The basic principle of n-1 security in grid planning states is that if a component – e.g. a transformer or circuit – should fail or be shut down in a network 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 criteria 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 very hazardous situation. In this case, the network 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).
See gross output.
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.
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.
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 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 for grid planning, grid optimisation has priority over grid enhancement and grid enhancement has priority over grid expansion.