User connection boundaries

When a customer applies in a specific region, several factors are considered before an offer can be generated. The availability of existing substation capacity, ongoing or planned Enabling Works or potential new assets required is assessed to produce an offer. Once the offer is signed and the project progresses through the relevant development stages, specific designs for connection (including siting studies for new assets) are confirmed. 

During development, a specific connection site will be provided.  Each substation site, whether existing or planned, can host multiple connection sites for multiple users.  Within a connection site, points of connection (POCs) will be designated.  These represent the exact points user assets connect to the National Grid.  For example, this could be a bay, or the end of a cable sealing end.

However, several factors can influence the precise boundary, where NGET responsibility ownership and maintenance begins and ends.

User boundary changes in asset type and configuration

Depending on the asset type and its configuration, the boundary between user owned assets and NGET assets may differ.

Air insulated substation (AIS)

AIS assets generally specify user boundary as the busbar clamp, or the end at a cable sealing end, or a disconnector which connects the user from their own equipment into the substation busbars.  Any equipment beyond that and into the substation is the responsibility of NGET. This configuration can differ in terms of the type of connection, for example, a pantograph disconnector is often used with generation connections, but in AIS there is generally a clear point of visual demarcation at which responsibility is transferred.

Gas insulated substation (GIS)

GIS assets can be more challenging. The boundary can be marked by the first busbar gas zone after the user’s busbar selectors, or the boundary may fall at the outgoing circuit gas zone as shown below. 

Generally, as GIS assets are enclosed, it can be more challenging to establish a clear visual boundary.  Isolation and maintenance of assets can also be more difficult, depending on interconnected equipment.  Users may have more complex agreements or more detailed discussions to establish a boundary for GIS assets to reflect their specific requirements.  The complexities of constructing new GIS substations for multiple user connections will also influence the basis of construction and enduring ownership.

User boundary changes according to connection type

Different forms of connection will also often require different user boundaries. This reflects the different infrastructure requirements connection types can need.

Generation/interconnector

Generation connections encompass a wide range of options. They can refer to older centralised plant, such as larger gas generators, or newer wind, solar or battery alongside others. Interconnectors also fall into this category, with more significant infrastructure being present. Generally, however, the requirements for user boundaries are largely similar- being the first point of connection onto the busbars of the substation. This could be through a busbar clamp onto the main or reserve bars, or a moving disconnector.

Demand

Demand as a sector is also subject to significant change. Areas such as data centres alongside larger industrial demand sites require a ramping up of capacity in many areas across the country. User boundaries for these demand assets also vary. Often, NGET construct a sole use connection asset for the demand connection, which is cabled out to the demand user. The user boundary is therefore marked by the disconnector or isolator connecting the low voltage cable into the user site.  Where the user is connecting into a shared NGET substation the user will own assets up to the connection clamp onto the busbar of the NGET substation.

Tertiary connections 

Tertiary connections use a third winding in transformers to accommodate connections of a much smaller capacity, with only 57MW of capacity available, designed for a single user to be connected.  For more information available on user connection configurations and commonly offered types, read more here.  Tertiary user boundaries are on the load side of the transformer, rather than the main busbar side which feeds back into the main substation- and are marked by the isolator or disconnector feeding into the user’s connection.

District Network Operators (DNOs)

DNO connections reflect the fact that distribution and transmission systems are interconnected to supply power to the end consumer. Therefore, NGET will own the connecting assets, up until the boundary point of the connection clamping onto the busbar of the DNO substation- or in the case of a shared NGET substation, the DNO will own the assets up to the connection clamp onto the busbar of the NGET substation.

Why doesn’t NGET own all the connecting assets?

As a transmission owner, NGET must ensure that it operates an efficient and economic network.  Any unnecessary costs incurred could reflect onto the end consumer.  Therefore, any works undertaken for new connections must be carefully considered. If a higher specification of connections asset or additional NGET assets requested by a user, these will be charged back through ‘one-off works’, as these are outside of the general allowances made by Ofgem for works relating to general transmission infrastructure.  One-off works requires that the requesting user pays for the works- so as to not increase the cost to the end consumer.

However, even through the one-off works process, NGET will still undertake ownership of the asset post commissioning.  This means NGET is responsible for maintenance and the liability of the asset- meaning that the undertaking of additional one-off works is always carefully assessed.

Therefore, wherever it is possible to do so- NGET will ensure all options are utilised under standard connection works before undertaking additional one-off works.