Electric Grid Modeling for Distribution Generation Applications
2012 M.Eng. thesis, McGill University
Written by Michael Nicholas George
Chapter 6:
Application Example of Methodology to Feeder
Table 2-1: General features of different distribution system types
Figure 5-1: Geographical representation of rural distribution feeder
This thesis focuses on a specific application example pertaining to a distribution feeder typical for rural Quebec. The feeder supplies about 11 MW of active power. Its nominal distribution line-to-line voltage is 25 kV at 60 Hz. The feeder contains a distributed generator (DG) in the form of a hydroelectric synchronous generator that supplies a constant power of 16 MW. The most distant load is connected to the substation through about 39.8 km of overhead line. The feeder contains an in-line regulator and shunt capacitor bank that provide compensation against voltage drops along the feeder length. The network is unbalanced, comprising a number of both three-phase and single-phase loads, as well as single-phase laterals. Because the DG is generating 16 MW of power and the network is consuming about 11 MW, it can be assumed that, even after considering line losses, it exports power back to the substation and subsequently back to the transmission network.
Figure 5-1 shows a DSAP geographical representation of the distribution feeder, indicating the locations of the substation, DG, regulator, and shunt capacitor. Both the substation and DG are connected to the 25 kV network through their own transformer. The substation transformer is delta-connected at the 120 kV source side and wye-connected on the 25 kV feeder side. The DG transformer is delta-connected at the 4.17 kV generator side and wye-connected on the 25 kV feeder side. Three-phase lines are represented by solid lines, while single-phase lines are represented by dashed lines.
The feeder contains several open switches along the main trunk that allow for interconnection with adjacent feeders (not shown). Some of these switches can be remotely operated, allowing for quick reconfiguration of the distribution system during maintenance operations or in cases of failure within a section.
Data for this feeder is extracted from the DSAP feeder model file. Any additional information that is needed for the benchmark that cannot be found in the DSAP steady-state analysis tool has been obtained from typical values found in analogous distribution systems throughout the literature.
5.1 Loads
Because this feeder is located in a rural area, the distribution of loads tends to be sparse along the length of the feeder. However, the feeder does contain a relatively densely populated area of three-phase and single-phase loads in this system, denoted by the box in Figure 5-1, presumably a small town. This area comprises over 5 MW of loads, about 45% of the total loads serviced by this distribution feeder. Thus, a great deal of load is concentrated within this small area.
Because this model is concerned with the primary feeder of the distribution network, it does not explicitly include the individual distribution transformers and secondary mains that would appear at each of the loads indicated in the model. These components are lumped into their respective constant-power load at their point of interconnection on the medium-voltage side of the distribution transformer, as illustrated in Figure 5-2. Because the time scale of interest in this benchmark is on the order of seconds, the loads can be considered constant values.
2.2 - Elements of a Distribution Feeder
Most rural feeders can be described by a set of components that is universal to this type of feeder arrangement. Table 2-2 lists these components, as well as the parameters that are essential to describing them for the benchmarking work. This framework derives from that used in describing urban and suburban distribution systems for their respective benchmarks. This set of components will form a template from which parameters and other details can be obtained to complete an appropriately descriptive benchmark for the rural feeder in this paper.
Chapter 5 describes the rural feeder that serves as a case study for this benchmarking work. The feeder is described in terms similar to the template outlined in Table 2-2.
Table 2-2: Elements Common in Rural Feeders
