The following terms are generally used by National Grid in relation to its transmission equipment:
cable
An insulated conductor designed for underground electricity transmission or distribution.
Central Electricity Generating Board (CEGB)
Until March 1990, the CEGB was responsible for the generation of electricity in bulk and the transportation of this power through a nation-wide transmission system called the national grid to the then Area Boards.
circuit
Term used to describe specific electrical paths on the transmission system. i.e. Overhead Line.
conductor
Wire strung between pylons, used for transmitting electricity.
damper
Metal devices fixed to insulators to avoid conductor damage in windy conditions which can cause vibration of the conductors.
development plan documents
Planning documents prepared by local planning authorities in England to outline key development goals of their local development frameworks. DPDs cover the core strategy for the area, a proposals map and site-specific development allocations.
earth wire
Wire strung between the tops of pylons, used for lightning and system protection. May also be used to carry telecommunication signals.
electricity lines
Either an overhead line or an underground cable used to transmit electricity.
EMFs
Electric and magnetic fields (EMFs) are produced by any electrical apparatus, including domestic appliances and overhead power lines.
flashover
A disruptive electrical discharge between equipment at phase voltage and earth, or between two phases, including breakdown across the surface of an insulator as well as sparkover through air.
high voltage
275,000 volts and over. National Grid’s transmission lines generally operate at 275,000 volts and 400,000 volts. Lower voltage lines, such as 132,000 volts and 33,000 volts are generally owned by local distribution companies.
insulator
Used to attach the conductors to the pylons preventing electrical discharge to the steelwork. Usually made from porcelain or glass units, joined together to form an insulator string.
kV
Kilovolt (one thousand volts).
local distribution companies
Generally own and operate lines with a voltage of 132,000 volts and below and supply electricity to homes and businesses.
MW
Megawatt (one million watts or one thousand kilowatts).
outage
The withdrawal from service of any part of the transmission system for a period of time in connection with repair, maintenance, or construction of the transmission system as a result of breakdown or failure.
permanent easement
Legal right in perpetuity granting National Grid the right to install, use and maintain its equipment. A permanent easement is granted in exchange for a one-off capital payment. Also known as a Deed of Grant of Easement.
pylon
See tower.
refurbishment
Repair and renewal of conductors, earthwire, fittings and insulators and where necessary remedial works to the tower and foundations.
route mile
The length, measured in miles, of the transmission line which connects two or more points on a transmission system, irrespective of the number of circuits of which the line is comprised.
spacer
Metal device which maintains conductor separation at intervals along the span between pylons.
substations
Transforming or switching stations to control the voltage and direction of electricity. Transforming stations are used to increase the supply of electricity (to 275 kV or 400 kV) into the national grid system for transmission, and to reduce the voltage to lower levels (to 132 kV) for distribution by the local distribution companies. Switching controls the direction of electricity and ensures fault protection.
system security
The ability of a transmission or distribution system to withstand a disturbance and/or the loss of certain circuits.
tower
Overhead line structure used to carry overhead electrical conductors, insulators and fittings. They are commonly known as pylons and are of a lattice steel construction. See Appendix II.
Wayleave agreement
A licence granted by the owner and occupier of land giving National Grid the right to install, use and maintain its equipment. Terms of the Wayleave Agreement provide for the annual rental and compensation payments to be made.