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): •
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; •
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. 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; •
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: {LOLD} = \frac {LOLE} {LOLF} == One-day-in-ten-years criterion ==