Value-based planning methodology for the restructuring and expansion of an electric utility sub-transmission network

Abstract

The main objective of this study is to develop a methodology to assist in the reconfiguration and expansion of an electrical sub-transmission network within the framework of Value-based planning. This methodology applies to typical municipal networks found in South Africa. A literature study indicates that most of the fundamental concepts for power system reliability is well established with extensive research done in North America, and other parts of the world. Reliability worth assessment of sub-transmission networks in South Africa, which include composite networks and substation reliability, is however not well developed. From a Value-¬based point of view the literature further does not provide much linkage to the evaluation of alternative long-term network options. This is especially true in terms of the life cycle cost assessment of network alternatives, which include the prediction of customer damages as a function of network performance. In this dissertation a methodology is proposed which utilises the basic network reliability concepts to assess the performance of existing and future alternative network options. The load point Expected Unserved Energy is used to quantify network performance and is obtained through a contingency enumeration process. An existing Geographical Load Forecasting technique defines all customers connected to a load point, on a homogeneous level. This information along with Sector Customer Damage Functions is used to predict existing and future Composite Customer Damage Functions at the associated load point in the sub-transmission network. To arrive at the total minimum cost, which is the objective of Value-based planning, the present worth for each alternative is obtained from the annual utility and customer cost over the life cycle of the alternative. The alternative that result in the lowest present worth is identified as the preferred alternative. A case study is conducted on the sub-transmission network of the Greater Pretoria Metropolitan Council (GPMC) in order to prove the methodology. The entire network is analysed in order to identify the sub-system with the worst performance from a reliability point of view. Alternative network options are identified and the methodology is used for the evaluation of these alternatives. The application of this methodology provides the network planner with the ability to make better decisions with regard to the allocation of reliability. Through the calculation of reliability indices, tangible guidelines can be provided to quantitatively assess the impact of different network alternatives. These guidelines assess contingency probabilities explicitly and along with reliability worth evaluation provide a fundamental tool to conduct Value-based planning. The application of this methodology can lead to significant savings in capital investment while maintaining an acceptable level of reliability.