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 Dynamic Simulation of Arc Furnace Operation and its Impact on Electrical Supply Network Electrical Supply Network 1 Introduction During scrap melting in an arc furnace the arcs are subject to disturbances, mainly due to scrap cave in and the electromagnetic forces created by the electrode currents in the opposite electrodes. In addition to this the arc voltage is not sinusoidal and a source for generation of harmonics. Due to these conditions the arc impedance and thus the electrode current will fluctuate, which can cause disturbances both in the low frequency range (flicker) and in the high frequency range (harmonics). Measurements on arc furnaces have shown that the time dependent “steady state” reactive power Q(t) = × u\$(t) × i\$(t) × sin (t) 1 2 ϕ changes from one half cycle to the next and that the sign of the time derivative of the reactive power also change randomly. In order to evaluate the impact of an arc furnace operation on the electrical supply network a computer model has been developed. With this model it is possible to simulate disturbances generated in the arc furnace and to calculate the resultant voltage fluctuation on the electrical supply line bus also with equipment for reduction of voltage fluctuations like Static Var Compensator (SVC) connected to the furnace bus. Measurements on several installations have shown that the model can be considered representative both with regards to the furnace as a source of disturbances and the potential reduction of flicker with a SVC system installed. 2 Simulation of Arc Furnace For the dynamic simulation of flicker generated by arc furnace operation it is sufficient to evaluate the influence from disturbances within the frequency range 1 to 30 Hz. In the model the RMS value of the arc impedance is represented by a random square wave function (2 to 5 Hz) and a superimposed random function with a frequency twice the network frequency with a mean value equal to zero and a standard deviation half of the value for the low frequency disturbance. A random generator is used for generation of standard distributed numbers for both amplitudes and frequencies in the three phases. The fluctuation function is mathematically described as: F(t) = F1(t) + F2 (t) F t F N F t t f F N F f t t f M I F M F s T M I F M F T s T 1 1 1 2 1 1 2 ( ) 1 ( ) ( , ); ( ) ( ) ( , ); ( ) = + − × − < × + − × × < − < ⎧ ⎨ ⎪⎪ ⎩ ⎪⎪ σ σ F2 t NF 0 F 1 2 ( ) = ( , ×σ ) f N T F T M = ( , T ) 1 σ where FM = Mean value of the fluctuation function σF = Standard deviation of the fluctuation function TM = Mean value of the fluctuation period time σT = Standard deviation of the period time ts = Start time for each square wave NF = Standard distribution sequence for the fluctuation function NT = Standard distribution sequence for the period time FM, σF, TM, σT, NF and NT are specified as input data.

Dr. Alberto Fragiacomo (Engineering Coordination Manager)