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Electrical utilities and system operators (SOs) are constantly looking for solutions to problems in the management and control of the power network. For this purpose, SOs are exploring new research fields, which might bring contributions to the power system environment. A clear example is the field of computer science, within which artificial intelligence (AI) has been developed and is being applied to many fields. In power systems, AI could support the fault prediction of cable joints. Despite the availability of many legacy methods described in the literature, fault prediction is still critical, and it needs new solutions. For this purpose, in this paper, the authors made a further step in the evaluation of machine learning methods (ML) for cable joint health assessment. Six ML algorithms have been compared and assessed on a consolidated test scenario. It simulates a distributed measurement system which collects measurements from medium-voltage (MV) cable joints. Typical metrics have been applied to compare the performance of the algorithms. The analysis is then completed considering the actual in-field conditions and the SOs’ requirements. The results demonstrate: (i) the pros and cons of each algorithm; (ii) the best-performing algorithm; (iii) the possible benefits from the implementation of ML algorithms.

Cable joints are the weakest part of underground energy transmission systems due to the presence at the interface between the insulation material and the cable conductor. Underground cables serve under heavy service conditions (dust, dirt, humidity, etc.). So, the tracking resistance of polymers used in joint points of underground cables needs to be determined. In the first section of the study, equivalent samples were prepared under vacuum conditions in laboratory conditions from PU-based filling material used as filler material in low voltage underground cable joints. Prepared samples were tested in an established CTI test setup according to ASTM D5288. Samples were tested in prepared test setup under 600 V, 500 V, 400 V, and 300 V voltages. In the second section of the study, leakage currents were analyzed with the recurrence plot method, which is frequently used in nonlinear times series analysis. Later, recurrence quantification analysis was made by Recurrence Rate (RR) and Determinism (DET) parameters. The behavior of the system occurs less linear with decreased Recurrence Rate in Recurrence Quantification Analysis (RQA). RR and DET parameters increased with the decrease in voltage levels. As a result of, it is revealed that the tracking formation behavior of the PU cable joint becomes more unstable with increasing voltage. Thus, the CTI and RQA are shown to be also available to determine the tracking resistance of cable joints.

CERN is developing high-current ReBCO conductor on round core (CORC) cables for application in future detector and accelerator magnets. A characterization test on a ReBCO-CORC cable sample and its joints is performed in the 10-T FRESCA cable test facility at CERN. The sample is taken from the first 12-m-long CORC production. Key is the characterization of the field- and temperature-dependent critical currents of the CORC cable at 1.9 K and 4.2 K. Secondary objectives include evaluating the response of the CORC cable to quenches and the performance of cylindrical low resistive cable terminals especially designed and manufactured for use on CORC cables. The 7.6-mm CORC cable features 8 kA at 4.2 K and 10 T, and the joint terminals show a $25\pm 5-{n}\Omega$ resistance for 20-cm length.

One of the parameters that has to be considered in designing underground cables is the thermal resistivity of the soil along their routes. In fact, the ampacity of the MV underground cables having different types of insulation is normally evaluated through the application of the IEC Standard 60287-x “Electric cables — Calculation of the current rating”. This series of IEC Standard is formed of three parts as in the following: part 1: Formulae of ratings and power losses; part 2: Formulae for thermal resistance; part 3: Sections on operating conditions. In Italy, the current capacity of the same MV cables is established by the Italian Standard CEI-UNEL 35027 (2009) “Power cables with rated voltages from 1 kV to 30 kV — Steady state current ratings: cables laid in air and in ground”, which are based on the above mentioned IEC Standard. These thermal ampacities of the underground cables are function of ambient temperature and the thermal resistivity of the soil. The soil thermal resistivity is a parameter not easy to evaluate and for this reason, several times, only typical values are assumed just in function of the kind of the interested terrain (organic, loam, quartz sand, etc.). This assumption ignores the fact that the thermal resistivity varies continuously day by day especially in function of humidity soil content, being strongly dependent from this parameter. This paper describes as important differences of thermal resistivity may be present in consequence of seasonal variation in moisture content of the soil. It is also shown as such variations may cause important anomalous increases of cable maximum working temperature, which may be assumed to be at the origin of unexpected failures especially in correspondence of MV cable joints. In fact, the joints are, still today, the weakest points of the underground cables where the breakdown easily occurs due to poor workmanship, moisture ingress and thermal degradation. This thermal degradation may be also due to circulation of fault current in the metallic sheaths.

Thermal aspects of power cable performance are an important field of research as power grids depend increasingly on the reliability of underground cable systems. Overheating is a possible cause of cable faults and it should be ensured that no part of the cable exceeds its rated operating temperature. A test setup was established in Aalto University to study the changes of temperature across different power cable layers in various cable operating modes. The setup also includes three different types of joints to identify differences in behavior during temperature change. Temperature measurement was achieved using thermocouples inserted into the cable and each of the joints: heat shrink joint, cold shrink joint and hybrid shrink joint. This paper discusses the structure of the test setup and the capacity of different tests available with the given setup.

