## 3 Material and Methods
### Indicators-Radar Chart Vertices  
This section includes the features selected for the power quality visualization tool and the decision tree. These parameters have been previously studied and compared using the signals available in Database #1.  
1. Skewness (Sk). The nominal value for skewness in 50 Hz signals is zero. Its deviation from this expected value is linked to the symmetry of the waveform. Generally, skewness is expressed by Equation (1). In Equations (1)-(4), xj is a sample register measured from 1 to sample size, N, and \(\sigma\) corresponds to standard deviation. \[Sk(x)=\frac{1}{N}\sum_{j=1}^{N}\left[\frac{x_{j}-\overline{x}}{\sigma}\right] ^{3}\] (1)
2. Kurtosis (K). Based on our own tests with undistorted 50 Hz signals, we observed nominal kurtosis value of 1.5, which is used here as a reference. Kurtosis variations are linked to the sinusoidal shape of the waveform. K is given by \[\text{K}(\text{x})=\frac{1}{N}\sum_{j=1}^{N}\left[\frac{x_{j}-\overline{x}}{ \sigma}\right]^{4}\] (2)3. Fifth-order statistic (FOS). Our research coincides with the only identified reference for the nominal value of the fifth-order statistic in 50 Hz, zero [9]. FOS is defined by \[FOS(x)=\frac{1}{N}\sum_{j=1}^{N}\left[x_{j}-\overline{x}\right]^{5}\] (3)
4. Sixth-order statistic (SOS). Given the absence of a universally agreed upon nominal value for the sixth-order statistic, the authors have taken as reference the nominal value obtained after the analysis of Database #1, which yielded results of a nominal value of 0.3125 for this statistic. SOS is calculated using \[SOS(x)=\frac{1}{N}\sum_{j=1}^{N}\left[x_{j}-\overline{x}\right]^{6}\] (4)
5. Crest factor (CF). Signals characterized by 50 Hz, distortion-free waveforms should manifest a crest factor of 1.4142. CF serves as an indicator of non-sinusoidal conditions, measuring how much the top of the sine wave is distorted, thus making it a valuable parameter for quantifying harmonic distortion. CF is determined by \[CF=\frac{V_{peak}}{V_{rms}}\] (5)
6. Signal-to-Noise Ratio (SNR) represents a commonly used metric within the realm of communication systems. The SNR serves to quantify the relationship between the desired signal and undesired noise within a signal, thereby indicating that a higher SNR corresponds to superior signal quality. This parameter has garnered attention in various research efforts [28,29]. Although there are no universally recognized standards for power quality monitoring, some authors establish a range between 30 and 70 dB for real signals [30,31]. SNR is expressed by Equation (6), where \(\mathrm{P_{S}}\) is signal power and \(\mathrm{P_{N}}\) is noise power. \[SNR=10\cdot\log\left(\frac{P_{s}}{P_{N}}\right)\] (6)
7. Total Harmonic Distortion (THD) measures the harmonic distortion present in a signal by comparing the sum of the powers of all harmonic components to the power of the fundamental frequency. The standard IEC 61000-4-7 [32] outlines that THD should be inferior to 8%. THD is given by Equation (7), where \(\mathrm{V_{n-rms}}\) is the RMS value of the nth harmonic component and \(\mathrm{V_{fund-rms}}\) is the RMS value of the fundamental component. \[THD=\frac{\sqrt{\sum_{n=2}^{\infty}V_{n-rms}^{2}}}{V_{fund-rms}}\] (7)