Sri Lanka’s island-wide blackout signals power supply reliability issue

Mar 15, 2016 (LBO) – Sri Lanka’s recent island-wide power blackout has raised concerns over the reliability of national power supply and its future. Issues are ranging from known areas such as the future of fossil and coal based power and renewable energy and to even more relatively new issues such as failing ‘n-1’ reliability criterion and related issues.

These issues were discussed in detail yesterday at a public forum organized by the Public Utilities Commission of Sri Lanka on consumer rights. Speaking at the forum, Additional General Manager of CEB Bandula Thilakasena said it is difficult for them to maintain the ‘n-1’ reliability standard in urban areas. In simple terms, it is getting hard for the CEB to guarantee an uninterrupted power supply in urban areas including Colombo and suburbs.



‘n-1’ reliability criterion refers to instances where one transmission line goes out of service due to whatever reason; the remaining lines must be able to carry the total load.
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If one line goes out of service, the remaining lines must be able to carry both the load they were carrying before the event, plus the load carried by the line that is out of service. As a example, the figure shown below depicts an instance where the middle line is out of service in a three parallel transmission lines network. The top line’s indicator shows that it is now operating at 129 percent of its capability and a transmission line cannot operate like this because the line gets too hot and can be damaged to the point of breaking.



So, in this case, the three transmission lines have failed the n-1 test and warrant a power outage. Rapid phase of urbanization and tighter restrictions have made things even difficult for CEB on routing new high voltage transmission lines above urban areas. “We can’t route power lines above houses as per new restrictions.



We even had issues when routing high tension power lines through areas where there were no houses,” Thilakasena said. “So it is getting difficult for us to build a ‘n-1’ reliability high voltage power transmission network in urban areas.

That is why we can’t maintain the n-1 reliability standard.” Thilakasena however said if a 300 Mw generator damaged the CEB has a system in the network to supply electricity without that generator. The issue of not maintaining the reliability standard may also leads to island wide power blackouts as the interconnected lines may get shutdown at different sub stations reducing the damage to high tension power lines and equipments. These shutdowns will intern leads to imbalances of real time power supply and demand over the network that may even end up causing power generator shutdowns in the national grid. “After a total failure some of our valuable equipments may get damaged and stay dormant. So, this is what we are really worried right now.” Thilakasena further stated.