• Instantaneous Service

    The ability to change deliveries on a pipeline simultaneously with a change in nominations on the same business day.

  • Integrated Demand

    Average of instantaneous demands over a time interval.

  • Integrated Gas Company

    A company that obtains significant portions of its natural gas revenues from the operations of both a retail natural gas distribution system and a natural gas transmission system.

  • Integrated Resource Planning (IRP)

    A public planning process and framework within which the costs and benefits of both demand and supply side resources are evaluated to develop the least total cost mix of utility resource options. In many states, IRP includes a means for considering environmental damages caused by electricity supply/transmission and identifying cost effective energy efficiency and renewable energy alternatives. IRP has become a formal process prescribed by law in some states and under some provisions of the Clean Air Act Amendments of 1992.

  • Interchange Arrangement

    The process of finding a seller and buyer for an interchange transaction, plus reserving transmission and Interconnected Operations Services.

  • Interchange Energy Agreements

    Interchange energy agreements assure all parties an equal ability to serve their firm loads. If a party cannot meet its load in a given month, that party has the right to request interchange energy from another that has a surplus. The party with excess is obligated to meet the request. The price of interchange energy is set by parties to the agreement.

  • Interchange (or transfer)

    The net of all power flows across the tie lines of a given control area or the net of all power flows between two adjacent control areas.

  • Interchange Schedule

    The planned energy interchange between control areas. It is the algebraic sum of all interchange transactions between two control Areas.

  • Interchange Transaction

    An agreement, arranged by purchasing-selling entities' merchant function, to transfer energy from a point of receipt to a point of delivery .

  • Interconnected Operations Services (IOS)

    Services offered on a voluntary basis by transmission providers to transmission customers in addition to ancillary services.

  • Interconnected System

    A system which has two or more power systems normally operating in synchronism and having connecting tie lines.

  • Interconnection

    When this term is capitalized (Interconnection), anyone of the four synchronized bulk electric system networks in North American Electric Reliability Council: Eastern, Western, ERCOT, and Quebec, which are only connected through DC ties. When this term is not capitalized (interconnection), the facilities that connect two systems or control areas.

  • Interface

    The direct interconnections between two areas or between two areas comprising one or more electrical systems.

  • Intermediary Control Area

    A control area with connecting facilities in the scheduling path between the sending and receiving control areas and operating agreements that establish the conditions for the use of such facilities.

  • Intermediate Capacity

    Capacity designed to operate less hours than baseload but more than peaking capacity (typically 20% -60%).

  • Intermediate Load (Electric System)

    The range from base load to a point between base load and peak. This point maybe the midpoint, a percent of the peakload, or the load over a specified time period.

  • Internal Combustion Plant

    A plant in which the prime mover is an internal combustion engine. An internal combustion engine has one or more cylinders in which the process of combustion takes place, converting energy released from the rapid burning of a fuel-air mixture into mechanical energy. Diesel or gas-fired engines are the principal types used in electric plants. The plant is usually operated during emergencies or periods of exceptionally high demand for electricity.

  • Interruptible Demand (Customer)

    The magnitude of customer demand that, in accordance with contractual arrangements, can be interrupted by direct control of the system operator, remote tripping, or by action of the customer at the direct request of the system operator.

  • Interruptible Gas

    Gas sold to customers with a provision that permits curtailment or cessation of service at the discretion of the supplier under certain circumstances, as specified in the service contract.

  • Interruptible Load

    Demand that can be interrupted by direct action of the supplying system's system operator in accordance with contractual provisions at times of seasonal peak load. It usually involves commercial and industrial consumers. In some instances the load reduction may be affected by direct action of the system operator (remote tripping) after notice to the consumer in accordance with contractual provisions. For example, loads that can be interrupted to fulfill planning or operation reserve requirements should be reported as Interruptible Load. Interruptible Load as defined here includes Direct Load Control and Other Load Management.

  • Interstate Market

    The market for natural gas that is consumed outside the state in which it is produced or is transported by an interstate pipeline pursuant to NGA authorization, or both. Gas sold to an interstate pipeline is sold in the interstate market.

  • Interstate Pipeline

    A natural gas pipeline company that is .engaged in the transportation of natural gas across state boundaries, and is therefore subject to FERC jurisdiction and/or FERC regulation under the NGA.

  • Intrastate Market

    The market for natural gas consumed in the same state as it is produced, without the natural gas having been transported by an interstate pipeline.

  • Intrastate Pipeline

    A natural gas pipeline company that is engaged in the transportation of natural gas not subject to the FERC jurisdiction under the NGA.

  • Inverted Block Rate (Graduated Rate)

    A rate structure that prices successive blocks of power use at increasingly higher per-unit prices. The more energy 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 purpose of providing electric power service and earning a profit for its stockholders.

  • Irregular Bill

    A bill covering service for a period less than or in excess of the regular billing cycle.

  • Island

    A part of one or more power systems electrically separated from the main grid as a result of the tripping of transmission system elements.

