The model derived in this paper is intended for the testing of control stra
tegies using off-gas variables in the control of an Electric Are Furnace (E
AF). The derivation of a multivariable non-linear state space model of an E
AF process is treated. Assumptions are made that facilitate the modeling ef
fort. First principles of thermodynamics, together with empirical relations
hips, are used to derive the model equations, A state-space model is develo
ped with physical variables such as carbon content in the steel as model st
ates. Rates of change such as decarburization are also considered. Typical
operating conditions for a furnace are discussed and initial conditions for
a simulation are derived from this. A timeline of events corresponding to
operating conditions is determined for the simulation. A simulation is cond
ucted starting with the initial conditions and proceeding with the line of
events. The results of the simulation are shown and discussed in terms of t
he purpose of the model.