2.23 100-%-Stator Earth Fault Protection with 3rd Harmonics (ANSI 27/59TN 3rd Harm.)
141
7UM61 Manual
C53000-G1176-C127-3
Different measuring procedures are applied, depending on how the displacement
voltage is detected (configuration parameter 223 UE CONNECTION):
1. neutr. transf.: Connection of the U
E
input to the voltage transformer at the
machine starpoint
2. broken delta: Connection of the U
E
input to the broken delta winding
3. Not connected: Calculation of the displacement voltage from the three phase-
earth-voltages, if the U
E
input is not connected
4. any VT: Connection of any voltage; the 100% stator earth fault protection function
is blocked.
Neutral Transform-
er
As an earth fault in the starpoint causes a reduction of the measured 3rd harmonic
compared with the nonfault case, the protective function is implemented as an under
-
voltage stage (5202 U0 3.HARM<). This arrangement is the preferred case.
Broken Delta
Winding
If no neutral transformer exists, the protection function is based on the zero compo-
nent of the 3rd harmonic of the terminal voltages. This voltage increases in a fault
case. In this case, the protection function is an over
voltage stage (5203 U0
3.HARM>).
Not Connected;
Calculation of U
0
As for the connection to the broken delta winding, an increase of the 3rd harmonic
during a fault also results for the calculated voltage. The 5203 U0 3.HARM> param-
eter is also relevant.
Connected to any
Transformer
With these connection types 100% stator earth fault protection is ineffective.
The following figure shows the logic diagram for the 100– %–stator earth fault protec-
tion.
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