COMETA

The COMETA (COnexión MEditerránea Transporte Alta tensión) HVDC project, also known as the Majorca-Valencia interconnector or the Romulus project, is an undersea electric power transmission system connecting mainland Spain with the Balearic Islands. This project was developed by Red Eléctrica de España to meet the increasing energy demand on the islands and provide a better electrical supply to the previously isolated Balearic grids.

Project Overview

The COMETA link connects Morvedre, near Valencia on the Spanish mainland, to Santa Ponsa, near Palma de Mallorca. The system consists of two bipolar high-voltage direct current (HVDC) cables, each with a transmission capacity of 200 MW and an operating voltage of 250 kV, along with a metal return cable. The total transmission capacity of the system is 400 MW.

The submarine part of the cable stretches for 240 kilometers, with an additional 7 kilometers of land cable. The cable reaches a maximum depth of 1,485 meters in the Mediterranean Sea, making it the second deepest submarine power cable after SAPEI at the time of its completion.

Technical Details

The COMETA project utilizes a bipolar interconnector design with a metallic return conductor. Siemens supplied two converter stations: one near Valencia on the Spanish mainland and another at Santa Ponsa on Mallorca. The mainland station connects to an existing power plant via a highly integrated switchgear (HIS) and HVAC cables, while the Mallorca station links to the island's 220 kV grid through gas-insulated switchgear (GIS).

The submarine link comprises three sea cables: one high-voltage cable per pole and one cable serving as the metallic return conductor. The system can operate in both bipolar and monopolar modes, with either ground return or metallic return.

Construction and Implementation

Contracts for the COMETA project were signed in late 2007. Cable manufacturers Nexans and Prysmian were contracted on September 26, 2007, while Siemens secured the contract for the converter stations on October 9, 2007.

Cable laying began in January 2011, with the first cable installed by the cable ship Giulio Verne and the second by Nexans Skagerrak. Trenching operations were carried out using waterjet technology from the Multipurpose Supply Vessel (MPSV) Edda Fjord and the dredger Argo I.

Operation and Impact

COMETA became operational in early 2012, initially at reduced capacity before reaching full operational status in August 2012. The total cost of the project amounted to €375 million. During its first operational quarter, the Spanish grid operator estimated annual savings of 25 million euros due to more efficient energy supply to the islands and reduced carbon rights.

The project has brought significant benefits to the Balearic power system, including reduced energy not supplied (ENS) due to generator trips, improved frequency regulation, lower generator costs, and decreased CO2 emissions. It has also helped avoid or delay the need for new generation capacity on the islands.

Future Expansion

Plans are in place to extend the connection to Ibiza and Formentera with a second underwater cable. This extension is expected to be 115 kilometers long, reaching depths of 800 meters, and operating at 132 kV AC.

The COMETA project provides the Balearic Islands with access to the generating capacities available on the mainland peninsula, addressing the growing energy requirements driven by tourism in the region.