Sarawak suffered two outage within a nine-hour period, with the first one which occurred at 6.38 pm yesterday and another outage at 3.30 am today.

Sarawak Energy in a statement today said the first outage affected Sibu, parts of Mukah and 30 per cent of Kuching, was caused by a double circuit tripping at the 275kV Kemena-Selangau line, causing system split.

"This was suspected to have been caused by heavy lightning activity in the area," said Sarawak Energgy group chief operating officer Lu Yew Hung.

He said Sarawak Energy's system defence scheme activated immediately and Kuching was successfully islanded to minimise the number of customers affected, with full restoration at 6.14am.

"This is a separate incident from the tripping at Oya-Selangau 275kV transmission lines yesterday evening," said Lu, adding that Sarawak Energy is currently investigating the cause of these two outages.

He said the risk of incidents like these would continue until the completion of the 500kV second transmission line - potentially two to three major outages could happen in a year until critical parts of the project are completed.

According to Lu, the 500kV transmission line would provide a second backbone transmission, avoiding major outages in the event of a double circuit trip such as what had happened in November 2015 and January 2016.

"With two parallel transmission backbones, power supply will continue from our major generation power plants concentrated in the north such as the Bakun and Murum HEPs to customers in Sarawak, particularly in the more densely populated southern region should the lines trip," he added. -- Bernama