ST Microelectronics power cut: Enemalta cites ‘extraordinary sequence of events’

An internal analysis by Enemalta Corporation on the "extraordinary" situation that led to a power cut which affected ST Microelectornics on Sunday found multiple faults in cables, despite efforts to repair the interrupted feed.

At around 2:26am on Sunday, the 33kV feeder line which supplies Kirkop Distribution Centre developed a fault. SCADA engineers diverted the load to the distribution centre's alternative supply, which consists of two 11kV cables, specifically used as a standby source of supply to ST Microelectronics, and supply was restored 10 minutes later at 2:36am.

But at around 6:15am, in view of the load, these two 11kV feeders tripped and since these were being operated in parallel it was not possible to establish which cable was the faulty one. 

The 33kV feeder, which supplies Kirkop DC, is made up of more than 5km of underground cables and more than 7km overhead lines. Enemalta engineers were deployed to have these dedicated feeds repaired.

This meant that all of the 5km underground cables needed to be pressure tested, while the 7km overhead cables visually inspected.

Parallel to this, Enemalta employees were also working to locate the fault on the 11kV cables which are underground.

In the early afternoon, a fault on one of the 11kV cables was identified and repair works started soon after whilst the second 11kV feeder is being checked today.

"Unfortunately these two 11kV feeders have in the past months suffered a considerable amount of stress after being dug up and re-laid due to the recent roadworks happening in Luqa. Such circumstances cause weak spots in the cable. These can only be identified by Enemalta once the cable trips," the corporation said in a statement.

Power was finally restored by 19:45pm.

"One needs to point out that under normal conditions ST Microelectronics is adequately supplied with the 33kV feeder which can be fed by both Marsa and Delimara power station, and the two 11kV feeders which are fed from Marsa power station," Enemalta said.

A second 33kV feeder to Kirkop DC, a distribution centre built specifically to supply ST Microelectronics directly from the high voltage network, has been planned and should be completed by the end of the year, ensuring further security of supply. This additional feeder will be laid in existing tunnels and will therefore not be susceptible to stresses caused by road works.