Functions
2.28 90-%-Stator Earth Fault Protection (ANSI 59N, 64G, 67G)
SIPROTEC, 7UM62, Manual
C53000-G1176-C149-7, Release date 03.2010
208
Figure 2-89 Logic Diagram of 90 % Stator Earth Fault Protection
2.28.2 Setting Notes
General
90 % stator earth fault protection is only effective and available if address 150 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 con-
nection, 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 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 Voltage
The criterion for the occurrence of an earth fault in the stator circuit is the emergence 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 operational asymmetries. This
is particularly important for machines in busbar connection since all voltage asymmetries of the network affect
the voltage starpoint of the machine. The pickup value should be at least twice the value of operational asym-
metry. 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 displacements during network
earth faults which affect the stator circuit via the coupling capacitances of the unit transformer do not lead to
pickup. The damping effect of the loading resistor must also be considered here. Instructions for dimensioning
the loading resistor are contained in the publication "Planning Machine Protection Systems" /5/. The setting
value is twice the displacement voltage which is coupled in at full network displacement. The final setting value
is determined during commissioning using primary values.
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