Electrical Term Definitions

Below is a list of commonly used electric industry terms.

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Alternating Current (AC) A periodic current, the average value of which over a period is zero. Unless distinctly specified otherwise, the term refers to a current that reverses its direction at regularly recurring intervals of time and that has alternately positive and negative values. Almost all electric utilities generate AC electricity because it can easily be transformed to higher or lower voltages.
Ampere The unit of measurement of electrical current produced in a circuit by one volt acting through a resistance of one ohm.
APPA American Public Power Association, the trade association of publicly held power entities.
Average Megawatt A unit of energy output over a year that is equal to the energy produced by the continuous operation of one megawatt of capacity over a period of time (in one year equal to 8,760 megawatt-hours).
Base Load The minimum amount of electric power delivered or required over a given period of time at a steady rate. The minimum continuous load or demand in a power system over a given period of time.
Blackout The emergency loss of the source of electricity serving an area caused by failure of the generation, transmission or distribution system.
Bonneville Power Administration (BPA) A power marketing and electric transmission agency of the United States government with headquarters in Portland, Oregon.
Brownout The partial reduction of electrical voltages caused by customer demand being higher than anticipated or by the failure of the generation, transmission, or distribution system. A brownout results in lights dimming and motor-driven devices slowing down.
Capacitor A transmission element designed to inject reactive power into the transmission network. Also utilized to increase voltages, reduce loadings, and increase available kW output from generators. Capacitor ratings are typically given in Megavars.
Circuit A conductor/system of conductors through which electric current flows.
Cogeneration The simultaneous production of both useable heat or steam and electricity from a common fuel source.
Combustion Turbine A fuel-fired turbine engine used to drive an electric generator. Combustion turbines, because of their generally rapid firing time, are used to meet short-term peak demands placed on power distribution systems.
Conductor A substance or body, usually in the form of a wire, cable or busbar that allows a current of electricity to pass continuously along it.
Cost of Service The total amount of money – including return on invested capital, operation and maintenance costs, administrative costs, taxes, and depreciation expense – to produce a utility service.
Current (Electric) A flow of electrons in an electrical conductor. The rate of movement of the electricity, measured in amperes.
Curtailment A temporary, mandatory power load reduction taken when there is a risk that the utility cannot meet its power requirements and retain a prudent reserve margin.
Demand Charge This portion of rates is expected to recover the costs associated with the level of demand for the particular service. Included in demand charges are capital-related costs and the cost of operation and maintenance of generation, transmission and distribution.
Direct Current An electric current that flows in one direction with a magnitude that does not vary or that varies only slightly.
Distributed Generation Electrical power produced elsewhere than a central station generating unit. Examples – fuel cell technology and on-site small scale generators.
Distribution The system of lines, transformers and switches that connect between the transmission network and customer load; the transport of electricity to ultimate use points such as homes and businesses; that portion of the electric system that is dedicated to delivering electric energy to an end user at relatively low voltages.
Drawdown The distance the water surface of a reservoir is lowered from a given elevation as the result of releasing water. Drawdown can be expressed in terms of the acre-feet of stored water released.
Electric System The generation, transmission, distribution and other facilities operated as an electric utility or a portion thereof.
Energy Charge This portion of the rates covers the product (energy), based upon kilowatt-hours consumed.
FERC Federal Energy Regulatory Commission, a regulatory agency within the Department of Energy, which has jurisdiction over interstate energy sales, wholesale electric rates, hydroelectric licensing, natural gas pricing, oil pipeline rates, and gas pipeline certification.
Firm Energy Energy sales which, although not subject to interruption for economic purposes, may be interrupted for unexpected/uncontrollable events.
Fuel Cell A device that generates direct current to electricity by means of an electrochemical process with little or no emission by-product.
Fuel Switching Substituting one fuel for another based on price and availability. Large industries often have the capability of using either oil or natural gas to fuel their operation and of making the switch on short notice.
