overvoltage protection or a residual differential protection. These protection schemes
are simple and have served well during many years. However, at best these schemes
protect only 95% of the stator winding. They leave 5% at the neutral end unprotected.
Under unfavorable conditions the blind zone may extend to 20% from the neutral.
Some dif
ferent ground fault protection solutions are shown in figure
213 and
figure 214.
Generator unit transformer
+
3V
0
ANSI06000317_3_en.vsd
ANSI06000317 V3 EN-US
Figure 213: Broken delta voltage transformer measurement of 3V
0
voltage
Alternatively zero sequence current can be measured as shown in fig
215
Generator unit transformer
- V
0
+
ANSI06000318_3_en.vsd
ANSI06000318 V3 EN-US
Figure 214: Neutral point voltage transformer measurement of neutral point voltage
(that is V
0
voltage)
Section 10 1MRK 502 071-UUS A
Voltage protection
466 Generator protection REG670 2.2 ANSI and Injection equipment REX060, REX061, REX062
Application manual
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