The IRR is used in capital budgeting to measure and compare the profitability of investments. The economic analysis without considering the outage cost found that the IRR of 115/22 kV substation with peak demand 4-9 MW and transformer rated 10-25 MVA are 3.81%-28.45% and 1.52%-18.44% for AIS and GIS, respectively. Furthermore, the IRR in case of considering outage cost are 11.53-45.03% and 6.12-30.73% for AIS and GIS, respectively. The economic assessment for construction 115/22 kV substation with peak demand 4-9 MW in term of IRR is demonstrated in Fig. 4.