Faulted Inter Bus Transformer (IBT) can cause power system instability. Therefore, it will be isolated to prevent the spreading of disturbance. IBT at the Ptn Substation which supplies Ptn - Grt and Dwt Subsystem is discussed in this paper. The event discussed is 2 of 3 IBTs are out of work so that only one left. So, load shedding of Dwt Subsystem is required to avoid further disturbance. However, after it is applied, the voltage at the Dwt Subsystem will increase beyond the allowed rating. Therefore, further action is required by releasing some capacitor banks of several substations that have the highest rated voltage until the voltage in all substations is within the permitted rating. Finally, The system return to stable after load shedding with total 226.45 MW and capacitor shedding with total 150 Mvar. © Published under licence by IOP Publishing Ltd.