Power system operations and control: Difference between revisions

Revision as of 17:19, 11 September 2022

Revision as of 10:04, 17 September 2022

Line 38:

* C is capable of 50 MW at $120/MWh (from 200 to 250 MW of system power).

At the expected demand is 150 MW (a vertical line on the graph), unit A will be engaged at full 120 MW power, unit B will run at the '''dispatch level''' of 30 MW, unit C will be kept in reserve. The area under the dispatch curve to the left of this line represents the cost per hour of operation (ignoring the startup costs, $30 * 120 + $60 * 30 = $5,400 per hour), the incremental cost of the next MWh of electricity ($60 in the example, represented by a horizontal line on the graph) is called '''system lambda''' (thus another name for the curve, ''system lambda curve'').

In real systems the cost per MWh usually is not constant, and the lines of the dispatch curve are therefore not horizontal (typically the marginal cost of power increases with the dispatch level, although for the [[combined cycle power plant]]s there are multiple cost curves depending on the mode of operation, so the power-cost relationship is not necessarily [[Monotonic function|monotonic]]).<ref name="BayónGarcía NietoGrau2013">{{cite journal | last1 = Bayón | first1 = L. | last2 = García Nieto | first2 = P. J. | last3 = Grau | first3 = J. M. | last4 = Ruiz | first4 = M. M. | last5 = Suárez | first5 = P. M. | title = An economic dispatch algorithm of combined cycle units | journal = International Journal of Computer Mathematics | date = 19 March 2013 | volume = 91 | issue = 2 | pages = 269–277 | issn = 0020-7160 | eissn = 1029-0265 | doi = 10.1080/00207160.2013.770482 | pmid = | url = https://www.unioviedo.es/bayon/osh/41.pdf}}</ref>

Line 49:

== 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}} 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 ==

=== Seconds-after control ===

The ''primary control'' is engaged automatically withingwithin seconds after the frequency disturbance. Primary control stabilizes the situation, but does not return the conditions to the normal and is applied both to the generation side (where the [[Governor (device)|governor]] adjusts the power of the [[Prime mover (engine)|prime mover]]) and to the load, where:{{sfn|NERC|2011|p=12}}

* induction motors self-adjust (lower frequency reduces the energy use);

* under-frequency relays disconnect [[interruptible load]]s;

Line 59:

=== Minutes-after control ===

The ''secondary control'' is used to restore the system frequency after a disturbance, with adjustments made by the balancing authority control computer (this is typically referred to as [[load-frequency control]] or [[automatic generation control]]) anand manual actions taken by the balancing authority staff. Secondary control uses both the [[Spinning reserve|spinning]] and non-spinning reserves, with balancing services deployed within minutes after disturbance (hydropower plants are capable of an even faster reaction).{{sfn|NERC|2011|pp=12-13}}

=== Tertiary control ===

Line 66:

== Time control ==

{{main|Time error correction (TEC)}}

The goal of the '''time control''' is to maintain the long-term frequency at the specified value within a [[wide area synchronous grid]]. Due to the disturbances, the average frequency drifts, and a ''time error'' accumulates between the official time and the time measured in the AC cycles. In the US, the average 60 &nbsp;Hz frequency is maintained within each [[Wide area synchronous grid|interconnection]] by a designated entity, '''time monitor''', that periodically forces a grid frequency change to bring the overall time offset within the predefined limits. For example, in the [[Eastern Interconnection]] the action (temporarily setting the frequency to 60.02 &nbsp;Hz or 59.98 &nbsp;Hz) is initiated when the time offset reaches 10 seconds and ceases once the offset reaches 6 seconds. Time control is performed either by a computer (''Automatic Time Error Correction''), or by the monitor requesting balancing authorities to adjust their settings.{{sfn|NERC|2011|pp=13-14}}

== References ==

{{RefListReflist}}

== Sources ==

Line 78:

* {{cite web |last1=WECC |title=Balancing Authority and Regulation Overview |url=https://www.wecc.org/Administrative/06-Balancing%20Authority%20Overview.pdf |website=wecc.org |publisher=[[Western Electricity Coordinating Council]]}}

* {{cite book |last1=NERC |title=Reliability Functional Model Technical Document Version 5.1 |date=July 2018 |publisher=[[North American Electric Reliability Corporation]] |url=https://www.nerc.com/pa/Stand/Functional%20Model%20Advisory%20Group%20DL/FM_Technical_Document_V5-1_clean_10082019.pdf}}

* {{cite book |last1=NERC |title=Balancing and Frequency Control |date=January 26, 2011 |publisher=[[North American Electric Reliability Corporation]] |url=https://www.nerc.com/comm/OC/BAL0031_Supporting_Documents_2017_DL/NERC%20Balancing%20and%20Frequency%20Control%20040520111.pdf}}

[[Category:Electric power generation]]

[[Category:Power engineering]]