AC loss simulation in a HTS 3-Phase 1 MVA transformer using H formulation

Abstract

One of critical issues for HTS transformers is achieving sufficiently low AC loss in the windings. Therefore, accurate prediction of AC loss is critical for the HTS transformer applications. In this work, we present AC loss simulation results employing the H-formulation for a 1 MVA 3-Phase HTS transformer. The high voltage (HV) windings are composed of 24 double pancakes per phase wound with 4 mmwide YBCO wire. Each double pancake coil has 38 ¼ turns. The low voltage (LV) windings are 20 turn single-layer solenoid windings wound with 15/5 (15 strands of 5 mm width) Roebel cable per phase. The numerical method was first verified by comparing the numerical and experimental AC loss results for two coil assemblies composed of two and six double pancake coils (DPCs). The numerical AC loss calculated for the transformer was compared with the measured AC loss as well as the numerical result obtained using the minimum magnetic energy variation (MMEV) method. The numerical AC loss result in this work and experimental result as well as the numerical result using MMEV at the rated current agree to within 20%. Further simulations were carried out to explore the dependence of the AC loss on the gap between the turns of the LV winding. The minimum AC loss at rated current in the 1 MVA HTS transformer appears when the gap between turns is approximately 2.1 mm turn gap in the LV winding. This is due to the change of relative heights between the HV and LV windings which results in optimal radial magnetic field cancellation. The same numerical method can be applied to calculate AC loss in larger rating HTS transformers.

Exploiting asymmetric wire critical current for the reduction of AC loss in HTS coil windings

“…An axisymmetric 2D H-formulation finite element method simulation was carried out using COMSOL to calculate the expected AC loss of the coil assemblies [25]. Details of the simulation can be found in our previous work [26]. A combination of a structured mesh [27], edge elements [28], and a homogenization method [29] were used to reduce computing time.…”

Overview of H-Formulation: A Versatile Tool for Modeling Electromagnetics in High-Temperature Superconductor Applications

“…Such magnet was proposed to be applied in a superconducting magnetic energy storage (SMES) system [103]. Using the same homogeneous bulk approximation, Song et al simulated an HTS three-phase 1 MVA transformer, and compared the loss results with those previously obtained with the minimum magnetic energy variation (MMEV) model, finding a reasonably good agreement [104].…”

Characterization of HTS Coils for Superconducting Rotating Electric Machine Applications: Challenges, Material Selection, Winding Process, and Testing

“…Accurate estimation of the AC loss of a coil and, as a result, its efficiency is very important for electric machine applications [36][37]. This AC loss causes extra heating and temperature rise if the cooling system does not work efficiently to dissipate it from the cryostat.…”