Abstract
Electric power consumption has been increasing rapidly across the globe; this increase specially accelerated in the last decade. Consequently, existing transmission lines are becoming overloaded beyond their power transfer capability. The inadequacy of the transmission lines has contributed to power interruptions and instability of the power system. Construction of new transmission lines can be a solution to mitigate these problems. However, to build the whole structure of a new transmission line, a huge investment is required. Besides this, environmental concerns would create further barriers that delay the accomplishment of the project. Therefore, the effective and quickest solution to tackle this problem is enhancing the power transfer capability and stability margin of existing transmission lines. This paper studied the techno-economic feasibility of converting an existing HVAC line into a simultaneous AC-DC power transmission system to enhance power transfer capability as well as to improve power system stability. Using the proposed method, the loadability of Tana Beles to Addis Ababa 400 kV, 476.2 km AC line has increased to more than double which is from 1091.66 MW to 2196.85 MW. The active power loss and corona loss evaluation of the two systems ensured that simultaneous AC-DC system is more efficient than HVAC system. It is also shown that the instability can be effectively improved by simultaneous AC-DC power transmission with fast DC power modulation. From the economic point of view, rather than constructing new HVAC line, converting existing HVAC line into simultaneous AC-DC transmission system has a price reduction of about 107,984,968.56 USD or 32.46% of the new HVAC line cost. Considering a 35-year project life cost analysis, it is observed that the life cycle cost of the simultaneous AC-DC transmission system is about 29.2% lower than the life cycle cost of a new 400 kV HVAC line. Thus, the designed simultaneous AC-DC power transmission system has better technical performance and also is less costly than constructing a new HVAC line.
Highlights
Ethiopia is a low-income country, with low electricity access and an inefficient power transmission network
Electricity access has increased by only 30% over the past 25 years and it reached 45% in 2018 [1]. ere are over 350,000 registered customers who have been waiting for a connection for the past many years, of which about 50,000 have already paid the full-connection fee [2]. To respond to these demands, in parallel to increasing the generation capacity, Ethiopia Electric Power (EEP) has been undertaking expansion of transmission lines. e resultant cost of this transmission expansion over the 25-year period is estimated at 14.362 Billion US$ [3]
The existing long HVAC lines are not fully utilized to their thermal limits as a sufficient margin is kept against transient instability considerations. is situation demands the review of traditional power transmission theory and practices on the basis of new concepts that allow full utilization of existing transmission facilities without decreasing system availability and security
Summary
Ethiopia is a low-income country, with low electricity access and an inefficient power transmission network. Ere are over 350,000 registered customers who have been waiting for a connection for the past many years, of which about 50,000 have already paid the full-connection fee [2] To respond to these demands, in parallel to increasing the generation capacity, Ethiopia Electric Power (EEP) has been undertaking expansion of transmission lines. Is paper has claimed that it is possible to load existing HVAC transmission lines to maximum values of their thermal limits by using simultaneous AC-DC Power transmission system. E impacts of line voltage, line reactance, and thermal limits of the conductor on the maximum power flow point are clearly investigated in this paper. E analysis of the paper reveals that the angle at which the maximum power flow obtained depends on three parameters which are line voltage, line length, and thermal limit of the conductor. This research forms a foundation to significantly improve both the power transfer capability and power system stability of Tana Beles to Addis Ababa 400 kV transmission using a detailed designed simultaneous AC-DC transmission system. e economic feasibility study of the model has been conducted to evaluate its practicability and costeffectiveness
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