IEC 61788-14:2010 pdf – Superconductivity – Part 14: Superconducting power devices – General requirements for characteristic tests of current leads designed for powering superconducting devices.
C) Thermal conduction method
The current leads are Installed In a cryoslat with known values of background heal leakage into the measurement region. The cooling portions of the current leads are thermally connected to the cold heads of the cryocooler. The heat leakage through the current leads Is evaluated by the increment of heat loads to the cold heads of the cryocooler.
NOTE I In the evaporation method, a part of evaporated coolant remains In the cryostat as a low-temperature gas. Because the density of a tow-temperature gas is large, it a necessary to correct the amount oU the evaporated coolant when th, mass flow rate is measured at th, outlet of the cryOStaI
NOTE 2 In R&D, the value of the h.it leakage through th, current lead is slimClad frgwn th• numerical solution of me energy balance equatIon along the conductor of the current lead. Temperatures of cold and warm ends are taken to be boundary values of the energy balance equation The form of the energy balance equation depends on the structure of I he current leads. In the case of the gas-cooled normal conducting current leads, the energy balance equation may consist of SUCh terms as neat conduction, aiwnic heat generation and heat eschange with cooling gas
6.3.1.3 Results
Test results shall be collated with the specifications and fully reported.
6.3.2 Rated current heat load lest
6.3.2.1 Purpose
This test shall measure the amount of heat load at the rated current.
6.3.2.2 Methods
The methods shall be pursuant to those of the non-current heat leakage test without current
(6.3.1,2).
6.3.2.3 Results
Test results shall be collated with the specifications and fully reported.
64 Rated current.carrylng test
6.4.1 Purpose
This test shall confirm performances of the current leads at the rated current under the normal operation conditions.
6.4.2 Methods
To compare the performances of the current leads to the design values, the temperature profile shall be measured, The measuring points of temperature shall be at least the three positions of the room-temperature end, the intermediate-temperature portion and the low-temperature end. It shall be noticed that the temperature of the room-temperature end is affected by boundary conditions such as size, cooling condition of the bus bar, and so on,
The temperature rise shall be measured usually by the thermometer method or the resistance method.
Prior to the test, all cooling conditions of the refrigerator, the cryogen level or others shall be confirmed.
The current of the leads shall be maintained at the rated value until the cooling condition settles down In the steady state,
A typical example of temperature profile during the rated current•carrying test Is shown in Clause Ci of Annex C.
6.43 Results
Test results shall be collated with the specilications and fully reported.
6.5 Contact resistance test
6.5.1 Purpose
This test shall measure the contact resistance between HTS parts and normal conductin9 parts at intermedtate•temperature portions. The contact resistance between HTS parts and LTS parts at low-temperature ends shall be measured. If it is required for the current leads.
6.5.2 Methods
The measurement of the total contact resistance, including the target contact section, shall be performed by the four-terminal method. The test results shall be corrected for the additional resistances due to other sections, except for that of the target contact.
NOTE For a curreot toad at sinati capacity less than a tow irA. the inttuence at the two-dimensionat current disinbution on the contact resistance can be disregarded. However, the measurement and the correction by analysis oi simulation consideing the Cuirent d,sk,but ion at tIle target 1oint shalt be necesSary tar the current lead at the large capacity, Therelore. It I. very ditticutt to get accurate vaiue of the contact rOirstance Even in thu case, it Is necessary to confirm the oontact r.s.stanc. is at least b.low th. tot.rano. value by correcling th. m,ssurem.nf with anatyis or S.inulatiofl Consideflflg the two-dimensionat Current distribution at the target joint
6.5.3 Results
Test results shall be collated with the specifications and fully reported.
6.6 Voltage drop test
6.6.1 Purpose
This test shall confirm that the voltage drop of the current leads under the rated current is as expected from design calculations,
6.6.2 Methods
The cooling conditions shall conform to those of the rated current-carrying test.
The voltage drop shall be measured by the voltage taps between the room-temperature end and the low-temperature end.
6.6.3 Results
Test results shall be collated with the specifications and fully reported.
6.7 High voltage test
6.7.1 Purpose
This test shall confirm that there is no abnormality in the voltage drop property having an influence on the insulation performance of current leads.