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ELIA GROUP 2011 ECONOMIC REPORT
Better coordination between European electricity transmission system operators is the key to security of supply.
Preventive management of critical grid situations As a power transmission system operator, the Elia Group is taking a series of preventive measures to maintain the balance of the grid and a secure power supply.
Managing the balance between generation and consumption As electricity cannot be stored in any great quantity (except by means of hydraulic pumping units), generation must be tailored at all times to consumption in this large grid – consumption that is the result of the actions and needs of more than 500 million inhabitants. Transmission system operators such as Elia and 50Hertz maintain this balance in their respective control area within strict limits and in compliance with common rules. To this end, each of the 41 transmission system operators reserves from generators, through European calls for tender, a generation capacity enabling them to adjust upwards or downwards the quantity of energy injected in their respective grid.
This generation capacity is differentiated according to the speed of response and the duration of the intervention. First of all, some generation units are equipped to adjust their generation almost automatically based on deviations from the frequency of reference (50 Hz in Europe) and the frequency measured on the grid, which depends on the instantaneous imbalance between the quantities of energy injected and taken off the entire interconnected grid. All the generation units connected to the large European grid will consequently react together to immediately offset the simultaneous loss of 3,000 MW (3 million kW), i.e. the equivalent of two of the largest generation units, irrespective of their location in continental Europe. The system operators, to which the defective powers stations are connected, will then use other means of generation to restore this automatic intervention capability as quickly as possible, until the situation is back to normal.
Black-start: progressive reconstruction of the grid In the event of an interruption of the power supply across a wide geographical area, the system operator concerned will use generation units specially equipped to start up autonomously, known as ‘black-start’ units. Each system operator has contracts for black-start services with generators in its area and regularly checks whether these units can start up independently as required. In 2011, Elia conducted detailed tests in two units located in Belgium. These generation units gradually allow to resupply a growing segment of the transmission system and therefore the other generation units can be restarted, while at the same time connecting up more and more consumers so as to continuously maintain a balance between the quantity of energy injected into the grid and the quantity of energy taken off it.