ABB RELION REX640, Техническое руководство, Страница: 948 / 1960

Table 907: Polarizing quantities for optional directional function for earth faults in
low-impedance earthed networks
Pol quantity GFC Polarizing
quantity
Operating
quantity Description
Zero seq. volt. -U
0
I
0
Zero-sequence voltage polarization
Neg. seq. volt. -U
2
I
2
Negative-sequence voltage polari-
zation
Zero seq. cur. I
oref
I
0
Zero-sequence current polarization
Zro vol. OR cur. -U
0
OR I
0ref
I
0
Dual polarization
The polarizing quantity is -U
0
and the operating quantity is I
0
in case of
zero-sequence voltage polarization.
The polarizing quantity is -U
2
and the operating quantity is I
2
in case of
negative-sequence polarization.
In case of zero-sequence current polarization "Zero seq. cur.", the zero-sequence
current I
0
of the protected line is the operating quantity while another reference
zero-sequence current I
0ref
is the polarizing quantity. I
0ref
, for example, could be
the current from the neutral of a power transformer. In case of zero-sequence
current polarization, the relay characteristic angle
Chr angle GFC is internally fixed
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
0
is high, U
0
is low, and when I
0
is low, U
0
is high. Hence the protection can benefit
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
Phase Sel mode GFC setting.
Table 908: Supported methods for phase selection
Setting Enumerator value
Phase Sel mode GFC
• Overcurrent
• Vol Dep Overcur
• Under impedance
• OC AND Und impedance
• 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.
Protection functions 1MRS759142 F
948 REX640
Technical Manual