Private power succeeds at Santa Branca12 January 2000
The development of hydroelectric generating facilities at the existing Santa Branca dam was carried out through an engineering, procurement, construction contract. Heitor Barreto Correa and Carlos E Araoz explain the work behind Brazil’s first privately owned hydro project to be completed using this approach
The privatisation of government-owned utilities in Brazil, as well as in other countries in South America, began about five years ago. The new private owners are often consortia composed of both local and international firms that have implemented changes to policies and approaches formerly used by government utilities for project construction.
The Santa Branca hydroelectric project, located in the state of Sao Paulo, is the first privately owned hydroelectric project in Brazil conceived, contracted, built, and commissioned using the engineering, procurement, construction (EPC) approach. The project owner, Light Serviços de Electricidade SA (Light), has used the EPC concept successfully to develop hydroelectric generating facilities at the existing dam, while meeting the economic criteria of a privately owned independent utility.
The Santa Branca dam
was completed in the late 1950s to regulate the flow in the Paraíba do Sul river. The 50m high, homogeneous earthfill embankment has an impoundment capacity of 438M m3 and a surface area of 27.5km2. Regulated minimum discharge flow from the reservoir, to supply water to existing hydroelectric plants and other users downstream, is 40m3/sec.
Existing hydraulic structures include an intake tower, outlet tunnel and surface spillway. Water enters the intake tower through two hydraulically operated wheel gates. The tunnel leading from the intake tower is 8m in diameter and lined with concrete for the first 180m, and 7.68m in diameter and steel-lined for the final 100m. Three Howell Bunger valves control flow through the tunnel. There is a bifurcation at the downstream portal: one branch feeds the release valves, while the other was sealed for future connection to a generating facility.
Flow over the 200m long concrete lined spillway is controlled by a pair of 18.3m wide, 6.35m high wheel gates. The spillway was designed to handle 1300m3/sec. Average annual river flow of about 80m3/sec is regulated by the large Paraibuna reservoir about 20km upstream from the dam.
The nearest towns are Jacareí, at a distance of about 15km, and Santa Branca, at a distance of about 7km. The project site can be easily reached by road from both Sao Paulo (about 110km), and Rio de Janeiro (about 385km). All federal and state roads from both Rio de Janeiro and Sao Paulo are paved and suitable for all project-related transportation.
Light, which supplies electricity to three million consumers in 30 towns in the state of Rio de Janeiro, was privatised in May 1996. The majority of stock is currently owned by a consortium comprising the US firms AES Corporation and Reliant Energy International (formerly Houston Energy Industries), French utility Electricité de France, and Brazilian partners including the steel company Companhia Siderurgica Nacional.
Shortly after becoming privatised, Light decided to develop the hydro power potential of the existing Santa Branca dam and reservoir to meet projected increases in energy demand. The anticipated 58MW facility represented an 8% increase in Light’s overall generating capacity.
In September 1996, Light retained black-veatch (B&V) to provide complete engineering services for the Santa Branca hydroelectric project. To perform these services, B&V was supported by its long-term ally in the hydroelectric field, Colenco Power Engineering of Baden, Switzerland. The turnkey/EPC approach to the project was proposed and defined by B&V to support project funding, and to optimise the per unit capacity.
For the Santa Branca project to be successful, three major criteria had to be fulfilled:
•Low overall cost.
•Minimal environmental impact.
Since the project was partly financed by Light, controlling costs and bringing the units online quickly was critical. B&V and Light decided that the best way to manage these factors was to use a lump-sum EPC contract that incorporated performance guarantees for meeting both the schedule and the required power output.
The Santa Branca project lent itself to an EPC approach because of the low risk associated with the rehabilitation work, and the fact that the only subsurface work consisted of excavation of the power house in an area of known geological conditions.
