Another susceptible configuration to ferroresonance is the system of Figure 9. The system is an ungrounded three-phase system. Such a systemcan result from a temporary disconnection of the grounding system in a part of a network. The
ungrounded system can also be formed subsequent to the energization of a transformer with an unloaded delta winding. Prior to the load or other equipment connection, the delta side remains temporarily ungrounded. Under such a condition,the VTs connected between phases and ground are prone to ferroresonance. A sufficient zero sequence
capacitance C0 can trigger the ferroresonance phenomenon in the VT.