On the evening of Friday, March 27, 2009, at around 8:45 p.m., an island-wide outage occurred when an insulator holding a conductor on one of our main 24,000 volt overhead lines broke off, creating a heavy fault on the system.
Normally, the automatic protective devices installed to protect the line, would have operated to isolate the faulty section, with minimal impact on customers other than those in the vicinity of the faulty section of line.
However, preliminary investigations have revealed that a delay in operation of one of the protective devices on the line resulted in the fault feeding back to our generating station, causing a cascade tripping of generators that resulted in the island-wide outage. Immediately, staff started their safety checks, the system was prepared for restoration and within 45 minutes of the outage, the restoration process started.
Thanks to the effort of all of those members of staff, who came out to assist with the restoration process, power was progressively restored and by 11:00 p.m. supply to all customers, other than those affected directly by the faulty section of line, were restored.
Thanks to David Slocombe and his crew, under the supervision of Jerry Thompson, the faulty section of line was repaired by 2:00 a.m. and the supply restored to the customers in the affected area.
This has been the fourth occasion over the last year that we have experienced an island wide outage. While our response to restoring supply after these outages has improved substantially, we do not consider this situation to be acceptable and regret the inconvenience that it causes to our customers. We are currently investigating the matter to determine the cause of the failure of our protective system to isolate the faulty section without impacting the wider customer base and to take whatever corrective action is required so we can avoid these unfortunate occurrences in the future.