ABB Relion 670 series, Technical Reference Manual, Page: 380 / 1232

The internal signal for detection of cross-country fault, DetectCrossCountry, that come
from the voltage and current discrimination part of the function can be achieved in
three different ways:
1. The magnitude of 3I
0
has been above the setting parameter Pickup_N for a time
longer than the setting of pick-up timer tIN .
2. The magnitude of 3I
0
has been above the setting parameter Pickup_N at the same
time as the magnitude of 3V
0
has been above the setting parameter 3V0Pickup
during a time longer than the setting of pick-up timer tVN .
3. The magnitude of 3I
0
has been above the setting parameter Pickup_N at the same
time as one of the following conditions are fulfilled:
•
the measured phase-to-phase voltage in at least one of the phase
combinations has been below the setting parameter
PU27PP for more than
20 ms.
• At least two of the phase voltages are below the setting parameter PU27PN
for more than 20 ms.
The second part, phase preference evaluation, uses the internal signal
DetectCrossCountry from the voltage and current evaluation together with the input
signal PHSEL together with phase selection pickup condition (from phase selection
functions) connected to input PHSEL, and the information from the setting parameter
OperMode are used to determine the condition for trip. To release the Phase preference
logic, at least two out of three phases must be faulty. The fault classification whether it
is a single phase-to-ground, two-phase or cross-country fault and which phase to be
tripped at cross-country fault is converted into a binary coded signal and sent to the
distance protection measuring zone to release the correct measuring zone according to
the setting of
OperMode . This is done by activating the output ZREL and it shall be
connected to the input PHSEL on the distance zone measuring element.
The release signals from phase selection will only be gated with the cross-country
check from I
N
and V
N
but without time delay. If no phase selection start has occurred,
the release is based on current and voltage discriminating part only.
The input signal PHSEL consist of binary information of fault type and is connected to
the output PHSEL on phase selection function. The fault must be activated in at least
two phases to be classified as a cross-country fault in the phase preference part of the
logic.
The input signals RELxxx are additional fault release signals that can be connected to
external protection functions through binary input.
The output BFI_3P and trip signals can be blocked by activating the input BLOCK
Section 6
1MRK505222-UUS C
Impedance protection
374
Technical reference manual