**9. Conclusions**

This paper investigates the partial demagnetization fault, the static angular and the static axis eccentricity fault, and the combination of partial demagnetization and static angular or static axis eccentricity fault in an AFPM synchronous double-sided rotor generator. The machine has been simulated while using 3D-FEA, while the EMF spectra are studied for fault diagnosis purposes in order to extract the fault related harmonics. In all cases one magne<sup>t</sup> is partially demagnetized. Firstly, the partial demagnetization fault without the coexistence of eccentricity is studied for two

di fferent percentages of partial demagnetization. This fault creates both even and fractional harmonics (with frequencies of 25 Hz, 75 Hz, 100 Hz, 125 Hz, 175 Hz, 200 Hz, and 225 Hz) in the EMF spectra and the harmonic amplitude increases when the severity of partial demagnetization also increases. In addition, the static angular and the static axis eccentricity faults are investigated. Both of the faults do not create new harmonics in the corresponding EMF spectra. However, these faults create new harmonic components in the phase EMF sum spectrum. The phase EMF sum waveform is a signal that has a fundamental frequency of 150 Hz (3fs), three times the fundamental frequency, fs, of the EMF waveform. When static eccentricity fault exists, either angular or axis, in the corresponding spectra of the phase EMF sum new harmonic components appear and harmonic component of frequency 50 Hz is the fault related harmonic component that, in the faulty case, its amplitude increases more than the amplitudes of other harmonics when compared to the corresponding healthy spectrum. In other words, this harmonic component in the phase EMF sum spectrum can predict eccentricity, but cannot identify whether the static eccentricity is angular or axis. Then the combined fault of partial demagnetization with static angular eccentricity is studied. The analysis proves that this fault creates new harmonics of frequencies 18.75 Hz, 25 Hz, 31.25 Hz, 43.75 Hz, 56.25 Hz, 68.75 Hz, 75 Hz, 81.25 Hz, 100 Hz, 125 Hz, 175 Hz, 200Hz, and 225 Hz in the EMF spectrum when compared to the healthy case. Comparisons are made when the level of demagnetization changes and the level of eccentricity remains constant and when the level of demagnetization remains constant and the level of eccentricity changes. In the first case, the amplitude of all fault related harmonics increases when the severity of demagnetization increases, while, in the second case, when the severity of eccentricity increases, the amplitude of the fault related harmonics increases too apart from the harmonics that also appear when only demagnetization exist in the machine (0.5th, 1.5th, 2nd, 2.5th, 3.5th, 4th, and 4.5th). In addition, the combined partial demagnetization and static axis eccentricity fault is studied. The fault related harmonics are of frequencies 18.75 Hz, 25 Hz, 31.25 Hz, 43.75 Hz, 56.25 Hz, 68.75 Hz, 75 Hz, 81.25 Hz, 100 Hz, 125 Hz, 175 Hz, 200Hz, and 225 Hz. Like previous cases, comparisons are made when the level of demagnetization increases, and the severity of eccentricity remains constant and when the level of demagnetization remains invariable and the level of static axis eccentricity changes. In the first case, all of the combined fault related harmonics increase in amplitude, while, in the second case, there is increment in the amplitude of all harmonic components apart from these that are related to demagnetization fault. A future step of this study is to find a formula that is able to separate the two eccentricity cases, because, as can be seen in both eccentricity faults, fault related harmonics of the same frequencies appear.

**Author Contributions:** The presented work was carried out through the cooperation of all authors. A.C.B. conducted the research and wrote the paper and J.C.K. supervised the whole study and edited the manuscript. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research received no external funding.

**Conflicts of Interest:** The authors declare no conflict of interest.
