The basic principle of n-1 security in network planning states 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 network 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 rule for technology is generally accepted throughout all network levels. Interruptions in supply are, however, tolerated to a certain extent in the distribution network 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 network 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 network 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).
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.
A network operator (operator of a transmission or distribution network) is responsible for the safe and reliable operation of the respective network in a defined area and also responsible for the connections to other networks. In addition to this, the operator of a transmission network also regulates transmission using the network, in due consideration of the exchange with other transmission networks. The operator looks after the provision of essential system services, thereby ensuring the reliability of supply.
The nominal output of a generating unit is the level of continuous output, which has been ordered from it in a supply agreement. If the nominal output is not clearly stipulated in the order documentation, new facilities are to make a one-time specification of an output value, which is achievable under normal conditions. The nominal output of combined heat and power plants refers to the nominal electrical output.
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, grid optimisation and enhancement have priority over the expansion of the grid.