Energization of a no-load transformer for power restoration purposes: modeling and validation by on site tests

The energization of power transformers following a complete or partial collapse of the system is an important issue. This paper describes a method for the modeling of the electric network between the source and a target transformer, taking into account the data accuracy which has a strong impact on the resonance frequency of the network and consequently on the temporary harmonic overvoltages involved. This methodology has been validated by on site tests, the resonance frequency and the initial conditions being derived from the measurements. Finally a comparison between measurements and EMTP (EPRI/DCG version 3.0) simulations has been performed, showing a good agreement on currents, the average discrepancy being equal to 5%, the value of the subtransient reactance of the generator and the capacitance of the line having a value within the accuracy initially stated.