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

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.