Simplified representation of a large transmission network for use in long-term expansion planning

This paper concerns the development of a new approach to the simplification of representation of the spatial dimension of a large transmission network in order that the influences on bulk power transfers can be assessed in a practical way and the main routes that should be reinforced readily identified. The main challenge is to achieve a satisfactory clustering to deliver a number of zones that is small enough to make subsequent analysis of the expansion panning problem manageable but not so small as to neglect key regions of the original system. Two particular methods that have previously been proposed are described: a K-means algorithm and Dodu's mixed integer linear programming based approach. Each of them has some disadvantages, in particular that a direct interface between two zones might be derived that has no equivalent on the real network; or that it is difficult to control the number of zones. Hence, this paper describes a new hybrid method that ensures that resulting zonal delineations make engineering sense from the point of view of physical connections and allow some control over the number of zones. Results are presented in respect of the transmission network in Great Britain. Applications of the simplified network are discussed, not only in long-term planning but also in respect of the potential for use in transmission charging.