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 network. The TYNDP 2014 identifies the necessity to invest approximately 150 billion euro in the optimisation and expansion of around 50,000 km of extra-high voltage power lines in 100 investment projects throughout Europe. Approximately 80% of the projects identified either directly or indirectly support the integration of renewable energy sources.

Tertiary control (minutes reserve)

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

Three-phase electric power

Three-phase electric power – also referred to as three-phase alternating current, rotary current or simply three-phase AC – is a term used in electrical engineering to indicate a type of polyphase alternating current comprising three separate alternating currents or alternating voltages of the same frequencies, which have a fixed phase separation to one another of 120°. The German extra-high voltage grid is operated using three-phase alternating current technology. High voltage direct current transmissions are an exception to this.

Three-phase system

Three electrical conductors that belong together, but are isolated from each other and from the surrounding area, used for the transmission of three-phase electric power (three-phase system).

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). 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.

Transient response

Transient responses are properties of the system. They occur as the system state changes to a different system state, for instance as a result of changes in loads, infeed or network topology. As long as no limits are exceeded and the transient response fades away fast 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.


Within the electricity industry, transmission refers to the technical and physical process of the simultaneous input 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 network.

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.

TSO Security Cooperation (TSC)

The “TSO Security Cooperation” (TSC) is a cooperation of eleven European transmission system operators (TSOs). They have set themselves the target of further increasing the safety 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 network operators 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.