## 4 Test Results
### Experimental Results with Static Rotor  
After installing the rotor, linear parts of coils that face inwards to the center axis of the assembly are now exposed to the magnetic field with a significant component perpendicular to the tape surface. Thus, this condition should affect the characteristics of the tape, and first of all, the critical current. To confirm this fact, the critical current of one of the phases was measured in five positions (Figure 5a,b) of the rotor: holes number \"0,\" \"4,\" \"8,\" \"12,\" and \"15,\" which corresponds to the rotor positions of 0, 25.6, 45, 76.8, and 90 degrees. A comparison with the critical current of the phase without the installed rotor (89.4 A) is given in Table 2.  
As follows from the table, the influence of the rotor position does not have a very large effect on the critical current (the difference between the maximum and minimum values is only 12%). However, after installing the rotor, the critical current decreased by half (the average value in column No. 3 of Table 2), which indicates the significant influence of the external magnetic field on the critical current of the used HTS tape. Further studies on alternating current were carried out. In contrast to the critical current measurement, the AC experiment involved all 15 angular positions of the rotor. Losses were measured at frequencies of 50, 100, and 200 Hz. For 50 Hz, the obtained curves differ in the level of losses depending on the angle of the rotor position (Figure 12). Figure 11: Comparison of high-frequency current fluctuations in a single coil (blue) and in the assembled phase (red). In addition, in the range from 5 to 15 A for several positions of the rotor, a certain break in the dependence of losses on current is noticeable. One of the explanations for this behavior is the effect that appeared during the experiment, associated with the vibration of the rotor. The alternating of, but not rotating of, the magnetic field generated by the test phase interacts with the rotor. At the same time, the equipment fixing the rotor (Figure 5) has a finite rigidity, which leads to an oscillation of the rotor relative to a given position with a visually noticeable angular amplitude, and, consequently, the occurrence of some mechanical power losses. At a frequency of 100 Hz, the pattern of loss dependence on the angle changes, becoming less noticeable (Figure 13). During the tests, the observed visual vibrations of the rotor relative to the fixing points were significantly reduced. A further increase in the frequency showed an even weaker dependence of the losses on the angle of installation of the rotor, while its visual vibration was absent. Figure 14  
Figure 12: Stator losses as a function of current at different rotor positions at a frequency of 50 Hz. Same frequency without rotor is depicted for reference. Figure 13: Stator losses as a function of current at different rotor positions at a frequency of 100 Hz. Same frequency without rotor is depicted for reference. shows the losses in the stator as a function of the current at different rotor mounting angles at a frequency of 200 Hz. Due to the parameters of the test bench at a frequency of 200 Hz, it was impossible to supply the phase with the RMS current value higher than 14 A; however, even at this amplitude, the losses reached a value of 80 W.  
At the end of the sequence of the experiment with the braked rotor, the phase was tested by modulated currents in different positions of the installed rotor. Similar to the case with a sinusoidal current, the loss levels showed a weak dependence on the angle of installation of the rotor, so, in this regard, the graph (Figure 15) shows the average values for each frequency. Figure 14: Stator losses as a function of current at different rotor positions at a frequency of 200 Hz. Same frequency without rotor is depicted for reference. Figure 15: Averaged (for positions 0, 8, 15) stator losses on modulated current waveforms as a function of current.