Surge Protection for Ladle Melt Furnaces: LMF Transformer Terminals were Equipped with Primary Surge Protection Consisting of Surge Arresters and RC Snubbers

Vacuum Circuit Breakers (VCBs) are commonly applied to the primary circuit to switch ladle melt furnace (LMF) transformers in melt shop applications that support rolling mill operations. Because of the well-documented phenomenon of switching transients induced on the line of the furnace transformer due to the opening and closing of the VCB, most LMFs in this application also have surge protection applied at the transformer terminals. This article contains an analysis of one such location with two identical LMFs, each fed by a VCB, where the LMF transformer terminals were equipped with primary surge protection consisting of surge arresters and resistor/capacitor (RC) snubbers. Recently, high transient counts and increased levels of combustible gasses in oil samples raised concerns at the location and led to a field investigation, electromagnetic transients program (EMTP) simulations, and evaluation of the surge protection of both LMFs. Power quality measurements were taken to identify the transients experienced by the surge arresters at the transformer terminals. EMTP simulations were conducted to reproduce the transients, determine a worst-case switching event, and properly size the surge protection for each LMF transformer.