ABB RELION 670 Series Technical Manual page 429

1MRK 502 066-UUS B
C
stat
ANSI11000009 V1 EN-US
Figure 226: Effective high-resistance generator grounding via a distribution transformer
Another alternative is shown in figure
delta transformer). In this case the transformer must withstand the large secondary current
caused by primary ground fault. The resistor typically has to be divided as shown in figure
limit the voltage to the injection equipment in case of ground fault at the generator terminal. This
voltage is often in the range 400 – 500 V. As the open delta connection gives three times the zero
sequence phase voltage this gives too high voltage at the injection point if the resistance is not
divided as shown in the figure
maximum voltage imposed back on injection equipment is equal to or less than 240V.
Technical manual
I
inj
a
+
R V
N inj
-
b
ANSI11000009_1_en.vsd
227 (High-resistance grounding via a grounded wye-broken
227 . By dividing the resistor in two parts it shall be ensured that
Section 7
Impedance protection
227 to
423