Definitions are given here to aid the user in understanding
the factors that affect index calculation. Many of these definitions were taken
directly from IEEE Std 100-1996. If there is a conflict between the definitions
in this guide and IEEE Std 100-1996, the definitions in this guide take
precedence. Others are given because they have a new interpretation within this
guide or have not been defined before.
connected load:
The connected transformer kVA, peak load, or metered demand
(to be clearly specified when reporting) on the circuit or portion of circuit
that is interrupted. When reporting, the report should state whether it is
based on an annual peak or on a reporting period peak.
customer count:
The number of customers or number of meters. The number of
customers is the preferred item to count if the counting system is not already
in place.
distribution system:
That portion of an electric system that delivers electric
energy from transformation points on the transmission system to the customer.
Note: The distribution system is generally considered to be anything from the
distribution substation fence to the customer meter. Often the initial
overcurrent protection and voltage regulator are within the substation fence.
duration interruption:
The period (measured in seconds, or minutes, or hours, or
days) from the initiation of an interruption to a customer or other facility
until service has been restored to that customer or facility. An interruption
may require step-restoration tracking to provide reliable index calculation. It
may be desirable to record the duration of each interruption.
forced interruption:
An interruption caused by a forced outage.
interrupting device:
A device capable of being reclosed whose purpose is to
interrupt faults and restore service or disconnect loads. These devices can be
manual, automatic, or motor-operated. Examples may include transmission
breakers, feeder breakers, line reclosers, and motor-operated switches.
interrupting device event:
The operation associated with the interrupting device for
cases where a reclosing device operates but does not lockout and where a switch
is opened only temporarily.
interrupting device operation:
The operation associated with a reclosing device for cases
where the switch opens and closes once but does not lockout.
interruption:
The loss of service to one or more customers. Note: It is
the result of one or more component outages, depending on system configuration.
See: outage.
interruptions caused by events outside of distribution: For
most utilities, this type of interruption is a small percentage of the total
interruptions. It will be defined here to account for the cases where outside
influences are a major occurrence. Three categories that may be helpful to
monitor are: transmission, generation, and substations.
lockout:
The final operation of a recloser or circuit breaker in an
attempt to clear a persistent fault. The overcurrent protective device locks
open their contacts under these conditions.
loss of service:
The loss of electrical power, a complete loss of voltage, to
one or more customers or meters. This does not include any of the power quality
issues (sags, swells, impulses, or harmonics).
major event:
A catastrophic event that exceeds design limits of the
electric power system and that is characterized by the following (as defined by
the utility):
a) Extensive damage to the electric power system;
b) More than a specified percentage of customers
simultaneously out of service;
c) Service restoration times longer than specified.
Some examples are extreme weather, such as a one in five
year event, or earthquakes.
momentary event interruption:
An interruption of duration limited to the period required
to restore service by an interrupting device. Note: Such switching operations
must be completed in a specified time not to exceed 5 min. This definition
includes all reclosing operations that occur within 5 min of the first interruption.
For example, if a recloser or breaker operates two, three, or four times and
then holds, the event shall be considered one momentary interruption event.
momentary interruption:
Single operation of an interrupting device that results in a
voltage zero. For example, two breaker or recloser operations equals two
momentary interruptions.
outage (electric power systems):
The state of a component when it is not available to perform
its intended function due to some event directly associated with that component.
Notes:
1. An outage may or may not cause an interruption of service
to customers, depending on system configuration.
2. This definition derives from transmission and
distribution applications and does not apply to generation outages.
reporting period:
A period assumed to be one year unless otherwise stated.
scheduled interruption (electric power systems):
A loss of electric power that results when a component is
deliberately taken out of service at a selected time, usually for the purposes
of construction, preventative maintenance, or repair.
Notes:
1. This derives from transmission and distribution
applications and does not apply to generation interruptions.
2. The key test to determine if an interruption should be
classified as a forced or scheduled interruption is as follows. If it is
possible to defer the interruption when such deferment is desirable, the
interruption is a scheduled interruption; otherwise, the interruption is a
forced interruption. Deferring an interruption may be desirable, for example,
to prevent overload of facilities or interruption of service to customers.
step restoration:
The restoration of service to blocks of customers in an area
until the entire area or feeder is restored.
sustained interruption:
Any interruption not classified as a momentary event. Any
interruption longer
than 5 min.
total number of customers served:
The total number of customers served on the last day of the
reporting period. If a different customer total is used, it must be clearly
defined within the report.
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