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Loss of load in an
electrical grid An electrical grid (or electricity network) is an interconnected network for electricity delivery from producers to consumers. Electrical grids consist of power stations, electrical substations to step voltage up or down, electric power tran ...
is a term used to describe the situation when the available generation capacity is less than the system load. Multiple probabilistic
reliability indices Reliability, reliable, or unreliable may refer to: Science, technology, and mathematics Computing * Data reliability (disambiguation), a property of some disk arrays in computer storage * Reliability (computer networking), a category used to des ...
for the generation systems are using loss of load in their definitions, with the more popular being Loss of Load Probability (LOLP) that characterizes a probability of a loss of load occurring within a year. Loss of load events are calculated before the mitigating actions (purchasing electricity from other systems,
load shedding Load shedding (LS) is a protective method of emergency power control where, during a large disbalance between supply and demand, the demand (load) is intentionally disconnected ("shed") so that the available electricity supply within a safe timefr ...
) are taken, so a loss of load does not necessarily cause a blackout.


Loss-of-load-based reliability indices

Multiple
reliability indices Reliability, reliable, or unreliable may refer to: Science, technology, and mathematics Computing * Data reliability (disambiguation), a property of some disk arrays in computer storage * Reliability (computer networking), a category used to des ...
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 N (e.g., for a yearlong interval N=365 if the increment is a day, N=8760 if the increment is an hour): * 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 Load shedding (LS) is a protective method of emergency power control where, during a large disbalance between supply and demand, the demand (load) is intentionally disconnected ("shed") so that the available electricity supply within a safe timefr ...
; * Loss of load expectation (LOLE) is the total duration of increments when the loss of load is expected to occur, = \cdot N. 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. 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; although in practice the relationship is close to
linear In mathematics, the term ''linear'' is used in two distinct senses for two different properties: * linearity of a '' function'' (or '' mapping''); * linearity of a '' polynomial''. An example of a linear function is the function defined by f(x) ...
, the coefficients vary from network to network; * 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); * Loss of load duration (LOLD) characterizes the average duration of a loss of load event: = \frac


One-day-in-ten-years criterion

A typically accepted design goal for LOLE is 0.1 day per year ("one-day-in-ten-years criterion" a.k.a. "1 in 10"), corresponding to = \frac \approx 0.000274. In the US, the threshold is set by the regional entities, like
Northeast Power Coordinating Council The Northeast Power Coordinating Council (NPCC) was formed on January 19, 1966, as a successor to the Canada–United States Eastern Interconnection (CANUSE). It was established to improve the reliability of electric service. NPCC is one of six ...
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See also

*
Value of lost load The Value of Lost Load (VoLL) is the estimated amount that customers receiving electricity Electricity is the set of physical phenomena associated with the presence and motion of matter possessing an electric charge. Electricity is related ...


References


Sources

* * * * * * * * * * * {{electric-stub Electrical engineering Reliability indices