Electrical Systems for Automatic Handling and Electric Heating of Slabs

The availability of large quantities of electrical power and sophisticated means of control has justified the use of induction methods in heating large steel slabs to rolling mill temperatures. Capable of delivering 210 MW, a unique power system, comprising power transformers, autotransformers, static switches, and capacitor banks, provides eighteen induction heaters with controlled electrical energy. The entire system can deliver 600 ton/h of steel to the rolling mill. The basic overall automatic control scheme involves the operations of slab handling control, heater control, static power switching, and computer control. The control functions, including phase balance and demand limit control, are described and discussed. The features and operation of the static power switch, capable of switching close to 10 000 A, are presented. Used as a protective device, the switch can clear up to 210 000-A faults in less than one cycle.