National Electric Transmission Congestion Study - W2agz.com

Operating transfer capability (OTC): The
amount of power that can be transferred in a reliable
manner, meeting all NERC contingency requirements,
considering the current or projected operational
state of the system. OTC is sometimes referred
to as TTC, or Total Transfer Capability.
Outage: A period during which a generating unit,
transmission line, or other facility is out of service.
Peak demand: Maximum electric load during a
specified period of time.
PJM: The RTO serving parts or all of the states of
Delaware, Illinois, Indiana, Kentucky, Maryland,
Michigan, New Jersey, North Carolina, Ohio, Pennsylvania,
Tennessee, Virginia, West Virginia and
the District of Columbia.
Rating: The safe operational limits of a transmission
system element under a set of specified conditions.
Redispatch: When transmission constraints or reliability
requirements indicate that specific levels of
generation across a set of power plants cannot be
maintained reliably, the grid operator redispatches
(changes the dispatch or operating instructions) for
one or more power plants (increasing generation on
one side of the constraint and reducing generation
on the other side) to restore a safe operational pattern
across the grid.
Reliability: Electric system reliability has two
components—adequacy and security. Adequacy is
the ability of the electric system to supply customers’
aggregate electric demand and energy requirements
at all times, taking 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 can be measured by the frequency, duration
and magnitude of adverse effects on electricity
delivery to customers.
RTO: Regional Transmission Operator, an independent,
federally regulated entity that coordinates
regional transmission in a non-discriminatory manner
and ensures the safety and reliability of the electric
system.
Shadow price: The shadow price equals the value
of the change in all affected generation if one more
MWh could flow across a constrained facility then
loaded to its maximum limit; the marginal cost of
generation redispatch required to obey the transmission
constraint.
SPP: The Southwest Power Pool, serving portions
of Arkansas, Kansas, Louisiana, Missouri, New
Mexico, Oklahoma, and Texas.
Stability: The ability of an electric system to maintain
a state of equilibrium during normal and abnormal
conditions or disturbances.
Stability limit: The maximum power flow possible
through some particular point in the system while
maintaining stability in the entire system or the part
of the system to which the stability limit refers.
System: A combination of generation, transmission,
and distribution components.
System operating limit: The value (such as MW,
MVar, amperes, frequency, or volts) that satisfies
the most limiting of the prescribed operating criteria
for a specified system configuration to ensure operation
within acceptable reliability criteria. System
Operating Limits are based upon certain operating
criteria. These include, but are not limited to, preand
post-contingency ratings for facilities, transient
stability, voltage stability, and system voltage.
System operator: An individual at a control center
(Balancing Authority, Transmission Operator,
Generator Operator, Reliability Coordinator)
whose responsibility it is to monitor and control that
electric system in real time.
Thermal rating: The maximum amount of electrical
current that a transmission line or electrical facility
can conduct over a specified time period before
it sustains permanent damage by overheating
or sags to the point that it violates public safety requirements.
TLR: Transmission loading relief, a procedure
used in the Eastern Interconnection to deal with a
situation where a transmission facility or path is at
its operating limit. In a TLR, the grid operator can
redispatch generation, reconfigure transmission, or
curtail loads to restore the system to secure operating
conditions.
U.S. Department of Energy / National Electric Transmission Congestion Study / 2006 69