Modelling of complex dynamic systems, such as power system is usually muchcomplicated because of the complexity of the Rotor angle system.Therefore, approximationprocedures are often used to reduce such complexities, in order to come up with simplermodels than the original models, for easy control implementations. This becomes necessary as the control laws may be too complex, with regards to practical implementations. In this Paper, optimalHenkel-norm approximation was applied, and the complexity of the linear rotor angle system was reduced.As the level of reliability of any system depends upon the cost considerations and for the use to which the system will be put, manufacturers producing equipment where reliability is of paramount importance, will need to expend much time and effort in design, building, testing and inspection stages, ensuring that the reliability meets the requirements. This could notbe possible to achieve when the system?s complexity is not reduced.