ABB Relion 670 Series Applications Manual page 497

1MRK 511 401-UUS F
LowTapOLTC1 : It defines the tap position number at which minimum voltage is possible for
OLTC1.
RatedTapOLTC1 : It defines the tap position number at which rated current and voltage of that
winding for OLTC1.
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).
17.12.3.4 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 pickup 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:
W1 I pickup : It defines the current pickup value for through fault detection in percentage of
winding 1
because currents below 3.5 times the rated current may generate due to overloads. Similarly,
current pickup values shall be set for winding 2 and winding 3 using settings which designated
W2 and W3 in the settings name.
with
t_MinTripDelay : 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.
17.12.3.5
Through fault
Through fault
exceeds the set limit in any one phase, an alarm is raised. The
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.
IB . This setting shall be set higher than the overload capacity of the transformer. This is
2
I t alarms
2
I t calculations are done for all windings and phase-wise, and when this integration
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GUID-EA8374AC-90DB-43E9-9DEA-49C2D962F9E3 v1
GUID-06C7135E-7082-488C-B64A-6A82F95E7C35 v1
2
I t limit shall be set winding-wise
Section 17
Monitoring
491