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substation is a part of an electrical generation, transmission, and distribution system. Substations transform voltage from high to low, or the reverse, or perform any of several other important functions. Between the generating station and consumer, electric power may flow through several substations at different voltage levels. A substation may include transformers to change voltage levels between high transmission voltages and lower distribution voltages, or at the interconnection of two different transmission voltages.

Substations may be owned and operated by an electrical utility, or may be owned by a large industrial or commercial customer. Generally substations are unattended, relying on SCADA for remote supervision and control.

There are four major types of electric substations. 

1.      switchyard at a generating station

2.      customer substation

3.      system station

4.      distribution station

Generating Station Switchyards

The first type is the switchyard at a generating station. These facilities connect the generators to the utility grid and also provide off-site power to the plant. 

  • Generator switchyards tend to be large installations that are typically engineered and constructed by the power plant designers and are subject to planning, finance, and construction efforts different from those of routine substation projects.
  • Because of their special nature, the creation of power plant switchyards will not be discussed here, but the expansion and modifications of these facilities generally follow the same processes as system stations.

Customer Substations

The second type of substation, typically known as the customer substation, functions as the main source of electric power supply for one particular business customer.

  •  The technical requirements and the business case for this type of facility depend highly on the customer’s requirements, more so than on utility needs.

System Stations

The third type of substation involves the transfer of bulk power across the network and is referred to as a system station. Some of these stations provide only switching facilities (no power transformers) whereas others perform voltage conversion as well. 

  •  These large stations typically serve as the end points for transmission lines originating from generating switchyards and provide the electrical power for circuits that feed transformer stations. 
  •   They are integral to the long-term reliability and integrity of the electric system and enable large blocks of energy to be moved from the generators to the load centers. 
  •  These system stations are strategic facilities and usually very expensive to construct and maintain.

Distribution Substation

The fourth type of substation is the distribution station. These are the most common facilities in power electric systems and provide the distribution circuits that directly supply most electric customers.

  •  They are typically located close to the load centers, meaning that they are usually located in or near the neighborhoods that they supply, and are the stations most likely to be encountered by the customers.
  •  Depending on the type of equipment used, the substations could be

o    Outdoor type with air-insulated equipment

o    Indoor type with air-insulated equipment

o    Outdoor type with gas-insulated equipment

o    Indoor type with gas-insulated equipment

o    Mixed technology substations

o    Mobile substations

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