Abstract
High temperature superconducting generators (HTSGs) have great potential of high power density for future large direct-drive wind turbines. As synchronous machines, HTSGs have rapid rise of field currents during a sudden short circuit fault which cause AC losses in the HTS tapes. This paper applies <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">H-A</i> formulation of Maxwell equations for finite element simulation of electromagnetic behavior of a 10 MW, 9.6 rpm HTSGs. The model is integrated to a short circuit model to calculate the characteristics of the HTS field winding, such as field currents and AC losses during a three-phase no-load short circuit fault at the armature winding terminal. Two HTSG designs are compared. The <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$n$</tex-math></inline-formula> value characterizing the sharpness of the superconducting-resistive state transition of the HTS tape and the number of armature winding segments are analyzed as key variables. The result indicates high AC losses are produced but more armature winding segments can effectively reduce the AC loss and the field current. A lower <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$n$</tex-math></inline-formula> value can also lower the AC loss level but only for the non-magnetic rotor design. The field current is not affected by the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$n$</tex-math></inline-formula> value for both HTSG designs.
Highlights
H IGH temperature superconducting generators (HTSGs) have great potential to be a high power density solution for future large direct-drive wind turbines
The latter rleads is constant, e.g. 20 mΩ, as an estimate from [21]. The former resistivity of the HTS tape (rHTS) contributes to all the AC loss so it can be calculated from the equality i2f rHTS = ls where if is the field current, and ls is the axial stack length of the generator
This is mainly because the total resistance of the field winding is low compared to the high leakage reactance (Xσf = 145 Ω for the fully iron-core (FIC) design and Xσf = 164 Ω for the non-magnetic rotor (NMR) design) the HTS resistance has significantly increased
Summary
H IGH temperature superconducting generators (HTSGs) have great potential to be a high power density solution for future large direct-drive wind turbines. They will become quite competitive and commercialized when the cost of HTS wires largely drops [1]-[4]. Previous studies on transients characterization for HTSGs did not model the superconductivity, e.g. non-linear resistivity of the superconductor as shown in (1), but used a nearly-zero constant conductivity with only A-formulation [5]-[9]. Models that consider the non-linear resistivity need to be developed for transients study of HTSGs since the resistivity may limit the current rise but produce considerable AC losses that may cause temperature rise or damage the HTS winding. The n value of the non-linear resistivity of HTS tapes as given by (1) and the number of armature winding segments are analyzed as key variables
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