Functions
2.30 100-%-Stator Earth Fault Protection with 3rd Harmonics (ANSI 27/59TN 3rd Harm.)
SIPROTEC, 7UM62, Manual
C53000-G1176-C149-7, Release date 03.2010
216
Measuring Principle
The content of the 3rd harmonic in the measurement value is the pickup criterion. The 3rd harmonic is deter-
mined from the displacement voltage measured over two cycles by means of digital filtering.
Different measuring procedures are applied, depending on how the displacement voltage is detected (config-
uration 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.
5. Rotor: Connection of the bias voltage for rotor earth fault protection; the 100% stator earth fault protection
function is then blocked.
6. Load. resistor: Connection of U
E
for the 100 % stator earth fault protection with 20 Hz. The function
100% stator earth fault protection with 3rd harmonic is then blocked.
7. Uen-winding: Calculation of the displacement voltage from the three phase-earth-voltages, if the U
E
input is not connected
Neutral Transformer
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 application.
Broken Delta Winding
If no neutral transformer exists, the protection function is based on the zero component of the 3rd harmonic of
the terminal voltages. This voltage increases in a fault case. In this case, the protection function is an over
volt-
age stage (5203 U0 3.HARM>).
In order to achieve increased sensitivity, the pickup value can be lowered in proportion to the active power. This
feature is set at address 5207 U0 3.H.(V/100%). Internally, the current pickup value is calculated from the
formula:
U
3H, corrected
= U
3H
+ U
corr
· (100 % – P
meas
)
Where:
U
3H, corrected
Internally used pickup value
U
3H
Value set at address 5203 U0 3.HARM> with an active power of 100 %
U
corr
Correction factor in volt/percent, set at address 5207 U0 3.H.(V/100%) (Note : set nega-
tive values)
P
meas
Measured active power
Figure 2-93 shows the operating principle.
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