Gas Turbine Plant A plant in which the prime mover is a gas turbine. A gas turbine typically consists of an axial-flow compressor, which feeds compressed air into one or more combustion chambers where liquid or gaseous fuel is burned. The resulting hot gases are expanded through the turbine, causing it to rotate. The rotating turbine shaft drives the compressors as well as the generator, producing electricity.
Geothermal Power generated from heat energy derived from hot rock, hot water or steam below the earth’s surface.
Grid The layout of the electrical transmission system or a synchronized transmission network.
Interruptible Load Refers to a contractual arrangement in which a customer’s energy load can be interrupted at times of seasonal peak load by direct control of the utility system operator, or by action of the customer at the direct request of the system operator. This usually involves commercial and industrial customers.
Inverted Block Rate A rate structure that prices successive blocks of power use at increasingly higher per-unit prices. The more electricity a customer uses, the greater the average price.
Investor Owned Utility (IOU) A utility organized under state law as a publicly traded corporation for the purposes of providing power service and earning a profit for its stakeholders.
Kilowatt (kW) One thousand watts.
Load The amount of electric power delivered or required at any specific point or points on a system. The requirement originates at the energy-consuming equipment of the consumer.
Load Management The management of load patterns in order to better utilize the facilities of the system. Generally, load management attempts to shift load from peak-use periods to other periods of the day or year.
Megawatt (MW) One million watts.
Mill One tenth of one cent. The common unit for pricing electricity.
NERC North American Electric Reliability Council, formed to promote the reliability and adequacy of bulk power supply in the electric utility systems of North America. It consists of 10 regional councils, including the Western Systems Coordinating Council, covering the Northwest.
Non-firm Energy Energy that is not guaranteed to be continuously available. Non-firm energy is available in varying amounts depending on season and weather conditions.
Ohm The unit of measurement of electrical resistance. The resistance of a circuit in which a potential difference of one volt produces a current of one ampere.
Peak Demand The maximum energy load during a specified time period.
Preference A legal directive that gives publicly owned utilities and cooperatives priority access to federal power, such as power from the Bonneville Power Administration.
PUD – Public Utility District Snohomish County PUD is a municipal corporation of the state of Washington, formed by a majority vote of the people for the purpose of providing electric and/or water service. There are a total of 28 PUDs in Washington.
Regional Transmission Organization (RTO) A plan set up by FERC to establish regional groups to expedite the coordination of wholesale wheeling. Regional groups include transmission system owners, wholesale purchasers and independent power generators.
Rotating Outage Also known as rolling blackouts, these are controlled events to turn off electricity to selected areas to keep the electricity supply and load in balance. To make sure that no one neighborhood or region bears the entire burden of energy shortages, outages are rotated through multiple areas of a utility’s service area.
SCADA Supervisory Control and Data Acquisition – A system of remote control and telemetry used to monitor and control a transmission system.
Spill Release of water from a reservoir over a spillway rather than putting it through turbines to produce electricity. A spillway is the overflow structure of the dam.
Spot Market A power market where goods are traded for immediate delivery.
Substation Facility equipment that switches, changes or regulates electric voltage.
Time of Use Rates A rate design imposing higher charges during periods of the day when relatively higher peak demands are experienced and lower charges during low demand periods.
Transformer A device for changing the voltage of alternating current.
Transmission The network of high-voltage lines, transformers and switches used to move electrical power from generators to the distribution system.
Unbundled Services The selling and pricing of services separately as opposed to offering services "bundled" into packages with a single price for the whole package.
Voltage Electromotive force or potential difference, usually expressed in volts.
Watt The electrical unit of power. The rate of energy transfer equivalent to one ampere flowing under a pressure of one volt at unity power factor.
Watt-hour (Wh) An electrical energy unit of measure equal to one watt of power supplied to, or taken from, an electric circuit steadily for one hour. Examples – kilowatt hour (kWh) and megawatt hour (MWh).
Wheeling The use of the transmission facilities of one system to transmit power for another system. Wheeling can apply to either wholesale or retail service.