Power system operations and control: Difference between revisions

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=== 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);

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== 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 ==

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=== 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 ==