This glossary provides clear, succinct explanations of the main technical and administrative terms used to discuss infrastructure projects.

  • Advance public information meeting

    Legally speaking, an advance public information meeting serves as the first official announcement of a project. At such meetings, a draft project is presented in detail and the public are given the chance to put forward their comments and suggestions, which are recorded then analysed as part of the Environmental Impact Study.

  • Alternating current (AC)
    Alternating current is an electric current that changes direction twice per period and carries equal quantities of electricity alternately in one direction, then the other. The current and voltage alternate 50 times per second (50 hertz).
  • Area Plan

    The Walloon Region is covered by 23 Area Plans, adopted between 1977 and 1987.
    The main purpose of the Area Plan is to define land uses at a scale of 1:10000 in order to ensure the harmonious development of human activities and avoid improper use of space.

    In terms of energy, the Area Plan includes the existing and planned route of the grid for major communications and fluid and energy transmission infrastructure.
    When it does not satisfy - or no longer satisfies - the identified needs, an application for a revision of the Area Plan can be submitted to the Walloon Government. This is the case for the Boucle du Hainaut project.

  • Backbone of the grid
    The electricity transmission grid is a meshed grid organised like a fishing net or the railway network. It therefore consists of different voltage levels, each playing a specific role in the transmission of electricity. The backbone of the grid is composed of 380 kV lines enabling the transmission of a large quantity of energy over a relatively long distance. This is the case with the Boucle du Hainaut or Mercator-Bruegel.
  • Basic application
    The basic application is one of the documents of the application for revision of the Area Plan. Its purpose is to present to the Government the arguments justifying the need to revise the Area Plan to implement a project.
  • Bird flight diverter
    Bird flight diverters were designed to make overhead lines visible to birds and thus prevent collisions. They are mainly used on bird migration routes and in protected areas.

  • CCATM: Commission Consultative d’Aménagement du Territoire et de Mobilité (or Advisory Committee on Spatial Planning and Mobility)
    This is a local advisory body allowing the population to participate in the management of the environment in which they live. CCATM is involved in the revision process for the Area Plan since Elia must submit its basic application to the Committee and the CCATM of the municipalities concerned can issue an opinion.
  • Congestion on existing lines
    With the additional production from offshore wind turbines and the opportunities to import energy from France and the United Kingdom, certain lines will not be able to accommodate this new energy. This has the effect of reducing the reliability of the grid and increasing the risks of overload, maintenance frequencies, incidents, etc.
  • Consultation period

    This official citizen consultation period is incorporated as part of the application for revision of the Area Plan, as well as within the context of the planning permit application.

    This period follows on from the Preliminary Information Meeting (or its equivalent in video format). Citizens can ask questions, make comments or propose a reasonable alternative during a period of 15 days.

    These questions, comments or reasonable alternatives will be examined by an independent consulting firm, in the Strategic Environmental Assessment (SEA - as part of an application for revision of the Area Plan) or in the Environmental Impact Assessment (EIA - as part of a request for an application for a planning permit).

  • Converter station
    Converter stations convert alternating current (AC) into direct current (DC).
  • Corridor

    As part of the Boucle du Hainaut project, the corridor represents the incorporation of a geographically defined territory within the Area Plan. This corridor will, in the second phase (planning permit application), make it possible to determine the specific location where the line will be installed.

  • Direct current (DC)
    Unlike alternating current, direct current flows continuously in a single direction. This type of electric current is used in battery-operated devices, for instance.
  • Directional drilling
    This drilling technique tends to be used for underground connections when the urban location so requires, e.g. where the cable route crosses tram tracks, train tracks or navigable waterways, or if there are major obstacles on the cable route. The drilling depth depends on the topology, but is generally between 3 m and 20 m. The diameter of the borehole is between 0.4 m and 1 m.
  • Earth wire

    The earth wire is the topmost cable on an overhead power line. Its purpose is to absorb any lightning strikes and route the lightning to the ground through the pylon.

