Energizing and de-energizing of a 250 MVA transformer of a pumped storage power-plant: Modelling and its validation by on site tests

This document describes the methodology developed for the simulation of phenomena observed when energizing and de-energizing a 250 MVA step-up transformer of a pumped storage power plant connected to the 400 kV network. Firstly, the modeling of the up-stream network and the modeling of the transformer have been described in detail, and some points specifically addressed as the representation of its saturation behavior. Secondly, a particular focus has been made, for the energization and the de-energization of the step-up transformer, on the determination of the closing times (respectively opening times) of the circuit breaker poles, which have to be accurate in order to reproduce the correct stresses on the transformer. A comparison between the tests carried out on site and the simulations performed have given very satisfactory results, both for the inrush currents when energizing the transformer and the residual fluxes when deenergizing it.