The existing induction furnace at the Hanover plant from 1977 was designed as a Steinmetz circuit with a balancing device and had mechanically operating load contactors of the Homa type, which switched on the power for each induction furnace. The expected service life of the switchgear and the individual components (balancing reactor, transformer, switchgear and compensation capacitors) had been reached. In addition, the system caused an unbalanced grid load depending on the load case.

Thanks to the conversion of the system to a modern IGBT direct converter carried out by extrutec, the balancing unit with 2 x 950 kVA could be completely omitted. Power capacitors in the coil base are also no longer necessary. The entire project was completed in-house at extrutec, from the design of the system through to installation.

Compared to the replaced system, the switchgear losses were reduced by 6 - 7%. A further improvement step is already being discussed for the future, as the new switchgear concept offers the possibility of significantly reducing the losses to be compensated in the field distributor.

A modern inverter switchgear of the MIB / ILD type has many advantages over a mechanical switchgear, such as

• Uniform grid load in every operating state
• Grid - power factor independent of load behaviour
• Stepless power control
• PID control behaviour
• Peak load reduction
• Energy management system
• Elimination of power contactors
• Monitoring in every operating state
• Integrated analysis tools