ABB RET670 Applications Manual page 400

Section 3
IED application
394
IBase: Base current level in A. The base current is used as reference for the neutral
current setting factor. Normally it is set to the current transformer rated current.
PU27PN: The setting of the phase-to- ground voltage level (phase voltage) which is
used by the evaluation logic to verify that a fault exists in the phase. Normally in a
high impedance grounded system, the voltage drop is big and the setting can typically
be set to 70% of base voltage (VBase)
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 can
typically be 40 to 50% of rated voltage (VBase) divided by √3, that is 40%.
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 by the system grounding. Note that the systems are high impedance
grounded which means that the ground-fault currents at ground-faults are limited and
the occurring IN above this level shows that there exists a two-phase fault on this line
and a parallel line where the IN is the fault current level in the faulty phase. A high
sensitivity need not to be achieved as the two-phase fault level normally is well above
base current.
tIN: The time delay for detecting that the fault is cross-country. 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.
tOffVN: The VN voltage has a reset drop-off to ensure correct function without timing
problems. Normal time setting is 0.1 s
1MRK504116-UUS C
Application manual