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2 Functions
Figure 2-46
2.21.2 Setting Notes
The 90% stator earth fault protection is only fully effective and available if address 150
General
S/E/F PROT. is set to directional, non-dir. U0 or non-dir. U0&I0 during
configuration. If non-dir. U0 was selected, the parameters affecting the earth
current are not displayed. If one of the options directional or non-dir. U0&I0
was selected, the parameters affecting the earth current are accessible. For machines
in busbar connection, one of the latter options must enabled since differentiation
between a power system earth fault and a machine earth fault is only possible by way
of the earth current. If used as "earth current differential protection", address 150
S/E/F PROT. = non-dir. U0&I0 is set. If the function is not required Disabled
is set. Address 5001 S/E/F PROT. serves to switch the function ON or OFF or to block
only the trip command (Block relay).
Displacement
The criterion for the occurrence of an earth fault in the stator circuit is the emergence
Voltage
of a neutral displacement voltage. Exceeding the set value 5002 U0> therefore
causes pickup for stator earth protection.
The setting must be chosen such that the protection does not pick up because of op-
erational asymmetries. This is particularly important for machines in busbar connec-
tion since all voltage asymmetries of the network affect the voltage starpoint of the ma-
chine. The pickup value should be at least twice the value of operational asymmetry.
A value between 5% and 10% of the full displacement value is normal.
For machines in unit connection, the pickup value has to be chosen such that displace-
ments during network earth faults which affect the stator circuit via the coupling capac-
itances of the unit transformer, do not lead to pickup. The damping effect of the loading
resistor must also be considered here. Instructions for the dimensioning the loading
resistor are given in the publication "Planning Machine Protection Systems", Order
No. E50400- U0089-U412-A1-7600. The setting value is twice the displacement
132
Logic Diagram of 100% Stator Earth Fault Protection
7UM61 Manual
C53000-G1176-C127-3
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