Ten Year Network Development Plan (TYNDP)

The Ten Year Network Development Plan (TYNDP) is prepared by ENTSO-E every two years. It applies throughout the European Community, is non-binding and is intended to ensure greater transparency surrounding the necessary expansion of the entire EU transmission grid. See also:

Tertiary control (minutes reserve)

Tertiary control is manually activated by the transmission system operators (TSOs) to support the secondary control. Suppliers must provide tertiary control within fifteen minutes of it being demanded by adjusting the power input from power plants or the power withdrawal of adjustable consumption loads.

Three-phase current

Three-phase current – also known as three-phase alternating current, rotary current or simply three-phase AC – refers to three separate alternating currents of the same frequency with a fixed phase separation to one another of 120°. The German extra-high voltage grid is operated using three-phase alternating current technology, with the exception of the high voltage direct currency transmission (HVDC) lines.

Three-phase system

Three related electrical conductors insulated from each other and the environment for the transmission of three-phase alternating current (three-phase current).

Transformer platform

An offshore structure to house the transformers and other offshore components of the grid connection concept, including all secondary installations.

Transformer station, substation

A transformer station, also known as a substation, is a component within the electricity grid that is used to connect grids with different voltage levels (e.g. 380 kV and 110 kV) via transformers. Similarly, these facilities can also be used to connect different sections of the same voltage network with one another or to switch certain sections off. In such cases, the term switchgear is used.

Transient responses

Transient responses occur as the system state changes to a different state, for instance as a result of changes in loads, feed-in or grid topology. As long as no limits are exceeded and the transient response subsides quickly enough, the overall operation of the system is not affected.


Transits are the transmission of power through a grid. Transits are the balance of a grid’s imports and exports.


Transmission refers to the technical and physical process of the simultaneous feed-in of electrical power at one or more transfer points and a corresponding withdrawal of electrical power at one or more other transfer points in a grid.

Transmission grid

The transmission grid transports electricity over large distances. It consists of high voltage lines and additional technical equipment. See also distribution grid.

Transmission System Operator Security Cooperation (TSC)

The “TSO Security Cooperation” (TSC) is a cooperation framework currently comprising 14 European transmission system operators (TSOs) with the goal of further increasing the security levels of the extra-high voltage grid in central Europe. The partners of the TSC are responsible for the energy supply of 170 million Europeans. The initiative includes a permanent security committee, works with a real-time information system (Real-Time Awareness and Alarm System, RAAS) and uses a shared IT platform. Information and safety calculations are made available to all participants equally using this platform. The TSC makes it possible for TSOs to better coordinate their work. This is especially helpful for the integration of energy from renewable sources and for improving the cross-border trade and transport of energy. See also

Transmission system operators (TSOs)

Operators of transmission networks are natural persons, legal entities or legally dependent organisational units of an energy supply company, who are tasked with the transmission of electricity and are responsible for the operation, maintenance and any necessary expansion of the transmission network in a defined area as well as the connection lines to other networks where necessary.