Figure 291: Connection of the current transformers of Type 2. The phase currents
and the neutral current have equal directions at an external earth-fault situation.
Phase earthing is inside and neutral earthing is outside the area to be protected.
Figure 292: Connection of the current transformers of Type 2. The phase currents
and the neutral current have equal directions at an external earth-fault situation.
Phase earthing is outside and neutral earthing is inside the area to be protected.
Internal and external faults
LREFPNDF does not respond to any faults outside the protected zone. An external
fault is detected by checking the phase angle difference of the neutral current and
the sum of the phase currents. When the difference is less than 90 degrees, the
operation is internally restrained or blocked. Hence the protection is not sensitive
to an external fault.
1MRS757644 H
Protection functions
620 series
Technical Manual
565
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