Calculation of transformer inrush currents occurring during the energizing of the Public Grid after a major black out

The paper describes simulations and a live test of the black-start procedure of an industrial power plant in the North of the Netherlands. After a total blackout of the Public Grid in the Netherlands, the restoration process shall start with so-called black-start units. To increase the probability that the re-energizing of the Public Grid indeed succeeds, the Dutch transmission system operator obliges units to prove their black- start capability by performing a live test. A crucial step in the re-energizing of the Public Grid is the energizing of large transformers. Problems can be expected due to the inrush current of the transformers. For one such generating unit extended simulations of the inrush phenomena of the transformers and calculation of inrush currents and overvoltages were performed. Based on the simulation results well-founded decisions were made on the most suitable start-up procedure. The simulations were followed by live tests of the black-start procedure.