• Frequency Error

    The difference between actual system frequency and scheduled system frequency.

  • Frequency Regulation

    The control of an interconnection's frequency through the combined efforts of the Control Areas' generation control.

  • Frequency Response (Equipment)

    Ability of a system or elements of a system to respond to changes in the frequency within the system.

  • Fuel

    Any substance that can be burned to produce heat; also, materials that can be fissioned in a chain reaction to produce heat.

  • Fuel Cell

    A device that generates direct current to electricity by means of an electrochemical process.

  • Fuel Expenses

    These costs include the fuel used in the production of steam or driving another prime mover for the generation of electricity. Other associated expenses including transportation and unloading the shipped fuel and all handling of the fuel up to the point where it enters the first bunker, hopper, bucket, tank, or holder in the boiler-house structure.

  • 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.

  • Fuel-Switching Capability

    The ability of an end-user to readily change fuel type consumed whenever a price or supply advantage develops for an alternative fuel.

  • Fuel Use Act

    A statute enacted in 1978. It limited the use of natural gas in power plant and industrial boilers and that portion of the Act was repealed in 1987.

  • Full-Forced Outage

    The net capability of main generating units that is unavailable for load for emergency reasons.

  • Functional Unbundling

    The FERC has proposed in its NOPR to implement full open access of the electric transmission industry that jurisdictional utilities separate their transmission, distribution, and generation functions.

  • Futures

    A standardized contract for the purchase or sale of a commodity which is traded for delivery in the future.

  • Futures Contract

    An exchange-traded contract promising to buy or sell standard commodities or securities at a future date at a set price. Futures are "paper" deals and involve profit and loss on promises to deliver, not possession of the actual commodity. The main difference between a futures contract and a forward contract is that a futures contract is cash 'Settled, or marked-to-market, daily. Additionally, the futures market requires that all market participants sellers and buyers alike - post a performance bond call margin.

  • Gas

    That state of matter which has neither independent shape nor volume. Gas expands to fill the entire container in which it is held. Gas is one of the three forms of matter: solid, liquid and gas.

  • Gas-Flow

    A set of standard record formats supporting the electronic data interchange of files, established by a joint Task Force of the Interstate Natural Gas Association of America (INGAA), the Council of Petroleum Accountants Society (COPAS), and the American Gas Association (AGA).

  • Gas Inventory Charge (GIG)

    A charge paid by a buyer to its supplier for holding natural gas supplies ready to be delivered to the buyer.

  • Gas-Reserves

    Natural gas in natural underground formation in wells, fields or pools.

  • Gas Transported for Others

    Natural gas owned by another company received into and transported through any part of a pipeline transmission system under a transportation agreement.

  • 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.

  • Gasification

    Any of various processes by which coal is turned into natural gas.

  • Gathering Line

    Network-like pipeline that transports natural gas from individual wellheads to a compressor station, treating or processing plant, or main trunk transmission line. Gathering lines are generally relatively short in length, operate at a relatively low pressure, and are small in diameter.

  • Gathering Station

    A compressor station at which natural gas is gathered from wells by suction because wellhead pressure is not sufficient to produce the desired rate of flow into a transmission or distribution system.

  • Genco

    The term used for that portion of a functionally disaggregated electric utility's business that involves the production of power which is operated separately from any other power functions which the utility owns or operates.

  • Generating Unit

    Any combination of physically connected generator(s), reactor (s), boiler(s), combustion turbine(s), or other prime mover(s) operated together to produce electric power.

  • Generation

    The process of producing electric energy by transforming other forms of energy such as steam, heat or falling water. Also, the amount of electric energy produced, expressed in kilowatt-hours (kWh) or megawatt-hours (mWh).

  • Generation Company (Genco)

    A regulated or non-regulated entity (depending upon the industry structure) that operates and maintains existing generating plants. The Genco may own the generation plants or interact with the short-term market on behalf of plant owners.

