A limited volume of electricity conforming to the system security criteria can be transmitted in a power grid. This is referred to as the grid's transmission capacity. Transmission capacity allocation and congestion management ensures that the power flows remain within the transmission capacity.
Fingrid provides the electricity market with as much transmission capacity as is possible without compromising the system security of the main grid.
Fingrid's Transmission capacity allocation and congestion management is based on systematic planning and predictability.
Transmissions planned for cross-border connections are determined on the day-ahead and intraday markets. In the day-ahead market auction, cross-border transmissions and the price of electrical energy in different bidding areas are simultaneously determined within the transmission capacity limits between the bidding areas. Any capacity which is left unused in the day-ahead market is offered to the intraday market.
Transmission outages which affect transmission capacity are planned cost-efficiently while bearing the system as a whole in mind. Transmission outages are scheduled for times during which they cause minimal disruption to the electricity markets and customers, taking technical boundary terms into account.
Transmission management in the nation-wide transmission grid is used for maintaining electricity transmissions within the limits permitted by the prevailing operation situation. These limits are specified by means of system security calculations, taking into account potential faults occurring in the power system. The transmission limits vary in different operation situations, and issues such as planned maintenance outages in the grid may have considerable influence on the transmission limits.
The transmission limits are ascertained individually in each case using calculations. The principle is that a dimensioning fault must not lead to the loss of synchronous operation, voltage collapse, shedding of loads, excessive voltage or frequency variations, overloading of parts of the grid, or self-sustained electromechanical fluctuations.
A point which restricts transmissions in the grid is referred to as a congestion or bottleneck. Short-term congestions in the transmission grid are taken care of commercially by means of counter trading, and long-term congestions are taken care of by means of price areas or by reinforcing the grid.
Counter trading is used for changing the geographical distribution of production by power plants, which is determined on a market basis. Fingrid purchases at its own cost the missing capacity in the relevant area and agrees on the down-regulation of a sufficient production volume in an area that feeds the congestion. Counter trading is used for ensuring system security in the entire power system.
In a situation with insufficient transmission capacity, for example if the transmission capacity between Finland and Sweden is below the need for transmissions, the electricity exchange segregates the prices into price areas. In accordance with methodology applied by the electricity exchange, electricity flows between countries from an inexpensive area to an expensive area.
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