1051-8223 (c) 2016 IEEE. Personal use is permitted, but republication/redistribution requires IEEE permission. See http://www.ieee.org/publications_standards/publications/rights/index.html for more information. This article has been accepted for publication in a future issue of this journal, but has not been fully edited. Content may change prior to final publication. Citation information: DOI 10.1109/TASC.2016.2646178, IEEE Transactions on Applied Superconductivity 3MPo2D-01 Study of Heat Localization in HTS Wires at Overload Conditions. Vitaly S. Vysotsky Senior Member, IEEE, Sergey Yu. Zanegin, Sergey S. Fetisov, Sergey M. Ryabov, and Vasily V. Zubko. Abstract — A common problem of superconducting devices is to survive during a fault with a current overload. At a fault, superconducting device will have strong overheating and burning out is possible. The problem becomes more serious in case if a high temperature superconducting wire has a weak point where the critical currents is less than the average over a wire. Such a weak point could be the point of origination of a strong overheating within a very localized area. This can lead to a burning and destroying of an HTS device. To study this problem, we developed the experimental set-up with the spatial resolution 2 mm and the time resolution 1 ms to observe a local temperature/voltage evolution in HTS tapes overloaded by currents. The preliminary experiments were performed to measure local heat/voltage development on 2G HTS tapes with an artificial weak point. Local heat/voltage evolutions have been measured and compared with calculations by our model developed earlier. Index Terms — Current overloads, Heat localization, Overheating of High Temperature Superconductors, Quench Development. I. INTRODUCTION HE POWER electro-technical devices (power cables, transformers, etc.) made with HTS wires must withstand fault currents several times more than their operating currents. In a case of a fault the overload current forcibly becomes much more than operating/critical current of a device. A concern is whether the fault current will over-heat the HTS conductor and degrade the superconducting properties or burn- out an HTS tape. In our experimental works to study of overload conditions [1] – [3] we often observed that if an HTS wire is burned out the burned part is very narrow. That is why, our major motivation in many studies was to understand why an area burned is so local. Our analytical studies of quasi – uniform heating at overloads of HTS objects by a current [4] – [5] demonstrated that two heat development regimes are possible: stable and unstable. There is the sharp border between stable and unstable regimes in relation to the current density change. This Automatically generated dates of receipt and acceptance will be placed here; authors do not produce these dates. This work was supported by the Russian Scientific Foundation under Grant №16-19-10563. (All authors contributed equally to this work.) (Corresponding author: Vitaly S. Vysotsky, e-mail: vysotsky@ieee.org) All authors are with Russian Scientific R&D Cable Institute, Moscow, 111024, Russia. V.S. Vysotsky is also with National Research Nuclear University MEPhI (Moscow Engineering Physics Institute), 115409, Moscow, Russia. behavior is typical for non-linear media which are HTS objects. If an HTS object has a local spatial disturbance the heat localization takes place and instability development time is less in comparison with a uniform heating [6] – [9]. By numerical experiments in [6] – [9], we showed that in HTS objects a heat development similar to the so called blow- up regimes [10] with strong heat localization could take place. So, our first suggestion was that “blow-up” regimes could be responsible for a heat localization and narrow burning area. In real HTS wires the weak points or local spatial disturbances with critical currents less than the average over the wire always could take place. Such a weak point could be the point of origination of strong overheating that could lead to a burning and destroying of HTS device. Numerical simulations [6] – [9] demonstrated that the problem of overheating with the heat localization on a local spatial disturbance does exist. The next task should be an experimental study of a heat localization. The motivation of the present work is to perform the direct experimental study of overheating of HTS wires that have a weak point, at least artificially made one. In this paper, we present the very first step in this direction: development and testing of the experimental set up to measure local heat/voltage evolutions in HTS tapes with artificially made local disturbances. The first measurements demonstrated that localization of the temperature during overloads takes place indeed. Experimental arrangements, results of measurements, computer modeling and comparison of calculations and experimental data are presented and discussed. This study is important for devices like resistive fault current limiters. Even at not very high current the localized weak point can to overheat and to burn out. II. EXPERIMENT A. Experimental set-up Because the spatially localized overheated areas could be rather short we developed a device that could measure voltage and temperature distribution along a rather short distance. The sketch of the test set up developed is shown in Fig.1. HTS tape measured was placed on a textolite support and connected to thick copper terminations. Connections with terminations were reinforced by 1G HTS tapes in silver matrix to avoid overheating of 2G HTS tape at the edges. Eight voltage taps V0 …V 8 were installed with step 2 mm in the middle of a tape tested (Fig.2). Voltage taps were gold coated needles and were pressed to an HTS tape by small springs. T