Energization of a no-load transformer for power restoration purposes: sensitivity to parameters

This paper describes a method for the modeling of the energization of power transformers taking into account the data accuracy (line capacitances, subtransient reactance of the generator, air core reactance of the target transformer) which has a strong impact on the resonance frequency of the network and also on the temporary harmonic overvoltages and currents involved. The influence on the results of the studies is described. Those parameters have been assessed inside their accuracy boundaries from on site measurements on a real network; in the case of the generator, the value derived from tests has been confirmed by 3D field programs. In the cases where little information is given by the manufacturers, the sensitivity to parameters has to be taken into account in order not to underestimate the overvoltages, and to determine the best palliative solutions in order to energize the transformers in good conditions