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3.4.6.1
Unit Connection
General
Calculation of
Protected Zone
7UM62 Manual
C53000-G1176-C149-3
In the event of an external (high-voltage side) short-circuit, an interference voltage is
transmitted via the coupling capacitance C
displacement voltage on the generator side. To ensure that this voltage is not
interpreted by the protection as an earth fault within the generator, it is reduced by a
suitable loading resistor to a value which corresponds to approximately one half the
pick-up voltage U0> (address 5002). On the other hand, the earth fault current
resulting from the loading resistor in the event of an earth fault at the generator
terminals should not exceed 10 A, if possible.
C
G
R
– Loading resistor
B
R
– Voltage divider
T
U
– Neutral displacement voltage at 7UM62
E
C
– Generator-earth capacitance
G
C
– Line–earth capacitance
L
C
– Winding–earth capacitance of block transformer
Tr
C
– Coupling capacitance of block transformer
C
Figure 3-31
Unit Connection with Earthing Transformer
Coupling capacitance C
(equivalent circuit diagram Figure 3-32), whereby R
the machine terminal circuit.
U
'
R
'
R
B
U
Rated voltage on upper–voltage side of block transformer
NU
U
Voltage at coupling capacitance C
C
C
Total coupling capacitance between upper–voltage and lower–voltage windings
C
U
'
Voltage across loading resistor
R
R
'
Loading resistor of earthing transformer, referred to machine circuit.
B
Figure 3-32
Equivalent Diagram and Vector Diagram
3.4 Primary Commissioning Tests with the Generator
(Figure 3-31) which induces a neutral
C
C
L
and loading resistor R
C
U
C
ωC
C
U
NU
~
√3
K
C
Tr
R
B
R
T
U
E
7UM62
represent a voltage divider
B
' is the resistance R
B
√
U
/
3
NU
U
C
C
C
referred to
B
U
'
R
375
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