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Stability of system frequency

In order to keep grid frequency stable in an interconnected power system, generation of power needs to be maintained in constant equilibrium with its consumption. In principle, the grid frequency of such an interconnected power system is the same at all points (with the exception of highly dynamic short-term effects), which is why the terms synchronous grid or synchronous area are also used.

Disturbances in the balance of grid frequency may be caused by power plant failures or unexpected changes in demand and lead to a deviation in the joint system frequency - irrespective of their geographic occurence in the synchronous area. To maintain the system frequency within strict limits, it is necessary to continuously offset such fluctuations by activating balancing services in power generation or demand facilities. 

The set-point value in the Continental Europe synchronous area is 50 hertz. System frequency should not deviate from the set-point value by more than 0.2 hertz.

APG’s responsibility

The Continental Europe synchronous area is divided into a number of load frequency control areas (hereinafter referred to as control areas). The responsibility for a proper organization of balancing services in these control areas lies with the control area managers. In its role as a control area manager, APG is responsible for procurement and activation of the balancing services needed in the APG control area.

Balancing market 

Since 2012, the required balancing services for the APG control area have been uniformly procured over APG’s tendering platform in regular tenders carried out by Austrian Power Grid AG. Any market participant that fulfils the technical prequalification requirements and has signed a corresponding framework agreement may participate in these tenders. For technical and economical reasons, three types of balancing services are distinguished.

Primary control – Frequency Containment Reserve (FCR)
The Frequency Containment Reserve, also known as the primary control reserve, is the first reaction to frequency disturbances. All systems within the synchronous area provide mutual support, no matter where the disturbance occurred. The aim is to prevent the synchronous frequency from diverging further from the set-point and stabilize it at a new level. In order to reach this goal, FCR is activated automatically within seconds. Hence, this balancing energy is a safety mechanism which is used to level out short-term imbalances between supply and demand.

In the Continental European synchronous area, reserves of +/-3,000 MW are held at all times for primary control purposes. Each control area contributes its share based on an arranged annual allocation key. The reserves to be held by the APG control area change slightly each year and currently amount to around +/- 73 MW.

FCR is reserved at suitable technical facilities such as power plants or industrial and commercial buildings, and is is activated automatically whenever the system frequency deviates from 50 Hz. Maximum activation takes place if the frequency deviation is 200 mHz or more. A deviation of this magnitude would result in the frequency containment reserve being completely exhausted. Maximum activation must be achieved within 30 seconds of the frequency deviation occurring and is required to be available for at least 30 minutes.

The costs for reserving FCR are charged to all Austrian electricity producers with an installed maximum electrical capacity of more than 5 MW in accordance with the 2010 Austrian Electricity Industry and Organisation Act (Elektrizitätswirtschafts- und -organisationsgesetz, ElWOG); the amounts charged depend on the producers’ annual generation volume.

Secondary control – Automatic Frequency Restoration Reserves (aFRR)
While the frequency containment reserve, to which all control areas provide mutual support, serves as an initial step to stabilise the frequency of the power grid, the control area in which the imbalance occurred is ultimately responsible for re-establishing the balance between power generation and consumption. This is done with secondary control or Automatic Frequency Restoration Reserves. Each control area is required to hold automated reserves individually for its own use. If an imbalance occurs in a control area, aFRR will be activated in this control area (only there). This eases the burden on Continental Europe’s common frequency containment reserve, allowing it to fulfil its function as a safety net again. Whereas the FCR needs to be deployed within seconds, the aFRR shall be activated within five minutes at the latest (Austrian requirement).

The level of aFRR required to be held differs from one control area to another depending on the operating conditions in the relevant control area, such as maximum demand or the biggest expected imbalance in the control area. This may be an outage of the largest power plant block in the control area. If aFRR are insufficient to restore the balance, manually activated reserves need to be deployed as a tertiary control mechanism.

Tertiary control – Manual Frequency Restoration Reserves (mFRR)
Manual Frequency Restoration Reserves are individual reserves too, but activated manually. mFRR exercise a supportive function by contributing to restore aFRR when required. In general, mFRR serve to avoid prolonged activation of aFRR for several consecutive 15-minute periods, since at some point in time no aFRR would be available anymore to balance out any further frequency deviations. Secondary and tertiary control together must be able to compensate for foreseeable balancing errors within 15 minutes. 

Prequalified balancing service providers in the APG control area 

This list shows currently prequalified providers for each type of balancing services: 





A1 Telekom Austria AG 


Energie AG Oberösterreich Kraftwerke GmbH 



GEN-I Vienna GmbH 


KELAG-Kärntner Elektrizitäts-Aktiengesellschaft 

Lechwerke AG 


Linz Strom GmbH 



Next Kraftwerke GmbH 


Norske Skog Bruck GmbH* 




ÖBB-Infrastruktur AG 


TIWAG-Tiroler Wasserkraft AG 

Salzburg AG für Energie, Verkehr und Telekommunikation 

VERBUND Energy4Business GmbH 

VERBUND Energy4Flex GmbH 

illwerke vkw AG 


Wien Energie GmbH 


NGEN F&E Projekte GmbH       X  

*) does not wish to disclose the type of balancing services offered 

Important legal bases for balancing

  • Commission Regulation (EU) 2017/1485 of 2 August 2017 establishing a guideline on electricity transmission system operation (SOGL) 

  • Commission Regulation (EU) 2017/2195 of 23 November 2017 establishing a guideline on electricity balancing (EBGL)

  • The ENTSO-E Synchronous Area Framework Agreement, Policy on LFCR 

  • The applicable versions and amendments of the Austrian Electricity Industry and Organisation Act (Elektrizitätswirtschafts- und -organisationsgesetz, ElWOG) and the System Charges Order (SNE-VO) 

  • The Technical and Organisational Rules for system operators and users (TOR)

Further information on the legal basis and on the balancing group coordinator for the APG control area can be found under Legal or on the APCS homepage. 

Primary control (FCR)

On this page you find the most important information for potential suppliers of the frequency containment reserve.

Secondary control (aFRR)

On this page you find the most important information for potential suppliers of secondary control reserve.

Tertiary Control (mFRR)

This page summarises the most important information for potential suppliers of tertiary control reserve.

Sunshine Regulation

APG publishes those suppliers who exceed a specified limit price when submitting bids in the tenders for secondary and tertiary control reserve. 

More information

Conditions of participation

In the APG control area, admission to the tenders is divided into two steps: Technical prequalification and framework agreement.


APG provides statistical data on grid control in the APG control area.

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