The scope of work for B&V included the preparation of performance oriented bid documents, pre-qualification of prospective EPC bidders, evaluation of bids, support during contract negotiations, construction inspection and quality assurance supervision. Construction pre-qualification for the project was finished by November 1996, and the requests for EPC proposals were issued in December 1996. The EPC contract was awarded in April 1997 to a team led by Argentine firm Impsa and including the Brazilian firm Promon and another Argentine firm, Cartellone. Project construction started in May 1997. The total value of the contract was approximately US$34M. The contract was structured to pay an incentive of about US$6400 per day for finishing unit 1 early, and US$3200 per day for early completion of unit 2 for a maximum of 60 days. Liquidated damages in the event of delay in project completion were about US$19,000 per day. Performance guarantees for each major piece of equipment were specified in the contract.
A formula referred to as the ‘guaranteed weighted average efficiency,’ or GWAE, was used to calculate the output of the two units in kilowatts. In the event the guarantees were not met, liquidated damages were to be assessed at a rate of US$1150/MW per day, and the deficiency would be corrected at the next regularly scheduled outage, with additional daily damages charged during the correction period.
The strategic project implementation, a plan to control the project costs and schedule conducted by Light and B&V at the beginning of the project, concluded that competitive bids with low contingencies were expected. A dynamic quality assurance plan was necessary to protect the economic and schedule benefits of the EPC contract from being endangered by low quality equipment or deficient construction practices.
It is sometimes difficult for project owners to allocate significant funds for quality assurance purposes on an EPC project because the equipment manufacturers and civil constructors theoretically are required to perform quality control and assurance functions as part of the contract. However, in the case of the Santa Branca project, the owner’s quality assurance efforts have paid off.
A combined quality assurance team led by Light and including B&V was established to review the quality and schedule of onsite construction activities, as well as work in the factories where major equipment was being manufactured. The quality assurance team included a full-time B&V quality assurance technician and a part-time B&V quality assurance hydromechanical engineer at Impsa’s factory in Mendoza, Argentina. This was where the Kaplan turbines, generators, inlet valves, bifurcation, penstock, bridge crane and control system were manufactured.
Periodic visits were also conducted for test witnessing by experts from Light’s offices in Rio de Janeiro and from B&V’s headquarters in Missouri, US. Through this process, the owner’s quality assurance team members were always respectful of the EPC contractors’ rights and responsibilities.
Another important goal identified during the strategic project implementation planning was the elimination of contractor claims during the construction phase so that firm economic and financial plans could be made and followed. Based on past experience with large projects involving significant claims, Light realised from the start that the project would succeed only if this difficult goal could be achieved. The low risk characteristics of this project and easy access to the site favoured this outcome, but it was concluded that the project EPC specifications would be the key for success. It had to be performance oriented to provide the benefits of the optimisation by the EPC contractor, but also had to be sufficiently clear to support identification of responsibilities in any potential situation where a conflict could arise between owner and contractor. During the construction phase, almost all discrepancies were settled quickly using the project specifications as the reference document.
On completion of the project, only two outstanding claims remained. One was associated with damage to the existing wall between the valve house and power house, and the second was for extra equipment.
At the beginning of 1997, Light submitted to Banco Nacional de Desenvolvimento Econômico e Social (BNDES) an application containing information on projects that were part of the investment plan for the period 1997-9.
The projects were divided into two categories:
•Distribution projects, including six substations and other small projects (transmission lines and telecommun-ication equipment).
•Generation projects, including the Santa Branca hydroelectric power plant.
The projected Santa Branca project disbursements amounted to approx-imately R$46M. In July 1997, after evaluating the project, BNDES agreed to finance 60%. Light received these funds in 1998 and 1999.
The conditions of the BNDES financing are:
•Interest: TJLP (long term interest at around 10%) + 4% annually.
•Principal grace period: 2 years.
•Maturity: January 2010.
At the beginning of 1997 Light also submitted an application to Centrais Elétricas Brasileiras (Eletrobras) to obtain other sources of financing for the Santa Branca project. Even though Eletrobras agreed to finance 30% of the projects disbursements, Light has not received any funding from this source to date. The conditions of the Eletrobras credit line have not been defined.
To make the project economically feasible and meet its commitments with the Electricity Regulatory Agency (ANEEL), Light needed to have the Santa Branca generating units in operation within approximately 24 months of signing the EPC contract. The contract included a schedule defining plant construction works and rehabilitation services to the existing structures.
