Glossary T to Z


Terawatt (TW) - One thousand gigawatts

Transformer - A device for changing the voltage of alternating current.

Transmission - The act or process of transporting electric energy in bulk.

Transmission and distribution (T&D) losses - Losses that result from the heating effect of current as it flows through wires to travel from the generation facility to the customer. Because of losses, the electricity produced by the utility is greater than the electricity that shows up on the customer bills.

Transmission and distribution (T&D) system - An interconnected group of electric transmission lines and associated equipment for the movement or transfer of electrical energy in bulk between points of supply and points at which it is transformed for delivery to the ultimate customers.

Transmission lines - Heavy wires that carry large amounts of electricity over long distances from a generating station to places where electricity is needed. Transmission lines are held high above the ground on tall towers called transmission towers.

Transmission network - the electricity transmission system operating at voltages above 132kV (in England and Wales) and including 132kV in Scotland)

TSO, TNO – (Electricity) Transmission System (or Network) Operator


Upgrade - Replacement or addition of electrical equipment resulting in increased generation or transmission capability.

Utility - A regulated vertically-integrated electricity company. "Transmission utility" refers to the regulated owner/operator of the transmission system only. "Distribution utility" refers to the regulated owner/operator of the distribution system which serves retail customers.


Volt – the unit of electrical potential. It is the electromotive force which, if steadily applied to a circuit having a resistance of one ohm, will produce a current of one ampere.

Volt-amperes - The volt-amperes of an electric circuit; the mathematical product of the volts and amperes. Equals the power in a direct current circuit.

Voltage - Measure of the force of moving electrical energy.


Watt - The electrical unit of power or rate of doing work. One horsepower is equivalent to approximately 746 watts.

Watt-hour - One watt of power expended for one hour.


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