Power Quality Assessment of a Hot Strip Mill with Cycloconverter Drive Systems

This paper presents the power quality assessment of a hot strip mill with cycloconverters for an integrated steel- making facility. Due to the stochastic operation characteristics of cycloconverters, the electric power consumed by the hot strip mill fluctuates dramatically with the harmonic currents of different integer orders and non-integer orders. Both of the harmonic distortion and voltage flicker problems have been introduced to deteriorate the power quality of the industrial customer. To mitigate the harmonic pollution and provide proper reactive power compensation at the same time, two single-tuned and three high-pass passive filters have been therefore applied according to the harmonic load flow analysis. After removing the resistor due to flash over damage, the 6.8th order high-pass filter has been converted to be a single-tuned filter. The impact of harmonic distortion on the existing filters and other equipments is investigated in this paper to ensure the harmonic distortion of the hot strip mill to be within the tolerance limit with the new configuration. To represent the harmonic current injection more accurately for the harmonic load flow analysis, the harmonic currents generated by cycloconverters are determined by field measurement. It is found that the total voltage harmonic distortion THDv solved by computer simulation is very close to the actual harmonic distortion. According to the harmonic load flow analysis, the serious harmonic pollution problem introduced by the cycloconverter drive system can be mitigated effectively by the implementation of proposed harmonic filter banks. Besides, the voltage flicker problem due to dramatic variation of large reactive power consumption of the hot strip mill can be solved by proper control of cycloconverters.