  • Generator

    A machine that converts mechanical energy into electrical energy. Generally rated in terms of real power (megawatts) and reactive power (Megavars) output or in terms or real power output (megawatts) and power factor. Generators require a source of mechanical energy input (typically a turbine) and ancillary equipment to interface with the transmission network.

  • Geothermal

    Power generated from heat energy derived from hot rock, hot water, or steam below the earth's surface.

  • Geothermal Plant

    A plant in which the prime mover is a steam turbine, driven either by steam produced from hot water or by natural steam that derives its energy from heat found in rocks or fluids at various depths beneath the surface of the earth. The energy is extracted by drilling and/or pumping.

  • Giga-NOPR

    A slang term referring to the Notice of Proposed Rulemaking in the electric power industry that launched the FERC's efforts to implement full open access of the electric transmission system. Docket No. RM 95-8-000. It is parallel to "Mega-NOPR", which was used to describe Order No. 636, which substantially completed the move to open access of the natural gas pipeline industry.

  • Gigajoule

    A unit of energy equaling 943,213.3 Btu.

  • Gigawatt (GW)

    One billion watts.

  • Gigawatt-hour (GWh)

    One billion watt-hours.

  • Grade

    Gas Revenue Accounting Data Exchange: A system for the electronic communication of natural gas production and sales data between companies in the energy industry.

  • Graduated Rate


  • Grandfather Clause

    A clause in a contract which maintains the prior rule or policy where a new rule or policy would otherwise be applicable.

  • Graveyard

    Light load hours. The time of the day when an electric power system would experience its lightest load, usually in the middle of the night.

  • Greenfield Development

    Development of a new power generating facility.

  • Greenhouse Effect

    The increasing mean global surface temperature of the earth believed to be caused by gases in the atmosphere (including carbon dioxide, methane, nitrous oxide, ozone, and chlorofluorocarbon). The greenhouse effect allows solar radiation to penetrate but absorbs the infrared radiation returning to space.

  • Grid

    The layout of the electrical transmission system or a synchronized transmission network.

  • Gross Actual Generation

    Actual number of electrical megawatt-hours (MWH) generated by the unit during the period being considered.

  • Gross Available Capacity (GAC)

    Greatest capacity at which a unit can operate with a reduction imposed by a derating.

  • Gross Dependable Capacity (GDC)

    GMC modified for seasonal limitation over a specified period of time.

  • Gross Generation:

    The total amount of electric energy produced by the generating units at a generating station or stations, measured at the generator terminals.

  • Gross Maximum Capacity (GMC)

    Maximum capacity a unit can sustain over a specified period of time when not restricted by seasonal or other deratings.

  • Haulageay

    Main transportation tunnel for deep mines in which rail tracks have been laid for mine cars.

  • Head

    The vertical height of the water in a reservoir above the turbine. In general, the higher the head, the greater the capability to generate electricity.

  • Headstation

    Mainline receipt point on a pipeline.

  • Heat Content

    The sum of the latent heat and sensible heat contained in a substance, above the heat contained at a specified temperature and pressure; expressed as Btu or calories per unit of volume or weight. Also CALORIFIC VALUE.

  • Heat or Heating Rate

    The measure of efficiency in converting input fuel to electricity. Heat rate is expressed as the number of Btu's of fuel (e.g., natural gas) per kilowatt hour (Btu/kWh). Heat rate for power plants depends on the individual plant design, its operating conditions, and its level of electric power output. The lower the heat rate, the more efficient the plant.

  • Heating Value

    The amount of heat produced by the complete combustion of a unit quantity of fuel. The gross, or higher, heating value is that which is obtained when all of the products of combustion are cooled to the temperature existing before combustion, the water vapor formed during combustion is condensed, and all the necessary corrections have been made. The net, or lower, heating value is obtained by subtracting the latent heat of vaporization of the water vapor formed by the combustion of the hydrogen in the fuel from the gross, or higher, heating value.

