Modeling Three-Phase Short-Circuits for Radial Distribution Systems


Monitoring radial distribution systems in short-circuit conditions represents a quite important issue of elec-tric power networks supplied by renewable sources. The method presented in the paper aims to establish in labora-tory conditions, using the similitude criteria, the real value and the duration of a three phase short-circuit current act-ing in renewable sources connected to the electric grids. Since, due to the high values of the short-circuit currents it is difficult to test the operation of the relays in situ, for in-stance in transformer stations or substations, it is manda-tory to test and set using the injection of secondary currents. Consequently, the paper presents the modeling of a real grid, in order to emulate, as accurate as possible. The results of the measurements, reported to the real grid, represent the real ones, existing at the three phase short-circuit level. Therefore, even from the early phase of design, one may choose the breaking equipment, capable to face the condi-tions of dynamic and thermal stability. Since the reporting factors are known, along with the possibility of using the accurate reported value of the real short-circuit current on the model, the tests on model present advantages in relation to the use of the devices of secondary currents injection. The results of the measurements on the model confirm the vi-ability of the last testing method here depicted. images