Power quality in coal longwalls

Abstract

Improvement of productivity and performance of coal longwalls is achieved by transition to extended lengths of longwalls up to 250–400 m at unavoidable increase in installed capacity of longwall mining machinery up to 4200–5600 kW. Advanced longwall equipment has variable frequency electric drives. Frequency converters essentially distort sine voltage in power supply networks. One of the facilities capable to improve power quality in supply systems with electric drives with semiconductor converters is passive harmonic filter (PHF). The PHF selection criteria are the low cost, simplicity and reliability. It is recommended to use the simplest PHF—capacitors with antiresonance reactors given they ensure the required-level ultraharmonics. The PHF facility design for underground mine power networks should take into account: specification of power supply diagram, cross-effect of frequency converters in adjacent lines, variability of loading, and change in number of concurrently operating frequency converters. To this effect, the power supply model is developed to analyze quality of input electric energy. This model includes topology of electric mains, parallel converters and actual drive loads. The modeling analysis was performed in two stages. First, the influence patterns of frequency converters on power quality without PHF were examined. Second, the influence patterns of frequency converters on power quality in the presence of PHF were studied. The research shows that the total harmonic factor of voltage in each line is affected by the converters in adjacent lines. Thus, it is necessary to take into account the frequency converters arranged in adjacent lines when selecting PHF.