ABB RELION REX640, Техническое руководство, Страница: 627 / 1960

Phase-to-phase under-voltage criterion
Monitoring of the magnitude of any phase-to-phase voltage (U
AB
, U
BC
or U
CA
) and
comparing it to setting
XC stage PP V Val during a detected earth fault:
(Equation 135)
During a single-phase earth fault phase-to-phase voltages are not affected, but
during a cross-country fault the phase-to-phase voltages are affected, refer to
Figure 356
. Default setting for
XC stage PP V Val is 0.9xU
n_PP
, where U
n_PP
is the
nominal phase-to-phase voltage.
In case all three phase-to-phase voltages (U
AB
, U
BC
and U
CA
) are under
setting for
XC stage PP V Val , such condition is considered as permanent
three phase under-voltage condition, not a cross-country fault.
Figure 356: Illustration of behavior of residual, phase-to-earth and phase-to-phase
voltages during an evolvement of single-phase earth fault into cross-country fault in
a 10 kV compensated network
The magnitude of phase-to-phase voltage between faulted phases during a cross-
country fault can be estimated using the following equation:
1MRS759142 F Protection functions
REX640
Technical Manual
627