The last three days was not very
successful.
We are running most of the time in
by-pass operation (no sync)
There are lots of control (DCS)
interface problems between (Hitachi, PAC and us) regarding the boiler feed
water control (which is Hitachi’s philosophy).
Alstom Belfort are in loop to give us
advise…
In addition Eskom is running out of fuel
oil. These previous nights were dedicated to re-fill the FO tanks.
ACTUAL
-
18:00
Synchronization (2 mills in service)
-
Load
increase to 320 MW
-
19:54
Blackout 400kV breaker open (see following STSN report) :
Alstom advises that at approximately 19:54 hr on the evening of 21 March 2015, the Unit 6 turboset/plant experienced yet another power blackout event.
At the time of the event, the Unit was on load of approximately 270 MW.
1. The details of the incident are as follows.
a. At approximately 19:54 hr the main transformer tripped – the emergency diesel generator did not automatically engage on loss of power.
b. We are aware that there was some work performed on the diesel generators during the course of last week – it is now clear following the loss of power, that the same generators were not placed in ‘stand-by’ mode following the said works.
c. As a consequence, the Unit 6 shaftline coasted-down to standstill in an abnormal manner, that is, the turbine ran down with only the emergency DC Lube Oil pump in operation, and no AC Lube Oil pump or Jacking Oil pump available due to the non-availability of AC power supply.
d. The diesel generators were eventually manually restarted locally, availing AC power for lube and jacking oil and providing the possibility of restarting of the turning gear.
e. However, it was not possible to put the shaft on barring – investigations revealed that although the ‘ON’ indication was given on the Control System as well as locally on the Machine Drive (- breaker), in actual fact the AC Lube Oil pump was ‘OFF’ with no disturbance indication at all.
f. It was only possible to resolve the fault and restart the AC Lube Oil pump by un-racking its breaker and then reinserting it.
g. Jacking Oil pump No. 1 was running with only DC Lube Oil supply.
h. Turning gear was eventually restarted with both Jacking Oil pumps in service.
i. A board change-over switched off the turning gear and the breaker had to be manually switched ‘OFF’ and ‘ON’ to be able to start the motor again.
j. At this point, the turbine shaft was really ‘tight’ and difficult to rotate manually, and the turning gear was not able to rotate the shaft due to the protection torque setting.
k. However with the shaftline having cooled down somewhat overnight, early on the next morning the turning gear was successfully restarted with the motor current at the normal operational level.
2. Alstom recommendations.
a. The turbine should be allowed to cool down to temperatures that allow the Contractor to safely
b. Inspect bearings 4, 5 and 6 – the bearings with the most load. In this respect, the Contractor reminds the Engineer of our correspondence referenced PM/PB/5039 dated 10 January 2012 in which we highlighted the requirement for the availability of the Emergency Lube Oil System for safe shutdown of the turbine in an AC blackout situation as well as the necessity of the Jacking Oil System for turning gear operation.
c. The turbine should not be restarted until all of the problems with the transformers, electrical boards, diesel generators are demonstrably resolved to avoid undue risk to the turboset unit.
d. The procedure of the Employer’s work permit system needs to be improved to ensure the avoidance of situations such as transpired as described earlier in our submission (- i.e., 1b.).
e. The causatives behind the frequent tripping of the coal mills need to be addressed prior to turbine restart to minimize the abnormal events that the unit is currently being subjected to and enable the stable continuation of hot commissioning activities.
f. The Employer should consider and take prudent action in respect of engagement with their insurers given the risk to the turbosets posed by continued instability of interfacing plant.
