Models for short circuit and incipient internal faults in single-phase distribution transformers

Internal winding faults resulting from the degradation of transformer winding insulation can be catastrophic and hence expensive. In the new environment of deregulation, utilities need to use inexpensive methods to detect such faults in the incipient stage. The development of an accurate internal fault diagnostic technique for transformers must be based on the analysis of quantities from fault scenarios. Considering the safety of personnel, the damage that will occur in the transformer, the consumed time, and related cost, simulation involving the modeling of transformers with internal faults is the best way to generate these fault cases.; To address this need, this dissertation presents new models for single-phase distribution transformers with internal short circuit and incipient winding faults. For each model, the simulation results were compared with field test results. One of the models was a nonlinear finite element analysis (FEA) model, whose parameters were calculated based on the physical information of the transformer using finite element analysis. The FEA model could simulate internal short circuit winding faults accurately; however, the simulation time was very long. To compensate for this shortcoming, two new neural network models were developed. One model used a back-propagation feedforward network and the other used a radial basis function network. The simulation results showed that properly designed and trained neural network models could model internal short circuit faults accurately and the simulation time for each case was shorter than using the FEA models.; New incipient fault models were implemented by combining deteriorating insulation models with the FEA model. The new deteriorating insulation model, including an aging model and an arcing model, was developed based on the physical behavior of aging insulation and the arcing phenomenon occurring when the insulation was severely damaged. The characteristics of the incipient faults from the simulation were compared with those from some potential experimental incipient fault cases. The comparison showed the experimentally obtained characteristics of terminal behaviors of the faulted transformer were similar to the simulation results from the incipient fault models.; The new models presented in this dissertation will be used to generate a database of fault cases.