Study on a real case of low frequency oscillation occurred in the black-start by a hydropower plant

This paper recaptures a low frequency oscillation occurred during simulation and finally being resolved in the real grid. Three hypothesis are proposed to tackle this issue, namely the ferro-resonance caused by hasty stepping up, the inrush current derived from remanence in transformer and the parameter resonance between the unit and experiment grid. After being refuted consecutively it is assumed that the auto-excitation system parameter resonates with grid. Expectedly the oscillation vanished by altering the control parameter with proof of some simulation results. At last two conclusions are presented from experimental analysis.