Garabi - Back-to-Back Converter Station

The Garabi HVDC project is a significant interconnection between Argentina and Brazil, designed to facilitate cross-border energy trading between the two countries. This back-to-back HVDC converter station, located in Brazil near the Argentine border, enables power exchange between the two nations despite their different power system frequencies (50 Hz in Argentina and 60 Hz in Brazil).

Technical Specifications

The Garabi HVDC system is capable of transmitting up to 2,200 MW of electricity, making it the world's most powerful back-to-back HVDC system. The project consists of two phases, each with a capacity of 1,100 MW, which are further divided into two blocks of 550 MW each. The first phase began commercial operation in 2000, while the second phase was commissioned in 2002.

The transmission system includes 490 km of AC overhead lines: approximately 135 km of 500 kV lines in Argentina and 355 km of 525 kV lines in Brazil. These lines connect the Rincón de Santa Maria substation in northern Argentina to the Itá substation in southern Brazil, with the HVDC converter station situated at Garabi.

Converter Technology

The Garabi project utilizes Capacitor Commutated Converter (CCC) technology, which is important for ensuring satisfactory performance at low short circuit levels and improving reactive power control. This technology eliminated the need for a synchronous compensator plant at Garabi, resulting in a more compact and efficient design.

The CCC technology, combined with ConTune self-tuning AC filters, enables smooth and continuous control of voltage and power flow. This combination allows the converter to act like a static compensator, providing reactive power as required by the system.

Modular Design

The Garabi HVDC station employs a modular design concept, which offers several advantages. It provides reduced construction time and simplified civil design, an environmentally acceptable solution, a compact layout requiring less land area, lower visual impact, and easier maintenance and future expansion.

The converter valves are housed in modular outdoor enclosures, which were factory-assembled, tested, and shipped to the site ready for operation. This approach significantly reduced installation and commissioning time.

Control and Protection System

The Garabi HVDC system initially utilized a PC-based control system called MACH 2. However, an upgrade is planned in 2026 to implement the latest MACH technology from Hitachi Energy. This upgrade will provide enhanced calculation capacity and enable a high degree of integration for all control and protection functions, improving the system's reliability and availability.

Technical Innovations

Several technological innovations were incorporated into the Garabi HVDC design. These include Capacitor Commutated Converters (CCC), self-tuning AC filters (ConTune), a spare AC filter phase, modular outdoor valve enclosures, compact AC breakers with optical current transformers, and special damping resistors for transient suppression.

System Performance

The Garabi HVDC system has demonstrated high reliability since its commissioning. In the first ten months of operation, the converter station showed a forced energy unavailability of 0.76% and a scheduled energy unavailability of 0.63%.

The CCC technology has performed well, ensuring satisfactory system performance under various conditions. The interconnection has typically transmitted full power to Brazil as required by hydrological situations, although transmission constraints between the south and southeastern systems in Brazil have occasionally limited this capacity.

Future Developments

An upgrade of the Garabi HVDC converter station is planned for 2025, which will involve implementing the advanced MACH control and protection system. This upgrade will be the first of its kind in Brazil and is expected to extend the life of the system while increasing its reliability and availability.