IEC 61788-14 pdf download – Superconductivity – Part 14: Superconducting power devices – General requirements for characteristic tests of current leads designed for powering superconducting devices

IEC 61788-14 pdf download – Superconductivity – Part 14: Superconducting power devices – General requirements for characteristic tests of current leads designed for powering superconducting devices
3.5
gas-cooled type current lead
current lead cooled by a cooling gas
NOTEIn some cases，the gas cooling is made between cooling via gas flow inside the leads and (additional)convection cooling on the outside surtace.
3.6
self-cooled current lead
vapour enthalpy cooled current lead
current lead capably cooled by an evaporated gas generated by heat load from current leadsinto cryogen
3.7
heat leakage
non-current heat leakage
heat conducted from higher temperature portion into lower temperature portion of the currentlead at zero current operation without any Joule heating
3.8
heat load
total heat induced into a cryogenic system through the current leads under current-carryingoperation
3.9
rated current heat load
heat load at a rated current operation
4Principles
The powering of superconducting equipment is made via components that provide the electricallink between the room temperature environment and the cryogenic temperature of the poweredequipment. These components are called current leads.Since they operate in a gradient oftemperature and they transport current into the cryogenic environment, they are one of the majorsources of a heat leakage into the cryostat.
The current leads can be classified into two types:
normal conducting current leads,made entirely from normal conducting section.These areusually joined at their cold end to a superconducting (SC) bus or link leading to the devicebeing powered;
high temperature superconducting (HTS) current leads,which incorporate a section of HTSmaterial. A normal conducting section is necessary to conduct the current from roomtemperature to the warm end of the HTS section. The latter must be maintained at asufficiently low temperature to ensure that it remains superconducting for the maximumrated current of the lead.The cold end of the HTS section is usually joined to the device bya sC bus.
Depending on the cooling method, the leads can be either non-gas-cooled or gas-cooled.Bothtypes of cooling methods can be used if the lead is subdivided into two, hydraulically separated,sections. lf the device being powered uses low temperature superconducting (LTS) material, thelink to the lead is usually via LTS cables or wires.
Optimized,self-cooled normal conducting current leads conduct into the helium bath 1,1 W/kA[1]1) to 1,2W/KA [2].This value can be reduced substantially by using HTS material. HTS current leads have been extensively studied, designed and tested, and are already being integrated intolarge-scale systems [3] [4].
The design of a current lead is uniquely linked to the system within which it has to operate.Thechoice of materials, the cooling method,the geometry，the electrical characteristics and theadmissible cryogenic consumptions are strongly influenced by boundary conditions imposed bythe whole system.System requirements are electrical , cryogenic,and mechanical, and includethe following:
maximum operating current, operation mode,current ramp rate,insulation voltage,circuittime constant,ambient magnetic fields;
cryogen availability, cryogen inlet/outlet temperature and pressure, admissible heat loads,time duration when the lead shall operate safely in case of failure of cryogen supply;
the volume available for integration, including mechanical support,vacuum insulation,andconnection to the hydraulic and electrical interfaces.
NOTE 1 The heat leakage for self-cooled current leads should make use of 1,2 WkA in the case of large currentcapacities.
NOTE 2 Typical current leads based on these principles are shown in Annex B.5 Characteristic test items
The following clauses describe the qualification tests that should be performed on a current leadat both room and cryogenic temperatures in order to verify its mechanical, electrical and thermalperformance. It is assumed that the design of the current lead has been carried out inconsideration of general versatility. Before application to an actual system, it is also necessaryto do the optimization of the current lead according to the constraints imposed by each system.The characteristic test items shown in Table 1 should enable the user to verify if the current leadmeets the specified requirements, and to judge if the test items meet the execution stage of thecurrent lead. lt is the responsibility of the user of this standard to select the appropriate testsaccording to Table 1 considering the boundary conditions of the current leads.