Rectifier transformers are used to provide DC for traction, usually stepping down from medium voltage levels. Special transformers for medium voltages produced by Končar D&ST have a long tradition and are well known worldwide. Special transformers production program is organized in a separate production hall, where each process is intended specifically for the production of special transformers - winding machines, hot air-drying plants, oil purification machines for several oil types (mineral oil, synthetic ester, natural ester, or silicon oil), testing station, etc.