IEC 61788-26:2020 pdf download

IEC 61788-26:2020 pdf download.Superconductivity – Part 26: Critical current measurement – DC critical current of RE-Ba-Cu-O composite superconductors
1 Scope
This part of IEC 61788 specifies a test method for determining the DC critical current of short RE (rare earth)-Ba-Cu-O (REBCO) composite superconductor specimens that have a shape of straight flat tape. This document applies to test specimens shorter than 300 mm and having a rectangular cross section with an area of 0,03 mm 2 to 7,2 mm 2 , which corresponds to tapes with width ranging from 1,0 mm to 12,0 mm and thickness from 0,03 mm to 0,6 mm. This method is intended for use with superconductor specimens that have critical current less than 300 A and n-values larger than 5 under standard test conditions: the test specimen is immersed in liquid nitrogen bath at ambient pressure without external magnetic field during the testing. Deviations from this test method that are allowed for routine tests and other specific restrictions are given in this document.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content constitutes requirements of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies. IEC 60050-815, International Electrotechnical Vocabulary (IEV) – Part 815: Superconductivity
3 Terms and definitions
For the purposes of this document, the terms and definitions given in IEC 60050-815 and the following apply. ISO and IEC maintain terminological databases for use in standardization at the following URLs: IEC Electropedia: available at http://www.electropedia.org/ ISO Online browsing platform: available at http://www.iso.org/obp/ 3.1 constant sweep rate method U-I data acquisition method where a current is swept at a constant rate from zero to a current above I c , and where the U-I data are acquired continuously or frequently 3.2 ramp-and-hold method U-I data acquisition method where a current is swept in stages from zero to a current above I c , where the current is held for an appropriate amount of time at each stage, and where the U-I data are acquired continuously or frequently
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) ( E c ) is reached. For any selected E c , there shall be a corresponding voltage criterion ( U c ) 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 U-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.
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.