Loss of load explained

Loss of load should not be confused with Load loss.

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. Multiple probabilistic reliability indices 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) 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):

{LOLE}={LOLP} ⋅ 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, the coefficients vary from network to network;

{LOLD}=

LOLE
LOLF

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

{LOLP}=

1
10 ⋅ 365

≈ 0.000274

. In the US, the threshold is set by the regional entities, like Northeast Power Coordinating Council:

See also

Sources

This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Loss of load".

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