Power system operations and control: Difference between revisions

Content deleted Content added
Minutes-ahead operation: Expanding article
 
(11 intermediate revisions by 2 users not shown)
Line 1:
{{Short description|Power plant operation}}
 
'''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 equipment failures) in order to provide reliable 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 ("[[grid balancing]]"). 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 operatorsoperator]]s. 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}}
 
== Day-ahead operation ==
Line 22:
 
=== Dispatch curve ===
{{Box|{{#chart:DispatchCurve.chart}}|align=right|width=50%}}
{{Graph:Lines
|<!-- vAnnotationsValues={"text": "Expected demand", "x": 150}
| table=System lambda curve 1.tab
| hAnnotationsValues={"text": "System lambda", "y": 60} -->
| type=linear| xField=demand
| series="cost"
| title=Dispatch curve
| yZero= | xAxis=Demand (MW) | yAxis=Cost ($/MWh) | yMax= | yGrid=y | width= | legend=-
| vAnnotationsValues={"text": "Expected demand", "x": 150}
| hAnnotationsValues={"text": "System lambda", "y": 60}
| hideSource=true
| right
}}
The decisions ("[[economic dispatch]]") are based on the '''dispatch curve''', where the X-axis constitutes the system power, intervals for the generation units are placed on this axis in the ''[[merit order]]'' with the interval length corresponding to the maximum power of the unit, Y-axis values represent the marginal cost (per-[[MWh]] of electricity, ignoring the startup costs). For cost-based decisions, the units in the merit order are sorted by the increasing marginal cost. The graph on the right describes an extremely simplified system, with three committed generator units (fully dispatchable, with constant per-MWh cost):<ref name=psu/>
* unit A can deliver up to 120 MW at the cost of $30 per MWh (from 0 to 120 MW of system power);
Line 49 ⟶ 41:
 
== Minutes-ahead operation ==
In the minutes prior to the delivery, a system operator is using the [[power-flow study]] algorithms in order to find the [[optimal power flow]]. At this stage the goal is reliability ("security") of the supply.,{{sfn|Conejo|Baringo|2017|p=10}} applying [[contingency analysis]]. The practical electric networks are too complex to perform the calculations by hand, so from the 1920s the calculations were automated, at first in the form of specially-built [[analog computer]]s, so called ''[[Network analyzer (AC power)|network analyzers]]'', replaced by digital computers in the 1960s.
 
== Control after disturbance ==
Line 61 ⟶ 53:
* [[ancillary services]] are engaged (load is reduced as procured via reliability services contracts).
 
Another term commonly used for the primary control is '''frequency response''' (or "beta"). Frequency response also includes the [[inertial response]] of the generators.{{sfn|NERC|2021|p=12}} This is the parameter that is approximated by the [[Frequency bias (electrical grid)|frequency bias]] coefficient of the [[area control error]] (ACE) calculation used for [[automatic generation control]].{{sfn|NERC|2021|p=14}}
 
=== Minutes-after control ===
Line 68 ⟶ 60:
=== Tertiary control ===
The ''tertiary control'' involves reserve deployment and restoration to handle the current and future contingencies.{{sfn|NERC|2011|p=13}}
 
=== Emergency control ===
In the event of a significant [[grid contingency]], like a major loss of generation capacity, emergency measures might be necessary to avoid a [[cascading failure]]. [[Load shedding]] (LS) is a standard emergency control action that reduces demand by disconnecting certain loads within an acceptable timeframe (0.2 - 3 seconds), thereby preventing the collapse of the grid.{{sfn|Bevrani|Watanabe|Mitani|2014|p=158}} Another emergecy control action is [[islanding]].{{sfn|Bevrani|Watanabe|Mitani|2014|p=178}}
 
== Time control ==