Many studies have been conducted on DC transmission. Of power apparatus for DC transmission, high voltage direct current (HVDC) cable systems are being evaluated because of the increase in power demand and transmission distance. Therefore, dc insulation characteristics of liquid silicone rubber (LSR), which has various advantages such as short curing time and the ease of maintenance, were investigated to assess its performance as a HVDC insulation material for cable joints. The electrical performance of LSR added to nano-aluminum trihydrate (ATH) were confirmed by measurements of the breakdown strength and electrical conductivity. In addition, field emission scanning electron microscope (FE-SEM) was used as a means of confirmation of nanofiller dispersion state. The LSR nanocomposite was prepared by compounding LSR filled nano-sized ATH filler. The dc insulation properties of LSR added to nano-sized ATH fillers were found to be superior to those of the LSR without a filler., {"references":["Y. Maekawa, A. Yamaguchi, C. Ikeda, Y. Sekii and M. Hara, Proceeding of Jicable91, B.9.3, pp.562-569 (1991)","K. Terashima, H. Suzuki, M. Hara and K. Watanabe, IEEE Trans. Pow. Delive., Vol.13, No.1, pp.7-16 (1998)","Y. Maekawa, C. Watanabe, M. Asano, Y. Murata, S. Katakai and M. Shimada, Trans. IEE of Japan, Vol.121-B, No.3, pp.390-398 (2001)","Y. Maekawa, T. Yamanaka, T. Kimura, Y. Murata, S. Katakai and O. Matsunaga, The Hitachi Densen, No.21, pp.65-72 (2002)","L. J. Hiivala, IEEE press, pp. 208-240 (2000)","R. Bodega, G. Perego, P. H. F. Morshuis, U. H. Nilsso and J. J. Smit, IEEE Int'l. Conf. Electr. Insu. Dielectr.(CEIDP), pp.507 (2005)","Ch. C. Reddy and T. S. Ramu, IEEE Trans. Dielectr. Electr. Insul., Vol. 17, pp. 221 -227 (2008)","D. Fabiani, G. C. Montanari and L. A. Dissado, IEEE Int'l. Conf. Properties Appl. Dielectr. Materials (ICPADM), No. D-2, pp.337-340 (2009)","L. Meyer, E.A. Cherney and S.H. Jayaram, IEEE Electr.Insul. Mag., Vol. 20, No. 4, pp. 13-21 (2004)\n[10]\tM. Kozako, M. Higashikoji, T. Tominaga, M. Hikita, G. Ueta, S. Okabe and T. Tanaka, IEEE Trans. Dielectr. Electr. Insul., Vol. 19, No. 5, pp.1760-1764 (2012)\n[11]\tI. B. Jeong, J. S. Kim, J. Y. Lee, J. Y. Shin and J. W. Hong, Trans. Electr. Electro. Materials, Vol. 11, No. 6, pp. 261-265 (2010)\n[12]\tL. Lei, W. Xishan and C. Dengke, IEEE Intern. Conf. Solid Dielectr.(ICSD), pp.804-807 (2004)\n[13]\tB. Venkatesulu and M. Joy Thomas, IEEE Trans. Dielectr. Electr. Insu., Vol. 17, No. 2 (2010)\n[14]\tS. Fang, Z. Jia, H. Gao and Z. Guan, IEEE Int'l. Conf. Electr. Insu. Dielectr.(CEIDP), pp.300-303 (2007)\n[15]\tHan, C. Diao, L. Dong and X. Zhang, IEEE Int'l. Conf. Solid Dielectr.(ICSD), pp.330 (2007)\n[16]\tS. Singha and M. J. Thomas, IEEE Trans. Dielectr. Electr. Insu.,Vol. 15, No. 1 (2008)\n[17]\tT. Tanaka, G.C. Montanari and R. Mulhapt, IEEE Trans. Dielectr. Electr. Insul., Vol. 11, pp. 763-784 (2004)\n[18]\tM.L. Frechette, M.L. Trudeau, H.D. Alamdari and S. Boily, IEEE Trans. Dielectr. Electr. Insul., Vol. 11, pp. 808-818 (2004)\n[19]\tY. Murata, Y. Sekiguchi, Y. lnoue and M. Kanaoka, Proceedings of 2005 Int'l. Symp. Electr. Insu. Materials, pp.650-653 (2005)T. W. Dakin, \"Application of Epoxy Resins in Electrical Apparatus\", IEEE Trans. Dielectr. Electr. Insul., Vol.EI-9, No.4, pp.121-128,"]}

A power cable is widely used for power supply in power distributing networks and power transmission lines. Due to limitations in the production, delivery and setting up power cables, they are produced and delivered in several separate lengths. Cable itself, consists of two cable terminations and arbitrary number of cable joints, depending on the cable route length. Electrical stress control is needed to prevent a dielectric breakdown at the end of the insulation shield in both the air and cable insulation. Reliability of cable joint depends on its materials, design, installation and operating environment. The paper describes design and performance results for new modeled cable joints. Design concepts, based on numerical calculations, must be correct. An Equivalent Electrodes Method/Boundary Elements Method-hybrid approach that allows electromagnetic field calculations in multilayer dielectric media, including inhomogeneous regions, is presented., {"references":["N. B. Raicevic, and S. R. Aleksic, \"One method for electric field\ndetermination in the vicinity of infinitely thin electrode shells\",\nEngineering Analysis with Boundary Elements, Elsevier, vol. 34, no. 2,\npp. 97-104, February 2010.","N. B. Raicevic, S. R. Aleksic, and S. S. Ilic, \"A Hybrid Boundary\nElement Method for Multilayer Electrostatic and Magnetostatic\nProblems\", Electromagnetics, Taylor & Francis, vol. 30, no. 6, pp. 507-\n524, August 2010.","N. B. Raicevic, S. R. Aleksic, and S. S. Ilic, \"One Numerical Method to\nDetermine Improved Cable Terminations\", Electric Power Systems\nResearch, Elsevier, vol. 81, no. 4, pp. 942-948, April 2011.","N. B. Raicevic, \"Conformal mapping and equivalent electrodes method\napplication on electric field determination at cable accessories\", in: F.\nLiu, G.M. Nguerekata, D. Pokrajac, X.Q. Shi, J.G. Sun, X.G. Xia (Eds.),\nDiscrete and Computational Mathematics. New York, USA: Nova\nPublishers, 2008, chapter14, pp. 205-214.","N. B. 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