FIELD: electrical engineering; starting of and ensuring energy-conservation modes for various induction and synchronous high-voltage drives. SUBSTANCE: proposed frequency changer designed for gradual multistep starting of high- voltage induction and synchronous drives of compressors, pumps, fans, gas and air blowers, metal- working plants and power units of thermal power stations during transfer to lower speeds by organizing additional output frequency steps of frequency changer in the range of 25 to 50 Hz has three potentially isolated three-phase voltage supplies each connected to three respective isolated three-phase voltage supplies, each of the latter being connected to two three-phase thyristor switches, and three-phase load; in addition it is provided with three three-phase thyristor bridges connected to respective potentially isolated three-phase power supplies. Anode and cathode groups of diodes in each of additional three-phase thyristor bridges are interconnected and connected to phase leads of three-phase load; six other three-phase thyristor bridges connected to three potentially isolated three-phase voltage supplies are assembled in two separate groups; three shorted-out bridges of one group carrying unidirectional rectified current are connected in series and three bridges of other group carry opposing rectified current. EFFECT: enlarged frequency regulation range. 1 cl, 5 dwg
