Brinsworth to High Marnham Substation: Frequently asked questions

Here you’ll find answers to some of the most frequently asked questions.

Please let us know if you have any further questions by emailing [email protected] or calling 0800 279 3408.

Why do we need this project?

The Government’s commitment to Net Zero by 2050 and the transition to cleaner sources of energy means a large amount of new generation capacity is planned to connect to the network. The existing transmission network was not originally designed to accommodate such large volumes of generation capacity and it will require significant reinforcements in the form of new substations and transmission circuits. Before building new lines, we look first at whether we can deliver more power carrying capability from the existing network by uprating or upgrading parts of it.

Each year the Electricity System Operator (ESO) considers what network reinforcements might be required and makes recommendations about those in their Network Options Assessment (NOA) report. Through that process, a need has been identified for a 400 kV upgrade of the Brinsworth to Chesterfield double circuit and the Chesterfield to High Marnham double circuit as well as new High Marnham, Chesterfield 400 kV substations and an extension or new Brinsworth 400kV substation.

Delivering this work will ensure that more low-carbon energy can get to homes and businesses in the Midlands and further afield. Doing so means we are able to get the most out of the existing network  and keeping electricity bills as low as possible for consumers, whilst carrying more power on the network.

What is a substation?

A substation is a piece of electrical equipment in an electric power system through which electrical energy is passed for transmission, transformation, distribution or switching.

What does ‘uprating’ on this project mean?

We are uprating by changing the operating voltage from 275kV to 400kV. We are retaining the existing conductors, which are already insulated to 400kV specification.

When will I get my say on the project?

Yes, we will be consulting local people where works are planned, most likely toward the end of 2023 when we will have more information to share. We want to listen carefully to the views of local people so that questions and concerns can be addressed before we apply for planning permission for the new substations.

What planning permission is required?

For the uprating of the existing overhead line, the route was originally consented as a 400kV transmission line in the 1960s and towers are built for 400kV operation, but the route currently operates at 275kV.

The new substations require consent under the Town and County Planning Act 1990.We have started our initial conversations with the Local Planning Authorities (LPAs).

Section 37 Consent applications will also be required for the overhead line connections into the new substations.

When is construction planned and when will it finish?

The project has a planned construction start date of Q2 2026 to meet the government’s 2030 net zero commitments.

What will the impact be on local traffic?

As we develop the proposals for the project we will consider potential effects on local traffic and will provide information on this at our consultation. We will also prepare an Outline Construction Traffic Management Plan. This will set out the good practice measures proposed to further reduce impacts on the local road network and traffic. It will include measures providing clear signage to make sure our construction traffic uses the agreed routes and construction workers using public transport and car sharing where practicable. We emphasise to our employees and contractors the special care that they need to take when driving to and from the areas we are working in.

For the safety of members of the public and our contractors we may need to close some public rights of way and roads temporarily when carrying out work. We will seek to provide alternative diversions and to keep the closure as short as practicable. The closures and any required diversions will be agreed with the local authorities and clearly communicated to local people.

Will the new substations be noisy?

We will fully assess the potential for noise impact of the new substations on surrounding residential areas and ensure the design incorporates the appropriate noise mitigation measures, as a result we anticipate that any change in noise emissions due to the operation of the new substations will be fully controlled and minimised.  National Grid will discuss any local requirements with the relevant planning authorities to ensure the appropriate environmental surveys and noise assessments are carried out.

Will uprating make the line noisier?

The existing overhead line is already amongst the quietest that National Grid operates anywhere in England and Wales, and many lines of this type already operate at 400 kV without any concerns regarding noise. While noise from the overhead line may increase following the voltage uprating, we do not expect the increase to be significant. National Grid recognises that people living very near to the overhead line might have concerns regarding noise.  If you have questions, please contact the project team.

What are electric and magnetic fields (EMFs) and are they safe?

EMFs are electric and magnetic fields. Electric fields are produced by voltage and magnetic fields by current flowing through a conductor. Overhead infrastructure is a source of two fields: the electric field (produced by the voltage) and the magnetic field (produced by the current).

National Grid takes the issue of health very seriously and relies on authoritative and independent scientific organisations, such as the World Health Organization (WHO) and the UK Health Security Agency (UKHSA), to review the worldwide body of scientific evidence on electric and magnetic fields (EMFs) and health, as well as reviewing the science ourselves. 

Health considerations are given a high priority in the process by which we arrive at any proposals for new routes for electricity connections. Our approach is to ensure that all our assets comply with the guidelines set by Government on advice from the UK Health Security Agency (UKHSA). A vast amount of research has been done into the possibility of health effects, without establishing any risks below these levels. 

Will uprating alter the electric and magnetic fields (EMFs)?

Increasing the voltage of the overhead line will increase the electric field, but we ensure these remain within the safe levels set by Government. The magnetic field will be largely unchanged by the voltage increase, because a similar current will flow before and after the voltage increase.  Both the electric and magnetic fields are highest directly under the overhead line but reduced very quickly as you move away from the line. More information on EMFs from these types of overhead lines can be found at