  • Heavy Load Hours

    Generally speaking, this refers to the time of day on a system that would be considered peak demand. Actual hours vary by individual power system.

  • Heavy Oil

    The fuel oils remaining after the lighter oils have been distilled off during the refining process.

  • Hedging

    To offset a position with the intent of managing risk. The process of protecting the value of an investment from the risk of loss in case the price fluctuates. Hedging is accomplished by protecting one transaction with another. A long position in an underlying instrument can be hedged or protected with an offsetting short position in a related underlying instrument.

  • Helium, Contained

    The helium constituent in crude helium.

  • Helium, Crude

    The mixture of elemental helium and other constituents of natural gas, principally nitrogen, extracted from natural gas by helium extraction plants. Crude helium is typically 60-80% contained helium.

  • Helium (HE)

    A light, colorless, nonflammable gaseous element found especially in conjunction with natural gas and used mainly in cryogenic applications, medical technology, military uses, and welding.

  • Helium, Refined

    Helium that is of a high level of purity after the processing of crude helium.

  • Herfindahl-Hirschman Index (HHI)

    A formula for defining market concentration by summing the squares of the individual market shares of all participants.

  • High Transmission Voltage

    A measure of frequency of electric current in North America. The standard frequency is 59.5 - 60.5 hertz.

  • Highwall

    The unexcavated face of exposed overburden and coal of a surface mine or the exposed face or bank of a hill on the uphill side of a contour mine excavation site.

  • Hinshaw Pipeline

    A pipeline company (defined by the Natural Gas Act and exempted from FERC jurisdiction under the NGA) defined as a regulated company engaged in transportation in interstate commerce, or the sale in interstate commerce for resale, of natural gas received by that company from another person within or at the boundary of a state, if all the natural gas so received is ultimately consumed within such state. A Hinshaw pipeline may receive a certificate authorizing it to transport natural gas out of the state in which it is located, without giving up its status as a Hinshaw pipeline.

  • Historic Sales Customers

    A pipeline's traditional customers who purchased bundled sales service from the pipeline prior to Order No. 636.

  • Hopper Cars

    Open freight cars with a floor sloping to one or more hinged doors for discharging bulk materials such as coal.

  • Host Control Area

    The control area within the metered boundaries a unit not owned by the host or a unit jointly owned by the host and another entity is physically located.

  • Hourly Peak

    The maximum demand for energy from a transmission or distribution system in any hourly period of time.

  • Hourly Value

    Data measured on a clock-hour basis.

  • Hub

    An interchange where multiple pipelines or electric transmission lines interconnect and form a market center.

  • Hydrocarbon

    Organic compound made up of carbon and hydrogen atoms. Heavier fossil fuels, such as coal, have a large ratio of carbon to hydrogen, while natural gas (methane) is the lightest hydrocarbon, with one atom of carbon and four atoms of hydrogen (CH4). Natural gas liquids are heavier than methane but lighter than crude oil. Crude oil is a complex of many hydrocarbons.

  • Hydroelectric Plant

    A plant in which the turbine generators are driven by falling water.

  • IER

    Incremental Energy Rate.

  • IHR

    Incremental Heat Rate.

  • Imbalance, Electric

    Occurs when the generation and interchange schedules do not match demand.

  • Imbalance, Gas

    A discrepancy between a transporter's receipts and deliveries of natural gas for a shipper. Most pipelines require that a shipper's deliveries to the pipeline and receipts from the pipeline remain in balance over a given period of time or the pipeline may assess charges until the imbalance is cured.

  • Imbalance Penalties

    Penalties implemented by a pipeline to provide an incentive for shippers to maintain actual receipts and deliveries at nominated and confirmed levels.

  • Impairment or Asset Impairment

    Impairment or asset impairment occurs when, due to changed circumstances, the previously allowed recovery of costs of a regulatory asset through rates is eliminated or removed by action of a regulatory body.

