Operational security standards 1 System security criteria The following criteria for system security are to be applied in those respects that are of significance as regards enabling operation of the power system to be upheld with the subsystems interconnected with each other. The criteria for system security shall be based on the n-1 criterion. This is an expression of a level of system security entailing that a power system is assumed to be intact apart from the loss of individual principal components (production units, lines, transformers, bus bars, consumption etc.). For faults having the largest impact on the power system, the term dimensioning faults is used. It is not normally the same type of fault that is dimensioning during frequency disturbances as during disturbances to the transmission system. The loss of the power system’s largest production unit is normally dimensioning as regards determining the frequency controlled disturbance reserve. The definition of serious operational disturbances is operational disturbances having a greater impact than activation of the frequency controlled disturbance reserve. The definition of normal state is an operational state entailing that all consumption is being met, that the frequency, voltage and transmission lie within normal limits and that the reserve requirements have been met. The power system has been prepared in order to deal with dimensioning faults. For the interconnected Nordic power system, the above entails that: a dimensioning fault on a subsystem must not bring about serious operational disturbances in other subsystems. This places demands on the frequency controlled disturbance reserve and the transmission capacity within and between the subsystems if the power system is not in normal state following an operational disturbance, the power system must have been restored, within 15 minutes, to normal state. This places demands on the available fast active disturbance reserve. If there are exceptions from the time requirement, or if there is a departure from the above definition of dimensioning faults, then there must be consultation between the system operators concerned. 2 System protection System protection is used to limit the consequences of faults over and above the disconnection of defective components. System protection can have as its purpose to increase the system security, the transmission capacity, or a
Each subsystem shall have at least 2/3 of the frequency controlled normal operation reserve in its own system for potential splitting up and island operation. The following example (for 2013) shows how the division of power for the frequency controlled normal operation reserve takes place: Annual consumption 2013 (TWh) Frequency controlled normal operation reserve (MW) Eastern Denmark 13.7 22 Finland 85.2 138 Norway 130.0 210 Sweden 142.5 230 Synchronous system 371.4 600 4.1.2 Frequency controlled disturbance reserve There shall be a frequency controlled disturbance reserve of such a volume and composition that a dimensioning fault does not cause a frequency below 49.5 Hz in the synchronous system. With regard to the frequency-dependence of consumption, the above requirement entails that the total frequency controlled disturbance reserve shall rise to a power which is equal to the dimensioning fault deducted by 200 MW. It must be able to utilise the frequency controlled disturbance reserve until the fast active disturbance reserve is activated. The activation of the frequency controlled disturbance reserve shall not result in other problems in the power system. When the transmission capacity is being determined, the location of the frequency controlled disturbance reserve shall be taken into account. Each subsystem shall have at least 2/3 of the frequency controlled disturbance reserve in its own system for potential splitting up and island operation. The frequency controlled disturbance reserve shall be activated at 49.9 Hz and shall be fully activated at 49.5 Hz. It shall increase virtually linearly within a frequency range of 49.9-49.5 Hz. Agreed automatic load shedding, e.g. industrial, district heating and electric boiler consumption in the event of frequency drops to 49.5 Hz can be counted as part of the frequency controlled disturbance reserve. The following requirements are applicable, however:
On the Western Danish side, Energinet.dk’s Control Centre at Erritsö has the right to initiate manual emergency power in the event of disturbances to the power balance or transmission network. On the Swedish side, Svenska kraftnät has the right to initiate manual emergency power in the event of disturbances to the power balance or transmission network. Manual emergency power of less than 100 MW and 100 MWh/calendar day may be activated without previous notification. Prior to activation over and above this, notification and approval shall take place between the staff of Energinet.dk’s Control Centre at Erritsö and SvK-VHI at Network Control at Sundbyberg. 4.6.3 System protection At the DC facilities, system protection is installed in the form of an emergency power function. Activation criteria for emergency power can be locally-measured frequency and voltage or via telecommunications on the basis of a supplied signal. In the event of activation, any ongoing normal regulation will be interrupted. Activation over and above the agreed limits and regulation back to plan may not occur until the counterparty has approved this. (See further in Appendix 5 – System protection). 5 Miscellaneous 5.1 System services 5.1.1 Transmission scope for operation reserves Available transmission capacity can be used for the automatic or manual activation of operational reserves. The Parties have the right to utilize idle transmission capacity after Elspot trading and Elbas trading for the transmission of system services. Configuration values, power limits etc. are agreed upon bilaterally.