The paper deals with full scale laboratory investigations on a circuit composed of three single phase voltage transformers (

kV, 50 VA) connected to an ungrounded source supply with a zero sequence capacitance. About a hundred energizing operations were performed. Some records of transient states obtained by varying the value of the capacitor bank and the voltage of the source are shown. The stroboscopic method and its original adaptation to the three single phase ferroresonance phenomenon are presented. Finally, observations are made about digital simulations.