Below is my root cause analysis (RCA) for the tripping of our 69kV Line. Since I could not speak for the Test and maintenance section-Relay Group, I presented the root cause using simple calculation and analysis. Please leave comments below for the improvement of this RCA.
BACKGROUND:
CUSTOMER FEEDER is a radial 69kV line connected at 69kV bus at our substation.
INITIAL ACTION/S TAKEN:
To verify if relays at CUSTOMER SS and our SS are properly coordinated.
Test and maintenance section-group, supervisors, Transmission engineers
Test and maintenance section-group to conduct verification and relay coordination if needed at CUSTOMER Substation.
BACKGROUND:
On July
5, 2012 at 193H, CUSTOMER 69 KV Line auto tripped but autoreclosed. Informed
concerned officials about the tripping. Transmission Line personnel were
dispatched to conduct line inspection.
PROFILE OF TRANSMISSION
LINE:
Commissioning date
of the line:
|
1996 |
Line/Cable
Specification:
|
336 MCM ACSR
|
Line Hardwares
Involve:
|
N/A
|
Right-Of-Way
Issue:
|
N/A
|
Date of last
Inspection/Maintenance/ Row Clearing;
|
CHRONOLOGY OF EVENTS:
Date/Time Out
|
Line/Equipment
|
Date/Time
Energized
|
Relay Target/Fault
Locator
|
July
5, 2012 / 1934H
|
CUSTOMER 69kV Line
|
July
5, 2012 / 1934H
|
SPAA 341C: I (time), Phase A B, C
SEG: I (time), Phase A, B, C (Ia=157A, Ib=130A,
Ic=143A)
|
Weather
Condition: Strong winds with heavy rains and lightning prevailed in the area.
Substation
Engineer on duty coordinated with Supervisors, TL Engineer and
Transmission Line Crew about the tripping of the line.
FINDINGS/ ANALYSIS:
The
probable cause of outage is miscoordination of relays at CUSTOMER SS
and our Substation. The low three-phase fault
current values registered by the SEG Overcurrent Relay is near the value of
fault current transformed at the secondary side of CUSTOMER SS power
transformer. Initial fault data at one of the 13.8kV feeders of CUSTOMER before tripping have the following values:
Indications
of 13.8kV Feeder 1 of CUSTOMER S/S before 69kV line tripping at
our substation:
Feeder
1-Lockout @ 1930H (4 minutes before the actual tripping of our 69kV Line)
Ia= 78A
Ib= 99A
Ic=1099A
Iground=
1014A
Converting
the said values at 69kV primary side will yield:
Ia= 15.6A
Ib= 19.8A
Ic= 219.8A
Iground=
202.8A
The fault current values at CUSTOMER FEEDER were used as reference only. The
values of Ic and Iground, 219.8A and 202.8A respectively, are near within the
magnitude of the fault currents retrieved at SEG relay on the time of tripping
(Ia=157A, Ib=130A, Ic=143A).
Therefore, fault along CUSTOMER sub-feeders which may not be isolated
by their overcurrent relays may have caused the tripping of CUSTOMER 69kV Line.
CORRECTIVE ACTION/S TO BE TAKEN:
To verify if relays at CUSTOMER SS and our SS are properly coordinated.
RESPONSIBLE GROUP:
Test and maintenance section-group, supervisors, Transmission engineers
SOLUTIONS/RECOMMENDATIONS:
Test and maintenance section-group to conduct verification and relay coordination if needed at CUSTOMER Substation.
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