n-0 criterion

In connection with grid planning, the n-0 criterion is defined as a grid connection system without redundancy. This means that the grid connection system will break down when one or more resources required for the grid connection fails. Compare with n-1 criterion.


n-1 criterion

The basic principle of n-1 security in grid planning states that if a component – e.g. a transformer or circuit – should fail or be shut down in a grid operating at the maximum forecast levels of transmission and supply, the grid security must still be guaranteed. This means that in this case undue interruptions in supply or the spreading of a failure must not occur. Furthermore, the voltage must remain within the permitted limits and the remaining resources must not be overloaded. This engineering principle is generally accepted throughout all grid levels. Interruptions in supply are, however, tolerated to a certain extent in the distribution grid depending on client structure and as long as they can be rectified within a defined time period. On the other hand, there are more delicate areas of the transmission grid where another measure in addition to the n-1 criterion is implemented when particularly sensitive clients like factories in the chemical or steel industry have to be supplied or where a failure could result in a more large-scale disruption or a very hazardous situation. In this case, the grid is constructed so that grid security can still be guaranteed even if one element is shut down for operational reasons and another should fail at the same time (n-2 case).

Net output

See gross output.

Network code

Network operators lay out and publish the minimum technical requirements for the connection of their network, for the feed-in from generating facilities into their network and for the use of interconnecting lines between transmission networks. These requirements are transparent and unbiased with regard to all interested parties.

Network coupling terminal (NCT)

A network coupling terminal couples parallel offshore network connection systems longitudinally to form an offshore network and third party networks laterally, such that a grid connection system can be operatively connected to grid connection points from separate systems. A network coupling terminal can, for example, be located on a converter platform or a collection platform.

Network Development Plan (NDP)

Up until the Network Development Plan (NDP) 2014, the transmission system operators (TSOs) included the year in which the plan was produced in the title. From the NDP 2025 onwards, the target year was added to the title instead. This change thus brings the plans in line with the nomenclature of the German Federal Network Agency (BNetzA), which has been exclusively using the target year of the ten year forecasts in its communication surrounding the NDP for a long time.

Network user

A network user (user of the transmission or distribution network) is every natural person or legal entity that has a contract of use for the network and accordingly uses the services of the network operator on a contractual basis.

Nominal output

The nominal output of a generation unit is the level of continuous output, which has been ordered from it in a supply agreement.The nominal output of combined heat and power plants refers to the nominal electrical output.

Normal operation

Normal operation is defined as follows:

  • all customers are adequately supplied
  • all limits are complied with (e.g. no overloading)
  • the n-1 criteria is satisfied everywhere and
  • there are sufficient power stations and transmission reserves available.
NOVA principle

NOVA is a German acronym for the optimisation, enhancement and expansion of the grid (Netzoptimierung, -verstärkung und -ausbau). According to this principle, established by the transmission system operators (TSOs) for grid planning, grid optimisation has priority over grid enhancement and grid enhancement has priority over grid expansion.