Distribution interconnections

We continue to receive numerous requests from local distribution companies (LDC’s) for new transmission to distribution (T-D) interconnections. These interconnection requests generally are categorized into one of four different types of projects: 

Constructing new T-D substations

This type of interconnection typically involves constructing a new T-D substation to serve normal load growth. They are usually located adjacent to an existing transmission line which is tapped or looped into the new substation. However sometimes, from a Best Value Planning perspective, the optimum site for the new substation cannot be located adjacent to the transmission line and we are required to construct a transmission line to the new substation site. In these instances, it may require a single circuit transmission tap to the new substation, or it may require a new transmission line from two existing substations to form a new network line. Depending on the redistribution of the load and type of new interconnection, the transmission system performance may not be materially impacted. However, a new network line may have a greater impact on the transmission system performance than just connecting a new substation to existing lines. 

Adding T-D transformers at existing substations

This type of interconnection involves expanding an existing T-D substation to accommodate a new T-D transformer. Typically, this type of interconnection is a way for a distribution company to increase capacity, allowing it to lower the loading on existing T-D transformers to meet increasing customer demand and/or to improve reliability by providing redundancy. The addition of the new T-D transformer may require transmission system reinforcements depending on how the distribution of load affects transmission system performance. 

Replacing existing T-D transformers at existing substations or substation rebuilds

This type of project is not technically a new interconnection since it is typically just an increase in the transformer capacity to reliably serve increasing customer demand. This type of project may also include increasing reliability by replacing old infrastructure and/or equipment at an existing substation. This type of project typically does not materially affect transmission system performance. 

Economic development projects

This type of project is designed to accommodate a large new load. These may include a new industrial load or an existing industrial load that is expanding their operation. Distributed generation is also included in some of these requests. Depending on the amount of generation and the load pocket it is connecting to, the transmission system may absorb some of the generation during part or all of the year. There may be a need for transmission system reinforcements, or a new substation, to reliably serve the new load.

A list of T-D interconnection requests that have been or are being jointly evaluated between ATC and each LDC is available on ATC’s Web site: www.atcllc.com/customer-relations/connecting-to-the-grid/.