ABB RELION REX640 Technical Manual page 953

1MRS759142 F
Start of element
I >> & I
B
EARTH_FLT
I > & I
C
EARTH_FLT
I >> & I
C
EARTH_FLT
I > & I
A
U
AB
I >> , I
A
I > & I
A
U
AB
< &
I >>, I
A
EARTH_FLT
I >
x
I >>
x
U <
x
U
xy
Faulted phase selection, the underimpedance method
The "Under impedance" and "OC AND Und impedance" methods use fault
loop impedance for identifying the faulted phases. The advantage of the
underimpedance criterion is that the sensitivity of the fault detection is
independent of the source impedance. The underimpedance function has six
impedance measuring elements. The phase-to-earth measuring elements are
calculated:
6
This applies to near three-phase faults. If voltages are still relatively high, all PP releases are
given.
7
This applies to near three-phase faults with EF indication. If voltages are still relatively high, all PE
and PP releases (except ABC Fault) are given.
REX640
Technical Manual
>> &
C
> & U < &
A CA
|
>> &
A
> & I &
B C
< & U < U < |
BC CA
6
>> & I >>
B C
> & I &
B C
< & U < U
BC CA
|
EARTH_FLT
>> & I >> &
B C
7
Phase current exceeds the
Phase current exceeds the
Phase voltage undershoots the
< Phase-to-phase voltage undershoots the
START_GFC STARTS_GF
C
TRUE CA Fault
TRUE ABC Fault
TRUE ABC Fault
Lo A Ph Sel GFC setting
Str A Ph Sel GFC setting
Ph V Ph Sel GFC setting
PP V Ph Sel GFC setting
Protection functions
RELEASE_P RELEASE_P
E P
CA Fault CA Fault
No fault ABC Fault
No fault ABC Fault
(Equation 261)
953