Abstract
The paper presents the application of the use case approach for developing reusable power system components. Object oriented, three phase load flow is introduced as an example. The three phase load flow development is based on the symmetrical components theory and the decoupled models of the untransposed transmission lines. The well known Newton Raphson and Fast Decoupled algorithms are chosen in the development The three phase load flow is solved by incorporating the solution of the positive sequence load flow and the negative sequence and zero sequence nodal voltage equations. The different use cases are studied before the code implementation. Based on these use cases, an analysis model is constructed. The clear advantage of the use case approach is that it defines the reusable objects before the code implementation.