Glossary (N through Z)

Native load (electric):  The end-use customers that the load-serving entity, or utility, is obligated to serve.

Net summer capacity:  The maximum output, commonly expressed in megawatts (MW), that generating equipment can supply to system load, as demonstrated by a multi-hour test, at the time of summer peak demand (period of June 1 through September 30.) This output reflects a reduction in capacity due to electricity use for station service or auxiliaries.

Net winter capacity:  The maximum output, commonly expressed in megawatts (MW), that generating equipment can supply to system load, as demonstrated by a multi-hour test, at the time of peak winter demand (period of December 1 through February 28). This output reflects a reduction in capacity due to electricity use for station service or auxiliaries.

North American Electric Reliability Corporation (NERC):  A nonprofit corporation formed in 2006 as the successor to the North American Electric Reliability Council established to develop and maintain mandatory reliability standards for the bulk electric system, with the fundamental goal of maintaining and improving the reliability of that system. NERC consists of regional reliability entities covering the interconnected power regions of the contiguous United States, Canada, and Mexico. See the North American Electric Reliability Corporation (NERC) Regions.

Ohm:  A measure of the electrical resistance of a material equal to the resistance of a circuit in which the potential difference of 1 volt produces a current of 1 ampere.

Open access:  A regulatory mandate to allow others to use a utility's transmission and distribution facilities to move bulk power from one point to another on a non discriminatory basis for a cost-based fee.

Open access (electric):  Federal Energy Regulatory Commission Order No. 888 requires public utilities to provide non-discriminatory transmission service over their transmission facilities to third parties to move bulk power from one point to another on a nondiscriminatory basis for a cost-based fee. Order 890 expanded Open Access to cover the methodology for calculating available transmission transfer capability; and improvements that opened a coordinated transmission planning processes.

Outage:  The period during which a generating unit, transmission line, or other facility is out of service.

Peak demand:  The maximum load during a specified period of time.

Peaking capacity:  Capacity of equipment normally reserved for operation during the hours of highest daily, weekly, or seasonal loads.

Power:  The rate of producing, transferring, or using energy, most commonly associated with electricity. Power is measured inwatts and often expressed in kilowatts (kW) or megawatts (mW). Also known as "real" or "active" power. See Active Power, Apparent Power, Reactive Power, Real Power

Power exchange:  An entity providing a competitive spot market for electric power through day- and/or hour-ahead auction of generation and demand bids.

Power marketers:  Business entities engaged in buying and selling electricity. Power marketers do not usually own generating or transmission facilities. Power marketers, as opposed to brokers, take ownership of the electricity and are involved in interstate trade.

Power pool:  An association of two or more interconnected electric systems having an agreement to coordinate operations and planning for improved reliability and efficiencies.

Rate base:  The value of property upon which a utility is permitted to earn a specified rate of return as established by a regulatory authority. The rate base generally represents the value of property used by the utility in providing service and may be calculated by any one or a combination of the following accounting methods: fair value, prudent investment, reproduction cost, or original cost. Depending on which method is used, the rate base includes working capital, materials and supplies, and deductions for depreciation.

Rate base (electric):  The value of property, upon which, a utility is permitted to earn a specified rate of return as established by a regulatory authority. FERC definition

Ratemaking authority:  A utility commission's legal authority to fix, modify, approve, or disapprove rates as determined by the powers given the commission by a State or Federal legislature.

Real Power:  The component of electric power that performs work, typically measured in kilowatts (kW) or megawatts(MW)--sometimes referred to as Active Power.

Regional Transmission Group:  A utility industry concept that the Federal Energy Regulatory Commission (FERC) embraced for the certification of voluntary groups that would be responsible for transmission planning and use on a regional basis.

Regulation:  The governmental function of controlling or directing economic entities through the process of rulemaking and adjudication.

Reliability coordinator (electric):  The entity that is the highest level of authority who is responsible for the reliable operation of the bulk electric system, has the wide area view of the bulk electric system, and has the authority to prevent or mitigate emergency operating situations in both next-day analysis and real-time operations.

Restructuring:  The process of replacing a monopoly system of electric utilities with competing sellers, allowing individual retail customers to choose their electricity supplier but still receive delivery over the power lines of the local utility. It includes the reconfiguration of the vertically-integrated electric utility.

