ABB RELION REX640 Technical Manual page 625

1MRS759142 F
Figure 355: Simplified illustration of a cross-country fault between phases A and C,
where two simultaneous single-phase earth faults occur in two different locations
and two different phases in the network
IFPTOC has an in-build dedicated functionality for cross-county fault detection and
tripping. Detection of cross-country fault is always enabled, but tripping may be
enabled or disabled with setting
instances of IFPTOC are applied in the protection configuration, only single instance
of IFPTOC requires cross-country fault tripping functionality to be enabled; in other
instances, cross-country fault tripping functionality may be disabled. As default
Enable XC Op mode = "on" i.e. tripping is enabled during cross-country faults.
There are two independent criteria for cross-country fault detection: The 1st
criterion requires that residual current exceeds a value which is higher than
maximum single-phase earth-fault current of the network, and the 2nd criterion
monitors voltage dip in any of the phase-to-phase voltages.
Residual over-current criterion
Monitoring of the magnitude of calculated residual current (I
setting
It should be noted, that setting value
In is phase current nominal value. Typical value for
amperes is few hundreds of amperes. The setting
higher than the estimated minimum cross-country fault current (I
the other hand it must be checked against the uncompensated earth-fault current
of the network (I
REX640
Technical Manual
XC stage A Str Val during a detected earth fault:
Calculated I is used to avoid problems in case of possible CBCT
o
saturation during high current cross-country fault.
) and setting of the low-set overcurrent stage (
eNet
Enable XC Op mode = "on" or "off". In case multiple
XC stage A Str Val is given in unit [xIn], where
XC stage A Str Val in primary
XC stage A Str Val should not be
Protection functions
) and comparing it to
o
(Equation 132)
), and on
F_XCmin
3I> ):
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