National Electric Transmission Congestion Study - W2agz.com

Transfer capability: The measure of the ability of
interconnected electric systems to move or transfer
power in a reliable manner from one area to another
over all transmission lines (or paths) between those
areas under specified system conditions. The units
of transfer capability are in terms of electric power,
generally expressed in megawatts (MW). The transfer
capability from “Area A” to “Area B” is not generally
equal to the transfer capability from “Area B”
to “Area A.”
Transformer: An electrical device for changing
the voltage of alternating current.
Transmission: An interconnected group of lines
and associated equipment for moving electric energy
at high voltage between points of supply and
points at which it is delivered to other electric systems
or transformed to a lower voltage for delivery
to customers.
Transmission constraint: A limitation on one or
more transmission elements that may be reached
during normal or contingency system operations.
Transmission path: A transmission path may consist
of one or more parallel transmission elements.
The transfer capability of the transmission path is
the maximum amount of actual power that can flow
over the path without violating reliability criteria.
The net scheduled power flow over the transmission
path must not exceed the path’s transfer capability
or operating nomogram limits at any time, even during
periods when the actual flow on the path is less
than the path’s transfer capability.
U90: The number of hours or percentage of a year
when a transmission path is operated at or above
90% of its safe operating limit.
U75: The number of hours or percentage of a year
when a transmission path is operated at or above
75% of its safe operating limit.
Voltage: Voltage is the difference in electrical potential
between two points of an electrical network,
expressed in volts. The North American grid is operated
using alternating current at 120 volts and 60
Herz frequency.
WECC: Western Electric Coordinating Council,
the reliability coordinator serving the western interconnection.
70 U.S. Department of Energy / National Electric Transmission Congestion Study / 2006