IEC11000009 V1 EN
Figure 137: Effective high-resistance generator earthing via a distribution
transformer
Another alternative is shown in figure 138 (High-resistance earthing via a delta,
grounded-wye transformer). In this case the transformer must withstand the large
secondary current caused by primary earth fault. The resistor typically has to be
divided as shown in figure 138 to limit the voltage to the injection equipment in case of
earth 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
138 . By dividing the resistor in two parts it shall be ensured that maximum
voltage imposed back on injection equipment is equal to or less than 240V.
1MRK502052-UEN B Section 7
Impedance protection
307
Technical manual
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