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  System services
Primary power control
Maintaining a primary regulation margin at the set level is a centrally co-ordinated service provided by transmission system operator (TSO). The primary control goal is to automatically increase/decrease the power of primary control ranked sources within a few seconds (in the scope of set control margin) in order to balance frequency deviations. The primary control has a proportional character and contributes to maintaining a balance between generation and consumption using a turbine power or speed regulator.
Secondary control of frequency and power
Secondary control of frequency and power is a centrally co-ordinated service provided by TSO. The secondary control goal is to maintain frequency at the nominal (required) value and balance with the interconnected systems at the required value. Secondary control must be harmonised with primary control. Primary control possibilities are preferred to frequency deviations, and secondary control is applied when a frequency deviation persists or in case of a deviation from the agreed balance.
Tertiary power control
Tertiary power control is a centrally co-ordinated service provided by TSO. The tertiary control goals is to support maintaining the required secondary control margin at operated sources and its extension with the capacity of units with a short start-up time. The tertiary control margin is used particularly for maintaining the agreed balance.
Dispatching reserve
Dispatching reserve is a sum of all power capacities of sources, which can be used to ensure the balance between sources and loads during the source power or load changes.
Voltage control and reactive power control
Voltage control differentiates the primary, secondary, and tertiary voltage control. Primary voltage control ensured required voltage at generator terminals. Secondary voltage control maintains voltage in specified grid nodes. Tertiary voltage control is centralised automatic service co-ordinating specified voltage in pilot nodes for a safe and economic operation of the transmission system as a whole. It is implemented by an optimisation software at TSO dispatching centre.
Transmission system stability
The transmission system stability is a co-ordination service that ensures a static stability control during the active power transmission through grid calculations and the system oscillation dumping. The transmission system stability is the ability to maintain a balance characterised by a synchronous operation of generators, during a normal operation and after transients caused by external factors, dispatching control, as well as equipment trips due to failures. Usually a static and dynamic stability is differentiated. The transmission system static stability is the ability to maintain the synchronous operation after transients, during which electrical parameter changes are relatively small and slow.
Black start
Black start is a process ensuring a step-by-step recovery of the transmission system operation, or of a part of it, by voltage provision from started-up units through specified lines, establishment of islands, their step-by-step synchronisation and connecting customers according to determined criteria and priorities. The system can break down completely or partially in case of a failure not considered in a protection plan against failure propagation. In case of such failures TSO must ensure the transmission system operation recovery through the System recovery plan. Monitoring and updating of the recovery plan is ensured by TSO dispatching centre.