This document presents a model for an AC electric arc furnace considering the highly nonlinear and time varying characteristics of this type of load. Using the nonlinear differential equation that describes the V-I (voltage vs. current) arc characteristic, both voltage fluctuations in the time domain and the arc length are established assuming periodic, stochastic and chaotic variations. The model is developed using PSCAD-EMTDC with parameters from a real steel company located in Colombia. The values for the short term flicker severity index (P <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ST</sub> ) were determined according to the IEC-61000-4-15 standard specifications. The simulation results are compared with real data obtained from the steel facility to demonstrate the validity of the models.