ABB REG650 Technical Manual page 292

Section 9
Voltage protection
286
-
- DV
- V +
3N
V
3N
ANSI06000448 V1 EN
Figure 131:
Generator 3
The generator is modeled as parts of a winding where a 3
induced along the winding, represented by the end voltages V
resistor) and V in the figure. Via the winding capacitances to ground and the neutral
3T
point resistor there will be a small 3
and V . It can easily be seen that the 3
3T
point (V ) will be close to zero in case of a stator ground-fault close to the neutral.
3N
This fact alone can be used as an indication of stator ground-fault. To enable better
sensitivity and stability also measurement of the generator's 3
is also used. In addition to the decrease of V
under the stator ground-fault close to the generator neutral point. Therefore the 3
harmonic voltage V , (which is a zero sequence voltage) is used by the protection. In
3T
rd
the 3 harmonic voltage differential protection algorithm equation
V
3
+
3
rd
harmonic voltage characteristic at normal operation
rd
harmonic current flow, giving the voltages V
rd
harmonic voltage in the generator neutral
the generator voltage V
3N
1MRK 502 043-UUS B
+
+
V
3T,A
-
+
V
3T,B
-
+
V
3T,C
-
V
3T
en06000448_ansi.vsd
rd
harmonic voltage is
(voltage drop across
3N
rd
harmonic voltage V
will increase
3T
rd
91 is used:
Technical Manual
3N
3T