# Voltage Problems on Farms with Agricultural Biogas Plants--A Case Study
## 3 Results and Discussion
### Analysis of the Feeding System of the Biogas Plant under Study
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline  & \multicolumn{2}{c}{**L1 Phase**} & \multicolumn{2}{c}{**L2 Phase**} & \multicolumn{2}{c}{**L3 Phase**} \\ \cline{2-7}  & **Phase Voltage** & \begin{tabular}{c} **Deviation from** \\ **the Rated Voltage** \\ **[V]** \\ \end{tabular} & **Phase Voltage** & \begin{tabular}{c} **Deviation from** \\ **[\%]** \\ \end{tabular} & **Phase Voltage** & \
\begin{tabular}{c} **Deviation from** \\ **the Rated Voltage** \\ **[V]** \\ \end{tabular} & **Phase Voltage** &
\begin{tabular}{c} **Deviation from** \\ **the Rated Voltage** \\ **[\%]** \\ \end{tabular} \\ \hline \hline \multicolumn{7}{c}{Before the changes} \\ \hline Average value & 238.913 & 3.452 & 238.120 & 3.109 & 233.096 & 0.934 \\ Minimum value & 203.260 & \(-\)11.986 & 200.130 & \(-\)13.341 & 197.070 & \(-\)14.666 \\ Maximum value & 258.650 & 11.999 & 257.120 & 11.336 & 248.810 & 7.738 \\ Quantile 95 & 253.480 & 9.760 & 252.110 & 10.167 & 244.450 & 10.850 \\ \hline \hline \multicolumn{7}{c}{After changes} \\ \hline Average value & 242.655 & 5.073 & 241.368 & 4.515 & 240.101 & 3.967 \\ Minimum value & 214.320 & \(-\)7.197 & 212.130 & \(-\)8.145 & 208.580 & \(-\)9.682 \\ Maximum value & 254.120 & 10.037 & 254.280 & 10.106 & 251.760 & 9.015 \\ Quantile 95 & 250.980 & 8.678 & 251.737 & 9.005 & 247.690 & 7.253 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Results of statistical analysis of tension levels. asymmetry coefficients, the analysis of the values presented in Table 3 did not reveal any significant differences in the values of this parameter before and after the change of the power supply cable. A summary of the results of the statistical analysis of the long-term flicker nuisance value (P\({}_{\text{lt}}\)) at the connection point of the agricultural biogas plant during the recording period is presented in Table 4. The values presented there show that the P\({}_{\text{lt}}\) factor in each analysed system exceeds the permissible value (1). However, replacing the power cable reduced the value of the 95% quantile by almost three times. In the primary system, non-compliance with the voltage distortion requirements from the sinusoidal waveform was observed (Table 5). The maximum THD\({}_{\text{U}}\) value is almost 1.7 times higher than the required (8%) [42,43]. The higher harmonics cause additional voltage and power losses (increased cable heating) in the biogas plant's power supply system. These overshoots are correlated with voltage drops occurring in the electricity network. Changing the power cable reduced the value of the voltage distortion factor by almost half. The issue of supply voltage is particularly evident in photovoltaic (P.V.) plants, where increased generation often causes the voltage at the plant's connection point to exceed current regulatory limits. This challenge arises due to the high prevalence of P.V. systems. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline  & \multicolumn{3}{c}{**Before the Changes**} & \multicolumn{3}{c}{**After Changes**} \\
**Parameter** & **P\({}_{\text{HL1}}\)** & **P\({}_{\text{HL2}}\)** & **P\({}_{\text{HL3}}\)** & **P\({}_{\text{HL1}}\)** & **P\({}_{\text{HL2}}\)** & **P\({}_{\text{HL3}}\)** \\ \hline Average value & 2.688 & 2.762 & 2.887 & 0.993 & 1.141 & 1.074 \\ Minimum value & 1.540 & 1.620 & 1.690 & 0.720 & 0.830 & 0.790 \\ Maximum value & 3.840 & 3.960 & 4.160 & 2.180 & 1.830 & 1.860 \\ Quantile & 3.500 & 3.580 & 3.767 & 1.384 & 1.691 & 1.440 \\
95 & & & & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Results of statistical analysis of the long-term flicker annoyance index values (P\({}_{\text{lt}}\)).