Services were completed in July 1999, with four- and five-month delays, respectively, in the startup of the two generating units. These delays required that the EPC contractor pay liquidated damages to Light. The contractor is currently negotiating these damages, together with two claims.
The 50m long power house, situated between the right abutment of the dam and the gated spillway, incorporates the existing valve house. The power house is founded on slightly weathered schist that was excavated by controlled blasting in order to avoid damaging the valve house.
The design of the turbines was dictated to a great extent by the operating conditions and the performance guarantees stipulated in the EPC contract. Operating elevation of the upstream pool ranges between 605m and 622m with an almost 20m range in gross head. Available flow to the powerhouse ranges from 40m3/sec and 170m3/sec with a minimum continuous flow of 40m3/sec. Minimum guaranteed per unit output at an upstream pool elevation of 622m was set at 25.8MW. In addition, tight controls were established on allowable cavitation throughout the full range of net operating heads and the corresponding outputs.
Because of the large variations in head and flow, Impsa decided to use a double regulation turbine system consisting of two Kaplan turbines with six runner blades each, combined with 24 wicket gates 115cm high to control flow. The turbines have a design operating speed of 225rpm. The turbine runner discharge diameter is 3.2m, and maximum flow through each unit is 75m3/sec.
The turbines were designed and fabricated by Impsa in its plant in Mendoza, Argentina.
The vertical shaft synchronous generators, also fabricated by Impsa, were designed to operate at a 0.95 power factor with a 13.8kV voltage rating and a rated frequency of 60Hz. Although the Santa Branca regional distribution system is currently operating at 88kV, it is expected to be upgraded to 138kV after the regional power transmission system is expanded and standardised. Therefore, the step-up transformers were designed for dual high voltage ratings of 88kV and 138kV, to avoid costly modifications later. Once in the power house, the electromechanical equipment is handled by a travelling bridge crane rated at 1000kN.
The Santa Branca power plant is being operated by a single operator through two man-machine interfaces (MMIs) located in the main operations room. Programmable logic controllers supplied by Impsa are located at each of the two units in the substation and at a central location to control the auxiliary equipment. The controllers are connected to a local network through fibre optic cables.
The entire control system is connected by modem through a dedicated communications line to Light’s control centre in Rio de Janeiro. Light has the option of controlling the Santa Branca plant from this remote control centre or from a notebook computer connected to the control system by a cellular telephone line.
The switchyard was constructed as two 138kV, two-position radial buses. Each bus is connected to one of the generating units and its associated step-up transformer through separate 138kV, 1600A circuit breakers. The two buses can be coupled through a disconnecting switch to enable the evacuation of energy through either of the two lines connected to the nearby Bandeirante substation.
To renew the old Santa Branca facilities, built in the late 1950s, and to bring them to the same operational level as the new plant, Light included rehabilitation services in the EPC agreement. This was estimated at less than 10% of the total contract value.
The access roadways were upgraded by increasing the drainage capacity, improving the operational conditions of the drainage devices, paving the 6m wide road and installing road signs. The natural slopes adjacent to the dam abutments included eroded areas, some of which were threatening the intake. Slope stabilisation measures included the use of geotextile blankets covered with concrete blocks, a technique never before used in Brazil.
An inspection of the intake structure conducted while the reservoir was at its minimum level revealed flaws such as corrosion of the metal grids and gate rails, and surface erosion and widespread cracks in the concrete structure. These flaws were primarily attributed to reservoir water with high levels of chloride and sulphate, which at elevated water temperature led to deterioration of concrete surfaces. The erosive power of water flow was a secondary cause of damage.
Repairs were made under both dry and submerged conditions. Metal components were cleaned and painted, cracks were filled, and concrete surfaces were levelled and made waterproof by coating with epoxy-based resins.
Inspection of the tunnel revealed erosion of the invert, cracks, and water infiltration in the steel-lined section. Repairs were made to restore the tunnels stability and original hydraulic discharge conditions. Surfaces were cleaned with high pressure water jets, the concrete/rock interface was made waterproof by injection of special cement, eroded concrete surfaces were repaired with high performance concrete, cracks were filled with epoxy resin, and the steel liner was repainted with epoxy-based paint. The concrete surface of the spillway was fully eroded after 40years of operation without maintenance. This structure was repaired with high performance epoxy resin-based cement.
