Power Transformer and Surge Arrester Modeling for Fast Front Overvoltages Using EMTP-RV

Inadequately rated surge protection devices in a power system can result in partial, complete as well as catastrophic damage to assets from overvoltages. A conservative approach could be to adopt the highest value(s) of rated insulation level for a given voltage class, however, this approach may be uneconomical and impractical. To determine the suitable rated insulation levels, an insulation coordination study is required. Such a study considers the magnitude of possible overvoltages including those from Temporary Overvoltages (TOVs), Slow Front Overvoltages (SFOs), Fast Front Overvoltages (FFOs) and Very Fast Front Overvoltages (VFFOs) to determine the quantity and ratings of surge protective devices including surge arresters. Data gathering and representative component modeling can be very challenging as well as inadequate given incomplete data and technical resource constraints. This paper outlines an approach to model power transformers and surge arresters for determining the expected FFOs due to lightning using the Electro-Magnetic Transient Program Restructured Version (EMTP-RV) simulation software. The existing software models for these equipment are reviewed and modified for application in a 220 kV insulation coordination study. The final recommended values for the models, with supporting performance results, are provided and the accurateness of model modifications discussed.