Rio Madeira HVDC System: Commissioning of the Ground Electrode for Bipole 2 at Porto Velho

Abstract

The original ground electrode of the Madeira River HVDC transmission system, bipole 2, was discarded due to the risk of saturation of the transformers in the Converter Substation of Porto Velho, located 15 km away, during the monopolar operation with ground return. After an extensive geophysical survey, a new site was selected, 40 km from the converter substation. For the confirmation of the new site, it was built in the central area of the site, a single-well 47 m deep test electrode, interconnected to the original 15 km electrode line by an additional 40 km long temporary line. A new electrode was then designed. This paper summarizes the test electrode procedure and the activities developed for the new electrode commissioning after its construction, which can be divided into two phases–pre-commissioning and commissioning. The electrode pre-commissioning was performed before its energization for the evaluation of the integrity of its components. The commissioning tests started with electrode energization, employing the electrode line, and an unbalanced bipole operation, which allowed the evaluation of its electrical performance. However, the main objective of the paper is the evaluation of the electrode resistance, which is an essential HVDC electrode parameter.

Comparison of Different Configurations for Shoreline Pond Electrode Station for HVDC Transmission Systems—Part I: Electric Field Study for Frames of Linear Electrode Arrangement Based on a Simplified Analytical Model

“…Practically unifying the considerations of CIGRE B4.61 675: 2017 [1], §5.5.3.1 and Figure 5. 35 and IEC TS 62344: 2013 [27], §6.1 and Figure 5, the dam is added according to Figure 2, where an electrode is placed on the shore (or on the seabed, in shallow waters), at the centre of the coast. The bottom of the sea is considered to be inclined, with respect to the horizon, forming an angle θ w .…”

“…The electric field strength of the k-th electrode is analysed in its components E x−k and E y−k , on xOx' and yOy' axes (as in Figure 5), utilising the coordinates (x k , y k ) of the electrode (x,y) of the point of interest (canvas points) and the corresponding distance r k : 18) • Determination of areas ensuring electric field strength and voltage limits according TS 62544:2013 and CIGRE B4.61 675:2017: In order for the operating conditions electrode station to be safe-under any operating conditions-whether it con the specialised maintenance staff, or people and living beings, in the areas of access, limits are set for the electric field strength, touch voltage, step voltage, m to-metal touch voltage, and absolute voltage with respect to remote earth. In p ular, taking the most unfavourable limits from the general guidelines of IE 62544:2013 [27] (p. 32) and CIGRE B4.61 675:2017 [1] (p. 65), as well as recomm tions about the pipe-to-soil potential difference based on the applied provisio cathodic protection [35], the necessary conditions that must be met (as they ar summarised in §2.5. of [2]) are as follows:…”

“…Essentially, it turns out that the estimation of the electric field strength through a single frame is not sufficient and the placement of the electrodes inside the respective pond, parallel to the axis of the dam, is marginally performed, achieving (in the area of the frame that does not operate for maintenance reasons/fault) electric field strengths of the order of 3 V/m, which are higher than the 2.5 V/m required by [1], for the unprotected diver next to the electrode. The corresponding easement area in front of the dam extends to 45 m in order to ensure an electric field strength of less than 1.25 V/m, which is set as a limit of non-disturbance of all kinds of marine mammals, according to [1,27,35]. However, this arrangement is the most typical of near-shore submerged electrodes and is distinguished for the easy suspension-lifting-positioning system of electrodes due to their proximity to the dam.…”

Alternative Simplified Analytical Models for the Electric Field, in Shoreline Pond Electrode Preliminary Design, in the Case of HVDC Transmission Systems

“…Especially in IEC TS 62344:2013 [34] (p. 32), the value 1.25 V/m is taken for continuous operating conditions in order to ensure no effect on marine mammals, and in [17] (p. 93, section 5.4.3, 2nd paragraph), the same value is reported as the generally accepted value of potential difference, per unit length, from the electrode surface, directly accessible to humans and marine fauna. In addition, based on [79], the value of 4 V is reported as the effect value on buried metal tubes (pipe to soil potential difference), as it is considered to be the maximum potential value that can be applied by a cathodic protection device. Therefore, in the present case, the following conditions were applied:…”

“…The above are expressed as safety distances r limit1 against voltage V limit_S with respect to infinity, r limit2 against average steady-state electric field strength E limit_S , r limit3 against average transient-state electric field strength E limit_T , r limit4 against steady-state point value of electric field strength E limit_S , and r limit5 against transient-state point value of electric field strength E limit_T . Limits V limit_S , E limit_S and E limit_T are 4 V, according to [79] (although considering specific points and not infinity); 1.25 V/m to 2 V/m, according to IEC TS 6234:2003, [34] (p. 32) or 2.5 V/m, according to CIGRE B4.61 675:2007 [17]; and 15 V/m according to CIGRE B.4.61 675:2007 [17], respectively, applying, in the present case, the most unfavorable values. In addition, the determination of the absolute electric potential, with respect to infinity (remote earth) and the equivalent ohmic resistance of the electrode station, with respect to remote earth, is of interest because they constitute basic criteria for dimensioning the insulation material of the switching devices and the return conductor of the HVDC interconnection.…”