Contents lists available at ScienceDirect Electric Power Systems Research journal homepage: www.elsevier.com/locate/epsr Steel reinforced concrete electrodes for HVDC submarine cables M. Pompili ⁎ , B.A. Cauzillo, L. Calcara, A. Codino, S. Sangiovanni University of Roma “La Sapienza” - Italy ARTICLE INFO Keywords: HVDC electrical transmission systems Submarine cables Seawater anodes Electrodes ABSTRACT In HVDC submarine cable connections, electrodes design is paramount for technical and economic feasibility. The cathode is designed as simple as possible, if bidirectional operations are not required since reduction re- actions does not produce corrosion of the material. The situation is completed reversed for the anodes submersed in seawater: in this case, the corrosion mechanism provokes removal of surface material. For this reason, in order to ensure a sufficiently high lifespan, the anode is usually made of different and more expensive materials, like titanium rods or meshes, coated with layers of a noble metal oxide, such as platinum, or a mixture of several of them. Sometimes the seawater anodes are also immersed in materials based on transition elements such as rare earths. In the present paper, an innovative prototype of seawater anodes, based on steel reinforced concrete, is presented. Moreover, its experimental comparison in seawater at corrosive phenomena is reported, comprising simple steel or titanium bars and titanium meshes protected by special multi metal oxides (MMO). These ex- periments have shown important reduction of the corrosion phenomena in the case of the prototype of anode made by steel concrete. 1. Introduction The seawater return circuit is fundamental in HVDC transmission systems of the submarine cables [1–5], being relatively simple and al- lowing important cost reductions. In fact, seawater has a very high conductivity of approximately 5 S/m due to its high concentration of ions and, hence, it is possible to obtain a low resistance return path. Nevertheless, important differences arise when considering the two opposite electrodes, where the electrons are or injected (cathode) or extracted (anode) into seawater. Conventionally, it is assumed that the anode is the electrode in which current is injected into the ground or in seawater. The much higher conductivity of the seawater in respect to return through earth makes the electrodes considerably smaller, even if the electric field decays more rapidly than in earth. On the other hand, seawater greatly enhances corrosive processes and electrodes in this environment are subjected to higher stresses. Sea and shore electrodes could be bidirectional but they are often designed as unidirectional with the possibility of withstanding current reversal for a short period of time. This choice originates from the asymmetry of the electro- chemical reactions that take place at the positive and negative elec- trodes. Designers take advantage of the less severe condition at the cathode by making it in a more economical way, adopting different features and materials. On the contrary, submarine anodes are much more complex because of the need to protect these components from the corrosive phenomena. For this reason, normally submarine anodes are made of very expensive materials, like titanium rods or meshes, coated with layers of a noble metal oxide, containing also platinum, iridium, plutonium, rhodium or ruthenium. The present paper presents an innovative prototype of anode, based on steel reinforced concrete. The role of current feeder is carried out by steel while concrete acts as a protective layer, able to create an alkaline environment near the surface of the feeder. Downsized and accelerated experimental tests presented in this paper have shown important re- duction of corrosive phenomena for this kind of innovative anodes. In fact, concrete is strongly alkaline (pH ≥ 12) and the experiments pre- sented here have shown as these steel-concrete anodes are capable to resist at the corrosive phenomena much better than other traditional anodes, often used, made of other more expensive materials, like tita- nium rods or meshes coated with layers of a noble metal oxides. 2. Introduction HVDC submarine cables electrode HVDC electrodes submarine cables are normally designed in com- pliance with the following specifications [6–8]: - continuously current of 20% greater of the nominal capacity; - lifetime expectation of about 20 years or more; - reversible functionality (cathode/anode) for a limited period; https://doi.org/10.1016/j.epsr.2018.05.010 Received 25 January 2018; Received in revised form 17 April 2018; Accepted 8 May 2018 ⁎ Corresponding author. E-mail address: massimo.pompili@uniroma1.it (M. Pompili). Electric Power Systems Research xxx (xxxx) xxx–xxx 0378-7796/ © 2018 Elsevier B.V. All rights reserved. Please cite this article as: Pompili, M., Electric Power Systems Research (2018), https://doi.org/10.1016/j.epsr.2018.05.010