  • Impedance

    The opposition in an electrical circuit to the flow of alternating current (AG). The ratio of electromotive force to the effective current.

  • Imprudence

    In the context of FERC rate methodology, a determination that certain of a pipeline's costs have not been prudently incurred, with the result that the pipeline is prohibited from placing such costs in its rates. See PRUDENT INVESTMENT.

  • Imputed

    In the context of FERC rate methodology, an arbitrarily attributed, rather than actual value.

  • In-Lieu Energy

    Energy exchanged between a reservoir owner and the owner of a downstream project. The agreement allows reservoir owners to retain water above a reservoir's energy content curve; however, owners of downstream projects may request release of such water. Upstream project owners must then release the water or provide an amount of energy in lieu of the release equal to the amount of energy which could have been generated downstream had the release been made.

  • In-the-Money Option

    The price relationship of an option's strike price to the current market price of the underlying instrument. A call option is in-the-money if its strike price is below the current market value of the underlying instrument. A put option is in-the-money if its strike price is above the current market price of the underlying instrument.

  • Inadvertent Energy Balancing

    A control area's accounting of its inadvertent interchange. Adjacent control areas must agree on these values daily. The difference is repaid usually with energy, not money.

  • Inadvertent Interchange

    The accumulated difference between the control area's net actual interchange and net scheduled interchange.

  • Incentive Rates

    Rates which permit increased profits as a reward for increases in cost savings and efficiencies.

  • Inch of Mercury

    A pressure unit representing the pressure required to support a column of mercury one inch high; 2.036 inches of mercury is equal to one pound per square inch at sea level.

  • Inch of Water

    A pressure unit representing the pressure required to support a column of water one inch high. Usually reported as inches W.C. (water column); 27.68 inches of water is equal to one pound per square inch.

  • Incremental Cost

    The change in total costs when. output is increased or decreased by an increment or block of output for which costs can be accurately determined, usually calculated as the change in cost divided by the change in volume (for example as cents per Mcf); marginal cost.

  • Incremental Energy Cost

    Cost incurred by producing or purchasing next available unit of energy (gas, electricity, oil, coal, etc.).

  • Incremental Heat Rate

    Efficiency of a plant in producing the next increment of additional output. Expressed in Btu/kWh.

  • Indefinite Price Escalator

    Contract provision that allows for future price adjustments that cannot be determined when the contract is executed; e.g., area rate clause, most favored nations clause.

  • Independent Power Producer

    A non-utility power generating entity, defined by the 1978 Public Utility Regulatory Policies Act, that typically sells the power it generates to electric utilities at wholesale prices.

  • Independent System Operator - ISO

    The independent system operator (ISO) has been granted the authority by multiple utilities to operate in a nondiscriminatory manner all the transmission assets of a fixed geographic area.

  • Index

    A measure of relative value attached to a specific commodity or group of commodities or stocks. An index option is an option contract based on an index instead of an individual stock or commodity. A measure of market trends.

  • Indexing

    Tying the commodity price of gas in a contract to published prices.

  • Industrial Bypass

    A situation in which large industrial customers buy power directly from a non-utility generator, bypassing the local utility system. Deregulation of generation and transmission in some instances has opened up the opportunity for large electricity users to purchase services from a supplier other than the local retail utility.

  • Industrial Customer

    The industrial customer is generally defined as manufacturing, construction, mining, agriculture, fishing and forestry establishments, Standard Industrial Classification (SIC) codes 01-39. The utility may classify industrial service using the SIC codes, or based on demand or annual usage exceeding some specified limit. The limit may be set by the utility based on the rate schedule of the utility.

  • Infill Drilling

    Drilling between existing well locations for the purpose of increasing reserves or productive capacity.

  • Injected Gas

    Natural gas placed in underground storage or returned to the producing reservoir to maintain pressure.

  • Input Rating

    The designed rate of fuel acceptance by a burner.

  • Instantaneous Demand

    Rate of energy use at any given instant.