Electric arc furnaces employed in smelting operations typically exhibit three distinct characteristic working stages:
Melting Stage Initiation: At the outset of the melting phase, the solid charge material undergoes melting, and this period is marked by the highest energy demand.
Initial Refining and Heating Stage: Following the melting stage, the furnace enters an initial refining and heating phase.
Refining Period: During the refining stage, the input energy required is merely sufficient to offset thermal losses.
The smelting cycle of a conventional alternating current (AC) electric arc furnace typically ranges from 3 to 8 hours, contingent upon factors such as the parameters of the power supply circuit, the furnace's capacity, and the specific smelting process employed. The melting period, which lasts approximately 0.5 to 2 hours, is characterized by a three-phase asymmetrical impact load. This results in highly unstable current flow and substantial power consumption, accounting for roughly 60% to 70% of the total energy expended throughout the smelting cycle. Conversely, during the oxidation and reduction refining periods, voltage fluctuations and power consumption are notably diminished.
The operational characteristics of electric arc furnaces during scrap smelting are as follows:
Arc Instability at Melting Onset: At the commencement of melting, the arc frequently extinguishes and then re-ignites.
Arc Fluctuations During Full Melting: Throughout the full melting period, arc fluctuations occur, leading to abrupt changes in current.
Short Circuits Due to Material Collapse: Material collapse within the furnace can induce short circuits.
The power factor of the operating point in a conventional electric arc furnace circuit typically ranges from 0.8 to 0.85. For high-power electric arc furnaces, this range is slightly lower, between 0.7 and 0.8. A lower power factor inevitably results in reduced power efficiency.
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