'''Power system operations''' is a term used in [[electricity generation]] to describe the process of [[decision-making]] on the timescale from one day ('''day-ahead operation'''{{sfn|Conejo|Baringo|2017|p=9}}) to minutes{{sfn|Conejo|Baringo|2017|p=10}} prior to the [[power delivery]]. The term '''power system control''' describes actions taken in response to unplanned ''disturbances'' (e.g., changes in demand or generatorequipment failures) in order to provide uninterrupted electric supply of acceptable quality.<ref name="Sivanagaraju2009">{{cite book | author = S. Sivanagaraju | date = 2009 | title = Power System Operation and Control | publisher = Pearson Education India | pages = 557– | isbn = 9788131726624 | oclc = 1110238687 | url = https://books.google.com/books?id=9GkhHYorvDAC&pg=PA557}}</ref> The corresponding [[engineering branch]] is called '''Power System Operations and Control'''. Electricity is hard to store, so at any moment the supply (generation) shall be balanced with demand. In an electrical grid the task of real-time balancing is performed by a regional-based control center, run by an electric utility in the traditional ([[vertical integration#Electric utilities|vertically integrated]]) electricity market. In the restructured [[North American power transmission grid]], these centers belong to ''[[balancing authority|balancing authorities]]'' numbered 74 in 2016,<ref>{{cite web |title=U.S. electric system is made up of interconnections and balancing authorities |url=https://www.eia.gov/todayinenergy/detail.php?id=27152 |website=eia.gov |publisher=[[United States Energy Information Administration]] |access-date=31 May 2022 |date=20 July 2016}}</ref> the entities responsible for operations are also called [[independent system operator]]s, transmission system operators. The other form of balancing resources of multiple power plants is a [[power pool]].{{sfn|Bhattacharya|Bollen|Daalder|2012|pp=54}} The balancing authorities are overseen by [[reliability coordinator]]s.{{sfn|NERC|2018|p=8}}