## 5 Results and Discussion  
### Results for the IM Operating at 31 Hz  
First, the results for the motor operating at 31 Hz are introduced. To demonstrate the advantages of the proposed methodology against other methodologies, a comparison is performed first with the conventional MCSA without removing the FFC, using a total of 160,000 samples (20 s) of the signal to obtain a 0.05 Hz resolution. Then, the comparison is performed with a NF-MCSA methodology that uses a NF for removing the FFC before applying the MCSA technique. The designed NF considers a notch frequency of 31 Hz and a 0.8 Hz bandwidth. Finally, the analysis is performed with the proposed methodology (GA-MCSA) which uses a GA for suppressing the FFC before applying the MCSA. To show the advantages of the GA-MCSA methodology, only 80,000 samples (10 s) of the signal are used to compute the signal spectrum at a resolution of 0.1 Hz. The IM under test is operated at three different load levels: high load (\(s=6\%\)), medium load (\(s=4\%\)), and low load (\(s=2\%\)). Figure 3 summarizes the results of applying the three methodologies at the three load levels in one of the current signals. It is observed that when the IM operates at high load, the MCSA is able to detect the failure harmonics by itself (see Figure 3a). At these operating conditions, the LSH appears at 27.4 Hz and the RSH at 34.6 Hz. However, it is noticed that the energy of the FFC is so high that it goes outside the graphic. When the NF-MCSA methodology is applied, the LSH and the RSH are also visible in the spectrum (Figure 3d). Additionally, it can be seen that the remaining energy of the FFC is now visible at 31 Hz with an amplitude of around 0.1 A. This situation proves that the NF is effective in the attenuation of the FFC. Notwithstanding, it can be seen that the leakage effect is present in the range between 28 and the 34 Hz. This problem does not seem to affect the identification because the failure harmonics are located beyond this range. When the GA-MCSA technology is used, it is appreciated that the attenuation of the FFC is higher than that presented by the previous technique (Figure 3g), and the failure harmonics are clearly visible at 27.4 and 34.6 Hz respectively. The fact that the attenuation is higher seems to be an advantage because the leakage effect around the FFC is also reduced, falling to the range between 30 and the 32 Hz. A similar analysis is carried out, but now for the IM operating at medium load. Here, the LSH is expected to appear at 28.5 Hz and the RSH at 33.5 Hz. The MCSA still can identify the failure harmonics (see Figure 3b) but their appearance is not as clear as in the previous case. The amplitude of the RSH is high, facilitating its observation; however, the amplitude of the LSH is not as high and it appears as a small peak in the spectrum of Figure 3b. By applying the NF, the results improve and it is easier to identify both failure harmonics (see Figure 3e). Although the identification improves, it is observed that the leakage around the FFC still appears between the 32 and the 34 Hz. Since the failure harmonics are now between this range, they appear mounted on the spectral leakage; therefore, the amplitudes regarding the failure harmonics are not reliable. When the GA-MCSA technique is used, the attenuation of the FFC is even better than in the high load case and the failure harmonics are easy to identify (see Figure 3h). Moreover, the spectral leakage around the FFC is reduced to the range between 30.5 and the 31.5 Hz; thus, the amplitudes of the failure harmonics remain unaltered. Figure 3: Spectrum for the motor current operating at 31 Hz using (**a**) Motor current signature analysis (MCSA) at high load, (**b**) MCSA at medium load, (**c**) MCSA at low load, (**d**) Notch filter (NF) and MCSA (NF-MCSA) at high load, (**e**) NF-MCSA at medium load, (**f**) NF-MCSA at low load, (**g**) Genetic algorithm (GA) and MCSA (GA-MCSA) at high load, (**h**) GA-MCSA at medium load, and (**i**) GA-MCSA at low.