    The earth wire may serve a number of other purposes:

    • evacuating some of the fault current in the event of a fault;
    • transmitting data between substations, if it contains optical fibres.
  • Electromagnetic field
    Electromagnetic fields are characterised by the frequency and wavelength of the radiation generated by their propagation. The frequency and wavelength of electromagnetic radiation are inversely proportional: the higher the frequency, the shorter the wavelength.
  • Environmental permit
    An environmental permit is a permit allowing certain types of activities to be carried out and/or certain facilities to be operated. By way of example, Elia needs to apply for an environmental permit whenever it wants to build a high-voltage substation.
  • Étude d’Incidences sur l’Environnement (EIE)
    The EIE is a study carried out before a permit application is submitted. It is used to gauge the probable effects of the project on the environment, justify the option that was selected and describe the measures that will be taken to eliminate, reduce or compensate for any damage that may be caused by the project. The study is submitted along with the permit application.
  • Évaluation Appropriée des Incidences sur l’Environnement (EAI)

    The EAI checks that a project does not harm the biodiversity of Natura 2000 sites or other nature conservation areas and does not jeopardise the conservation targets that were set for these locations. An EAI may also specify which compensatory measures should be taken to offset any damage caused, and may set out guidelines to be observed while work is being carried out.

  • Federal Development Plan
    The Federal Development Plan is an official document that is binding for Elia and is approved by the Minister of Energy. It sets out the programme of investments that the grid operator has committed to implement in response to the needs identified. It takes account of the need for adequate reserve capacity and factors in projects of common interest designated by the institutions of the European Union in connection with trans-European systems. The FDP focuses on upgrading and expanding the domestic grid, expanding the offshore grid, and upgrading and expanding interconnectors.
  • Future Grid

    Future Grid is a strategic project included in Elia’s Federal Development Plan. Specifically, it encompasses major infrastructure projects to meet the challenges of the energy transition:

    • Development of the main 380 kV electricity transmission grid with, in particular, the creation of a corridor between Avelgem and Courcelles (Boucle du Hainaut) and a corridor between Stevin and Avelgem (Ventilus);
    • Development of interconnectors;
    • Connexion and integration of offshore wind power.
  • Grid disruption
    In order to ensure a sustainable, reliable and accessible grid, grid disruptions must be kept to a minimum. Numerous elements can, in practice, disrupt the grid: an overload, maintenance, a technical incident, etc.
  • GRUP
    Abbreviation for Gewestelijk Ruimtelijk Uitvoeringsplan, Regional Spatial Implementation Plan. A plan in which the Flemish Region regulates what may or may not be built or renovated for an existing area. It thus gives a land destination to a particular plot or group of plots and shows how an area can look in the future.
  • High-voltage connection
    Just like the transport network, the high-voltage grid is made up of different kinds of ‘roads’ for electricity. Each type is associated with a different voltage level. We draw a distinction between overhead lines and underground cables, which are connected to one another through high-voltage substations. High-voltage lines are also known as conductors, because they carry energy from one point to another.
  • High-voltage grid
    The high-voltage grid can be compared to a network of electricity highways. Elia uses the high-voltage grid to transmit electricity from power producers to large industrial customers and distribution systems. The distribution systems, in turn, transmit it to end consumers (i.e. homes, businesses, and so on).
  • High-voltage substation

    A high-voltage (HV) substation is a central point to which various grid components are connected. These components may be connected to one another through a system of busbars, with the exact arrangement being determined by the company. A grid component may be: a high-voltage line or cable, a transformer (bay), a capacitor bank, or a busbar.

    There are two types of high-voltage substation:

    • Air-insulated substations (AIS): AIS facilities with voltages of 380 kV to 36 kV are generally located in the open air, while substations with lower voltages are usually located inside buildings.
    • Gas-insulated substations (GIS): in this type of substation, all the functional components are placed inside a fully shielded enclosure, which is insulated with gas (usually SF6). Since this gas has a far greater insulating capacity than air, GIS facilities can be much more compact and take up far less space.
  • Junction
    When building an underground connection, junctions between the sections of cable are needed at fairly regular intervals (every 500 to 800 m) along the entire route. Junction equipment takes up far more space than the cables themselves: junction trenches can be up to 15 m long and 3 m wide.
  • Junction trench
    When a cable is laid, it is not all laid at once, but rather in sections measuring around 1 km. The process of joining up these sections of cable is sometimes known as ‘jointing’. The junction trench is the place where two cable sections are joined.
  • Landing location
    The location where the cables from the offshore wind farm can arrive at land. 
  • Meshing
    In a meshed network, high-voltage substations are always connected to other high-voltage substations via multiple connections. Meshing ensures that the failure of one connection does not affect the security of supply. Meshing is also called looping.
  • Microtunnelling

    This technique is used for underground connections. It is applied when several connections are to be laid in the same location, or when directional drilling cannot be used for technical reasons (e.g. when the cable needs to pass through schist and there is a risk that the borehole will be unstable).

