A sensor failure that led to an anomalous high temperature caused the total shutdown of both power stations twice on June 16, according to a report compiled by Enemalta engineers.
There was a total failure at both power stations twice that day, first at 10:30 a.m. and subsequently at 4 p.m.
The report said that the remaining generating units tripped moments later as a result of this fault.
Enemalta said in a statement that although its engineers immediately suspected what had happened, the alarm log could not precisely identify this that morning.
The subsequent investigation revealed that the GT-9 turbine failure led the other steam units, particularly those at Marsa to lose synchronisation. They subsequently tripped together with all other generating units in service at the time.
In the second shutdown, the cause was much more distinct, as
the first unit to trip was the GT-9 and no fluctuation in the load was noted as in the previous case.
The investigation revealed that the GT-9 unit tripped due to an anomalous high temperature and since there was no indication of any type of fault immediately prior to this, it was clearly established as the main cause indicating a possible fault in the fuel or combustion system of the turbine.
At the time of the incident the peak demand stood at 340MW. On June 16, the actual reserve capacity stood at 30MW, however this was due to unplanned outages on boiler 7, rated 70MW (Steam) and which was taken out of service on June 12 due to a tube leak. Prior to the unplanned outage on boiler 7, the reserve capacity was of 100MW, greater than the size of the largest running unit and hence was a satisfactory reserve capacity.
The availability of such reserve capacity would have ensured sufficient power to restore supply to all load, even in the event of a prolonged
outage of the faulty unit
In this specific case, had GT-9 been unavailable following the trip, the available reserve capacity would have still been sufficient.
However, even if the reserve capacity had been higher at the time of the incident, this would not have prevented either the trip of the gas turbine, or given the circumstances, stop the cause of the tripping of the remaining generating units which led to the system shutdown.
This led the engineers to conclude that the outage was caused by the combined reaction of unconnected causes that would not have caused the outage had they occurred separately.
Enemalta said that under normal circumstances, its resources and equipment, as well as the procedures and policies for regular maintenance and repair would have prevented this outage as they did on every other day of the year.
However, even in this context abnormal circumstances were both unfortunate and though rare, possible.
The complete report is being tabled at the House of Representatives on Tuesday.
Enemalta again apologised for the inconvenience caused.