Electric system reliability has two components: adequacy and security.  Adequacy is the ability of the electric system to supply the electrical demand and energy requirements of the customers at all times, taking into account scheduled and unscheduled outages of system facilities.  Security is the ability of the electric system to withstand sudden disturbances, such as electric short circuits or unanticipated loss of system facilities.  The degree of reliability may be measured by the frequency, duration and magnitude of adverse effects on consumer services