Akhaltsikhe - Back-to-Back Converter Station

The Akhaltsikhe back-to-back HVDC project is an important component of the Black Sea Transmission Network, designed to facilitate power transmission between Georgia and Turkey. The project involves the construction of a high-voltage direct current (HVDC) converter station near the town of Akhaltsikhe in southern Georgia, close to the Turkish border.

Project Overview

The Akhaltsikhe substation is a 500/400/220-kV facility located approximately 13 km from the city of Akhaltsikhe, at an elevation of about 1100 meters above sea level. It is connected to the main Georgian 500 kV transmission system through two new 500 kV links from Gardabani and Zestaponi substations. The substation is also connected to the Turkish high-voltage grid at Borçka via a 400 kV overhead transmission line.

Technical Specifications

The HVDC back-to-back converter station at Akhaltsikhe consists of multiple units. Initially, two 350 MW back-to-back HVDC units were installed, with plans for expansion. The latest information indicates that a third 350 MW unit is being added, bringing the total capacity to 1050 MW.

Each HVDC link in the station is designed to convert the three-phase alternating current (AC) from the 500 kV Georgian network into direct current (DC) and then back to AC for the 400 kV Turkish network. This process allows for asynchronous connection between the two countries' power grids, which is necessary due to Turkey's plans to join the synchronous grid of continental Europe.

The converter station employs three 140.4-MVA, 500/40/40-kV single-phase converter transformers on the Georgian side and three 140.4-MVA, 400/40/40-kV single-phase converter transformers on the Turkish side for each HVDC link. The system is capable of transmitting 350 MW of power in both directions.

Additional Features

To maintain reactive power balance, three synchronous condensers, each with a capacity of 60 MVAR, are installed on the 400 kV side of the substation. These are connected through individual 63-MVA, 400/11-kV transformers and help keep the reactive power at near-zero levels during HVDC link operation.

The substation's control, protection, and measurement systems are designed with redundancy to ensure reliability. The facility can be operated either from a local control room or remotely from the national dispatch center.

Construction and Challenges

The construction of the Akhaltsikhe substation faced several challenges, particularly in terms of logistics. The transportation of heavy equipment, such as the 14 converter transformers weighing 120 tons each (without oil), required careful planning and execution.

Project Timeline and Financing

The construction of the Akhaltsikhe HVDC station began in 2010, with the first two HVDC back-to-back units becoming operational in 2013. The project was financed by several European institutions, including the European Investment Bank, the European Bank for Reconstruction and Development, and the German development bank KfW.

Significance

The Akhaltsikhe back-to-back HVDC project plays an important role in enhancing energy security and facilitating electricity trade in the Caucasus region. It allows for increased power exchange between Georgia and Turkey, stabilizes the Georgian electricity system, and creates an electricity hub for energy exchanges with neighboring countries. Additionally, the project helps to balance the supply and demand of electricity within Georgia, as generation is primarily located in the western part of the country while consumption centers are mostly in the east.