Electrical power system simulation involves power system modeling and network simulation in order to analyze electrical power systems using design/offline or real-time data. Power system simulation software's are a class of computer simulation programs that focus on the operation of electrical power systems. These types of computer programs are used in a wide range of planning and operational situations for: Electric power generation - Nuclear, Conventional, Renewable, Commercial facilities, Utility transmission, Utility distribution, Railway power systems, Industrial power systems. Applications of power system simulation include: long-term generation and transmission expansion planning, short-term operational simulations, and market analysis (e.g. price forecasting). These programs typically make use of mathematical optimization techniques such linear programming, quadratic programming, and mixed integer programming.Key elements of power systems that are modeled include: Load flow (power flow study), Short circuit or fault analysis, Protective device coordination, discrimination or selectivity, Transient or dynamic, stability, Harmonic or power quality analysis, Optimal power flow. There are many power simulation software packages in commercial and non-commercial forms that range from utility-scale software to study tools.