“…were extracted to substitute 1000 potentially redundant data points. The full list of 21 characteristic indexes in time domain and frequency for voltage data [87] included maximum value, minimum value, mean value, peak-to-peak value, corrected mean value, variance, standard deviation, kurtosis, skewness, root mean square factor, waveform factor, peak factor, pulse factor, margin factor, the center of gravity frequency, mean square frequency, root mean square frequency, frequency variance, frequency standard deviation, power spectrum entropy, and singular spectrum entropy.…”