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Figure 2.18 shows the load voltage profile when the system is under intentional islanding condition. A healthy working condition between 0.0 and 1.0 s, the load voltage observed as 1 pu. A three-phase to ground fault initiated between 1.0 and 1.5 s. A sudden drop in voltage occurs at 1.0 s and then a spike due to intentional islanding is seen at the instant of 1.0 s. After the occurrence of fault at 1.02 s generator at bus number 3 and load at the bus no. 5 get islanded from the main system. During islanding conditions (i.e. between 1.02 and 1.5 s), the load voltage rises to 1.25 pu. The load voltage becomes normal to 1.0 pu when the islanded part of the system reconnected with the main system at 1.5 s and remains at 1.0 pu till t = 2.0 s.

Figure 2.16 IEEE 9 bus system.

Figure 2.17 IEEE 9 bus test system MATLAB simulation model.

Figure 2.18 Load voltage profile in test case-1.

During the single-phase to ground fault (i.e. between 2.0 and 2.5 s), the load voltage rises to 1.25 pu due to the intentional islanding of the generator at the bus no. 3 and load at the bus no. 5. The voltage profile improves due to the islanding of a balanced system.