Ramping refers to a change in power flow (or power generation) from one time unit to the next. Ramping restrictions limit the allowed net flow variations on consecutive hours on specific lines. Ramping restrictions are also handled on day-shifts by including information about the flow in the last hour from the previous day in the calculation.
In the day-ahead and intraday markets, all trading across the HVDC cables is subject to a ramping restriction of 600 MW. The restrictions imply that trade plans on all HVDC connections cannot be changed with more than 600 MW from one hour to the next. This restriction can be put on each of the cables individually or to a set of cables.
Handling of ramping restrictions in the day-ahead price calculation
The HVDC connections listed below are all subject to specific ramping restrictions. The restrictions have been imposed by the national transmission system operators Svenska Kraftnät, Energinet.dk and Statnett.
The ramping restriction between the Nordic synchronous system and the Continent (UCTE) is imposed separately on the DC links listed below.
In addition, there is also a joint restriction for the KontiSkan and Skagerrak. The ramping restriction sets a limit on the total incoming/outgoing power flow from Jutland on the two connections combined, which is due to the internal grid limitations on Jutland, called Cut B.
|Name of connection||Connection points|
|Estlink||FI <-> EE|
The reasons for ramping restrictions
When imposing the ramping restrictions, the Nordic transmission system operators have stated that frequent large changes in production and flow in fully loaded corridors in the grid make it more difficult to control the frequency. The transmission system operators are therefore imposing the ramping restrictions on HVDC connections in order to reduce risks that might threaten the security of supply.
Without restricting the maximum change of flow per hour (ramping) on interconnectors, very large ancillary services and operational reserves would be needed to handle imbalances within the operative hours.