Three-phase transformer for supplying semiconductor rectifiers

In the case of this three-phase transformer, each phase has a mains winding (3) and a valve winding (4), which windings are arranged concentrically on the corresponding limb of the core. The windings (3, 4) are divided into four parts (5, 6, 7, 8; 54, 55, 56, 57) along the height of the limb. Half of the parts (54, 56) of the valve winding (4) of the phases are connected in star and the other half of the parts (55, 57) are connected in delta. The parts (5, 6, 7, 8) of the mains winding in each phase are connected in two parallel branches. One branch of each phase is formed by parts (5, 7; 6, 8) connected in series. The parts (54, 55, 56, 57) of the valve winding (4) in each phase are arranged such that the parts (5, 7; 6, 8) of the mains winding (3) of the corresponding phase are located opposite those parts (54, 56; 55, 57) of the valve winding (4) which are connected in the same way. The mutual arrangement of the corresponding parts of the mains winding and of the valve winding ensures a minimal voltage drop in the converter unit in operation and that short-circuit currents are limited in the event of faults.