All‐superconducting rotating machines have the potential for meeting the high power density and high efficiency required for electrical aircraft applications.However,very high AC loss encountered in superconducting a...All‐superconducting rotating machines have the potential for meeting the high power density and high efficiency required for electrical aircraft applications.However,very high AC loss encountered in superconducting armature windings could hinder their development.Multifilamentary MgB_(2) wires are one of the promising candidates for the stator windings,due to their potentially low AC loss properties with small filament size and twist pitches.As the first step,the dependence of critical current and n‐value on magnetic fields and temperatures I_(c)(B,T)and n(B,T),which are basic input parameters for AC loss simulation,needs to be measured.In this work,we present transport I_(c)measurements in three non‐magnetic multifilamentary MgB_(2) wires(MgB_(2)/Nb/CuNi/CuZn):one large wire with a 0.70 mm diameter and 25 mm twist pitch,and two small wires with a 0.48 mm diameter each and a 10 mm and 30 mm twist pitch respectively.A four‐probe direct current method is used to measure I_(c) of the MgB_(2) wires with variations in temperature(15-35 K)and magnetic field(0-5.5 T).Full I_(c) data for the small wire with 10 mm twist pitch was obtained,and the n‐values were mostly less than 20.While the I_(c) data for the large wire at low fields was more limited due to heating,the n‐values were higher and could be up to around 100.The difference is attributed to the different filament sizes.Experiments also found that there is no significant hysteresis in the transport critical current measured by decreasing or increasing magnetic fields due to the non‐magnetic sheaths.This non‐hysteretic characteristic is critical for lowering AC loss because the additional losses from magnetic sheaths can be eliminated.From the magnetic‐field dependence of critical current density,an empirical expression has been developed that provides suitable extrapolations to lower fields for the large wire.展开更多
基金supported by CSC(Chinese Scholarship Council)and was partly supported by the New Zealand Ministry of Business,Innovation and Employment under the Advanced Energy Technology Platform program.This program is the“High power electric motors for large scale transport contract number RTVU2004”supported by the Royal Society of New Zealand Catalyst:Seeding New Zealand-Japan Joint Research Project Programme contract number E4153.
文摘All‐superconducting rotating machines have the potential for meeting the high power density and high efficiency required for electrical aircraft applications.However,very high AC loss encountered in superconducting armature windings could hinder their development.Multifilamentary MgB_(2) wires are one of the promising candidates for the stator windings,due to their potentially low AC loss properties with small filament size and twist pitches.As the first step,the dependence of critical current and n‐value on magnetic fields and temperatures I_(c)(B,T)and n(B,T),which are basic input parameters for AC loss simulation,needs to be measured.In this work,we present transport I_(c)measurements in three non‐magnetic multifilamentary MgB_(2) wires(MgB_(2)/Nb/CuNi/CuZn):one large wire with a 0.70 mm diameter and 25 mm twist pitch,and two small wires with a 0.48 mm diameter each and a 10 mm and 30 mm twist pitch respectively.A four‐probe direct current method is used to measure I_(c) of the MgB_(2) wires with variations in temperature(15-35 K)and magnetic field(0-5.5 T).Full I_(c) data for the small wire with 10 mm twist pitch was obtained,and the n‐values were mostly less than 20.While the I_(c) data for the large wire at low fields was more limited due to heating,the n‐values were higher and could be up to around 100.The difference is attributed to the different filament sizes.Experiments also found that there is no significant hysteresis in the transport critical current measured by decreasing or increasing magnetic fields due to the non‐magnetic sheaths.This non‐hysteretic characteristic is critical for lowering AC loss because the additional losses from magnetic sheaths can be eliminated.From the magnetic‐field dependence of critical current density,an empirical expression has been developed that provides suitable extrapolations to lower fields for the large wire.
