This paper describes a furnace retrofit involving the replacement of a variable reactance transformer (VRT) with an IGBT-controlled mid-frequency direct current (MFDC) transformer. The two transformers are similar in size and all other variables remained essentially equivalent. A typical heating cycle was initiated with a ramp rate of 10°F/min to a soak temperature of approximately 1900°F. Cross-sectional data was taken during the ramp phase and soak phase. Based on power measurements and adjusting for differences in thermal loads, the retrofit achieved a 40% reduction in kilowatt consumption, a 14% reduction in peak current draw, and an improvement in power factor throughout the cycle.

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