Loss of load

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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.[1] Multiple probabilistic reliability indices for the generation systems are using loss of load in their definitions, with the more popular[2] being Loss of Load Probability (LOLP) that characterizes a probability of a loss of load occurring within a year.[1] 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

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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   (e.g., for a yearlong interval   if the increment is a day,   if the increment is an hour):[3]

  • 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;[4]
  • Loss of load expectation (LOLE) is the total duration of increments when the loss of load is expected to occur,  . 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.[5] 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;[6] although in practice the relationship is close to linear, the coefficients vary from network to network;[7]
  • 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);[8]
  • Loss of load duration (LOLD) characterizes the average duration of a loss of load event:[9]  

One-day-in-ten-years criterion

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A typically accepted design goal for   is 0.1 day per year[10] ("one-day-in-ten-years criterion"[10] a.k.a. "1 in 10"[11]), corresponding to  . In the US, the threshold is set by the regional entities, like Northeast Power Coordinating Council:[11]

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

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References

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Sources

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