  • Joint Control

    Automatic generation control of units which are jointly owned by two or more entities.

  • Joint Use Facilities

    A facility that is used in common by two or more entities or power generating units. Also know as Common Use Facilities.

  • Joules

    A measure of energy equal to 1 watt second.

  • Jurisdictional Agency

    The state or federal agency having regulatory jurisdiction over the production, transportation, or sale of natural gas.

  • Jurisdictional Sale

    A natural gas sale subject to the jurisdiction of the FPC or its successor, the FERC.

  • Just and Reasonable Rate

    A rate for natural gas supply or transportation service subject to the NGA or the NGPA. "Just and reasonable" has been defined generally to mean a rate that is based on the properly allocated cost of providing service.

  • Kilowatt-hour (kWh)

    A unit of electrical energy which is equivalent to one kilowatt of power used for one hour. One kilowatt-hour is equal to 1,000 watt-hours. An average household will use between 800 - 1300 kWh per month depending upon geographical area. It is equivalent to 3,412 Btu.

  • Kilowatt (kW)

    A unit of electrical power equal to one thousand watts.

  • Kilowatt-year (kW-Y)

    A unit of electrical capacity demanded for 8760 hours.

  • Lambda (I)

    The measure of the rate at which fuel is consumed relative to electric output, expressed in Btu's per kWh.

  • Lateral

    A pipe that branches away from the central and primary part of the system.

  • Lease

    Any instrument that gives a producer the right to drill for, produce, and dispose of oil and natural gas in, under, and from the lands described therein.

  • Levelized Life-Cycle Cost

    The present value of the cost of a resource, including capital, financing and operating costs, converted into a stream of equal annual payments.

  • Leverage Ratio

    The ratio of total debt to total assets; i.e. a measure that indicates the financial ability to meet debt service requirements.

  • Liability

    An amount payable in dollars or by future services to be rendered.

  • Life Line Rates

    A charge for a specified basic block of residential .electricity followed by a higher rate for use beyond that block. Such rates are to assure that certain categories of customers have enough electricity for basic uses.

  • Light-Handed Regulation

    Regulatory approval of rate levels resulting from arm's length negotiations, rather than calculated on a cost of service basis, and subject to challenge only under a complaint proceeding.

  • Light Load Hours

    Generally speaking, the term for that time of day on a system that could be considered off peak. Actual hours will vary with each power system.

  • Light Oil

    Lighter fuel oils distilled off during the refining process. Virtually all petroleum used in internal combustion and turbine engines is light oil.

  • Lignite

    Low-rank, brown coals which are distinctly brown and woody or claylike in appearance, and which contain relatively high moisture contents of between 30 and 70 percent of the fuel by weight. Sulfur may range from low to high and heating value may range from 3,500 to 7,000 Btu/lb.

  • Limit

    In a futures trading session, the maximum advance or decline in a futures price.

  • Limit Order

    A contingent order in futures trading specifying a maximum or minimum price.

  • Limiting Element

    The device in a system that has the lowest energy rating, there by setting the maximum amount of energy that can be transferred.

  • Line Loss

    The reduction in the quantity of natural gas flowing through a pipeline that results from leaks, venting, and other physical and operational circumstances on a pipeline system.

  • Line Pack and Draft

    Packing the line increases the amount of gas in the system by adding gas and/or increasing pressure and drafting the line decreases the amount of gas in the system by decreasing gas and/or decreasing pressure.

  • Liquidation

    The closing of futures positions.

  • Liquidity

    A high level of trading activity.

  • Liquids, Natural Gas

    Those liquid hydrocarbon mixtures that are gases at reservoir temperatures and pressures, but can be recovered by condensation or absorption. Natural gasoline and liquefied petroleum gases fall in this category.

  • 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 consumers. The load of an electric utility system is effected by many factors and changes on a daily, seasonal, and annual basis, typically following a pattern. Electric System load is usually measured in megawatts (MW). Also, to "load" a governor is to set the governor to maintain a given pressure as the rate of gas flow through the governor varies. Compare DEMAND. .

  • Load (Base)

    See Base Load.

  • Load Building

    Refers to programs that are aimed at increasing the usage of existing electric equipment or the addition of electric equipment.

  • Load Centers

    A geographical area where large amounts of power are drawn by end users.

  • Load Curve

    A curve of power versus time showing the level of a load for .each time period covered.

  • Load Cycle

    Time period spanning one peak load.

  • Load Density

    The concentration of natural gas load for a given area expressed as an amount of natural gas per unit of time and per unit of area.

  • Load Duration Curve

    A curve of loads, plotted in descending order of magnitude, against time intervals for a specified period. The curve indicates the period of time load was above certain magnitude. Load duration curves are profiles of system demand that can be drawn for specified periods of time (e.g., daily, monthly, yearly). The coordinates may be absolute quantities or percentages.

