Liquid nitrogen level meter for high-temperature superconductor (HTS)

Abstract

Many kinds of high temperature superconductor (HTS) power machines such as HTS cable, HTS fault current limiter and HTS magnet are cooled by liquid nitrogen. The level of liquid nitrogen should be monitored and controlled to ensure the thermal stability and the dielectric strength as well. To measure the level, capacitance method and differential pressure method are usually used. However, each method has installation difficulties and measurement errors for unsteady state operation with varying system pressure. A new liquid level meter using a 2G HTS conductor is described, which has similar structure with the liquid helium level meter with NbTi filament. The level meter is fabricated with a parallel connected heater, which helps the separation of the superconducting region and normal region, considering the critical temperature, large heat capacity of conductor and cooling characteristics. The level of liquid nitrogen can be obtained from the measured voltage signal along the 2G HTS conductor. Design, fabrication and test results of the new liquid nitrogen level meter are presented.

Keywords

high temperature superconductivity / liquid nitrogen level meter / quench

References

[1] ChoJ.-w., SimK.-d., BaeJ.-han.. 2 design and experimental results of a 3 phase 30 m HTS power cable [J]. IEEE Transactions on Applied Superconductivity, 2006, 16(2): 1051-1054

[2] MasudaT., YumuraH., WatanabeM.. Recent progress of HTS cable project [J]. Physica C, 2008, 468(15–20): 2014-2017

[3] KotariM., KojimaH., HayakawaN.. Development of 2 MVA class superconducting fault current limiting transformer (SFCLT) with YBCO coated conductors [J]. Journal of Physics: Conference Series, 2010, 234: 032070

[4] GambleB., SnitchlerG., MacdonaldT.. Full power test of a 36.5 MW HTS propulsion motor [J]. IEEE Transactions on Applied Superconductivity, 2011, 21(3): 1083-1088

[5] KimS., SimK., KimH. J.. Thermal characteristics of conduction cooled 600 kJ HTS SMES system [J]. IEEE Transactions on Applied Superconductivity, 2008, 18(2): 750-753

[6] CheonH. G., ChoiJ. H., ChoiJ. W.. Insulation design of HTS transformer with the use of continuous transposed conductor [J]. Physica C, 2010, 470(2): 1679-1683

[7] KooJ. Y., LeeS. H., ShinW. J.. Measurement of partial discharge inception characteristics in sub-cooled liquid nitrogen [J]. Physica C, 2011, 471(21/22): 1565-1569

[8] HayakawaN., YamaguchiR., UkaiY.. Partial discharge activities under AC/impulse superimposed voltage in LN2/polypropylene laminated paper insulation system for HTS cables [J]. Journal of Physics: Conference Series, 2010, 234: 032020

[9] BaekS. M., RyooH. S., KimS. H.. A study on the surface flashover characteristics for a HTS cable termination [J]. Cryogenics, 2005, 45(1): 51-55

[10] MatsumotoK., SobueM., AsamotoK.. Capacitive level meter for liquid hydrogen [J]. Cryogenics, 2011, 51(2): 114-115

[11] LerschD., PascoviciG.. The liquid nitrogen fill level meter for the AGATA triple cluster detection [J]. Nuclear Instruments & Methods in Physics Research (Section A): Accelerators, Spectrometers, Detectors and Associated Equipment, 2011, 640(1): 133-138

[12] American Magnetics. http://www.americamagnetics.com.