Ensuring Security of Supply in Estonian Transmission Grid PÕHIVÕRK Ensuring Security of Supply in Estonian Transmission Grid Raul Uuring Grid Management 11.05.2009

Topics: Overview of the company and Estonian power system How does Estonian Transmission Grid provide security of power supply

Estonian Transmission Grid: OÜ Põhivõrk Established in 1998 Main task is to transmit electric power from producers to major industrial consumers and distribution networks Responsible for security of supply of the whole power system

Total length of lines – 5300 km Estonian Power System PÕHIVÕRK Total length of lines – 5300 km 144 substations Peak load in 2008 – 1525 MW

Power loop PÕHIVÕRK

Providing security of supply Fulfilling Grid Code requirements Ensuring transmission capacity N-1, N-1-1 events must not cause major interruptions for customers N-2 event must not cause system blackout System stability has the highest priority System must have enough quick power reserve capacity

System operation after disturbance Classification of disturbances: System operation before disturbance   ST-0 ST-1 ST-2 ST-3 N-1 – common disturbances N-2 and N-X – rare disturbances System normal condition System unnormal condition All essential elements of the system are operating Planned maintenance of one element of the system System operation is disturbed, as one essential element is dead because of fault System operation is disturbed, as more than one essential element is dead because of fault N-1 One element is switched off A B C N-2 Two elements are switched off N-X More than two elements are switched off Consequences of disturbances: A System is stable and there may be some local power interruptions B There are some regional power interruptions C System may become unstable and collapse, that causes blackouts in several regions  

Providing security of supply – On-design phase Examples: New Tartu-Sindi 330kV line New international connections (e.g. Estlink II, Sindi-Riga 330kV line) New gas turbine station for quick power reserve Large investments for renewal of existing substations and lines

Investment volumes PÕHIVÕRK

Investment plan 2009-2013 PÕHIVÕRK Total volume: 336 MEUR

Providing security of supply – Grid operation phase Examples: Emergency stand-by contracts (for lines and for substations) No planned maintenance works are allowed to do during winter time when n-1-1 criteria is not fulfilled Planned switching operations are not allowed to do if outside temperature is –15°C or below Mixed type of maintenance policy – both condition and interval based

Providing security of supply – Emergency contingencies Comprehensive load shedding automation (by frequency and by voltage) Separation of Estonian power system from Russian and Baltic systems System blackstart function via Estlink