At the existing 9" press line P4 at the Hydro Vetlanda site, the entire power supply of the inductive billet heating with a total output of 3750 kW was replaced by modern, powerful IGBT converters in the summer of 2022. In addition to a new converter transformer and the protection devices for the induction reheater, which were supplied by Vattenfall, the entire power cabling was renewed and the central control system was adapted. In order to continue using the existing induction coils, the coil interconnections were modified to a single-phase system.

A newly designed ILD-type direct converter was installed at the inductive base heating, which is operated directly on the existing coil without compensation capacitors. The 3-phase coil was converted accordingly to a single-phase system for this purpose in order to eliminate the different power ratios within the coil. One challenge was the coupling of the load with a rated current of 14 kA to the converter, which is equipped with several inverters. To adjust the coil filling level to the block lengths, the coil is equipped with a length adjustment.

For the inductive reheating, a 6-zone IGBT converter of the MIB type was installed. Here, too, a single-phase system was created from a 3-phase coil in order to achieve better temperature control at the taper furnace.

This ambitious and challenging project was installed and commissioned within the 3 week summer shutdown.