ABB RELION REX640 - Faulted phase selection, the underimpedance method

Start of element START_GFC STARTS_GF
C
RELEASE_P
E
RELEASE_P
P
I
B
>> & I
C
>> &
EARTH_FLT
I
C
> & I
A
> & U
CA
< &
EARTH_FLT |
I
C
>> & I
A
>> &
EARTH_FLT
TRUE CA Fault CA Fault CA Fault
I
A
> & I
B
> & I
C
&
U
AB
< & U
BC
< U
CA
< |
I
A
>> , I
B
>> & I
C
>>
6
TRUE ABC Fault No fault ABC Fault
I
A
> & I
B
> & I
C
&
U
AB
< & U
BC
< U
CA
< & EARTH_FLT |
I
A
>>, I
B
>> & I
C
>> &
EARTH_FLT
7
TRUE ABC Fault No fault ABC Fault
I
x
> Phase current exceeds the Lo A Ph Sel GFC setting
I
x
>> Phase current exceeds the Str A Ph Sel GFC setting
U
x
< Phase voltage undershoots the Ph V Ph Sel GFC setting
U
xy
< Phase-to-phase voltage undershoots the PP V Ph Sel GFC setting
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:
(Equation 261)
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.
1MRS759142 F Protection functions
REX640
Technical Manual
953