Retail sales (electric):  Sales made directly to the customer that consumes the energy product.

Right-of-way (electric):  A corridor of land on which electric lines may be located. The transmission owner may own the land in fee, own an easement, or have certain franchise, prescription, or license rights to construct and maintain lines.

Stability (electric):  The ability of an electric system to maintain a state of equilibrium during normal and abnormal conditions or disturbances.

Substation:  Facility equipment that switches, changes, or regulates electric voltage.

Supervisory Control and Data Acquisition (electric):  A system of remote control and telemetry used to monitor and control the transmission system.

Switching station:  Facility equipment used to tie together two or more electric circuits through switches. The switches are selectively arranged to permit a circuit to be disconnected or to change the electric connection between the circuits.

System (electric):  Physically connected generation, transmission, and distribution facilities operated as an integrated unit under one central management or operating supervision.

System operator (electric):  An individual at a control center whose responsibility it is to monitor and control that electric system in real time.

Thermal rating (electric):  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 sags to the point that it violates public safety requirements.

Tie line (electric):  A circuit connecting two parts within an individual electrical system

Transformer:  An electrical device for changing the voltage of alternating current.

Transmission (electric):  An interconnected group of lines and associated equipment for the movement or transfer of electric energy between points of supply and points at which it is transformed for delivery to customers or is delivered to other electric systems. Also, the movement or transfer of electric energy over an interconnected group of lines and associated equipment between supply points at which it is transformed for delivery to consumers or is delivered to other electric systems. Transmission is considered to end when the energy is transformed for distribution to the consumer.

Transmission constraint (electric):  A limitation on one or more transmission elements that may be reached during normal or contingency system operations.

Transmission line (electric):  A system of structures, wires, insulators and associated hardware that carry electric energy from one point to another in an electric power system. Linesare operated at relatively high voltages varying from 69 kV up to 765 kV, and are capable of transmitting large quantities of electricity over long distances.

Transmission operator (electric):  The entity responsible for the reliability of its localized transmission system, and that operates or directs the operations of the transmission facilities.

Transmission owner (electric):  The entity that owns and maintains transmission facilities.

Transmitting utility:  A regulated entity which owns and may construct and maintain wires used to transmit wholesale power. It may or may not handle the power dispatch and coordination functions. It is regulated to provide non-discriminatory connections, comparable service, and cost recovery.

Ultimate customer:  A customer that purchases electricity for its own use and not for resale.

Unbundling:  Separating vertically integrated monopoly functions into their component parts for the purpose of separate service offerings.

Utility distribution companies:  The entities that provide regulated services for the distribution of electricity to customers and serve customers who do not choose direct access. Regardless of where a consumer chooses to purchase power, the customer's current utility, also known as the utility distribution company, will deliver the power to the consumer.

Vertical integration:  The combination within a firm or business enterprise of one or more stages of production or distribution. In the electric industry, it refers to the arrangement whereby a utility owns its own generating plants, transmission system, and distribution lines to provide all aspects of electric service.

Voltage reduction:  Any intentional reduction of system voltage for maintaining the continuity of service of the bulk electric power supply system.

Watt (W):  The unit of electrical power equal to one ampere under a pressure of one volt. A Watt is equal to 1/746 horse power.

Watthour (Wh):  The electrical energy unit of measure equal to one watt of power supplied to, or taken from, an electric circuit steadily for one hour.

Wheeling service:  The movement of electricity from one system to another over transmission facilities of interconnecting systems.

Wholesale competition:  A system whereby a distributor of power would have the option to buy its power from a variety of power producers, and the power producers would be able to compete to sell their power to a variety of distribution companies.

Wholesale power market:  The purchase and sale of electricity from generators to resellers (who sell to retail customers), along with the ancillary services needed to maintain reliability and power quality at the transmission level.

Wholesale sales:  Energy supplied to other electric utilities, cooperatives, municipals, and Federal and state electric agencies for resale to ultimate consumers.

Wires charge:  A broad term referring to fees levied on power suppliers or their customers for the use of the transmission or distribution wires.

Source:  U.S. Energy Information Administration (www.eia.doe.gov).