## 3 Electrode Station Configuration  
### General Data  
The preliminary basic design is based on the use of a rubble-mound breakwater, as shown in Figure 11 and Figure 12 of [2], for the cases of Stachtoroi in the Argosaronic Gulf and Korakia in Crete, respectively, regarding the HVDC interconnection between Crete and Attica in mainland Greece. The basic characteristics of the HVDC interconnection and the electrode stations are listed in Section 3.4 of [2]. In this case, those that directly concern the study of the electric field of the electrode stations are the following:  
* At monopolar steady-state operation, each pole has a nominal power of 500 MW at a nominal voltage of 500 kV. Hence, the nominal current of the station is at 1000 A. * The maximum transient current of the station reaches a peak value of 12,800 A, with a duration of 0.5 s during fault clearing. * The fully reversible electrode to be used is a high-silicon iron, tubular, type 4884 SZ, Centertec Z series, by ANOTEC, conforming to ASTM A518 G3, with a connection resistance of 1 m\(\Omega\), weight of 143 kg, diameter of 122 mm (=2\(\cdot\)\(r_{d}\)), length of 2130 mm (=\(L_{d}\)), and maximum electric current density up to 20 A/m\({}^{2}\) for successful reversible operation of the electrode, according to the manufacturer [33]. * The electrodes are suspended vertically, in order to obtain the largest possible water zone, when analysing the near-electric field and also because it is the structurally easier suspension mode in the case of concrete breakwaters with vertical walls. * In the area of Stachtoroi (Argosaronic Gulf, Attica), the angle \(\theta_{g}\) on the plan view of Figure 1 is taken to be equal to 210\({}^{\circ}\) based on the location of the electrode station (see Figure 11 in [2]), while the respective water angle \(\theta_{w}\) of Figure 2 is equal to 0.272\({}^{\circ}\) (see the worst-case scenario for the Aegina region of Table 1 in [2]). The available dam length is about 50 m.
* In the area of Korakia (Crete), the angle \(\theta_{g}\) on the plan view of Figure 1 is taken to be equal to 248\({}^{\circ}\) based on the location of the electrode station (see Figure 12 in [2]), while the respective water angle \(\theta_{w}\) of Figure 2 is equal to 2.29\({}^{\circ}\) (see the worst-case scenario/far region of Table 1 in [2]). The available dam length is about 70 m.
* The seawater electrical resistivity takes a value of 0.25 \(\Omega\cdot\)m, despite the fact that its value ranges from 0.167 to 0.212 \(\Omega\cdot\)m for both areas. In this way, the uncertainty that can arise from salinity reduction, due to freshwater inflow to seawater, is addressed, especially in the Korakia region where there are also two small dry rivers. In addition, the electrodes will always be placed at a greater depth than the breaking wave water can reach (which has a significantly greater electrical resistivity equal to 2.00 \(\Omega\cdot\)m). * The dam electrical resistivity takes a value of 100 \(\Omega\cdot\)m due to the water circulation openings in the breakwater [5; 6]. * For reasons of reliability, the number of linearly positioned frames \(N_{framm}\) is 5, adding an extra one as reserve. Therefore, the total number of electrodes required \(N_{min\_el}\) is 67 as a result of the application of Equation (1), assuming a total electric current, \(I_{tot\_st}\), of 1100 A at steady state and under overload conditions. Hence, for each frame, the necessary electrodes, \(N_{el\_frame}\), are 13, amounting to a total of 78 (including those in the reserve). Considering the increment factor \(\beta\) (=6.1%) [2] and implementing Equations (2) and (3), the final current density values \(J_{fit\_lo\_st}\) (under full-load conditions) and \(J_{int\_st}\) (under periodic maintenance) result as equal to 18.33 A/m\({}^{2}\) and 22.00 A/m\({}^{2}\), respectively.