電業自由化乃現今各國電力發展之趨勢，其目的係引進競爭機制。為提高競爭力，輸電部門必須提昇營運效率，包括降低投資成本，並選擇高效益的投資方案。因此在編擬輸變電投資計畫進行效益評估益顯重要。過去由於輸電部門具有地區獨佔性質，遂缺少效率，此外輸電部門既不發電、亦不直接售電於用戶，其電價收益實不易計算，因此難以針對輸變電投資計畫進行完整的投資效益評估。爰此，本論文之主旨即為發展出一套評估方法，以符合現今電業自由化的需要。對於未自由化的電業，亦可作為編擬輸變電投資計畫的重要參考依據。
本論文主要分為三個部分，第一部份，首先參考、彙整國外電力公司的現行作業方法，包括韓國電力公司、澳洲Transgrid、Powerlink及Western Power等四家電力公司，再深入探討、比較國內外輸變電計畫現行編擬流程與評估方法；第二部分係提出輸變電計畫效益評估方法，本評估方法分為必要性評估與效益性評估，其中必要性評估係以供電轄區內整體變電所利用率是否超過70％來作為變電所新建工程之評估指標；效益性評估係以擴大供電能力、減少線路損失及提高供電可靠度等三項可幣值化的效益作為輸變電計畫效益之評估指標；第三部分，就本論文所提出的評估方法，以現正執行的第六輸變電修正計畫進行試算，驗證本評估方法的合理性。

Nowadays the liberalization of electric power industry has become the trend of power industry structures in developed countries ,and its purpose is to bring in competition mechanism. For improving competitiveness, transmission departments have to raise their operation efficiency, including costing-down investments and choosing high-return investments. Therefore, the implementation of the benefit/cost evaluation on the investment plan is more needed ever than before during the drafting of the investment plan. In the past, transmission or network companies were regionally monopolized, and thus had less incentive to improve their operation and also investment efficiency. Besides, what these companies offered are transmission service, not electricity produced, in most occasions, and they do not sell electricity directly to the customers. It is difficult to estimate an appropriate revenue to account for their service offered, so to evaluate the cost/benefit of transmission and substation (T&S) investment plan. This thesis intends to propose a numerical model with the effective measures of the cost/benefit evaluation for the need of liberalization of electric power industry nowadays. For those countries which are still not liberalized, the numerical model can be an important reference material as well.
This research consists of three parts: first, to make discussion and compare with the evaluation processes of T&S investment in KEPCO, Transgrid, Powerlink and Western Power Electric Company in Australia. The second part proposes the estimation method of T&S investment plan with necessity analysis and benefit/cost calculation. In necessity analysis, the transformers’ average utilization ratio in peak hours for each power supplied district is selected as the index to evaluate the necessity of power substation expansion. As for the benefit/cost calculation, the increment of power supply capacity, the reduction of network loss and the improvement of power supply reliability are taken as the three key evaluation indices which are converted into the currency to clearly measure the project benefit. The last part is to evaluate Taipower’s sixth T&S investment plan with fore-mentioned methods to ensure that they are feasible.

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