Network structure in sub-transmission systems. Features and practices in different countries

The authors deal with network architecture in general and the role of sub-transmission in particular. They describe the results of a study carried out by a combined CIRED/CIGRE Working Group. It gives condensed information on the practice in about 14 different countries and examples of network structures in the United Kingdom, Belgium, Italy and the Netherlands. The density and size of substations and the number of transformers are examined. Relevant planning aspects regarding sub-transmission network structures are studied. Some aspects of the planning and design process are described. Quality of service and reliability are treated. An important parameter determining the reliability is the available reserve capacity in the network