Technical and compatibility issues in the design of HVDC sea electrodes

The HVDC (High Voltage Direct Current) transmission system, although in use since about half a century, is gaining new popularity in recent years, as it can allow to transmit very large amounts of power over long distance at reasonable costs. Many plants are being commissioned and many others are in the design phase, both for mainland and submarine links. Ground/sea electrodes are normally used in such applications, either operated on a full time basis, or during partial failures of one pole of bipolar plants. Due to the adverse effects that stray currents dispersed by such electrodes may have in terms of corrosion to nearby structures, and to the growing concern for environmental issues, the design of sea electrode has to be defined with increasing attention. This paper deals with the technologies and with the design criteria that can be adopted to develop satisfactory sea electrodes.