Electric Grid Modeling for Distribution Generation Applications
2012 M.Eng. thesis, McGill University
Written by Michael Nicholas George
Chapter 2:
Characteristics of Typical Distribution Feeders
2.1 - Characterization and Classification
Distribution systems vary among geographic areas. The biggest differences in topology and operational philosophies are between systems in North America and those in Europe. These differences are related to grounding configuration, the share of lines comprised by the primary and secondary levels of the distribution system, phasing, and nominal frequency (50 Hz vs. 60 Hz systems).
In Canada, distribution systems are classified into three distinct categories – urban, suburban, and rural. These categories are distinguishable by their voltage levels, topology, loading, and protection scheme. Table 2-1 highlights these characteristics. Distribution feeders can be further classified into overhead and underground feeders, depending on the type of layout used. Overhead feeders are typically used for rural distribution, while underground construction is more common in high-density urban systems.
Table 2-1: General features of different distribution system types
Rural feeders have a number of features that distinguish them from the urban and suburban types. Because they serve a relatively large geographical area, their topologies feature long backbones with a large number of laterals. Because power is traditionally delivered over a greater length of overhead lines, higher voltage levels are used in order to mitigate losses. The associated voltage drop in these long lines is typically compensated by at least one in-line voltage regulator. The geographical vastness and the sparseness of loads of such feeders justify the design and operational differences in such feeders.
Because of the fundamental differences between each type of distribution system, the benchmark feeders generated by the methodology presented in this thesis will be confined to rural feeders consisting of overhead lines in a radial layout. Rural feeders are suitable candidates for DG integration for several reasons. Many DG’s are located at sites away from major population centers in order to avoid problems with pollution (in the case of fuel-burning microturbines) or noise pollution (in the case of wind turbines). Additionally, reclosing protective devices are found exclusively on rural overhead feeders and pose a risk to DG out-of-phase reclosing in the case of a temporary fault and temporary island scenario. Because rural feeders are typically radial and do not redundant service paths during contingencies, DG integration provides a great deal of potential improvement in the reliability of service provided to customers. For these reasons, rural feeders will be the focus of these benchmarking efforts.