Hydraulic analysis of the dissipation basin showed the need to adjust the basin’s hydraulic profile to the change in operating conditions resulting from the construction of the Paraibuna reservoir and dam, upstream from Santa Branca. The Paraibuna facilities have been functioning since the 1970s and have brought about a considerable decrease in the flow to Santa Branca. The hydraulic profile was adjusted by replacing the existing dissipation structure with a new roller bucket-type facility.
The left bank of the river just downstream of the spillway discharge had been severely eroded by the action of the water. Covering the affected slope with riprap protected this bank.
Since the Santa Branca reservoir was constructed, environmental laws and jurisdiction have changed significantly in Brazil. In compliance with the current federal and state environmental standards, Light applied for an environmental permit for the construction of the Santa Branca power plant with the Secretary of the Environment of the State of Sao Paulo. A preliminary approval was granted in July 1994, with a list of requirements to be met for final licensing of the project.
Light met those requirements and received an install-ation licence in March 1997, two months prior to the start of construction. A five-year operating permit was issued in October 1998.
Among other activities, Light was responsible for planting more than 50,000 native trees and for recovering eroded areas using technologies appropriate for this region.
Light has worked closely with the local population in both the development and the implementation of mitigation measures. The region’s inhabitants frequently take part in activities that foster cleaning up the riverbanks.
Commercial fishing and predatory hunting were eliminated in the area with the support of the Forest Police Corps, while amateur fishing activities are being encouraged. With the support of the inhabitants of the cities located on the banks of the reservoir and river, Light is reversing environmental damage that began in the 1950s.
Related ArticlesSpotlight on... South America
|The Santa Branca hydro project|
|Location: Paraiba do Sul River, in Sao Paulo State, Brazil; downstream of Paraibuna reservoir Owner: Light Serviços de Electricidade SA. Installed capacity: 58MW Reservoir level (elevation): Flood: 623.4m Normal maximum operating: 622m Minimum operating: 605m Net head: 42m Mean annual flow: 80m3/sec Minimum regulated discharge: 40m3/sec year- round Average annual generation: 270GWh On-line date: 10 July 1999 Cost: US$34M|
|Existing project structures|
|Dam: Homogeneous earthfill Height: 50m Length: 320m at crest Spillway: 200m long concrete lined channel Two wheel gates, 18.3m wide, 6.35m high Reservoir : Capacity: 438M m3 Surface area: 27.5km2 Intake tower: Two hydraulic wheel gates Tunnel: Length: 280m Diameter: 7.68-8.0m Lining: concrete and steel Valve house: Three Howell Bunger valves Maximum discharge 280m3/sec|
|Contractors and suppliers|
|Engineering services: Black & Veatch - owner's engineer. EPC contractors: Indústrias Metalúrgicas - consortium leader. Pescarmina SAICyF (Impsa) - hydromechanical and generators. Promon - design and auxiliary electromechanical equipment. Jose Cartellone -civil works. Equipment suppliers: Impsa - automation equipment, bridge crane, bus bar, control systems, draft tube, generators, generator monitoring system, turbines and inlet valve. ABB-Alstom - switchyard. Tubos Transelectric, Argentina - transformers. Canadian Steel Foundries - turbine blades.|
|Scope of the EPC contract|
|Equipment Two vertical shaft Kaplan turbines, rated at 29MW, with 3.2m diameter runners and a speed of 225rpm Two vertical synchronous generators, rated at 29.5MVA and 60Hz 13.8kV 0.95 power factor Step-up transformers: ONAN/ONAF, rated at 13.8/138kV and 31.5MVA Operations monitoring: Control room and remotely at dispatch centre Controls: Distributed control system Construction Reinforced concrete power house Two welded carbon steel penstocks, 12m long with 4.2m nominal diameter Substation: 138kV Rehabilitation Intake: seal cracks and damaged surfaces, rehabilitate guides for steel racks and gates Outlet tunnel: seal concrete cracks and damaged surfaces, seal and paint damaged steel lining Spillway: repair erosion and cavitation damage Embankment slopes: stabilise reservoir shore and abutments|