Replacement of 110 kV cable connections in the HPP Senj

Abstract

HPP Senj is a high-pressure derivation plant that uses the waters of the Lika and Gacka rivers, in such a way that it transfers the waters of the Lika rivers into the Gacka river and brings them through a joint derivation system through the Gacko polje and Velebit to its coastal side. The engine room of HPP Senj is located underground and three production units with Francis turbines are installed in it, which have a constructive drop of 410 m, an installed flow of 20 m3/s and a power of 72 MW, with generators of rated power of 80 MVA, voltage of 10.5 kV, current of 4400 A and cos φ=0, 9. The generators are connected to the HV network via the associated block transformers, G1 via BT1 at 220 kV network, and G2 and G3 via BT2 and BT3 to the 110 kV network. The cables that connected the generator block transformers G2 and G3 to the 110 kV switchgear, type FXKJ 1x300/50 mm2 - Cu, manufactured by SIEVERTS KABELVERKA, have insulation from cross-linked polyethylene XLPE), Cu conductor with a cross section of 300 mm2, 3 x (1 x 300/50 mm²), were installed in 1980. The replaced cables were in operation for 35 years, and problems with insulation breaks occurred several times in the plant, as a result of which a short circuit would occur and the cable had to be repaired by inserting cable connectors and cables. The condition of the cable after 2011. significantly worsened (breakdowns in 2011, 2013 and 2015), and their service life was at the very end, due to multiple breakdowns of the XLPE insulation, resulting in a reversible process of its accelerated aging, i.e. degradation of the insulation, and there was a high risk that the breakdown of one of the 110 kV cables would threaten the production of HPP Senj for a long period of time, since it takes a certain amount of time for production and supply as well as laying of a new cable and installation of connecting accessories. Due to all of the above, the HPP Senj plant made a decision to replace the 110 kV HV cable with a new one of suitable characteristics, in accordance with the conditions at the installation site. The choice of technical characteristics of the new cable was made in accordance with the current legislation, taking into account the specifics of the environment in which the cable will be in operation and experience from the exploitation of existing cables that are being changed.

Tonći Modrić

Associate Professor | Department of Electrical Intallations and Systems

Researcher and Full Professor at the Faculty of Electrical Engineering, Mechanical Engineering, and Naval Architecture in Split. His research focus is numerical modeling and calculation of the electric and magnetic fields in power systems and transmission lines, with an emphasis on the development of advanced models for interpreting geoelectrical ground survey data. Additionally, he is involved in the analysis of electromagnetic transients in systems with a high share of renewable energy sources, using finite element techniques.