This part of IEC 61788 covers a test method for the determination of the d.c. critical current of Nb3Sn composite superconductors which are fabricated by either the bronze process or the internal tin diffusion process and have a copper/non-copper ratio larger than 0,2.

This method is intended for use with superconductors which have critical currents of less than 1 000 A and n-values larger than 12 under standard test conditions and at magnetic fields of less than or equal to 0,7 times the upper critical magnetic field. The test specimen is immersed in a liquid helium bath at a known temperature during testing. The Nb3Sn composite test conductor has a monolithic structure with a total round-cross-sectional area that is less than 2 mm2. The specimen geometry used in this test method is an inductively coiled specimen. Deviations from this test method which are allowed for routine tests and other specific restrictions are given in this standard.

Nb3Sn conductors with critical currents above 1 000 A or total cross-sectional areas greater than 2 mm2 can be measured with the present method with an anticipated reduction in precision and a more significant self-field effect (see Annex C). Other, more specialized, specimen test geometries may be more appropriate for larger conductor testing which have been omitted from this present standard for simplicity and to retain precision.

The test method given in this standard should in principle apply to Nb3Sn composite wires fabricated by any other process. This method is also expected to apply to other superconducting composite wires after some appropriate modifications.