  • Load Factor

    The ratio of average load to peak load during a specific period of time, expressed as a percent. The load factor indicates to what degree energy has been consumed compared to maximum demand or the utilization of units relative to total system capability. An electric system's load factor shows the variability in all customers' demands.

  • Load Following

    An electric system's or plant's ability to regulate its generation to follow the instantaneous changes in its customers' demand.

  • 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.

  • Load Shape

    The variation in the magnitude of the power load over a daily, weekly or annual period.

  • Load Shedding

    Removal of pre-selected customer demand from a power system, asa result of the occurrence of an abnormal condition, in a effort to maintain the integrity of the system and minimize overall customer outages.

  • Load-Shifting

    DSM programs designed to shift load from on -peak times of the day to off-peak times.

  • Load Valley

    A period of reduced load, as contrasted with peak load.

  • Local Distribution Company (LDC)

    A company that obtains the major portion of its revenues from the operations of a retail distribution system for the delivery of electricity or gas for ultimate consumption.

  • Long (or long position)

    The position of a party who has bought and is holding futures or options contracts or owns a commodity that has not been settled by sale or delivery.

  • Long Position

    A position of a futures contract buyer which requires the buyer to accept a delivery unless the contract is liquidated with an offsetting 'sale.

  • Long Run Marginal Costs

    All costs associated with the lowest cost incremental unit including variable production costs, fixed O&M, and capital costs.

  • Longwill Miner

    A deep mining machine that uses a steel plow or rotating drum, which is pulled mechanically back-and-forth across a long face of coal. The loosened coal falls onto a conveyor for removal from the mine.

  • Longwill Mining

    An underground mining process in which a panel or block of coal is completely extracted.

  • Lookback Option

    An option that allows the buyer the right, retroactively to buy (sell) the underlying commodity or security at its minimum (maximum) price within the look back period.

  • Loop Flow

    The tendency of electricity to flow along the path of least resistance, which may not necessarily be the same as that intended in the contract between the two transmitting entities. If power sold along a contractual path utilizes a different physical path, the power-flow may interfere with control of the systems which were unaware of the contractual power transfer.

  • Looping

    Laying additional pipeline beside and connected to an existing pipeline in order to increase the capacity of the system.

  • Loss of Load Probability (LOLP)

    A measure of expectation that system demand will exceed capacity during a given period, often expressed as the expected number of days per year (e.g., one day in ten years).

  • Loss Supply

    An ancillary service where the wheeling utility provides supplemental power to compensate for losses incurred in the power system during transmission.

  • Lot

    The standard unit of futures trading specifying a definite quantity of the commodity of uniform grade.

  • LP Gas-Air Mixture

    Mixture of liquefied petroleum gas and air to obtain a desired Btu value, capable of being distributed through a distribution system; also used for standby and peak shaving by natural gas utilities.

  • Main Extension

    The addition of pipe to an existing gas main to serve new customers.

  • Main, Gas

    Pipe used to carry natural gas from one point to another. As contrasted with service gas pipes, mains usually carry natural gas in large volume for general or collective use. See PIPELINE SYSTEM.

  • Mainline


  • Maintenance Derating

    The removal of a component for scheduled repairs that can be deferred beyond the end of the next weekend, but requires a reduction of capacity before the next planned outage.

  • Maintenance Outage

    The removal of a unit from service to perform work on specific components that can be deferred beyond the end of the next weekend, but requires the unit be removed from service before the next planned outage.

  • Margin

    Money that buyers and sellers of futures and exchange-traded options must put up with the clearinghouse to assure performance on the contracts. For over-the-counter options, margins are negotiated between the counterparties. In both cases, the amount of margin required varies with the price fluctuations of the underlying contract. Open positions are marked-to-market daily and, in times of extreme volatility, marked-to-market intra-day as well.

  • Marginal Cost

    The increase or decrease in total costs brought about by a one unit increase or decrease in output.

  • Marginal Cost Pricing

    A system of pricing designed to ignore all costs except those associated with producing the next increment of production. Sometimes referred to as incremental cost pricing.

  • Marginal Price of Power

    Price for power from a unit which is already running. Includes only fuel and variable O&M plus a markup. (System Lambda + markup.)

  • Marked-to-Market

    The readjustment in the value of a derivative instrument or product position with respect to the current market value of its underlying instrument.

  • Market-Based Sales Rates

    Sales rates resulting from arm's length negotiations, rather than the pipeline's or its affiliate's actual costs of supplies.

  • Market Center

    See HUB.

  • Market-Clearing Level

    The maximum price at which all of an available commodity (natural gas or electricity) can be sold in a specified market.

  • Market Makers

    Various commercial and investment banks that make a market in swaps and hold significant portfolios of swap contracts. A market participant who provides liquidity to the markets by continuously quoting prices at which he/she will buy or sell a particular instrument.

  • Market-Out

    A provision in an energy sales agreement that allows one or both parties to demand re-negotiation of the sales price and/or terminate the contract if the contract sales price no longer reasonably reflects the current market.

  • Market Price

    The current price of an underlying instrument in the marketplace.