Fault current limiting HTS transformer with extended fault withstand time

Abstract

We describe the design, construction, and testing of a proof-of-principle 45 kVA, 450/450 V, single phase superconducting transformer with fault tolerant capability. This small-scale transformer demonstrates extended short circuit withstand time as a result of the high thermal mass of the windings as well as improved recovery under load due to the high heat transfer achieved in subcooled liquid nitrogen with wire coated to optimise boiling heat transfer. Primary and secondary windings consist of 38-turn single layer solenoids wound in helical trenches milled in glass-reinforced epoxy formers. The thermal mass of the 0.4 mm thick brass-laminated conductor provides for adiabatic fault withstand times over 1 s, allowing greater flexibility in the design of protection systems required to isolate faults. Enhanced heat transfer from the windings to the liquid nitrogen coolant allows the transformer to recover from the short circuit event, cooling from around 300 K to return to the superconducting state even while current close to the rated current continues to flow. Two factors contribute to the high heat transfer. Firstly the HTS transformer operates in subcooled liquid nitrogen, at 65 K–66 K at atmospheric pressure, significantly increasing the heat transfer compared to operation at saturated vapour pressure. Secondly, the HTS conductor is coated with solid polymer insulation with optimised thickness, which allows efficient cooling by nucleate boiling to take place over an extended range of conductor temperature.

Computational and experimental study of air-core HTS transformer electrothermal behaviour at current limiting mode

“…Because a direct measurement of the windings temperature is rather difficult, the temperature curves based only on the simulation results are provided. Note that the results of current and temperature simulation for the transformer match closely with the corresponding electrothermal behaviour curves for a current limiter [20][21][22][23][24][25]. Let us focus on two observations resulting from the obtained results.…”

Experimental and Simulation Study of Resistive Helical HTS Fault Current Limiters: Quench and Recovery Characteristics

“…There are a lot of studies on the current limiting and recovery characteristics of coated superconductors and resistive SFCLs, by the means of experiment and numerical modelling [10][11][12][13][14][15][16][17][18][19][20].…”

“…Yazdani-Asrami et al investigated heat transfer and recovery characteristic enhancement methods for metal and superconducting tapes under high current pulse, and improved the fault current limiting behavior. The fault withstand time was extended up to 2 s under load, achieved by coated conductor with solid polymer insulation with designed thickness operated in sub-cooled 65 K cryogenic environment [15,16].…”

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

“…F. Marignetti is with Department of Electrical Engineering and Information Technology, University of Cassino and Southern Lazio, Cassino, Italy. (email: marignetti@unicas.it) (CC), possess several unique properties which make them quite attractive for being utilized in a wide range of large-scale power applications [1][2][3][4]. Adoption of HTS materials for power applications would be of great advantage due to their remarkable loss and efficiency performances as well as the fact that operating temperature can be set within the liquid nitrogen (LN2) temperature range.…”