Loss of load

From KYNNpedia

Loss of load in an electrical grid is a term used to describe the situation when the available generation capacity is less than the system load.<ref name="FOOTNOTEAscend Analytics2019">Ascend Analytics 2019.</ref> Multiple probabilistic reliability indices for the generation systems are using loss of load in their definitions, with the more popular<ref name="FOOTNOTEElmakias2008174">Elmakias 2008, p. 174.</ref> being Loss of Load Probability (LOLP) that characterizes a probability of a loss of load occurring within a year.<ref name="FOOTNOTEAscend Analytics2019">Ascend Analytics 2019.</ref> Loss of load events are calculated before the mitigating actions (purchasing electricity from other systems, load shedding) are taken, so a loss of load does not necessarily cause a blackout.

Loss-of-load-based reliability indices

Multiple reliability indices for the electrical generation are based on the loss of load being observed/calculated over a long interval (one or multiple years) in relatively small increments (an hour or a day). The total number of increments inside the long interval is designated as <math>N</math> (e.g., for a yearlong interval <math>N=365</math> if the increment is a day, <math>N=8760</math> if the increment is an hour):<ref name="FOOTNOTEDuarteSerpa2016157">Duarte & Serpa 2016, p. 157.</ref>

  • Loss of load probability (LOLP) is a probability of an occurrence of an increment with a loss of load condition. LOLP can also be considered as a probability of involuntary load shedding;<ref name="FOOTNOTEWangSongIrving2010151">Wang, Song & Irving 2010, p. 151.</ref>
  • Loss of load expectation (LOLE) is the total duration of increments when the loss of load is expected to occur, <math>{LOLE} = {LOLP} \cdot N</math>. Frequently LOLE is specified in days, if the increment is an hour, not a day, a term loss of load hours (LOLH) is sometimes used.<ref name="FOOTNOTEElaMilliganBloomBotterud2018134">Ela et al. 2018, p. 134.</ref> Since LOLE uses the daily peak value for the whole day, LOLH (that uses different peak values for each hour) cannot be obtained by simply multiplying LOLE by 24;<ref name="FOOTNOTEBillintonHuang20061">Billinton & Huang 2006, p. 1.</ref> although in practice the relationship is close to linear, the coefficients vary from network to network;<ref name="FOOTNOTEIbanezMilligan20144">Ibanez & Milligan 2014, p. 4.</ref>
  • Loss of load events (LOLEV) a.k.a. loss of load frequency (LOLF) is the number of loss of load events within the interval (an event can occupy several contiguous increments);<ref name="FOOTNOTENERC201813">NERC 2018, p. 13.</ref>
  • Loss of load duration (LOLD) characterizes the average duration of a loss of load event:<ref name="FOOTNOTEArteconiBruninx2018140">Arteconi & Bruninx 2018, p. 140.</ref> <math>{LOLD} = \frac {LOLE} {LOLF}</math>

One-day-in-ten-years criterion

A typically accepted design goal for <math>LOLE</math> is 0.1 day per year<ref name="FOOTNOTEMeier2006230">Meier 2006, p. 230.</ref> ("one-day-in-ten-years criterion"<ref name="FOOTNOTEMeier2006230">Meier 2006, p. 230.</ref> a.k.a. "1 in 10"<ref name="FOOTNOTETezak20052">Tezak 2005, p. 2.</ref>), corresponding to <math>{LOLP} = \frac {1} {10 \cdot 365} \approx 0.000274</math>. In the US, the threshold is set by the regional entities, like Northeast Power Coordinating Council:<ref name="FOOTNOTETezak20052">Tezak 2005, p. 2.</ref>

resources will be planned in such a manner that ... the probability of disconnecting non-interruptible customers will be no more than once in ten years

— NPCC criteria on generation adequacy

See also

References

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Sources