![Spot Network](https://upload.wikimedia.org/wikipedia/commons/7/74/Spot_Network.svg)
In
electricity distribution
Electric power distribution is the final stage in the delivery of electric power; it carries electricity from the transmission system to individual consumers. Distribution substations connect to the transmission system and lower the transmissio ...
networks, spot network substations (network transformers) are used in interconnected distribution networks. They have the secondary network (also called a grid network) with all supply
transformer
A transformer is a passive component that transfers electrical energy from one electrical circuit to another circuit, or multiple circuits. A varying current in any coil of the transformer produces a varying magnetic flux in the transformer' ...
s 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 arranges the station and branches like a tree 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.
In a
secondary network
A low-voltage network or secondary network is a part of electric power distribution which carries electric energy from distribution transformers to electricity meters of end customers. Secondary networks are operated at a low voltage level, which ...
the transformers are distributed across an area (e.g. in streets) and have multiple supplies. The transformers are wired together on the secondary side. The system is arranged so that nearby transformers do not use the same feeder. In case of an issue with a feeder (or transformer) the load is fed by nearby transformers, so there is no interruption, although a voltage drop for said load may then be present. A fault on the secondary side may cause damage to the transformers before the primary-side protection system detects and clears the fault.
A spot network is basically a secondary network condensed to a point. Several transformers have multiple supplies and their secondaries are bussed together. Besides a region-wide
blackout, they are vulnerable to a bus fault, which is extremely rare. The simplest case is where each transformer connects to one feeder and vice versa ("unit system"). High-voltage switching can be used to handle more cases, e.g., working transformer but faulty feeder or the reverse.
Network protector
A network protector is a type of electric protective device used in electricity distribution systems. The network protector automatically disconnect its associated distribution transformer from the secondary network when the power starts flowing i ...
s, (reverse current relays), are used to detect any open circuits that are letting the electrical current flow back towards its source.
Examples
In large cities, many electric
utility companies
A public utility company (usually just utility) is an organization that maintains the infrastructure for a public service (often also providing a service using that infrastructure). Public utilities are subject to forms of public control and ...
use grid feeders to make interconnected distribution networks to serve the downtown core. The interconnected network has multiple connections to the points of supply. Some of New York City's downtown areas are powered by submersible network transformers of 500 to 2,500 kVA. Usually these transformers are in vaults below metal grates in the sidewalks.
Urban (spot) network transformer substations can be used to make interconnected distribution networks to serve a single facility. These substations may consist of two to eight or more primary transformers connected to the same secondary bus to provide reliable facility power. Examples of such single facilities include airports,
hospitals
A hospital is a health care institution providing patient treatment with specialized health science and auxiliary healthcare staff and medical equipment. The best-known type of hospital is the general hospital, which typically has an emerge ...
, major data processing centers (especially those using
uninterruptible power supplies
An uninterruptible power supply or uninterruptible power source (UPS) is an electrical apparatus that provides emergency power to a load when the input power source or mains power fails. A UPS differs from an auxiliary or emergency power system ...
), and sports arenas that regularly broadcast nationally televised events.
St. Jude Children's Research Hospital in
Memphis, Tennessee
Memphis is a city in the U.S. state of Tennessee. It is the seat of Shelby County in the southwest part of the state; it is situated along the Mississippi River. With a population of 633,104 at the 2020 U.S. census, Memphis is the second-mos ...
has eight primary transformers that are connected to the same secondary bus. The
FedExForum
FedExForum is a multi-purpose arena located in Downtown Memphis, Tennessee. It is the home of the Memphis Grizzlies of the NBA and the NCAA Division I men's basketball program of the University of Memphis, both of whom previously played home ...
in Memphis has a network of four primary transformers connected to the same secondary bus. In some arrangements with four transformers, any of the transformers can carry all of its connected loads. The
Toronto Pearson International Airport
Lester B. Pearson International Airport , commonly known as Toronto Pearson International Airport, is an international airport located in Mississauga, Ontario, Canada. It is the main airport serving Toronto, its metropolitan area, and the surr ...
is electrically fed by four grid feeders, each capable of carrying the entire 20+ MW load.
Toronto Pearson International Airport, see page 13 of 15
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References
{{Reflist
External links
EATON , Spot Network Equipment
General Electric Company Safe-NET Network Transformers
Siemens , POWER PRODUCT Technical , October 2019 , See Figure 7. Simple Spot Network System
NIH Design Requirements]
High containment (BSL-3/ABSL-3) facility electrical design , different primary substations or by one double-ended utility substation
KINECTRICS INC - page 125 , 33. Network Transformers , Asset Depreciation Study
for the Ontario Energy Board
Electric power distribution