Mathematical Simulation of Acoustic Characteristics of Super-Power Arc Discharges in Electric Steel Furnaces

Mathematical model of appearance and progress of noise characteristics in super-power electric arc steel furnaces is considered in the paper. It is shown that noise generation is coupled with pulsations of axial plasma flows in arc discharge caused by fluctuations of electrodynamic pressure on discharge column formed by interaction between its own magnetic field and current flowing in the arc. Simulation results have shown that pressure in arc axis alternates at frequency 100 Hz with amplitude 6600 N/m2 for arc current 80 kA. Basic frequencies of arc noise are aliquot to 100 Hz, that fact is verified by exploitation practice of arc steel furnaces. Sound intensity level in workspace riches 160 dB, but thanks to shielding by case and fused metal and slag it falls to 115–120 dB on service area of furnace. It has shown that maximal amplitudes in frequency spectrum of the noise are in range 5–150 Hz. Generated noise amplitudes and frequency ranges depend on arc discharges' resistance, which are defined by ionization level of gases. According to Saha equation, iron vapor is ionized by 70 %, calcium vapor – by 95 %, and ionization level of air is no more than 1.5 %. It has been experimentally shown that in melting of stock coated with lime noise intensity is decreased by 6–8 % against no-lime iron melting because of lower calcium ionization potential (6.11 eV). It has been ascertained that for long arc with high voltages the sound intensity is decreased by 3–4 % as compared with short arc of the same current. It has shown that suppression of low-frequency components of noise energy is possible by optimization of electromechanical oscillations of electrodes, electrode-holders and cable strips, additionally to inclusion lime in stock mixture. The appropriateness of improvement electric arc furnaces hermeticity and development of the furnaces for operation with lowered currents and enlarged transformers' voltages have been approved.