Analysis of Technical and Economics Overhead Transmission Line 150 kV Construction from Mine Mouth Coal Fired Power Plant to External Customer Substation

Received 4 May 2023; 1 Revision 4 May 2023; 2 Revision 22 May 2023; Accepted 28 May 2023 DOI: https://doi.org/10.24036/jptk.v6i2.32723 ABSTRACT Mine Mouth Steam Coal Fired Power Plant (PLTU) has a capacity of 2x18MW while the power supplied to internal consumers is 3.6MW or around 10% of the total generating capacity (20% of one generating unit). To operate according to its specifications, the load is increased by operating the load bank. Excess generating capacity can be sold to external consumers outside the mining area, so it is necessary to build one circuit overhead transmission line 150kV as long 48.38km. The construction of overhead transmission line 150kV from the PLTU to the external consumer substation can increase sales of electricity and can replace the loadbank function. This study aims to evaluate the technical feasibility and economic aspects of the construction overhead transmission line 150kV from the PLTU to an external consumer substation. The research method uses financial indicators IRR, NPV and ROI. Overall, the construction of one circuit overhead transmission line 150kV can increase sales of electricity and replace the function of load bank. The NPV value is IDR 1,604,887,094 with an IRR of 12.53%, and ROI of 9.03 years.


INTRODUCTION
The Mine Mouth Coal Fired Power Plant (PLTU) in Central Kalimantan has two generating units with a gross capacity of 2x18MW which only one generating unit operates to meet the demand for electric power in the mining area. Electrical energy is transmitted to internal customers using a 36kV overhead transmission line as long about 120 km. PLTU has a minimum load to operate according to its specifications. Currently, the internal customer load is still below the minimum generation load, so it is necessary to operate the load bank. The provided loadbank has a total capacity of 5.2MW. The minimum generation load is around 40% while the average customer load is about 3.6MW or around 20% of the generator capacity. The small internal load and the operation of the loadbank cause the PLTU's cost of generation (BPP) to be high. Excess generator capacity can be transmitted to external loads by build a one-circuit 150kV overhead transmission line with 150 mm2 ACSR conductor as long 48.38km from the PLTU to the external customer substation. Construction of a 150kV overhead transmission line can increase PLTU electricity sales and replace the use of load banks. Steps

and Flowcharts
This study aims to evaluate the technical and economic aspects of the construction of a 48.38km single-circuit 150kV overhead transmission line from the mine mouth power plant to the external consumer substation. The research was conducted by evaluating the calculation of the investment cost of the power plant, the investment cost of the 150kV transmission, the sale of electricity, the load projection, the projected increase in internal electricity rates and generation costs. This research was conducted through several steps as shown in the flowchart as follows:

B. Power Generation Economics Approach
To calculate electricity rates, a cost-based approach is used, namely pricing starting from identifying costs for production (cost of raw materials, human resources, etc. Component E is the cost of distribution or transmission These components are then divided by the production of electrical energy (kWh) in a year to see the amount of production costs per component or in total.

C. Investment 150kV Transmission Line
150kV Transmission line investment of 143 towers with 150mm2 ACSR conductors for one circuit as long 45.38km from the PLTU to the external consumer substation was obtained from transmission vendor offers. Investment is divided into 2 parts, namely investment in goods and investment in installation services.

D. Economic Analysis Methods
Economic analysis is divided into 3 steps: a. Data collection, including: ➢ Investment cost for power plant ➢ Investment cost for 150kV transmission line ➢ Generating cost ➢ Eksternal sales electricity tariff ➢ Internal sales electricity tariff ➢ Electricity production data ➢ Internal electricity demand projection ➢ Internal tariff projection ➢ Generating cost projection b. Data processing to get cash flow. Cash flow is obtained by adding up all the components of income and expenses. The value of each year's cash flow is then converted to a uniform annual cash flow to calculate the time of return on investment (ROI). c. Economic calculation to get NPV, IRR, and ROI parameters. NPV is the difference between the present value of cash inflows and the present value of cash outflows in a given period In the calculation used a discount value of 12.5%. Economic analysis is calculated from investment costs compared to sales of electricity using some data, these data include investment costs for power plant, investment costs for 150kV overhead transmission line, sales of electricity, electricity rates, projected load increases, projected increases in electricity rates and generation costs.

RESULT
The electricity production that is sold to PLTU's internal customers is 3.6MW or around 20% of the generating capacity so that the main cost of generation is relatively high. The 150kV transmission is used to send 7.7 MW of electricity to external customer substations. The selling price to external consumers is 90% of local area electricity generation cost, while the electricity tariff to internal customers is 20 c$/kWh. The assumptions used as the basis for calculating the economic analysis are as follows  Ye ars The assumption of selling electricity to external customers continues to decline throughout the year in line with the projected increase in the PLTU's internal load.

DISCUSSION
The current PLTU average load is 3.6 MW or around 20% of the one generating capacity. Loadbank operation is required to achieve a minimum generation load. The relatively small internal load and the use of a loadbank cause high cost of generation. Selling electricity to external consumers can reduce the cost of generating electricity and replace the use of load banks. The external load distance from the PLTU is around 48.38km, so it is necessary to build a 150kV transmission line to connect between the PLTU and external consumer substations. The selling price of electricity to external customers is quite high compared to the selling price of electricity for PLTU in general. However, the high cost of generating electricity in the local area, the selling price of PLTU electricity is still at an economic level.

CONCLUSION
That the construction of a 48.38km transmission line 150kV using a 150mm2 ACSR conductor to transmite excess capacity from the mine mouth steam coal power plant to external consumers is feasible because the additional investment cost for the 150kV transmission line of Rp.73,067,812,793 produces a positive NPV of Rp.1,604,887,094 with an IRR of 12.53% and the entire capital can be returned in 9.03 years.