The objective of this research project was to develop and implement a model for an A.C circuit breaker in the Electromagnetic Transients Program (EMTP). Various models for the arcing process were evaluated, and the modified Mayr equation was chosen for the model. Other equations were added to demonstrate the generality of the algorithm developed. Since the Electromagnetic Transients Program was not designed to accommodate directly elements whose resistance varies with time, such as an electric arc, several strategies for interfacing the model with the program were studied. The compensation method was selected, and was used for interfacing the circuit breaker model with the program. After implementation of the model, it was validated by comparing its performance with experimentally verified results reported previously. In order to render the model more practical, an auxiliary breaker parameter estimation routine was developed and tested. / M.S.