Observations during pre-commissioning of Muktagacha 132/33kV grid sub-station

1. Relay testing has been performed using arbitrary relay settings due to the absence of the
approved relay settings calculation. Power Grid approved relay settings need to
be uploaded and demonstrated before proceeding with the commissioning.
2. During witnessing busbar protection testing, both bus 1 & bus 3 have been found
tripped for any fault between bus section CT & CB whereas one side busbar tripping
is enough to clear the fault. This scheme shall be modified and tested.
3. Auto reclosing scheme has not been tested for Mymensingh-1 & 2 circuits due to problem
in closing coil of breaker. This shall be rectified immediately before commissioning.
4. Power swing inside protection zone over 2 seconds has been found blocked instead
of tripping. It shall be rectified.
5. BCU testing is not done yet. All BCU LEDs used for alarms shall be tested before
commissioning.
6. Tele-protection panels are not available at site. To ensure faster selective tripping
for line, it is mandatory.
7. SAS panels are not installed yet. For smooth operation of the grid, it needs to be
installed at the earliest.
8. All CB tripping redundant path from lockout relays and bay units need to be tested.
9. For BBP tripping, only 96 relay has been used without considering redundancy. It may be
paralleled with 86.1/86.2 to keep the redundant tripping path.
10. All auxiliary contact from line PT MCB need to be wired up to protection relay
and BCU input. VT Fuse Fail function shall also be tested considering PT MCB (protection
core) fail input.
11. For ES local interlock, ‘no voltage in line’ signal shall be established at local.
12. Transformer feeders do not have any PT at 132kV side for which no provision is
available to check transformers’ 132kV side live portions.
13. BUS-2 PT voltage (3-phase) shall be connected dedicatedly to a BCU to monitor it
from SAS.
14. Transformers parallel tap change operation needs to be established perfectly.
15. The Winding Temperature Indicator (WTI) and Oil Temperature Indicator (OTI)
meters require checking and calibration to ensure their accuracy and proper operation
before commissioning.
16. Transformer 1 & 3 is not possible to operate in parallel due to interlocking in 33kV
bus section DS. Also, if 33kV switchgear short circuit rating allow three transformers to
operate in parallel, it will not be possible due to the interlocking of 33kV bus section DS.
33kV bus section DS interlock scheme needs to be modified.
17. For manual CB opening of line bay it is not possible to operate manually if
trip coil 1 is out of service. Both trip coil 1 & 2 shall be used redundantly for manual
CB opening.
18. Live operation of bus DS for each bay shall be considered only for remote
operation (from control room) instead of both from control room and from DS local
panel. From operational point of view, local live operation is not acceptable to
ensure human safety.
19. During the interlock bypass condition in CRP panel in control room, DS/ES may
be possible to operate from local panel of the respective DS/ES. Local interlock
bypassing option shall not be available from remote (control panel) to allow life
threatened loaded DS operation at local.
20. Live operation of all CB at local found in the scheme shall not be allowed for human
safety.
21. In bus coupler and bus sectionalizer bay interlock scheme, only respective bus
 DS open status is enough instead of both DS of coupler/section for the operation of ES
associated with bus 1, 3 & 4.
22. QBD DS status along with all bus-2 DS open (bus-2 dead conditions) have not been
considered for the interlock of QC2 ES of bus sectionalizer when bus coupler is in close
position.
23. For 33kV feeder ES interlock, line DS status is enough.
24. 132kV lines, transformers, bus coupler and bus sectionalizer bay panels have not
been considered regarding their actual physical position which may create complicity
during operation. Bus number shall also be shown in the switchyard.
25. Bus is considered as sectionalized with 4 numbers of sections (Bus 1, Bus 2, Bus 3 &
Bus 4). Each section is considered with earth switch except bus section number 2,
whereas two numbers of ES are considered for bus section number 3. Also, in PSLD,
bus earth switches are shown inside of bus coupler/bus sectionalizer though all ES
are physically present at bus side.
26. Numbering of the bus isolators has been found without considering the actual bus
position/ number. For bus 3 DS and bus 4 DS, QB1 and QB2 numbering have been used
respectively instead of QB3 and QB4. It may create complicity during operation. So,
Rectification is required in panel physically and reflection of it is required throughout the
whole drawing as well as there where it is required.
27. Numbering of the bus earth switches has been found without considering
the actual bus position/number. In bus sectionalizer, bus 3 ES is numbered as QC2
whereas in bus coupler, bus 3 ES is numbered as QC1. Again, in bus coupler, bus 4
ES is numbered as QC2. It may create complicity during operation. So,
Rectification is required in panel physically and reflection of it is required throughout
the whole drawing as well as there where it is required.
28. Operator sitting position in the control room has been considered on the opposite side
of switching station for which any incident occurred in the switchyard will not be
visible instantly through doors/windows. From operational point of view, this type
of arrangement is unprofessional and response time for any kind of incident will be
more.
29. Status of DC changeover between DC1 & DC2 needs to be provided as an alarm
to become alert which may avoid complete DC outage in panels.
30. In DCDB panel DC-1 & DC-2 sources along with coupler are not indicated with a
SLD (mimic). It will make confusion during operation of DC sources.
31. SLD drawn in ACDB panel is wrong where both ACDB-1 & ACDB-2 indications are
shown towards one charger only which needs to be corrected.
32. Single pole circuit breakers shall have provision to operate in single phase electrically
from local CB box.
33. In PSLD, though sync. Check (25) option is available for backup protection relay; it
is not reflected in the drawings/scheme.