AC loss measurements of a high critical temperature superconductor transporting sinusoidal or non-sinusoidal current

Abstract

In electrical engineering, static converters generate harmonics; consequently the losses in the conductors increase. To use High-Tc superconductors for current transportation, it is important to evaluate and to measure their losses. Under the assumption that the superconductor is only exposed to its self-field, Bean's model is used to compute these losses. This work deals with the losses in a cylindrical High-Tc superconductor current-lead. It is made of compacted composite of Bi-Pb-Sr-Ca-Cu-O-2223, the value of its critical current is about 100 A (measured with I /spl mu/V/cm criteria). Two types of measuring methods are used. The first of them uses a differential amplifier associated with a computer, which calculate the instantaneous power by numerical integration. The second series of experiments, valid only with sinusoidal current, are made using a lock-in amplifier measuring the R.M.S. voltage. The value of transport current is high enough to be compatible with applications. Both methods give nearly the same results for sinusoidal signal. Measurements are made with non-sinusoidal current, to do that the superconductor sample is fed by a dimmer switch. The experiments show that the losses are essentially a function of the maximum value of the current, not of the firing angle. We conclude that the shape of the current is not important compared to its peak value.