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Figure 2.22 shows the load voltage profile with an active GUPFC based sub-system. The load voltage remains constant during the entire simulation period. The intentionally islanded load has almost constant voltage. The brief spikes observed during switching in the system at 1.0 and 2.0 s. The fuel cell embedded GUPFC improves the load voltage profile during the three-phase to ground fault and single-phase to ground fault. The GUPFC, as compared to previous test cases, receives power for improving load voltage profile during fault due to fuel cell connected to its common DC bus. The load voltage profile using active GUPFC during intentional islanding condition shows almost constant load voltage of 1 pu during the simulation.

Figure 2.21 Load voltage profile in test case-4.

Figure 2.22 Load voltage profile in test case-5.

By examining different test cases, it can be seen that load voltage remains constant with active GUPFC. The percentage load voltage deviation from the rated load voltage calculated as:

(2.19)

Figure 2.23 illustrates the graph of percentage load voltage deviation from the rated value of 1 pu in line to ground fault and Figure 2.24 illustrates for three-phase to ground fault.

The observations are listed below:

1 The system without GUPFC and without fuel cell shows maximum percentage deviation of load voltage under the non-islanding condition and intentional islanding connection with rated load voltage of 1 pu. It observed that the percentage variation in intentional islanding conditions is less than that of non-islanded conditions.

2 The system without GUPFC and with fuel cell shows improvement in the load voltage profile in intentionalislanding connection but fails to maintain load voltage profile with the non-islanding condition during the fault. Figure 2.23 Summary of simulation: Percentage load voltage deviation from rated value for line to ground fault.Figure 2.24 Summary of simulation: Percentage load voltage deviation from rated value for three phase to ground fault.

3 The system with GUPFC and without fuel cell shows improvement in load voltage profile during 27a fault in intentional islanding condition but with the non-islanded condition, the load voltage deviation in this system matches the system without GUPFC and without fuel cell.

4 The system with GUPFC and with fuel cell shows improved results and lower percentage load voltage deviation from rated load voltage during the fault. The percentage deviation of the load voltage is minimum in intentional islanded system operation compared to the non-islanded system.

5 The system with active GUPFC i.e. GUPFC embedded with the fuel cell shows minimum percentage load voltage deviation from its rated value during the fault on the system. The most probable fault, single phase to ground fault, has minimum percentage load voltage deviation as compared to three-phase to ground fault during non-islanding and intentional islanding conditions.

6 The graphs in Figures 2.23 and 2.24 illustrate the deviation of load voltage from rated value under different network situations.

7 The load voltage in ‘without GUPFC and without fuel cell’ and ‘with GUPFC and without fuel cell’ shows maximum deviation from rated value.

8 The load voltage in ‘without GUPFC and with fuel cell’ shows medium deviation from rated value.

9 The system in ‘with GUPFC and with fuel cell’ has a lower deviation.

10 The load voltage in ‘with active GUPFC’ has the lowest deviation from the rated load voltage.