impedance grounded system, the voltage drop is big and the setting can typically be set to
70%, which is 70% of UBase divided by √3.
PU27PP: The setting of the phase-to-phase voltage level (line voltage) which is used by
the evaluation logic to verify that a fault exists in two or more phases. The voltage must
be set to avoid that a partly healthy phase-to-phase voltage, for example, B-C for a A-B
fault, picks-up and gives an incorrect release of all loops. The setting value should
therefore not, without special reasons, be set higher than 50% (of UBase), which
corresponds to 85% of the minimum voltage for the partly healthy loops (i.e. 85% of
UBase divided by √3).
3V0PU: The setting of the residual voltage level (neutral voltage) which is used by the
evaluation logic to verify that an ground-fault exists. The setting can typically be 20% of
base voltage (VBase).
Pickup_N: The setting of the residual current level (neutral current) which is used by the
evaluation logic to verify that a cross-country fault exists. The setting can typically be
20% of base current (IBase) but the setting shall be above the maximum current generated
during a single ground-fault. A high sensitivity is not crucial as the two-phase fault level
normally is well above base current.
tIN: The time delay for detecting that the fault is cross-country. It should be set longer than
the expected duration of a transient residual current appearing for a single earth-fault.
Normal time setting is 0.1 - 0.15 s.
tVN: The time delay for a secure VN detecting that the fault is an ground-fault or double
ground-fault with residual voltage. Normal time setting is 0.1 - 0.15 s. It should not be set
shorter than tIN because that might bypass tIN prematurely.
tOffVN: The VN voltage has a reset drop-off to ensure correct function without timing
problems. Normal time setting is 0.1 s.
In the High speed distance protection ZMFPDIS, setting INReleasePE needs to be set
lower than the expected residual current during a cross-country fault. Otherwise the
distance protection might operate in the phase-to-phase loops which will bypass the Phase
preference logic.
Section 8 1MRK 506 369-UUS -
Impedance protection
486 Line distance protection REL670 2.2 ANSI
Application manual
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