The 2Nd And 5Th Harmonic Analysis - ABB RELION 650 Series Applications Manual

1MRK 505 363-UEN A
protection zone, due to long duration of transformer inrush current the parameter should be
set to 60 s. Otherwise a setting of 1 s is sufficient.
IdUnre
IdUnre is set as a multiple of IBase . Values of differential currents above the unrestrained limit
generate a trip disregarding all other criteria, that is, irrespective of the internal or external
fault discriminator and any presence of harmonics. It is intended for fast tripping of internal
faults with high fault currents. The recommended setting is 120% of the highest through fault
current that can appear on the protected line. Consequently, to set this value properly, the
fault current must be calculated in each specific case.
For a short line or a situation with a 1½ breaker bay, the through fault current might be
practically the same as the differential current at an internal fault. Extreme unequal CT
saturation at external faults could then be a risk of unwanted operation if the unrestrained
operation is used. Consequently, if the through fault currents can be of the same order as the
maximum differential currents at internal faults, for example, when there is a source of power
only on one side (in the branch with the first CT), and only load on the other side (in the branch
with the other CT), it is recommended to refrain from using the unrestrained operation, by
setting the max value
On long lines, the through fault current is often considerably less than the maximum
differential current at internal faults, and a suitable setting of the unrestrained level is then
easy to calculate.
When a transformer is included in the protected zone, the maximum inrush current must be
considered when the unrestrained level is calculated. The inrush current appears from one side
of the transformer, while the maximum differential current at internal faults is limited by the
source impedances on all sides of the transformer. Observe that if the power transformer is
energized via a power line, even a short one, the inrush phenomenon is much less pronounced.
The fundamental frequency of the inrush current will not be as high as when the power
transformer is connected directly to a source with very low internal impedance.
EndSection1
EndSection1 is set as a multiple of IBase . The default value 1.25 is generally recommended. If
the conditions are known more in detail, other values can be chosen in order to increase or
decrease the sensitivity.
EndSection2
EndSection2 is set as a multiple of IBase . The default value 3.00 is generally recommended. If
the conditions are known more in detail, other values can be chosen in order to increase or
decrease the sensitivity.
SlopeSection2
SlopeSection2 is set as a percentage value: [delta operate current/delta restrain current] ×
100%. The default value 40.0 is generally recommended. If the conditions are known more in
detail, other values can be chosen in order to increase or decrease the sensitivity.
SlopeSection3
SlopeSection3 is set as a percentage value: [delta operate current/delta restrain current] ×
100%. The default value 80.0 is generally recommended. If the conditions are known more in
detail, other values can be chosen in order to increase or decrease the sensitivity.
6.2.3.3

The 2nd and 5th harmonic analysis

nd
The 2
transformer (A or B, alternatively both A and B) is part of the protected circuit. This is a must
due to phenomena specific for power transformers, such as inrush and over-excitation. If there
is no power transformer included in the protected multi-terminal line circuit, then the 2
th
5 harmonic block scheme is only active under the following conditions:
Application manual
IdUnre = 50 × IBase .
th
and 5 harmonic block scheme is permanently active only if an in-line power
Section 6
Differential protection
M12541-180 v5
M12541-186 v3
M12541-189 v3
M12541-192 v4
M12541-195 v4
M12541-198 v5
nd
and
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