The use of frequency converter and active rectifier of voltage for the power quality improvement in coal longwalls

Abstract

Improvement of productivity and performance in coal longwall mining is achievable via transition to longwalls to 250–400 m long and by increasing installed capacity of longwall equipment systems up to 4200–5600 kW. The up-to-date longwall mining uses energy- and resource-saving machines equipped with variable frequency motors. In this case, inclusion of the frequency converters in the machinery electrics results in essential distortion of voltage from the nominal sine waveform and leads to the power quality degradation in longwalls. With a view to enhancing power quality in longwall networks, the authors propose to use variable frequency motors with frequency converters with active rectifiers of voltage. When selecting a frequency converter with the active rectifier for voltage in underground power network, it is recommended to take into account the longwall power supply specifics, the cross-effect of the frequency converters operating in neighbor lines, the variable nature of power system loads and the change in the number of the frequency converters in simultaneous operation. To that end, the power supply model is developed to study consumed power quality with regard to the power network topology, parallel-operating frequency converters and actual loads of electric motors. The modeling has determined the mechanisms of effect exerted by the frequency converters on the power quality in operation with active rectifiers of voltage. The carrier frequency and inductance of the buffer reactor of the threelevel active rectifier, which ensure the standard quality power supply in longwall, are substantiated.