| Access | The contracted right to use an electrical system to transfer electrical energy. |
| Blackout | A total power failure over a large area; usually caused by the failure of major generating equipment or transmission facilities. |
| Capacitor banks | System elements (equipment) that support the voltages necessary to provide reliable service to customers. |
| Capacity | The load-carrying ability, expressed in megawatts (mw) of generation, transmission or other electrical equipment. |
| Circuit | A path of conductors (wires) that an electric current follows. |
| Conductor | A material through which electric current flows easily. ATC often refers to wires as conductors. |
| Contingency | An 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. |
| Demand | The 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. |
| Distribution | An 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. |
| FERC | Federal Energy Regulatory Commission; an independent agency that regulates the interstate transmission of natural gas, oil and electricity. |
| Generation | The 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). |
| Grid | The transmission and distribution networks operated by electrical utilities. |
| Heavy loads | High volume of electricity flowing on a line, transformer or other equipment to meet a high demand for electricity, using during hot weather. |
| Import/export | Ability of the transmission system to bring power into or out of an area in order to serve load. |
| Insulator | A material that opposes the flow of electric current; the ceramic piece that holds the conductor (wire) to the structure. |
| Load | All the devices that consume electricity and make up the total demand for power at any given moment, like factories, distribution substations, etc. |
| Loading relief | A system change or reinforcement that results in lower power flows on equipment that is heavily loaded or overloaded. |
| Low voltages | Situation 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. |
| kV | Kilovolt; 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. |
| Margin | The 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). |
| MISO | Midwest Independent System Operator |
| MW | Megawatt |
| NERC | North 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. |
| Network | A system of interconnected lines and electrical equipment |
| Operating guides | Procedures carried out by transmission operators when certain events occur on the system that may compromise system reliability if no action is taken. |
| Outage | The unavailability of electrical equipment; could be planned for maintenance or unplanned (forced) by weather or equipment failures. |
| Overloads | Occur when power flowing through wires or equipment is more than they can carry without incurring damage. |
| Parallel path flows | When 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 flows | Electricity moving through lines or other equipment. |
| Rebuild | Removing an existing line and replacing it with a new, higher capacity line. |
| Reliable | Meets standard industry and specific ATC performance criteria. |
| Reliability | The 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. |
| Reserve | The difference between an electric system's capability and the expected peak demand for electricity. |
| Serve load | Reliably deliver the amounts of electricity needed to match what consumer would needs at any given time. |
| Stability | The ability of an electric system to maintain a state of equilibrium during normal and abnormal system conditions or disturbances. |
| Substation | Place 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 Planning | The 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 interconnection | Transmission to distribution interconnection; place where local distribution substations connect to transmission system. |
| 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 before it violates public safety requirements. |
| Thermal overloads | Power flows on lines or equipment that exceed their capacity limits. |
| 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 between those areas under specified system conditions. |
| Transformers | Devices that changes voltage levels. |
| Transmission | An 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. |
| Uprates | Make 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. |
| Voltage | A type of "pressure" that drives electrical charges through a circuit. Higher voltage lines generally carry power longer distances. |
| Voltage collapse | Can 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 stability | System is able to maintain the proper voltages needed to serve load. |
| Watt | Unit of power equal to volts x amps. |
