Regulator asks CEB to inform of actions taken to prevent power failures

Following the spate of unprecedented outages recently, the Public Utilities Commission of Sri Lanka (PUCSL) has asked what actions the Ceylon Electricity Board (CEB) has taken to prevent such power failures in future.

The PUCSL in a letter to the General Manager of CEB M. C. Wickramasekara said it was the responsibility of the CEB to maintain an uninterrupted power supply throughout the country, which has been violated three times in the last six months by way of island wide power failures.

The three total power failures occurred on 27 September 2015, 25 February 2016 and 13 March 2016.

"Therefore, you are required to inform the Commission on actions the Transmission Licensee (CEB) has taken in order to prevent repetition of an island-wide power failure after 27 September 2015," the PUCSL told the CEB.

Further, the Commission highlighted that a single element failure in the power system shall not result in island wide power failures and the Transmission Licensee is responsible for maintaining the system fulfilling this criterion.

The PUSCL has conducted a comprehensive study with the assistance of the Manitoba HVDC research centre on the failure on 27 September 2015 and observed several shortcomings.

The Manitoba HVDC research centre has concluded that the dynamic transmission system model used by the CEB transmission planning and system control branches are not accurate enough for dynamic response analysis, and the model data needs to be verified with field tests for system elements, along with accurate modeling of loads.



Furthermore, based on the reactive power limits used by the CEB for modeling the network, system control center does not utilise the full reactive power capability of the generators connected to the network.

Te CEB has a practice of allowing ±10% tolerance for voltage control in 132kV and 220kV lines, while the internationally accepted tolerance level is ±5% - a risky practice considering that this limit is very close to the overcurrent protection limit of many system devices.

Following the study, the MHVDC centre has recommended adopting several short and medium term solutions immediately.

The MHVDC has recommended ensuring that all major generating stations have their generator exciters on AVR control and that the reactive power limits of the generators are not curtailed.

The system control centre shall use all available reactors (or capacitors) to maintain the system voltage at ±5% and, as an interim measure, the MHVDC recommended using 'transformer tap staggering' to improve voltage control during low load periods.

It asked the CEB to specify a few 'must run' generator units for voltage support (outside merit order).

"You are hereby directed to design long term measures to avoid such system failures in the future, after fully reviewing the system models used for both steady state and dynamic modeling," the Commission told the CEB.

The PUCSL asked the CEB to inform the commission before 24 March 2016 if it doesn't agree with the MHVDC recommendations.