Airport ground lighting (AGL) systems provide visual reference to aircrafts during airport operations. In AGL systems, constant current regulators feed a beacon circuit supplied through isolation transformers. Component modeling is necessary to simulate AGL systems, and thus characterize and predict their behavior. This paper presents an isolation transformer model including transformer core saturation. Moreover, a procedure to estimate transformer model parameters is proposed. Both the model and the estimation method are validated with extensive measurements on more than 20 isolation transformers of different power ratings and trade names.