A thesis submitted in partial fulfilment of the requirements for the degree of Master of Engineering

Thesis (M.Eng.) - Asian Institute of Technology

Among various power-polluting apparatus, electric arc furnace (EAF) is considered as an exceptional case, since it contributes for multitude of problems such as transients, harmonics, voltage imbalance and voltage flicker. Finding means for mitigation of these undesirable effects requires extensive studies, which are often based on computer simulations. Such studies largely depend on the availability of an accurate simulation model. In this study, a simulation model of an EAF based on the field measurements was developed. The model includes dynamic behavior of the electric arc and stochastic variations in the arc resistance during the initial melting period, which results in worse conditions in terms of voltage flicker and harmonics and was implemented in EMTDC. Accurate representation of electric arc requires modeling of the dynamic behavior of the arc due to nonlinear V -I characteristics as well as the changes in the equivalent arc resistance due to scrap and electrode movements. The changes due to latter ranges from momentary short circuits to open circuits and occur in a random fashion. These random changes were incorporated into classical Cassie arc model as random changes in the arc resistance to derive a realistic representation of the behavior of electric arc furnace. A novel feature of this study is the systematic treatment of this randomly changing part of the arc resistance. Analysis of the frequency spectrums and the auto-correlation functions of the noise samples indicated that the random deviations of arc resistance can be approximately represented by a first order Markov process. The parameters of this first order noise model were estimated from the sample waveforms using standard techniques adopted in signal processmg. Computer simulation of the EAF model and its supply circuit was implemented in EMTDC. Analysis of harmonics of the simulated voltages and currents at different points of the supply system are generally in agreement with field measurements, although one to one comparison is impossible due to the non-characteristic nature. Flicker calculations were performed using an IEC flicker meter simulated in MATLAB SIMULINK environment. Simulated instantaneous flicker level and short duration (2s) PST are in the range of those of the measured waveforms. Further, the simulation model developed was used for investigating the flicker and harmonics levels under the simultaneous operation of two EAFs present in the BSI steel mill. The developed model can be used to study the adverse effects of electric arc furnace operation under various scenarios and options for their mitigation through simulations.