Banking on support from the IDB30 June 2011
The Inter-American Development Bank is providing a US$700M loan for the largest energy efficiency project ever undertaken in Latin America. Alejandro Melandri gives an insight into why the bank is keen to support refurbishment of Venezuela’s Guri project, and others like it.
The Simon Bolivar hydropower plant, also known as the Guri dam, is located in the State of Bolivar in the eastern region of the Bolivarian Republic of Venezuela. More precisely the dam closes the Necuima Canyon; some 100km upstream from where the Caroni river enters the Orinoco river; about 80km from the city of Ciudad Guayana - Puerto Ordaz; and approximately 18km upstream from the power project Central Manuel Piar (Tocoma), currently under construction.
To ensure its steady flow of 4800m3/sec, the reservoir stores an average of 135Bm3 (at elevation 266) and a maximum of 180Bm3 (at elevation 271). At its highest volume, the lake reaches 4250km2 of water surface.
Guri is Venezuela's largest dam and the eighth largest dammed volume of water in the world. Because of its installed capacity, the plant is the second largest in South America after Itaipu, and the third in the world. The annual average energy production reported by its state owned operator Corpoelec-Edelca is 46,650GWh/yr. In 2009 this energy amounted to 52,600GWh, the substitute of a near equivalent consumption of 300,000 barrels of oil per day.
This giant hydropower project comprises a concrete dam and was developed in two phases. The first phase began in 1963 and allowed for the start of commercial operation of Unit 1 in December 1968. Unit 10, the last one to be completed in powerhouse I, started operations in January 1978. The height of the structures in this phase allowed for a maximum reservoir level at height 215masl. The Guri A, 400KV, 230KV, 34.5KV and 13.8KV switchyards were built in the same period. The second phase, known as Guri final stage, included the increase of the reservoir to 272masl and the construction of powerhouse II. This phase was completed in 1986 together with Guri B, a 765KV switchyard.
Powerhouse I has a total rated power of 2785MW, provided by 3x175MW units (group 1, units 1 to 3); 3x220MW units (group 2, units 4 to 6); and 4x400MW units. Powerhouse II has ten units of 730MW of nominal power each, totaling 7300MW.
After over-elevation of the reservoir in the Guri final stage the hydraulic height increased by about 53m, and the turbines of group 1 had to operate outside their optimum range. Also due to the original power of their generators, the opening of vanes had to be limited. Consequently, the efficiencies of these turbines are between 8-10% below normal efficiency. The units in group 2 are also operating outside their optimum range with reduced efficiencies, which have been estimated to be below 84%.
The rehabilitation programme
The equipment in units in units 1 to 6 are reaching between 33 and 42 years of intensive use, coupled with the consequent technological obsolescence of control and auxiliary system of powerhouse I, which were built in the 1960s with some designs dating from the 1050s. The generators in units 1 to 6 were designed to dispense power consistent with net hydraulic heights between 92-105m. Under the current net heights range between 110 and 143m the flow that runs through the turbines needs be restricted by partially opening the vanes to avoid overloading them. Hydraulic performance values are also typical of the technological state of the art of the sixties and seventies and therefore they are far from what an updated optimal design could deliver today.
Under these circumstances, the power available to the electrical system from the aforementioned units is limited, both for their performance as bounded by the restrictions operating on the flow.
On the other hand, while units 1 to 6 were subject to scheduled maintenance and overhaul in the late eighties and early nineties, the electro-generation equipment and auxiliary systems remained virtually as original which makes them technologically outdated by today’s standards. This diagnostic can be also be applied to switchyards Guri A and Guri B.
Such a situation moved Corpoelec-Edelca to consider the feasibility of a programme to upgrade units 1 to 6 of the powerhouse I, including the respective auxiliary and control systems, mechanical systems and electrical equipment and the reconfiguration and refurbishment of the Guri A switchyard. The programme is integrated within the broader framework of the modernisation project of Guri, which includes the refurbishment of the ten 730MW units in powerhouse II, as well as the four remaining 400MW units in the powerhouse I. Therefore the programme’s target is to restore and increase Guri´s output capacity and it is not related to safety issues other than those associated to securing the energy supply.
Scope of the works
The programme is expected to raise the rated power of all the units 1 to 6 without modifying the existing contours of the respective hydraulic outlet works, penstock, spiral chambers and discharge rings. The nominal unit capacity of turbines in group 1 will be enhanced from 175MW to 270MW while those in group 2 will increase from 220MW to 370MW.
The new mechanical power available to the turbine shaft necessitates resizing of the shaft, the guide and thrust bearings, the drive system of distributors, as well as the rotors and stators of the generators which must be replaced in its entirety. The current rotating exciters will also be replaced with state of the art static excitation system.