3. Alstom requests.
Given the foregoing and in order to have clarity on the conditions under which we are having to operate the turbine and generator plant and where possible be able to anticipate possible implications, the Contractor requests transparency from the Employer as follows.
a. A detailed explanation of the events leading to and causatives behind, the transformer trip and/or blackout event including clear details of what the Employer is doing to avoid a repeat of such an event.
b. A
detailed explanation of the failure of the AC Lube Oil pump machine-drive and
the corrective actions to be taken to ensure faultless operation going forward.
c. Confirmation and objective justification that such machine-drive fault is not a risk inherent in all other similar drives for vital turbine facilities.
d. How the Employer intends to proceed in respect of the foregoing Contractor recommendations submitted under ‘2’ above.
e. Specifically, we understand that Employer instruction has already been given in yesterday’s commissioning meeting, for the Contractor to continue with the inspection of bearings 4, 5, and 6 and request that this be officialised before Wednesday 25 March 2015 to avoid delay to such works.
a. At approximately 19:54 hr the main transformer tripped – the emergency diesel generator did not automatically engage on loss of power.
b. We are aware that there was some work performed on the diesel generators during the course of last week – it is now clear following the loss of power, that the same generators were not placed in ‘stand-by’ mode following the said works.
c. As a consequence, the Unit 6 shaftline coasted-down to standstill in an abnormal manner, that is, the turbine ran down with only the emergency DC Lube Oil pump in operation, and no AC Lube Oil pump or Jacking Oil pump available due to the non-availability of AC power supply.
d. The diesel generators were eventually manually restarted locally, availing AC power for lube and jacking oil and providing the possibility of restarting of the turning gear.
e. However, it was not possible to put the shaft on barring – investigations revealed that although the ‘ON’ indication was given on the Control System as well as locally on the Machine Drive (- breaker), in actual fact the AC Lube Oil pump was ‘OFF’ with no disturbance indication at all.
f. It was only possible to resolve the fault and restart the AC Lube Oil pump by un-racking its breaker and then reinserting it.
g. Jacking Oil pump No. 1 was running with only DC Lube Oil supply.
h. Turning gear was eventually restarted with both Jacking Oil pumps in service.
i. A board change-over switched off the turning gear and the breaker had to be manually switched ‘OFF’ and ‘ON’ to be able to start the motor again.
j. At this point, the turbine shaft was really ‘tight’ and difficult to rotate manually, and the turning gear was not able to rotate the shaft due to the protection torque setting.
k. However with the shaftline having cooled down somewhat overnight, early on the next morning the turning gear was successfully restarted with the motor current at the normal operational level.
2. Alstom recommendations.
a. The turbine should be allowed to cool down to temperatures that allow the Contractor to safely
b. Inspect bearings 4, 5 and 6 – the bearings with the most load. In this respect, the Contractor reminds the Engineer of our correspondence referenced PM/PB/5039 dated 10 January 2012 in which we highlighted the requirement for the availability of the Emergency Lube Oil System for safe shutdown of the turbine in an AC blackout situation as well as the necessity of the Jacking Oil System for turning gear operation.
c. The turbine should not be restarted until all of the problems with the transformers, electrical boards, diesel generators are demonstrably resolved to avoid undue risk to the turboset unit.
d. The procedure of the Employer’s work permit system needs to be improved to ensure the avoidance of situations such as transpired as described earlier in our submission (- i.e., 1b.).
e. The causatives behind the frequent tripping of the coal mills need to be addressed prior to turbine restart to minimize the abnormal events that the unit is currently being subjected to and enable the stable continuation of hot commissioning activities.
f. The Employer should consider and take prudent action in respect of engagement with their insurers given the risk to the turbosets posed by continued instability of interfacing plant.
3. Alstom requests.
Given the foregoing and in order to have clarity on the conditions under which we are having to operate the turbine and generator plant and where possible be able to anticipate possible implications, the Contractor requests transparency from the Employer as follows.
a. A detailed explanation of the events leading to and causatives behind, the transformer trip and/or blackout event including clear details of what the Employer is doing to avoid a repeat of such an event.
c. Confirmation and objective justification that such machine-drive fault is not a risk inherent in all other similar drives for vital turbine facilities.
d. How the Employer intends to proceed in respect of the foregoing Contractor recommendations submitted under ‘2’ above.
e. Specifically, we understand that Employer instruction has already been given in yesterday’s commissioning meeting, for the Contractor to continue with the inspection of bearings 4, 5, and 6 and request that this be officialised before Wednesday 25 March 2015 to avoid delay to such works.
