the
network side of the transformer. Also, the short circuit reactance of
the transformer has to be added to the network short circuit reactance
if the voltage is measured at the generator side of the transformer.
'
X
y
kG
(( . 1 1 0 67
+ −
' '
X X
X
+
+
kG d
y
1
(( . 0 43 0 33 . ) 0 33
+ − −
1 3 33 .
+
1MRS756378 D
' = 0.3 × (10/150)² Ω = 0.0013 Ω.
y
'
X
y
. ) ( 1 0 67 . ) )
− −
' '
X X
+
y
kB
0 001 . 3 3
. ) 0 83 .
=
0 0044 0 0013 . .
+
Application Manual
)
=
(Equation 10)
REF615