Loss of load

Template:Short description Template:Distinguish 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.Template:Sfn Multiple probabilistic reliability indices for the generation systems are using loss of load in their definitions, with the more popularTemplate:Sfn being Loss of Load Probability (LOLP) that characterizes a probability of a loss of load occurring within a year.Template:Sfn 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 $N$ (e.g., for a yearlong interval $N=365$ if the increment is a day, $N=8760$ if the increment is an hour):Template:Sfn

• 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;Template:Sfn
• Loss of load expectation (LOLE) is the total duration of increments when the loss of load is expected to occur, $LOLE=LOLP\cdot N$. 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.Template:Sfn 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;Template:Sfn although in practice the relationship is close to linear, the coefficients vary from network to network;Template:Sfn
• 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);Template:Sfn
• Loss of load duration (LOLD) characterizes the average duration of a loss of load event:Template:Sfn $LOLD=\frac{LOLE}{LOLF}$

One-day-in-ten-years criterion

A typically accepted design goal for $LOLE$ is 0.1 day per yearTemplate:Sfn ("one-day-in-ten-years criterion"Template:Sfn a.k.a. "1 in 10"Template:Sfn), corresponding to $LOLP=\frac{1}{10\cdot 365}\approx 0.000274$. In the US, the threshold is set by the regional entities, like Northeast Power Coordinating Council:Template:Sfn Template:Quote

See also

• Value of lost load

Sources

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