Mounting and Commissioning
3.3 Commissioning
SIPROTEC, 7UM62, Manual
C53000-G1176-C149-7, Release date 03.2010
430
3.3.16 Checking the Stator Earth Fault Protection
General
The procedure for checking the stator earth fault protection depends mainly on whether the generator is con-
nected to the network in unit connection or in busbar connection. In both cases correct functioning and protect-
ed zone must be checked.
In order to check interference suppression of the loading resistor, and to verify the protected zone of the earth
fault protection, it is appropriate to test once with an earth fault at the machine terminals (e.g. with 20 % of the
rated transformer voltage) and once with a network earth fault.
Unit Connection
In the event of an external (high-voltage side) short-circuit, an interference voltage is transmitted via the cou-
pling capacitance C
coup
which induces a 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 re-
sistor R
L
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.
Figure 3-33 Unit connection with earthing transformer
Calculation of Protected Zone
Coupling capacitance C
coup
and loading resistor R
B
represent a voltage divider, where R
B
’ is the resistance R
B
referred to the machine terminal circuit.
Figure 3-34 Equivalent diagram and vector diagram
To Next Page
Loading...
Need help?
General
