## 5 Results and Discussion
All the harmonics except the supply-fed one were the function of slip and tended to move away from the parent supply component with the increase in load. As discussed earlier, the legibility of those harmonics in the current spectrum not only depended upon slip but the fluctuating load, and the drive's controller also made the detection of desired components challenging. To avoid all those problems, the inspection of the motor current under the transient regime showed promising results. For an increase in the transient time for better time-frequency resolution, the supply voltage could be reduced using a three-phase transformer or the industrial inverter, as discussed previously. With the increase in the applied voltage, the motor took less time to reach a steady state interval. Under the transient regime, the continuously decreasing slip moved the RHS and LHS frequency components toward the fundamental component. It made a V-shaped pattern whose width depended upon the transient time. An exceptional intention was needed here, as there were several slip-dependent frequency components, which could make similar patterns in the transient region. Those frequencies are the spatial and inherent dynamic eccentricity-based harmonics, which develop near all supply-fed higher-order harmonics. Figure 9: The generation of spatial harmonics in the stator current of the healthy machine (**a**) under a steady state regime with 50% of the rated load in the bandwidth of 100–400 Hz and (**b**) under a steady state regime with 50% of the rated load in the bandwidth of 500–1000 Hz. Figure 10 shows the harmonics' development in the transient and steady state regime under the healthy condition with the attenuated fundamental component. It is evident that in the transient region, the rotor slotting and eccentricity-based harmonics made the V-shaped patterns, as in Figure 10a. Those patterns started from 50 Hz and vanished completely as they approached the parent supply component, as in Figure 10b. It is essential to differentiate them from the actual faulty patterns to avoid false alarms. Figure 11 shows the time-frequency response, with the respective regions containing 85% of the total spectral energy in the contour plot for the healthy and broken bar cases. In the presence of the fundamental component, the faulty pattern is barely visible even in the extended current, as in Figure 11c. Moreover, the influence of the most potent supply component on the visibility of the fault pattern is evident in the contour plot. Although the faulty pattern is visible to some extent in the magnitude scalogram, it is absent in the contour plot, as the maximum spectral energy remained in the region near the fundamental component. This pattern was not very legible because the sideband frequencies were lower in amplitude than the fundamental component. This pattern can be made very clear by attenuating the fundamental component, as shown in Figure 12. The IIR band-stop filter, having a filter order of two and a stopband attenuation of 40 showed promising results, while attenuating a narrow bandwidth of frequencies from 49.9 Hz to 50.1 Hz. Figure 12a shows the transient current envelope, while the evolution of spatial frequencies in the transient regime is presented in Figure 12b. The development of a faulty pattern with good legibility is shown in Figure 12c,d for one and two broken bars, respectively. Figure 10: The generation of spatial harmonics in the stator current of the healthy machine. (**a**) The development of time–frequency patterns due to the space harmonics. (**b**) The time-frequency spectrum under a steady state regime under 50% of the rated load. Figure 11: The results based on the measurements taken at 10% of the rated supply voltage. (**a**) The time–frequency response of the healthy motor’s phase current in the transient regime. (**b**) The respective contour plot. (**c**) The time–frequency response of the faulty motor’s phase current in the transient regime. (**d**) The respective contour plot with a 95% confidence interval.