ABB Relion 670 series, Technical Manual

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The polarization quantities used for the mho circle are 100% memorized positive sequence
voltages. This will give a somewhat less dynamic expansion of the mho circle during faults than a
plain cross polarized characteristic. However, if the source impedance is high, the dynamic
expansion of the mho circle might lower the security of the function too much with high loading
and mild power swing conditions.
The mho distance element has a load encroachment function which cuts off a section of the
characteristic when enabled. The function is enabled by setting the setting parameter
LoadEnchMode to Enabled. Enabling of the load encroachment function increases the possibility
to detect high resistive faults without interfering with the load impedance. The algorithm for the
load encroachment is located in the Faulty phase identification with load encroachment for mho
function FMPSPDIS (21), where also the relevant settings can be found. Information about the load
encroachment from FMPSPDIS (21) to the zone measurement is given in binary format to the input
signal LDCND.
7.3.6.3 Basic operation characteristics
SEMOD154224-21 v9
Each impedance zone can be switched OnEnabled and OffDisabled by the setting parameter
Operation.
Each zone can be set to Non-directional, Forward or Reverse by setting the parameter DirModeSel.
The mho characteristics can be classified into -
Offset or Directional. The directional mho
characteristics can be set to
Offset, Forward or Reverse by the setting parameter DirMode. The
offset mho characteristic can be set to
Forward or Reverse or Non-Directional by the setting
parameter
OffsetMhoDir.
The operation for phase-to- ground and phase-to-phase fault can be individually switched
Enabled
and
Disabled by the setting parameter OpModePG and OpModePP.
For critical applications such as for lines with high SIRs as well as CVTs, it is possible to improve
the security by setting the parameter ReachMode to Underreach. In this mode the reach for faults
close to the zone reach is reduced by 20% and the filtering is also introduced to increase the
accuracy in the measuring. If the ReachMode is set to Overreach no reduction of the reach is
introduced and no extra filtering introduced. The latter setting is recommended for overreaching
pilot zone, zone 2 or zone 3 elements and reverse zone where overreaching on transients is not a
major issue either because of less likelihood of overreach with higher settings or the fact that
these elements do not initiate tripping unconditionally.
The offset Mho characteristic can be set in
Non-directional, Forward or Reverse by the setting
parameter
OffsetMhoDir. When Forward or Reverse is selected a directional line is introduced.
Information about the directional line is given from the directional element and given to the
measuring element as binary coded signal to the input
DIRCND
.
When
DirMode is set to offset and offsetMhoDir is set as Non-Directional, ZDMRDIR does not have
any effect on the measurement loop and operation of the function. When
DirMode is selected as
Forward or Reverse, a directional line is introduced. Information about the directional line is given
from the directional element (ZDMRDIR) and given to the measuring element as binary coded
signal to the input
DIRCND
.
The zone reach for phase-to- ground fault and phase-to-phase fault is set individually in polar
coordinates.
The impedance is set by the parameters
ZPG and ZPP and the corresponding angles by the
parameters
ZAngPG and ZAngPP.
Section 7 1MRK 502 066-UUS B
Impedance protection
220
Technical manual