In electricity distribution networks, spot network substations are used in interconnected distribution networks. They have the secondary network (also called a grid network) with all supply transformers bussed together on the secondary side at one location. Spot networks are considered the most reliable and most flexible arrangement of connecting power to all types of loads. Switching can be done without interrupting the power to the loads.

Description

Electricity distribution networks are typically of two types, radial or interconnected. A radial network leaves the station and passes through the network area with no connection to any other supply. This is typical of long rural lines with isolated load areas. In general, the radial distribution network has more power failures than the interconnected distribution networks.

Urban [Spot] network substations can be used to make the interconnected distribution networks to serve a single campus or facility. Examples of such single campuses and facilities include airports, hospitals, major data processing centers (especially those using uninterruptible power supply), and sports arenas that regularly broadcast nationally televised events.

EPRI lists urban network supply systems has having Momentary and Long-duration Interruptions on 50 year intervals .

In large cities, many electric utility companies use grid feeders to make interconnected distribution networks to serve the downtown core. The interconnected network has multiple connections to the points of supply.

Reverse current relays are used to detect any open circuits that are letting the electrical current flow back towards its source.

Examples

A local spot network of 2 to 8 primary transformers can be connected to the same secondary buss to provide reliable power to a particular facility, like a large hospital or computer and major data processing center. St. Jude Children's Research Hospital in Memphis, Tennessee has 8 primary transformers that are connected to the same secondary bus. The FedExForum(home of the NBA Grizzlies basketball team) in Memphis has a network of 4 primary transformers connected to the same secondary buss. In some arrangements with 4 transformers, any of the 4 transformers can carry all of its connected loads. The Toronto Pearson International Airport is electrically fed by 4 grid feeders, each capable of carrying the entire 20+ MW load.

References

External links

• NIH Design Policy and Guidelines
• Single Line Diagram of 3 Primary Feeders and 1 Emergency Feeder, Page 518 of 713
• Distributed Resources on Spot Networks at ComEd
• General Electric Company Network Transformers
• Consolidated Edison Company of New York, Third Generation, page 7