Functions
2.31 100-%-Stator Earth Fault Protection with 20 Hz Voltage Injection (ANSI 64G - 100%)
SIPROTEC, 7UM62, Manual
C53000-G1176-C149-7, Release date 03.2010
228
Correction Angle, Transfer Resistance
The parameter PHI I SEF (default setting 0 °) at address 5309 is used to compensate the angle errors of the
CTs and angle distortions caused by a nonideal earthing or neutral transformer. The correct setting for this pa-
rameter can only be determined with a primary test. The adjustment should be made for the tripping value.
The same is true for the transfer resistance of the earthing or neutral transformer. This advanced parameter
can be set with the DIGSI communication software (not possible in local operation). As a rule this resistance is
negligible. For this reason, the default setting SEF Rps = 0.0 Ω was selected at address 5310. However, the
transfer resistance of the voltage transformer is no longer negligible if the 20 Hz voltage is fed to a primary-side
loading resistor via a voltage transformer.
In large power units with generator circuit breaker, applications arise where there is some additional loading
equipment on the low-voltage side of the unit transformer to reduce the influence by the zero voltage when the
generator circuit breaker is open. The 20 Hz source is connected via the neutral transformer in the generator
starpoint. With the generator circuit breaker closed, the protection measures the loading resistance on the unit
transformer side, which can be mistaken for an earth resistance. The advanced parameter address 5311
allows this additional loading resistance to be set. The default setting for Rl-PARALLEL is ∞. No additional
loading resistance is assumed.
100 % Stator Earth Fault Protection with Primary Load Resistor
Some power systems with generators in unit connection have a load resistor installed directly in the generator
starpoint to reduce interference. The following figure shows the necessary connection of the 20 Hz generator
and the band pass in this application, and the integration of the protection device. The 20 Hz voltage is injected
into the generator starpoint via a powerful voltage transformer and drops off at the primary load resistor. In the
presence of an earth fault, an earth current flows through the CT in the starpoint. The protection function detects
and processes this current in addition to the 20 Hz voltage.
Figure 2-100 Connection: 100 % Stator Earth Fault Protection to a Primary Load Resistor
The connection designations for 7XT3300–0*A00/DD are given in Appendix A.3, Figure A-29.
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