Power Quality and Load-Dependent Harmonic Regimes in Open-Pit Lignite Mining Electrical Systems: Field Measurements and Simulation-Assisted Interpretation

Open-pit lignite mines contain high-power converter-fed drives whose operating state strongly affects current harmonics and internal power-quality conditions. The primary objective of this study is to experimentally characterize load-dependent voltage and current harmonic regimes in an operating open-pit lignite mining electrical system and to use a simplified MATLAB/Simulink R2021b inverter-motor model only as a trend-interpretation tool. In situ measurements were obtained on the E05 SRS 1300-26/3.5 bucket-wheel excavator and associated conveyor systems. The measurements show low voltage distortion at the monitored internal points (the Total Harmonic Distortion of Voltage (THDU) below 1.5% in the reported cases) and strongly load-dependent current distortion, including high relative the Total Harmonic Distortion of Current (THDI) during low-current operation. The simulation reproduces selected qualitative drive-side trends but does not represent the upstream network, feeder impedances, transformer behavior, capacitor-bank interaction, or background supply distortion; it is therefore not presented as an independently validated network model. A separate Battery Energy Storage System (BESS) calculation is retained only as an illustrative resilience scenario based on an assumed four-hour duty profile and is not used as evidence for the measured harmonic findings. The main contribution is an experimentally supported case study of load-dependent harmonic behavior in an operating lignite-mine electrical system, complemented by simulation-assisted physical interpretation and clearly separated prospective modernization implications.