AC Loss Characteristics of HTS Wires Carrying Currents With Different Waveforms
When applying high-temperature superconductor (HTS) devices in power systems, ac loss is a significant obstacle from an economic perspective. Many studies have been performed to investigate this issue, but the ac losses for different current waveforms have rarely been reported. However, in power systems, many nonlinear devices can distort current waveforms. For example, currents of converters have ripples, no-load currents of transformers are peaked waveforms, and currents of motors are normally nonsinusoidal. To investigate the influence of current waveforms on ac losses, three types of currents with different waveforms, namely, sine waves, peaked waves, and flat-topped waves, are studied using three types of HTS wires, namely, Bi2223 wire, YBCO wire with nonmagnetic substrate (Hastelloy C276), and YBCO wire whose substrate is ferromagnetic (Ni-5at.%W). The experimental results show that ac losses of HTS wires are independent of frequency when carrying sine currents and that they are dependent on frequency when carrying peaked and flat-topped wave currents. Moreover, for all types of measured wires, particularly YBCO wire with ferromagnetic substrate, measured ac losses are highly dependent on current waveforms. In the end, the authors provide a discussion for the experiment phenomenon from the point of magnetic flux creep.