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Gas turbine power plant (PLTG) is one of the power plant that has a flexibility in used. It can use the gas fuel and/or oil fuel for operation. During operation of electric power systems, there is often a change in load demand, whether it is full load or based load. Moreover, to address this fluctuating demand the power plant have to maintain the fuel availability. When the full load demand by P2B (Load Control Center) and gas fuel supply is insufficient to operate the PLTG, it needs High Speed Diesel (HSD) as additional fuel. The problems that occur in the PLTG are not only limited to thermal efficiency, but also at the cost of efficient generators. This study aimed to minimize plant operating costs or fuel costs with the same load on each unit. The method used in this research was to find the best variation of loading pattern in PLTG Priok block 1 unit 1.1, 1.2 and 1.3. Furthermore, the heat rate value, Specific Fuel Consumption (SFC) and thermal efficiency were calculated based on ASTM PTC-22 2005, then performed the calculation of operating costs (cost / kWh). Operation data and gas turbine specific data for analysis were taken from a power generating company which was the object of research. Operation cost that can be saved by PLTG block 1 Priok with the use of two types of fuel (HSD and Gas), at 360 MW with load pattern of 123 MW - 115 MW - 122 MW, 330 MW with load pattern 115 MW - 100 MW - 115 MW, and 300 MW with a load pattern of 90 MW - 120 MW - 90 MW, were obtained cost savings per hour Rp. 9.149.387, Rp. 11.879.814, and Rp 7.141.120, respectively. Meanwhile, the operating costs thet can be saved of full gas fuel at 360 MW with load pattern of 123 MW - 115 MW - 122 MW, 330 MW with load pattern of 110 MW - 120 MW - 100 MW, and 300 MW with 90 MW - 100 MW - 90 MW, were obtained cost savings per hour of Rp. 4.045.499, Rp. 7.713.610, and Rp. 25.132.922. These results indicated a good plant performance.

fuel; operating cost; efficiency; load pattern; SFC