ABB Relion 670 Series Applications Manual page 523

1MRK 511 401-UEN Rev. K
HighTapPsOLTC1 : It defines the tap position number at which maximum voltage is possible for
OLTC1.
StepSizeOLTC1 : It defines the change per OLTC1 step (for example, 1.5% of the rated voltage
of that winding).
18.12.3.4 Through fault detection
The transformer is subjected to electrical and mechanical stress when a fault current flows
through it, which is more than the transformer overload current. In general, stress reduces the
transformer life and it becomes even worse when stress occurs due to through faults. The
function checks the measured RMS currents against the set start level for through fault
detection. If the measured RMS current is above the set threshold limit and sustains even after
the set time delay, then through fault is detected. This time delay is used to ignore inadvertent
detection of faults. Also, for resetting through fault detection, a hysteresis has been
considered to avoid oscillations in boundary conditions.
The following settings are related to through fault detection which are set under basic
settings:
W1I> : It defines the current start value for through fault detection in percentage of winding 1
IB . This setting shall be set higher than the overload capacity of the transformer. This is
because currents below 3.5 times the rated current may generate due to overloads. Similarly,
current start values shall be set for winding 2 and winding 3 using settings which designated
W2 and W3 in the settings name.
with
tMin : It defines the minimum duration of fault to start any calculations. It is used to ignore
accidental detection and calculations if the fault current drops below the lower threshold level
within a short time.
The function monitors the time between last two subsequent through fault detections and it
gives a warning signal when the time difference is below the set time. This indicates that the
transformer has faults very frequently and it may undergo heavy electrical and mechanical
stress. Thereby, the utility can take prior attention and undertake preventive actions to avoid
serious consequences. This warning signal resets if no more faults occurred within the same
set time.
tMultiThroFlt : It defines the time window to detect multi through faults. This setting shall be
set based on the maximum allowed number of through fault per time period, which may be
indicated by the transformer manufacturer.
18.12.3.5
Through fault
Through fault
integration exceeds the set limit in any one phase, an alarm is raised. The
winding-wise and once the alarm is raised, then control actions can be taken such as changing
auto-reclosing settings.
MaxI2tW1 : It defines the I
setting shall be set based on the withstand capability of each winding with respect to
corresponding rated current. Similarly, the threshold limit for winding 2 and winding 3 shall be
set using
Bay control REC670
Application manual
The above settings are defined for OLTC1. Similar settings shall be set for
second on-load tap changer designated with OLTC2 in the setting names, for
three winding configurations.
2
I t alarms
2
I t calculations are done for all windings and phase-wise, and when this
2
t threshold limit for an individual event or fault per phase. This
MaxI2tW2 and MaxI2tW3 settings.
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Section 18
Monitoring
GUID-EA8374AC-90DB-43E9-9DEA-49C2D962F9E3 v1
GUID-06C7135E-7082-488C-B64A-6A82F95E7C35 v1
2
I t limit shall be set
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