Reasonable compliance with reliability standards in service delivery has compelled Corpoelec-Edelca to include the renewal of mechanical and electrical auxiliaries of each group, including oil hydraulic control systems, speed control, control tension, lubrication and cooling, among others.
The programme will also include retrofit of auxiliary systems for general mechanical systems such as those of the bilge drain well, emptying of the generating units, powerhouse ventilation and industrial air conditioning, electric equipment corridors and the control room.
Current control systems of units 1 to 6 will be replaced by a distributed control system with local access in each unit and manual/automatic remote access from the panel in the powerhouse I control room via fibre-optic communications, which in case of emergency will allow operating in local mode.
The switchyard transmission systems at 400KV and the 230KV substation Guri A, will be retrofitted to ensure service reliability. In the first one, the power equipment will be replaced while foundations and support structures will be kept. Control and status signals from each group will converge to a hub and communicate to the control board via optical fiber. The 230KV yard will be reconfigured.
Schedule, outcomes and impacts
Corpoelec-Edelca expects to complete the upgrading program of Units 1 to 6 towards the end of 2016. The schedule provides for completion of bidding documents during 2011 and to complete the award of the works early on in 2012. The design, manufacture and transport of equipment and supplies to the site are contemplated to be executed in three years from the award of work until the end of 2014. The whole programme, including architectural and general equipment renewal is expected to be completed by 2016. The refurbishing yards in substation Guri A will be consistent with schedules to allow testing for commissioning and commercial operation of the units.
It is estimated that the availability rate of Guri will be between 70-85% of total installed capacity during the intervention period when work is being carried out at units 1 to 6. Once completed the refurbishment programme will result in a better performance from units 1 to 6, which are expected to increase their availability from 85% (2008) to 90% (2016), as well as their efficiency from 84% (2008) to 95% (2016).
The Program will also finance studies to assess the potential impacts that climate change might have on the Caroni Basin´s hydrology. The acquired knowledge is expected to expand water resource management capabilities by incorporating information and technical tools to check or adjust models, forecasts and eventually procedures.
Total construction costs have been estimated at US$923M. this included:
• Rehabilitation of units 1-5 and modernisation of auxiliary mechanical and electrical machines in powerhouse I and control of units 1 to 6 (US$649.2M).
• Reconfiguration and refurbishment of switchyards Guri A US$235M).
• Architectural and environmental suitability of the facilities, plus modernisation of electrical and mechanical auxiliary systems in Powerhouse I (US$39M).
Programme expenses should also cover costs for preparation of detailed engineering, factory and site works inspections, external expert advisory services, organisation expenses and environmental mitigation costs, which were estimated at US$119M. Therefore the estimated overall total direct cost to complete the programme is equivalent to USD 1042M.
This refurbishment programme is consistent with the Inter-American Development Bank's (IDB’s) long term support for the development of sustainable energy resources in Venezuela. IDB involvement in the power sector in Venezuela started with a loan to help finance Guri; and continued with the projects Caruachi and Tocoma; and currently this programme with a US$700M loan.
The IDB is looking positively at hydroelectric generation projects, particularly the rehabilitation of power stations to promoting a clean energy source with minimal environmental impacts. As part of this strategy, the IDB has approved in recent years financing for projects such as Porce III (Colombia), Manuel Piar, Tocoma (Venezuela); Misicuni (Bolivia); Segredo, Dona Francisca, Cana Brava, and Campos Novos (Brazil). The renovations and rehabilitation projects include the project Peligre (Haiti), the Central America and Santa Barbara (Nicaragua) and a proposal for the rehabilitation of hydros Furnas and Luiz Carlos Barreto (Brazil).
This is the largest energy efficiency project ever undertaken in Latin America. Beyond the concrete technical and economic results expected from it, IDB is keen to highlight the importance of refurbishing and upgrading ageing hydro schemes to continue contributing to the region´s renewable energy matrix. Great efforts and large investments were made in the 1960s and 1970s to build a strong hydropower generation capacity which gives the region not only a firm and economical energy base, but also an almost carbon free component of its energy matrix. These assets deserve to be preserved and updated to retain their economical value and IDB is willing to support this process contributing to structure financial support consistent with the project requirements.
The IDB energy division expects to identify more of these opportunities in the region since a large number of hydro projects are t entering a critical stage. Constructed 40-50 years ago they will soon require major overhauls of their electromechanical equipment, and in some cases also of their civil infrastructure. The bank’s energy division is screening this type of project in search of opportunities across the region to increase installed capacity with a high benefit over cost ratio, while having a minimum or negligible environmental impact.
Alejandro Melandri, Energy Lead Specialist, Energy Division, Inter-American Development Bank, 1300 New York Ave NW, Washington, DC 20577, US. Email: [email protected] www.iadb.org
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