## 1 Introduction  
Power consumption in transport and power systems has been growing rapidly during recent years. In this case, electrical machines, which are one of the main parts of such systems, should provide high output and specific power. Electrical machines with both an HTS field and armature windings are the most promising [1, 2, 3, 4]. The application of coils and cables based on high-temperature superconductors (HTS) possess the advantage of carrying high electrical current density [5] and increased electromagnetic loads. Superconducting electrical machines are complex technical devices, the creation of which requires the solution of a whole series of scientific and engineering problems related to many fields of science and technology. Along with the solution of traditional problems of the usual \"warm\" electrical engineering, one has to solve the problems associated with cooling of superconducting windings and the stability of their superconducting state under the action of external heat leakage, centrifugal, and ponderomotive forces, as well as vibrations [6]. Besides, when HTS coils are operating with alternating current (AC), or in the presence of a time-varying magnetic field, they still sustain AC losses. Taking into account this type of loss, it is necessary for the correct determination of the thermal state of the windings. Several groups of authors provide different modeling approaches for AC loss determination. For example, in papers [7, 8], theoretical aspects of AC losses calculation and modeling are provided. Works [9, 10, 11] expand such approaches to electrical machines levels. Besides, a great experimental work also was done during the last few years in this area [12, 13, 14, 15, 16]. Even if a lot of work has been done on the characterization of superconducting elements (bulks and tapes), the transition from the element to the system is not obvious, because the behavior of an isolated HTS element is very different when it is integrated into a system [14]. In this context, in this work, experimental research of individual coils, windings, and devices is provided. AC loss values are obtained for different frequencies, transport current values, and waveforms. In recent works such as [17, 18], studies are conducted for a sinusoidal current and an external field, which is a fundamental harmonic distorted by one or more harmonics from the 2 nd to the 5 th order. In our case, the experiment is carried out both on the pure sine and on the current form obtained by high-frequency modulation with a frequency not less than 30 times higher than the fundamental harmonic. This mode is typical for semiconductor power devices (inverters, converters). Experimental research will provide useful information for a deeper understanding of the AC loss dynamics in power applications. Finally, it will provide an opportunity to develop a new method of calculating AC losses in AC windings of different devices.  
In the first part of this paper, a description of measurement methods and test benches (static and rotating) is provided. Then research objects, which are coils, windings, and rotating devices, are described. Finally, the results of the tests and their discussion is provided.