ABB Relion Technical Manual page 320

Section 9
Voltage protection
314
-
- DV
- V +
3N
V
3N
ANSI06000448 V1 EN
Figure 144:
Generator 3
The generator is modeled as parts of a winding where a 3
along the winding, represented by the end voltages V
V in the figure. Via the winding capacitances to ground and the neutral point resistor
3T
rd
there will be a small 3
harmonic voltage in the generator neutral point (V
stator ground-fault close to the neutral. This fact alone can be used as an indication of
stator ground-fault. To enable better sensitivity and stability also measurement of the
rd
generator's 3 harmonic voltage V
generator voltage V will increase under the stator ground-fault close to the generator
3T
neutral point. Therefore the 3
is used by the protection. In the 3
equation 94 is used:
V
3
+
3
rd
harmonic voltage characteristic at normal operation
harmonic current, giving the voltages V
is also used. In addition to the decrease of V
3T
rd
harmonic voltage V
rd
harmonic voltage differential protection algorithm
1MRK 502 048-UUS A
+
+
V
3T,A
-
+
V
3T,B
-
+
V
3T,C
-
V
en06000448_ansi.vsd
rd
harmonic voltage is induced
(voltage drop across resistor) and
3N
and V
3N 3T
) will be close to zero in case of a
3N
, (which is a zero sequence voltage)
3T
Technical manual
3T
rd
. The 3
the
3N