ABB REG670 - Page 437

Under unfavorable conditions the blind zone may extend to 20% from the neutral.
Some different earth fault protection solutions are shown in figure 213 and
figure 214.
Generator unit transformer
+
IEC06000317-2-en.vsd
3U
0
IEC06000317 V2 EN
Figure 213: Broken delta voltage transformer measurement of 3U
0
voltage
Alternatively zero sequence current can be measured as shown in fig 215
Generator unit transformer
IEC06000318-2-en.vsd
- U
0
+
IEC06000318 V2 EN
Figure 214: Neutral point voltage transformer measurement of neutral point
voltage (that is U
0
voltage)
In some applications the neutral point resistor is connected to the low voltage side of
a single-phase distribution transformer, connected to the generator neutral point. In
such a case the voltage measurement can be made directly across the secondary
resistor.
1MRK 502 071-UEN - Section 10
Voltage protection
Generator protection REG670 2.2 IEC and Injection equipment REX060, REX061, REX062 431
Application manual