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

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

3. 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

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

5. Power loop
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6. 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

7. 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

8. 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

9. Investment volumes
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10. Investment plan
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Total volume: 336 MEUR

11. 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

12. 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