Sunday, October 21, 2012

BELO MONTE - Hydropower Project

The largest hydroelectric dam in Brazil and the third in the world

Description        

Name                                    Belo Monte

Country                                Brazil

Installed capacity             11,233 MW

Mean annual energy      40,042 GWh Energy equivalent energy 191,600 BEP day

 

 

Reasserting its condition of technological leader worldwide, IMPSA´s efficiency obtained in its hydraulic laboratory and offered to the winning consortium was superior to all other machinery that will be part of this provision.

In order to maximize local manufacture, IMPSA expanded its Production Center in Recife, in the state of Pernambuco, with state-of-the-art tool machinery so that high value-added turbine and generator components are fabricated in Brazil. To this end, some 500 local workers from different disciplines were hired. They are being trained to make the best transfer of technology to professionals and technicians.

To achieve sustainable development, Brazil has always prioritized the use of renewable energies. In this context, the Belo Monte project, in the state of Pará, northeastern Brazil, is one of the best options for expanding the country's power generation capacity. Not only for the amount of energy it can produce but also for the propitious conditions for integration into the interconnected national grid and.

Only the market leaders participated in bidding for the generation equipment. IMPSA obtained the supply of electromechanical equipment under “turnkey” conditions which includes four of the eighteen 620.2 MW Francis generating units with their respective speed governors and excitation systems, generator related equipment, penstocks for the 18 units and lifting equipment.

 

Technical characteristics

Turbines

Hydraulic Design

Tests of the Belo Monte turbine scale model have been performed at the Hydraulics Laboratory of IMPSA's Technology Research Center in Argentina. The development process comprised:

·         Hydraulic design of turbine components.

·         Computational fluid dynamics (CFD): spiral chamber, stay ring, distributor, runner and draft tube.

·         Mechanical design of the reduced scale model.

·         Scale model test.

Project requirements, such as efficiency, cavitation, runaway speed, pressure fluctuations, hydraulic thrust and hydraulic torque of different components are checked using the tests performed on the model on the high head universal test rig of the Hydraulics Laboratory.

Mechanical Design

For mechanical design, a computerized 3D model is used to verify component stresses, deflections and natural frequencies using the finite element method (FEM).

The spiral case is made of welded steel plates designed for maximum operation pressure. The stay ring has two parallel plates welded onto 24 stay vanes. This component is tested at site at the design pressure.

The distributor has 24 wicket gates driven by two servomotors through an operating ring. The wicket gates are equipped with self-lubricating bushings.

The runner is made of casting in 13.4 stainless steel.

The shaft utilizes a thin-wall welded design. Because of its inertia, this solution increases the safety margin in the event of critical speeds and provides greater vibration stability and reduces manufacturing costs.

 

Governor

IMPSA's governor is of the digital electro-hydraulic type with PID control. The control electronics, composed of high-quality standard PLCs in a redundant “hot” stand-by configuration, is highly reliable and easy to maintain. The system architecture consists of both a main and a manual backup controller. This ensures high fault tolerance in the event of main controller failure and prevents the generating unit from shutting down; otherwise, the load would be rejected and the power system would be adversely affected. The software includes all speed and power control functions required for these types of units.

The oil pressure system (air/oil) has a pumping unit with three pumps to pressurize the system and an air/oil tank. The pumping unit and the air/oil tank were fully designed in 3D.

 

Generators

The units are three-phase, vertical shaft, salient pole synchronous machines, with a unit capacity of 679 MVA, 90rpm and a 18 kV rated voltage. With its 8.1 MVA specific power per pole, it is a piece of equipment of high technological complexity.

Integral dimensioning of the generator is performed with the ARGEN®, expert integrated system fully developed by IMPSA, which analyzes the equipment's behavior, both in steady and transient states as well as under normal and fault conditions. This tool synthesizes all the design fields required for this type of generator: electromagnetism, electrical and magnetic circuits, fluid mechanics and heat transmission, machine components, strength and fatigue of materials, tribology (lubricants-wear-bearings), shaftline stability, vibrations and oscillatory behavior.

Generators are designed with CAD (Computer Aided Design) and verification studies are carried out with tools developed by IMPSA and integrated into the PROGEN ® expert system, as well as with applications using FEM (Finite Element Method).

The stator's magnetic core is made from 0.5 mm non- oriented -grain magnetic steel sheets which are die-cut, varnished and stacked. The stator winding is mounted on the slots and the whole set is supported by the stator frame, a welded mechanical structure that directs the air from the core to the heat exchange units of the cooling system.

The rotor consists of a steel-welded spider, a rotor rim made of die-cut stacked segments (for radial ventilation) and the pole inductors that generate the rotating magnetic field in the machine's air gaps.

The shaft line arrangement includes a guide bearing on the generator's rotor, a combined bearing below the generator's rotor, and a guide bearing in the

turbine to maximize the rotor's dynamic stability.

Design characteristics include the lower support cone of the thrust bearing mounted on the turbine cover and a lower bracket which transmits radial stresses to the foundation minimizing the machine's length. This makes it possible to achieve significant savings in the project's civil structure.

The symmetric radial ventilation system uses the rotor to generate pressure for machine cooling.

 

Excitation System

The excitation system includes:

Digital regulation system: It is made up of two automated systems that actuate the manual/automatic regulation channels and of field current controllers linked to each SCR (thyristor) bridge rectifier. This 100% redundant structure ensures independent control at different levels: input/output, regulation channels and current controllers.

Power control system: It is made up of two bridge rectifiers in cold stand-by to ensure double power redundancy without jeopardizing the other SCRs in the event of a power failure near the bridge rectifiers. Each bridge rectifier has its own air/air heat exchange unit and protection system.

Field discharge: In the event of a normal shutdown, the system performs a fast DE excitation by delaying the trigger pulses in the rectifier without opening the field breaker. The energy stored in the rotor is returned to the excitation transformer. In the event of an emergency shutdown, the system performs a fast DE excitation by opening the field breaker and discharging the energy stored in the rotor into a non-linear resistor.

Excitation transformer: The epoxy-encapsulated winding is protected with its corresponding cell, which is connected to the segregated phase bus duct. It is specially designed to withstand harmonics generated by the bridge rectifier. Current transformers in the primary circuit provide protection against overcurrent’s.

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