Abstract
Direct current (DC) arc furnaces require the use of complex high-power rectifiers in order to convert the grid alternating current into direct current. The severely inductive load of a DC arc furnace combined with the chaotic nature of the arc could prove detrimental to the reliability of the rectifier components. This dissertation investigates the failure modes of silicon-controlled rectifiers (SCRs), which are critical components in the AC-to-DC conversion process. The goal is to gain a comprehensive understanding of various protection methods to enhance the reliability of SCRs.
An inverted teardrop approach was employed, beginning with a broad exploration of AC and DC theory, DC arc furnaces, and their rectifiers, before focusing on SCRs and their protection. This approach included designing, simulating, and building test circuits to deepen the understanding of SCRs, SCR failure modes and their protection mechanisms. The theory, simulation results and practical test model that is presented in this dissertation show that by implementing snubber circuitry in a rectifier circuit one can reduce unwanted current spikes, voltage spikes, oscillatory behaviour (electromagnetic interference) and losses. The effects hereof substantially reduce the likelihood of SCR failure.
The results of the work in this dissertation show that with the correct assumptions, design methods, simulations and optimization techniques one can successfully implement SCR protection schemes that enhance and improve the reliability of DC arc furnace rectifiers.