ORIGINAL PAPER Multi-segment Winding Application for Axial Short Circuit Force Reduction Under Tap Changer Operation in HTS Transformers Ahmad Moradnouri 1 & Mehdi Vakilian 1 & Arsalan Hekmati 2,3 & Mehdi Fardmanesh 1 Received: 22 February 2019 /Accepted: 9 April 2019 # Springer Science+Business Media, LLC, part of Springer Nature 2019 Abstract High-temperature superconducting (HTS) transformers have remarkable appealing advantages over conventional ones. But higher brittleness of HTS windings with respect to copper windings makes HTS transformers more vulnerable in short circuit and inrush current situations. During tap changer operation, appreciable asymmetry and non-uniform distribution of ampere-turn along the windings causes high axial component of short circuit forces and makes the situation more severe. In this paper, multi- segment winding method is employed for reduction of axial short circuit forces. An analytical method is presented for calculation of axial component of short circuit forces under tap changer operation. Analytical method shows that with utilizing HLHLHLH asymmetrical multi-segment windings, during tap changer operation, the axial component of short circuit forces reduces signif- icantly. The results of the analytical method are compared with the results of finite element method (FEM) model simulations, and the consistency is demonstrated. Keywords High-temperature superconducting (HTS) transformers . Finite element method . Multi-segment winding method . Axial short circuit force . Tap changer 1 Introduction High-temperature superconducting (HTS) transformers have re- markable promising features with respect to conventional ones. Based on theoretical calculations and test results on manufactured HTS transformers, researchers mention these transformers are smaller and lighter and they have higher efficiency, greatly ex- tended overload capability, better voltage regulation, lower life cycle cost, lower environmental burden, and lower potential fire risk with respect to conventional transformers [1–5]. Remarkable electromagnetic forces arise during short cir- cuit or inrush current situations which may cause elastic and plastic deformations on transformer windings and catastrophic failure of transformer [6–10]. Failure of transformers due to the short circuit forces is a major concern of transformer users and there are continuous efforts by transformer manufacturers to improve short circuit withstand of this equipment [11]. Due to higher brittleness of HTS windings with respect to copper windings, short circuit withstand of HTS transformers are lower than conventional ones [12, 13]. Copper stabilizer has been added to the 2G HTS tapes for protection of REBCO HTS conductors and production of rounded edges which are beneficial for high voltage applications [14]. SCS12050, 2G HTS tape produced by SuperPower® has 12-mm width and 0.1-mm thickness. The thickness of REBCO HTS conductor is 1 μm while two 20-μm copper stabilizers surround the REBCO HTS conductor, Hastelloy substrate, and silver over-layers. Critical tensile stress of SCS12050 at 77 K is more than 550 MPa, also 0.45% critical axial tensile strain at 77 K and 11-mm critical bend diameter (tension and * Ahmad Moradnouri Moradnouri_ahmad@ee.sharif.edu; moradnouri.ahmad@gmail.com Mehdi Vakilian Vakilian@sharif.edu Arsalan Hekmati ahekmati@nri.ac.ir; hekmati@usc.ac.ir Mehdi Fardmanesh Fardmanesh@sharif.edu 1 Electrical Engineering Department, Sharif University of Technology, Tehran 11365-11155, Iran 2 Electrical Engineering Department, University of Science and Culture, USC, Tehran 14619-68151, Iran 3 Electrical Machine Research Group, Niroo Research Institute, Tehran 14686-13113, Iran Journal of Superconductivity and Novel Magnetism https://doi.org/10.1007/s10948-019-5109-1