ABB RELION REX640 Technical Manual page 948

Protection functions
Table 907: Polarizing quantities for optional directional function for earth faults in
low-impedance earthed networks
Pol quantity GFC Polarizing
Zero seq. volt.
Neg. seq. volt.
Zero seq. cur.
Zro vol. OR cur.
In case of zero-sequence current polarization "Zero seq. cur.", the zero-sequence
current I
zero-sequence current I
the current from the neutral of a power transformer. In case of zero-sequence
current polarization, the relay characteristic angle
and is equal to zero degrees. The zero-sequence current direction must remain
unchanged during all network configurations and faults. Therefore, all transformer
configurations or constructions are not suitable for polarization.
In case of dual polarization "Zro vol. OR cur.", the zero-sequence voltage polarization
and zero-sequence current polarization elements are logically OR:ed. Typically, when
I is high, U
0
from both elements as the two polarization methods complement each other. If the
zero-sequence current polarization source is switched off for service, the flexibility
is increased as the zero-sequence voltage polarization can be used.
Faulted loop phase selection
A reliable identification of a fault and faulted phases is needed to guarantee a
selective operation of the distance protection. This information is used to release
correct measuring elements of the protection zones.
In DSTPDIS, the faulted phase selection can be done in various ways and defined
with the
Table 908: Supported methods for phase selection
Setting
Phase Sel mode GFC
• The "Overcurrent" method is the basic method for identifying the faulted phases.
It can be used in applications where the fault current magnitude exceeds the load
current despite the changes in the network configuration and fault type.
948
quantity
-U
0
-U
2
I
oref
-U OR I
0 0ref
The polarizing quantity is -U
zero-sequence voltage polarization.
The polarizing quantity is -U
negative-sequence polarization.
of the protected line is the operating quantity while another reference
0
is the polarizing quantity. I
0ref
is low, and when I
0
Phase Sel mode GFC setting.
Operating Description
quantity
I Zero-sequence voltage polarization
0
I Negative-sequence voltage polari-
2
zation
I Zero-sequence current polarization
0
I Dual polarization
0
and the operating quantity is I
0
and the operating quantity is I
2
Chr angle GFC is internally fixed
is low, U is high. Hence the protection can benefit
0 0
Enumerator value
• Overcurrent
• Vol Dep Overcur
• Under impedance
• OC AND Und impedance
1MRS759142 F
in case of
0
in case of
2
, for example, could be
0ref
Technical Manual
REX640