A Study on Reduction of Harmonic Distortion caused by AC Arc Furnaces

Abstract

In AC arc furnaces, arc ignition is stabilized by inductors which are connected across its supply lines. They cause power factor degradation in the system. When furnaces are modelled as linear RL load, the arc nonlinearity reduces the impact of this degradation to a significant extent. Furnace Power factor is improved by the DC voltage on the arc. In this research study, power factor of AC furnaces is estimated on the assumption that DC voltage on the arc is constant and furnace operates in steady state. Primary objective of this research was to determine the power factor of the furnace in steady state. However, other states of operation such as bidirectional arc and unidirectional arc ignition were also taken into consideration while computing the power factor of the furnace. Secondary objective of this research was to understand the effects of harmonics on arc furnace and design filter parameters to mitigate the impact of harmonics caused by the transient operation of the furnaces. Random extinction and ignition of individual arc furnaces help reduce current distortion of ultra-high-power ac arc furnaces using resonant harmonic filters. This operation can be conducted in condition of fast varying parameters of the furnace. On the other hand, this resonant harmonic filter can be built practically only as a constant-parameters device. Filters built on fixed parameters cannot be well coordinated to the furnace. This discrepancy can cause a decline in the filter’s efficacy of harmonics reduction. A reference model using MATLAB was developed to simulate different conditions on the circuit. Also, use of different resonant filters to reduce these harmonics was performed to find the most efficient filter that will increase the efficacy of this process. This efficiency was investigated, specifically, in a melting mode of an arc furnace operation. A reference arc furnace was used in this study which enabled to draw some qualitative and quantitative conclusions on possibilities of current harmonic reduction at a supply of ultra-high-power furnaces by resonant harmonic filters