The Effect of Biogas Generation and Fermenter Mixer Operation on Power Quality in a Local Power System

This study analyses the effect of an agricultural biogas plant on power quality at the connection point of a dairy cattle farm. The main objective was to determine how power generation and fermenter mixer operation affect selected power quality parameters. Four characteristic operating states of the system were analysed, differing in terms of power generation and mixer operation. The measurement results showed that generator operation stabilised the voltage in the low-voltage network. When the generator was switched off, the voltage decreased from approximately 234 V to approximately 226 V, confirming the clear effect of local generation on the supply voltage level. At the same time, the analysis of total harmonic distortion (THDU) showed that the greatest differences occurred when the generator was switched off, particularly between states with the fermenter mixers operating and inactive. In this case, the mean difference (Δmean) in phase L3 reached 0.31, indicating increased susceptibility of the system to non-linear loads in the absence of local generation. Mixer operation caused only a moderate voltage reduction and minor changes in power quality parameters. Its effect was therefore weaker than that of power generation. Statistical analysis, including the Games–Howell test, confirmed significant differences among most operating states, particularly between states with and without generation.