  • Note d’Évaluation des Incidences sur l’Environnement (NEIE)
    The NEIE evaluates how a project may impact the environment in the broadest sense (e.g. soil and subsoil, water, air, energy and climate, biological environment, landscape, urban and spatial planning, mobility and transport, waste, health and safety, socio-economic aspects) and issues recommendations.
  • Open trench

    A standard open trench is the most common form of excavation in the world.

    Trenches are usually dug at a width of around 0.65 m per circuit, depending on the depth. Cables are laid at a depth of around 1.2 m. Once the cables have been laid, the trench is filled in with a special type of backfill material (such as dolomite) so as to maintain the thermal conductivity of the cables by evacuating the heat generated by energy transmission. When laying the cables, work areas measuring 6 to 15 m across must be used, depending on the number of connections and the cable type. There are junctions every 500 to 800 m, depending on the length of the cable sections

  • Overhead connection
    Overhead connections consist of metal three-phase transmission lines, supported by pylons or masts.
  • Phase-shifting transformer
    Unlike transformer substations, phase-shifting transformers do not transform electricity from one voltage level to another. Phase-shifting transformers operate at a consistent voltage level, regulating the flow of electricity on the grid. They can determine the direction and size of energy flows.
  • Plan-MER
    The plan-MER analyses the potential effects of certain activities or procedures on humans and the environment. It is an integral part of a regional land-use plan (“GRUP”). It is drawn up before a plan is finalised or a project is implemented. Its purpose is to assess the impact on humans and the environment at an early stage so that the necessary measures can be taken.
  • Planning permit
    A planning permit is a permit issued by the relevant administrative authority to allow the work required for a project to go ahead. The permit application procedure differs from one region of Belgium to another.
  • Preliminary scoping
    The preliminary scoping is, as its name indicates, a preliminary step before the legal procedures that Elia carries out.
    This preliminary phase consists of carrying out in-depth technological and territorial studies. These are aimed at identifying the corridor that best meets the needs of the project, while taking into account the territorial context. This step also makes it possible to initiate numerous discussions with all parties affected by the project.
    At the end of this scoping phase, Elia is able to propose an initial draft corridor to be included in the Area Plan.
  • Price convergence
  • Public consultation
    When a permit application is submitted for a project, a public consultation is held. Local residents can review the full planning permit application file and have 30 days to submit their comments to the municipal authorities.
  • Road permit
    A road permit application must be submitted for work that will occupy the public space, be it under ground or in the air. This type of permit allows work to be carried out by the roadside or on public land.
  • Route
    The route defines the precise location where the infrastructure will be installed. It results from the planning permit application.
    Specifically, it concerns the location of the pylons within the corridor which will be defined beforehand following the application for revision of the Area Plan.
    It must therefore not be confused with the corridor, which is considered at Area Plan scale and is determined during the Area Plan revision application phase.
  • SEA - Strategic Environmental Assessment
    This is a study carried out by a consulting firm approved by Wallonia to examine the impact of a draft application for revision of the Area Plan on the environment in the broad sense of the term: fauna, flora, etc.
  • Substation location
    The location where the high-voltage substation may possibly be located. This high-voltage substation forms a node at which the electricity arrives and is then distributed further.
  • Three-phase transmission line
    A three-phase transmission line is the set of three transmission cables making up a three-phase overhead line. Depending on the voltage level, there may be one, two, three or four three-phase transmission lines, each of which may consist of several high-voltage lines or conductors.
  • Transformer substation

    High-voltage transformer substations are the points at which connections are made with the electricity grid. They transform the electricity’s voltage level to enable a connection.

  • Transition substation
    A transition substation is an electrical substation that acts as the transition point between an underground connection and an overhead connection.
  • Underground connection

    Underground connections mainly consist of:

    • the high-voltage cables required to transmit energy (usually three – one per phase);
    • the junctions connecting the sections of cable (usually one every 500 to 800 metres);
    • the terminal boxes (or cable ends) connecting the cable to the equipment in the high-voltage substation. 
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