Wrong ‘generation mix’ led to islandwide power outage

By Namini Wijedasa
CEB engineers shed light on blackout

Monday’s island-wide blackout was caused by high voltage in the power system that led to a “cascade collapse”, Ceylon Electricity Board (CEB) engineers said. It is the first time in five years that such an outage occurred.

ElectricityGraphic
Status of Electrification – Sri Lanka 2014

“There were nine island-wide power system failures from 2006 to 2010 but there were none since 2010 till the last incident,” said Athula Wanniarachchi, President of the CEB Engineers’ Union (CEBEU).

“This is due to the successful implementation of automatic system restoration methods adopted by the CEB in 2010.”

“However, if CEB advice is ignored and the generation mix is decided by non-experts, we will be going gradually back to the previous era inheriting an unstable power system,” he cautioned. CEB engineers have long warned against political interference in the highly-specialised power sector.

“Generation mix” refers to the various methods by which power is produced such as hydro, solar, biomass, wind, coal, diesel, and so on. Experts say that the right combination must be preserved for the whole system to work effectively.

Politicians, policy makers not listening to us: Wanniarachchi

Engineers have long complained that politicians disregarded the advice of professionals in the Ceylon Electricity Board (CEB) to the detriment of the country’s power and energy sector.

They claim policymakers are pushing the utility to take on more and more non-conventional renewable energy from the private sector without considering the consequences—such as Monday’s countrywide blackout.

“There is a certain share of mini-hydro and wind that we can accommodate,” said Athula Wanniarachchi, President of the CEB Engineers’ Union. “Our professional advice is not being taken by policymakers and politicians.”

CEB sources alleged that certain policymakers pushed for high-priced renewable energy because 99 percent of it was produced by the private sector and bought by the CEB for high prices. “The pressure is high for us to accept more and more renewable energy, disregarding technical issues,” Mr Wanniarachci explained.

“We are an island,” Mr Wanniarachchi. “Our system is weak and not interconnected such as in Europe. We can absorb only a certain amount of renewable power that happens to be outside of the control of the CEB.”

As at December 2014, mini-hydro power stations added 288 mw to the national grid; wind, 128 mw; and others such as solar and biomass, 21 megawatts. The total is 437 mw—a sizeable amount.

“Though the Ceylon Electricity Board initiated renewable energy development, it is presently the private sector, which is mainly involved in the NCRE development,” states the CEB’s Long Term Generation Plan 2015-2034, released in July. It says the renewable energy industry was growing rapidly, with both local and foreign investment.

“In comparison with the conventional large power plants, the total contribution from the NCRE sector to the National Grid still remains small but continues to increase and in 2014 the energy share of NCRE was 9.8%,” it states.

The report also warns: With the increase share of non-dispatchable NCRE power plants in the power system, problems related to power quality, power system stability, economic operation due to intermittency could be experienced.

Hence, special consideration should be given when integration of especially wind and solar to the national grid due to the intermittent nature of these sources.”

It recommends detailed system planning and operations studies to determine the share of non-conventional renewable energy share of both dispatchable and non-dispatchable plants that could be connected to the system.

Dispatchable power refers to the ability of a power-producing facility to provide required amounts of power on demand of the grid operator, regardless of the time of day or weather conditions.

A committee appointed to investigate the blackout is still analyzing vast amounts of data. Power was restored within four hours.

Mr Wanniarachchi offered a technical explanation for the failure. Real-time operation of a power system is complicated. “It is due to this reason that we need to have the correct generation mix in a system,” he said.

“The supply-demand balance in a power system must be exactly maintained, megawatt-to-megawatt, every second.”

Today, the CEB has substantial generation in the system which cannot be controlled by operators, Mr Wanniarachchi said. These include output from mini-hydropower stations and wind power producers.

“They start, stop and change their load at their own will,” he explained. “The system operators find it difficult to maintain the power balance in the system.”

“This situation gets aggravated during periods of low demand when a substantial portion of that (energy) demand is taken up by small plants outside the control of system operators,” he continued. Voltage in the power system also needs to be maintained within limits.

This is achieved either by generating or absorbing what is called ‘reactive power’.”

For this, too, CEB operators need controllable generators. “But when the demand to be met by CEB producers is low, we find it difficult to maintain the voltage,”

For this purpose too, CEB operators require controllable generators. However, when available system demand met by CEB-controlled generators is low, it is difficult to maintain optimum voltage.

“On this particular day, just before the failure, about a quarter of the total demand was met by mini-hydro and wind generation,” Mr Wanniarachchi said.

Consequently, the Lakvijaya coal power plant tripped first. As a result, the “reactive power” which was being absorbed by that plant re-entered the system, raising the voltage.

Other “controllable” power plants in the system were insufficient in number and capacity to absorb the excess “reactive power” within a short period and thereby lower the voltage. So equipment connected to the power system tripped one by one, leading to a cascade collapse.

“The CEBEU has all along maintained that the correct generation mix has to be carefully planned and added,” Mr Wanniarachchi insisted. “We should not simply open our doors to any power plant to be connected to the system just because it is renewable energy.

This is why the CEB attempted to impose certain minimal restrictions to non-controllable, intermittent power plants such as wind, drawing a lot of criticism from the business community.”

He said this was also why the CEB started a 100 megawatt wind plant in Mannar which is, to some extent, controllable, as a means of testing a new operating strategy before opening out to large-scale absorption of wind power.

“It is time for the authorities to let the CEB plan and decided on its own operation mix as we have the best expertise and experience in operating the local system,” Mr Wanniarachchi said. “We know the local power requirements best.”

The CEB’s long term generation plan 2015-2034, launched in July, says that by the end of December 2014 approximately 98 per cent of the total population had access to electricity from the national grid.

Electricity requirement has been growing at an average annual rate of around six per cent during the past 20 years.

At the early stages, electricity demand was mainly supplied by hydro generation with thermal generation being minimal. With time, thermal generation has gained prominence and is now much higher than hydro, the report says.

Hydropower is still the main “renewable” source of generation in the power system and is mainly owned by the CEB. However, other renewable sources such as mini-hydro, wind, solar, dendro, and biomass are also connected to the system.

They are owned by private sector developers. “With regard to the energy, it is apparent that coal will be the major source of power during the study period with its share reaching 40% by 2020 and 60% by 2034,” it states.

“However, the contribution from renewable energy power plants too will be considerable with a share of more than 40% by 2025 and 35% by 2034.”

This is contrary to an undertaking former Power and Energy Minister Patali Champika Ranawaka gave at a conference this year that the Sampur coal power plant will be Sri Lanka’s last such project.

Original Article: Link

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