System operation

Every day, preparations are made to maintain the balance for the next day. To this end, the generation plans, forecasted consumption and planned trading of all market participants are aggregated into the system’s balancing schedule. Based on the schedule, the operation of the power system is monitored and controlled. In the event that actual consumption and generation differ too much from the planned quantities or if a generator should shut down in an emergency, options have been established beforehand to restore the balance of the system – for this purpose, contracts are entered into for the use of regulating capacities and emergency reserve capacities.

The integrity and operability of the system must be maintained even in the event of interruptions in the network. The system’s performance must also be statically and dynamically stable. To this end, the operation and development of the system is planned in such a way that all possible emergency situations are analysed proactively and based on this, the admissibility of repairs to network elements and the system’s import and export capacity are decided.

The maximum import and export capacities depend on the thermal transmission capacity of the power lines, on the one hand, and on the system stability limit determined during mode calculations, on the other hand. The final limit is determined based on the lower of the two indicators.

Voltage control

By managing the balance of voltage and reactive power, Elering's control center ensures permissible voltage levels across the entire transmission grid and optimizes system operation from the perspective of minimizing transmission losses.

To maintain voltage levels more effectively and reduce additional losses, the preferred approach is to minimize the exchange of reactive power between different voltage levels—whether between networks, network-connected consumers, different regions of the grid, or neighboring systems.

When it comes to compensating for reactive power flowing into or out of the grid, the guiding principle is that if the reactive power flow is not controllable by the grid operator, the party causing the flow pays the grid operator for each kilovolt-ampere reactive hour (kVarh) passed through a connection point.

However, if the grid operator is able to use the reactive power for regulating voltage within its own network, the grid operator in turn pays for it. During times when the voltage control function is activated, Elering purchases and sells reactive energy to power plants at a rate of 0.088 euro cents per kVarh. This price has been in effect since April 1, 2022. This model is used, for example, for power plants connected to the transmission grid that support voltage regulation in the electricity system.

Power plants willing to provide additional voltage regulation services to Elering can submit a corresponding request to Elering account manager. A reactive power compensation service agreement will be concluded with those plants whose reactive power flow Elering is able to control.

Baltic frequency control block (Baltic LFC block)

In the Continental Europe Synchronous Area, the Baltic system operators are obligated to comply with the structural division of responsibilities for frequency control in the frequency area. Specific obligations are set out for the frequency area, frequency control blocks and frequency control areas. The Baltic system operators have established a common frequency control block, which includes three frequency control areas. For this purpose, the Baltic Frequency Control block operational agreement has been drawn up and entered into, which sets out the obligations and methodologies to be applied by the frequency control block and frequency control areas.

The main task of the frequency control area (LFC area) is to identify and balance the current system error by using the activation of aFRR and mFRR reserves. Each Baltic system operator assesses the system error in its region and performs frequency reserve activations to address it.

The main tasks of the frequency control block (LFC block) are to dimension the FRR capacities for the frequency control block, which would ensure sufficient aFRR and mFRR capacities so that the frequency control block can cover system errors 99% of the time or at least cover the largest event failure in both excess and deficit energy. The frequency control block has specific system error limits in the synchronous area, based on which the adequacy of reserves is assessed. If an LFC block includes several LFC areas, the LFC block must also provide for coordinated actions to ensure minimal system failure of the LFC block as a result of joint actions.

Countertrade

Countertrade is used in a situation where an event occurs in the power system that causes an overload at the cross-section of interstate lines or a physical interruption of power transmission.

Countertrade is carried out based on the following principles:

• Cross-border energy trade that took place before the overload of interstate lines or the physical interruption of power transmission is fully guaranteed by system operators, i.e. previously confirmed deliveries are not cancelled.
• The system operator in whose direction the power flow is (was) moving organises the activation of additional generating capacity in the necessary volume within its area of responsibility.
• The system operator who provides (has provided) capacity organises the reduction of generating capacity to the necessary extent within its area of responsibility.

Technical limitations of the power systemgud

Cross-border transmission capacities are calculated according to the common capacity calculation method of the transmission system operators of the Baltic Capacity Calculation Region for the day-ahead and intraday periods. The methodology has been approved by the decision of the Competition Authority on 27 November 2024.  In accordance with the principles described in the aforementioned methodology, Elering calculates transmission capacities and obtains an approval for them from the system operators of neighbouring countries.

The restrictions imposed on the system by the transmission system operators, their reasons and impact on the power system can be found on the Nord Pool website. In addition, the same website provides information about actual outages in transmission systems.

Significant grid users

Chapter II of Commission Regulation (EU) 2017/2196 establishing a network code on electricity emergency and restoration provides for the obligation of the transmission system operator to develop and implement a system defence plan. Among other things, Article 11(3)(c) of the aforementioned Regulation provides that one part of the system defence plan must be a list of significant grid users. The list must be published by the transmission system operator. For the purposes of Commission Regulation (EU) 2017/1485 establishing a guideline on electricity transmission system operation, significant grid users are type B, C and D generating modules. A list of significant grid users of the Estonian electricity system is provided here (in estonian)..