A Modified OPGW Cable to Account for Higher Temperature Capacity During Short Circuit and Lightning Events João T. Pinho 1 , Sérgio Colle 2 , Victor Dmitriev 1 , Luciana Gonzalez 1 , Júlio N. Scussel 2 , Marcelo A. Andrade 3 , João C. V. da Silva 3 , Mauro Bedia 3 1 Department of Electrical Engineering / Federal University of Pará Belém – Pará – Brazil +55-91-32111299 - jtpinho@ufpa.br 2 Department of Mechanical Engineering / Federal University of Santa Catarina Florianópolis – Santa Catarina – Brazil +55-48-32342161 -·colle@emc.ufsc.br 3 Prysmian Telecomunicações Cabos e Sistemas do Brasil S.A. Sorocaba – São Paulo – Brazil +55-15-32359209 -·marcelo.andrade@prysmian.com Abstract This paper presents a concept of an OPGW cable, which was designed to optimize its highest temperature capacity, to account for the high current regimes present at short circuit and lightning events, which may occur during normal operation, and cause severe faults, even resulting in the rupture of the cable. Concerning the thermal effects, a cable with the proposed configuration was manufactured and preliminary short circuit tests were performed for comparison with the calculated results using the analytical model developed. For the electromagnetic effects, simulations were carried out using the finite element method and the results for the proposed structure (aluminum covered steel/aluminum alloy) are compared to those of three other different configurations: armor steel wires only, steel and aluminum alloy, and only aluminum covered steel. Keywords: Modified OPGW cable, numerical analysis, current density, skin effect, temperature capacity. 1. Introduction The OPGW is a multilayer structure, which is specially designed to be installed as overhead cable on power transmission lines to protect them against lightning, and simultaneously transmit information through its optical fibers. The overhead lines present some advantages compared to underground cables such as lower installation and maintenance costs [1], better safety, and since the optical fibers pack is placed in a metal tube in the center of the cable structure, they are immune to electromagnetic interference. Thus, the cable can be used for high-speed transmission of data and to be part of long distance telecommunication lines with high reliability [2]. A typical OPGW is composed of a dielectric core (optical fibers pack) protected by an aluminum tube, which is covered by armor wires usually made of steel [3-5]. Although these armor wires can vary in number, the cable considered in this work is made of 12 wires at all analyzed structures. In the OPGW the physical parameters as thermal and electric conductivity are different for each layer and, consequently, the current distribution and the heat generated by Joule’s Effect during the occurrence of a short circuit or lightning are not uniform [2]. The physical and geometrical characteristics of the cable determine the degree of damage that can occur. Therefore, the goal of the modified cable is to obtain a more uniform current density distribution, and the heat thus developed, over the cable’s cross section, consequently reducing the temperature at all points and making the cable more resistant to the above mentioned electrical and thermal stresses. The proposed structure for the cable is based on the normal extruded aluminum tube which contains the optical fibers and is embedded in armor aluminum covered steel/aluminum alloy wires. The so obtained cross section is shown in Figure 1, and its first theoretical thermal analysis was presented in the 56 th IWCS [6]. For the electromagnetic analysis, the results for the modified cable are compared to those of three other different configurations. 2. The common problems which occur in OPGW cables When an OPGW is submitted to short circuit or lightning conditions, heat is generated by Joule Effect in the metal layers. The heat produces a fast increase in temperature in the aluminum tube before the heat transfer from the tube to the armor wires begins. Due to the skin effect the current over the conductor cross section is unevenly distributed, existing mostly at the surface of the external conductors [7]. This effect increases with frequency and is more significant in magnetic materials due the larger values of their magnetic permeability. The increase in temperature caused by current flow, may not only cause serious damage to the tube and wires, but also to the optical fibers. Therefore, the maximum temperature absorbed in the aluminum tube should be less than the allowable temperature in the core with the optical fibers [2]. The armor wires of the OPGW are usually made of steel, which may cause high magnetic hysteresis and eddy current losses. To reduce magnetic losses, non magnetic materials such as aluminum are used [1]. Aluminum has a much smaller permeability than steel, and its thermal and electrical conductivities are higher than those of steel. Thus, inserting aluminum in the armor wires, it is expected that a more uniform current distribution can be achieved, International Wire & Cable Symposium 64 Proceedings of the 57th IWCS