"In the early history of commercial electricity in heavy load density areas, the d.c. Edison Network was developed extensively. As far as reliability is concerned it is exceeded by no system. At the present time it has been developed to the extent of automatic and non-automatic converters, motor-generator sets, booster sets and storage battery reserve capacity.
This type of network is fed from several substations in the area at utilization voltage.
As load densities have increased, the large amounts of copper required, the cost of substation sites and large rotating conversion equipment have made the expansion of the d.c. Network economically prohibitive. Also, since these substations are inherently noisy, it has become increasingly more difficult to find suitable substation sites.
With these disadvantages in mind, a similar a.c. Network suggests itself as a replacement for the high-cost d.c. system, due to the comparative compactness and quietness of operation of transformers, and the fact that low-loss high voltage feeders may be brought into the network area from more distant substations.
The Secondary Network (Figure 1) is an interconnected low-voltage system forming a grid in which common mains are fed from a number of sources throughout the area. Network systems are employed generally only where load densities are forming a complete mesh over the area. The mains operate at utilization voltage from which consumer taps are taken. The secondary network is fed by three or more feeders through transformers and network protectors. These feeders may, and often do, operate at sub-transmission voltages. They can come from either a generating station, a bulk power substation or a distribution substation. By using three or more feeders the network can be kept in operation and the load maintained over the other feeders when one feeder is out of service. By interlacing the feeders, as indicated in Figure 1, better load distribution is obtained under such abnormal conditions.
This paper will consider an ideal condition only, covering one square mile of area, with uniformly distributed loads of 10,000, 20,000, 30,000, 50,000, arid 75,000 Kva peak load per square mile. This idealization will serve to determine the average data for actual systems.
This network will be similar to that of Figure 1, inasmuch as three feeders will be employed with complete interlacing. However, transformers will also be located at intervals other than that shown, with corresponding changes in lateral feeders. There will be one hundred and eighty secondary main sections, each six hundred feet in length, regularly spaced as indicated.
The load density and the distribution of load will influence the location and capacity of the network transformers.
In general, the larger the transformer, the lower the cost per Kva, and the wider the spacing of transformers in the network, resulting in a reduction in the length of primary feeder required. However, as the spacing is increased, the secondary mains must be increased in size in order to prevent excessive voltage drop, and to provide sufficient current carrying capacity, the same being true of the feeders.
Therefore, the ideal size of transformer is one which will not only provide sufficient capacity to carry the required load; but also result in a minimum total cost of secondary main, primary feeder, duct, automatic protector and transformer"--Introduction, pages 1-3.
Lovett, I. H.
Electrical and Computer Engineering
M.S. in Electrical Engineering
Missouri School of Mines and Metallurgy
v, 72 pages
© 1951 Charles F. Cromer, All rights reserved.
Thesis - Open Access
Electric power distribution -- Economic aspects
Electric power systems -- Load dispatching
Electric power systems -- Mathematical models
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Link to Catalog Record
Cromer, Charles F., "Economic analysis of secondary distribution networks" (1951). Masters Theses. 3047.