A general model for representing arbitrary unsymmetries in various types of network analysis

When dealing with unsymmetric faults various proposals have been put forward. In general they have been characterized by specific treatment of the single fault in accordance with the structure and impedances involved. The model presented is based on node equations and was originally developed for transient stability studies in order to allow for an arbitrary fault representation as seen from the positive sequence network. The method results in impedances -or admittances-combining the negative sequence and zero sequence representation for the symmetrical network with the structure and electrical constants of the unsymmetry involving one or more buses. These impedances are introduced in the positive sequence network in the nodes involved in the unsymmetrical conditions. In addition the model can be used for static fault current analysis and presents also in this connection a general method of solution; the method is easy to use since the task of user is limited to establishing the node admittance matrix of the unsymmetry expressed in phase coordinates. The paper is completed with two examples showing the application of the method, one fault for which a well known representation exists and one complicated fault situation which has not been treated before for traditional transient stability analysis.