IEC 61788-26-2020 pdf free download

IEC 61788-26-2020 pdf free download.Superconductivity — Part 26: Critical current measurement — DC critical current of RE-Ba-Cu-O composite superconductors
Supraconductivité — Partie 26: Mesu rage du cou rant critique — Courant critique continu des
composites supraconducteurs de RE-BaCu-O.
4 Principle
The critical current of a composite superconductor specimen shall be determined from a voltage—current (U-I) characteristic measured in a liquid nitrogen bath at ambient pressure. To get a U-I characteristic, a direct current is applied to the superconductor specimen and the voltage generated along the specimen is measured. The current is increased from zero and the U-I characteristic is recorded. The critical current shall be determined as the current at which a specific electric field strength criterion (electric field criterion) (Es) is reached. For any selected E, there shall be a corresponding voltage criterion ((Jo) for a specified voltage tap separation.
5 Apparatus
5.1 General
The apparatus required for the present test method includes the critical current measuring system. Additional information relating to the apparatus is given in Annex A.
5.2 CritIcal current measuring system
The apparatus to measure the LI-I characteristic should consist of a specimen probe, an open bath and a U-I measurement system.
The specimen probe, which consists of a specimen and a measurement holder, is inserted in the open bath filled with liquid nitrogen. The U-I measurement system consists of a DC current source and necessary data acquisition system, preamplifiers, filters or voltmeters, or a combination thereof. Suitable measurement holder materials are recommended in A.3.1.
A computer assisted data acquisition system is recommended.
6.2 Mounting of the specimen
The specimen shall be mounted to the flat surface of the holder. Both ends shall be fastened
or soldered to the current contact blocks.
The voltage taps shall be placed in the central part with or without solder.
The current contacts and the voltage taps shall be on the superconducting layer side. Voltage leads shall be twisted as close to the voltage taps as possible.
7 Critical current measurement
The critical current shall be measured while minimizing mechanical strain.
The specimen shall be inserted slowly into the liquid nitrogen bath. The volume of the liquid nitrogen bath shall be sufficiently larger than the specimen and the measurement holder. The depth of the bath shall be sufficiently higher than the height of the measurement holder. The specimen shall be cooled from room temperature to liquid nitrogen temperature until the specimen and the measurement holder are sufficiently cooled by liquid nitrogen that boils with microbubbles, i.e. steady state. It takes several tens of seconds.
When using the constant sweep rate method, the sweep rate shall be selected not to influence the voltage measurement.
When using the ramp-and-hold method, the current sweep rate between stages shall be lower than the equivalent of ramping from zero current to I in 3 s. Data acquisition at each stage shall be started as soon as the flow or creep voltage generated by the current ramp can be disregarded. The current drift during each current set point shall be less than 1 % of I.IEC 61788-26-2020 pdf free download.