Glossary

Glossary

AccessThe contracted right to use an electrical system to transfer electrical energy.
Capacitor banksSystem elements (equipment) that support the voltages necessary to provide reliable service to customers.
CapacityThe load-carrying ability, expressed in megawatts (mw) of generation, transmission or other electrical equipment.
CircuitA path of conductors (wires) that an electric current follows.
ConductorA material through which electric current flows easily. ATC often refers to wires as conductors.
ContingencyAn outage of a transmission line, generator or other piece of equipment, which affects the flow of power on the transmission network and impacts other network elements.
DemandThe rate at which electric energy is delivered to or by a system or part of a system, generally expressed in kilowatts (kw) or megawatts (mw), at a given instant or averaged over any designated interval of time.
DistributionAn interconnected group of lines and associated equipment for the local delivery of low-voltage electricity between the transmission network and end users. ATC does not operate local distribution system.
FERCFederal Energy Regulatory Commission; an independent agency that regulates the interstate transmission of natural gas, oil and electricity.
GenerationThe act of converting various forms of energy input (thermal, mechanical, chemical and/or nuclear energy) into electric power. Also, the amount of electric energy produced, usually expressed in kilowatt hours (kwh) or megawatt hours (mwh).
GridThe transmission and distribution networks operated by electrical utilities.
Heavy loadsHigh volume of electricity flowing on a line, transformer or other equipment to meet a high demand for electricity, using during hot weather.
Import/exportAbility of the transmission system to bring power into or out of an area in order to serve load.
InsulatorA material that opposes the flow of electric current; the ceramic piece that holds the conductor (wire) to the structure.
LoadAll the devices that consume electricity and make up the total demand for power at any given moment, like factories, distribution substations, etc.
Loading reliefA system change or reinforcement that results in lower power flows on equipment that is heavily loaded or overloaded.
Low voltagesSituation that can occur in parts of the system that are heavily loaded or which have high motor loads. Think of a clothesline pulled taut with nothing hanging on it, but which then tends to sag when more and more clothes (i.e. loads or motors) are attached.
kVKilovolt; a measure of voltage. ATC operates its transmission system at 69 kV, 138 kV and 345 kV. A few 230 kV lines exist on the system as well.
MarginThe difference between (1) generation resources and electric demand or (2) the difference between the capacity of a transmission line and the power flowing on that line. Margin is usually expressed in megawatts (MW).
MISOMidwest Independent System Operator
MWMegawatt
NERCNorth American Reliability Council; a not-for-profit company formed by the electric utility industry in 1968 to promote the reliability of the electricity supply in North America. NERC consists of nine Regional Reliability Councils and one Affiliate whose members account for virtually all the electricity supplied in the United States, Canada, and a portion of Mexico.
NetworkA system of interconnected lines and electrical equipment
Operating guidesProcedures carried out by transmission operators when certain events occur on the system that may compromise system reliability if no action is taken.
OutageThe unavailability of electrical equipment; could be planned for maintenance or unplanned (forced) by weather or equipment failures.
OverloadsOccur when power flowing through wires or equipment is more than they can carry without incurring damage.
Parallel path flowsWhen electricity flows from a power plant over the transmission system, it obeys the laws of physics and flows over the paths of least resistance. Though there may be direct connection between a power plant and a particular load area, some of the power will instead flow over other network lines "parallel" to the direction connection.
Power flowsElectricity moving through lines or other equipment.
RebuildRemoving an existing line and replacing it with a new, higher capacity line.
ReliableMeets standard industry and specific ATC performance criteria.
ReliabilityThe degree of performance of the elements of the bulk electric system that results in electricity being delivered to customers within accepted standards and in the amount desired. The ability to deliver uninterrupted electricity to customers on demand, and to withstand sudden disturbances such as short circuits or loss of system components.
ReserveThe difference between an electric system's capability and the expected peak demand for electricity.
Serve loadReliably deliver the amounts of electricity needed to match what consumer would needs at any given time.
StabilityThe ability of an electric system to maintain a state of equilibrium during normal and abnormal system conditions or disturbances.
SubstationPlace where transmission lines connect to each other and where protective equipment is located. Also where transformers are located to step the voltage up or down in order to put power into or take power out of the transmission network.
System PlanningThe process by which the performance of the electric system is evaluated and future changes and additions to the bulk electric systems are determined.
T-D interconnectionTransmission to distribution interconnection; place where local distribution substations connect to transmission system.
Thermal ratingThe 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 before it violates public safety requirements.
Thermal overloadsPower flows on lines or equipment that exceed their capacity limits.
Transfer capabilityThe 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 between those areas under specified system conditions.
TransformersDevices that changes voltage levels.
TransmissionAn interconnected group of lines and equipment for transporting electric energy in bulk on a high voltage power line from a source or sources of power supply (e.g. power plant) to a point of use within a utility system or to a point of interconnection with another utility system or power grid.
UpratesMake the transmission system element able to carry more electricity than it currently can. This can include increasing line clearances or replacing limiting pieces of equipment to enable the safe transport and delivery of more power.
VoltageA type of "pressure" that drives electrical charges through a circuit. Higher voltage lines generally carry power longer distances.
Voltage collapseCan occur after a contingency where the voltage dips low enough and cannot recover quickly enough. In this situation protective equipment will automatically disconnect lines and/or transformers, causing load to be shed.
Voltage stabilitySystem is able to maintain the proper voltages needed to serve load.
WattUnit of power equal to volts x amps.