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Electric Glossary

A-Z Terms

  • A

    Actual Load

    The Load Serving Entity's total load per Electric Distribution Company zone, as determined through meter readings and EDC load profiling methods.

    Adjacent System or Adjacent Control Area

    Any control area directly interconnected with another control area.


    An entity appointed by an RTO member to do business in RTO on behalf of the member.


    Aggregate A group of more than one individual bus into a pricing node (pnode) that is considered as a whole in the Energy Market and other various systems and Markets within RTO.

    Alternating Current

    An alternating current is the movement of an electric charge that periodically reverses direction. This is compared to the flow of electric charge in direct current, which moves in only one direction. Electric power is delivered to homes and businesses through alternating current.

    Analog Control

    A signal which, with respect to time, varies continuously in proportion to the measured quantity.

    Ancillary Services

    Ancillary services help balance the transmission system as it moves electricity from generating sources to ultimate consumers. RTOs operate in addition to several other non-markets for ancillary services such as black start service.

    Annual Demand Resources

    Demand Resources which can be called on an unlimited number of times any day of the delivery year, unless on an approved maintenance outage.

    Area Control Error (ACE)

    A measure of the imbalance between sources of power and uses of power within the RTO. The ACE calculation uses the difference between scheduled and actual net interchange plus the RTO frequency bias contribution.

    Area Regulation Signal

    A signal generated by the RTO Control Center and sent to the plants, stations and/or RTO members scheduled to provide regulation to change generation quickly to keep the RTO area control error within allowable limits. It is used to control for small fluctuations in load.

    Auction Revenue Rights (ARR)

    Entitlements allocated annually to Firm Transmission Service Customers that entitle the holder to receive an allocation of the revenues from the Annual FTR Auction.

    Automatic Generation Control (AGC)

    Equipment that automatically adjusts a Control Area generation to maintain its interchange schedule plus its share of frequency regulation.

    Available Flowgate Capability

    A measure of the flow capability remaining on a Flowgate for further commercial activity over and above already committed uses. It is defined as TFC less Existing Transmission Commitments (ETC), less a Capacity Benefit Margin, less a Transmission Reliability Margin, plus Postbacks and plus Counterflows. (NERC definition)

    Available Transfer Capability (ATC)

    The amount of energy above “base case” conditions that can be transferred reliably from one area to another overall transmission facilities without violating any pre-or post-contingency criteria for the facilities in the RTO Control Area under specified system conditions.

  • B

    Balancing Authority

    The responsible entity that integrates resource plans ahead of time, maintains Demand and resource balance within a Balancing Authority Area, and supports Interconnection frequency in real-time. [See NERC definition]

    Balancing Authority Area

    The collection of generation, transmission, and loads within the metered boundaries of the Balancing Authority. The Balancing Authority maintains load-resource balance within this area.

    Balancing Energy Market

    Matches the power output of the generators within the electric power system(s) and energy purchased from entities outside the electric power system(s) with the load within the electric power system(s).

    Balancing Operating Reserves

    Generation and demand response resources that operate as requested by the RTO are guaranteed to recover the costs of their offer amounts through balancing operating reserve credits that are charged to market participants. Accounting for these "make-whole" costs is performed on a daily basis, for both the Day-Ahead Energy Market and the Real-Time Energy Market.

    Balancing operating reserve costs are out of the market and as such are not included in the pricing signals that are visible and transparent to the entire market. When these "uplift" payments are charged to the market, they are not predictable and cannot be hedged on a forward basis.

    Behind-the-Meter Generation

    Behind-the-Meter Generation Generation that is physically located behind the retail meter and does not participate in the wholesale market as a generation resource.

    Bilateral Transaction

    Bilateral Transaction An agreement between two entities (one or both being RTO Members) for the sale and delivery of a service.

    Black Start Service

    Black Start Service enables Transmission Providers and Transmission Owners to designate specific generators called Black Start Units whose location and capabilities are required to re-energize the transmission system following a system-wide blackout.

    Black Start Unit

    A Black Start Unit is a generating unit that has equipment enabling it to start without an outside electrical supply or a generating unit with a high operating factor (subject to Transmission Provider concurrence) with the demonstrated ability to automatically remain operating, at reduced levels, when disconnected from the grid.

    Blackout (Load Shed)

    A power outage (also power cut, blackout, or power failure) is a short- or long-term loss of electric power to an area. In other words, the lights go out at homes and businesses in the impacted area. This system shutdown can be brought on by an emergency-forced outage in the generation, transmission, or distribution system serving the area.

    Bulk Electric System

    Includes individual generation resources larger than 20 MVA or a generation plan with an aggregate capacity greater than 75 MVA that is connected via a step-up transformer(s) to facilities operated at voltages 100 kV or higher. (See NERC definition)


    A point of interconnection to the system where power produced becomes available for transmission. Also, an electrical conductor that serves as a common connection for two or more electrical circuits.

  • C


    An electronic component that stores an electric charge and releases it when required. A capacitor is a device for storing a large quantity of electric charge. When connected to the power system, capacitors will provide reactive power and thereby increase the voltage on the system.


    System capacity is the total amount of electricity resources available to use if needed. Throughout the year, RTO must have enough resources, plus an additional reserve, to supply the greatest amount of electricity used in one hour.

    Capacity Emergency Transfer Limit (CETL)

    Capacity Emergency Transfer Limit (CETL) is the capability of the transmission system to support deliveries of electric energy to a given area experiencing a localized capacity emergency as determined in accordance with the RTO Manuals.

    Capacity Factor

    The ratio of the total energy generated by a generating unit for a specified period to the maximum possible energy it could have generated if operated at the maximum capacity rating for the same specified period expressed as a percent.

    Capacity Interconnection Rights

    The rights to input generation as a Generation Capacity Resource into the Transmission System at the Point of Interconnection where the generating facilities connect to the Transmission System.

    Capacity Resource

    A generating unit, demand resource, energy efficiency resource, or an aggregate resource that has obligated itself to deliver electricity or reduce load whenever RTO determines it is needed to meet power system emergencies.

    Charging Current

    The current flows into a capacitor when a voltage is first applied.


    A system of conductors and their component parts through which an electrical current flows or is intended to flow.

    Circuit Breaker

    A circuit breaker is a switching device capable of starting, carrying, and stopping electrical currents under normal circuit conditions. It also can start and carry currents for a specified time and stop currents under specified abnormal conditions such as a short circuit.

    Coincidental Peaks

    The unrestricted load of a zone, LSE, or end-use customer, coincident with one of the five highest loads used in the weather normalization of the RTO seasonal peak. 5 CP values are used in the allocation of the RTO and zonal normalized peaks.

    Combined Cycle

    An electric generating technology in which electricity and process steam are produced from otherwise lost waste heat exiting from one or more combustion turbines. The exiting heat is routed to a conventional boiler or to a heat recovery steam generator for use by a conventional steam turbine in the production of electricity. This process increases the efficiency of the electric generating facility.

    Combustion Turbine

    A generating unit in which a combustion turbine engine is a prime mover for an electrical generator. It is typically used for peak shaving operation due to quick response capability.


    A condition that arises on the transmission system when one or more restrictions prevents the economic dispatch of electric energy from serving load.

    Congestion Cost

    The price represents the inability to use the least expensive generation to meet the electricity demand due to transmission limitations. Congestion Cost is one of the three components of Locational Marginal Pricing.


    An event, usually involving the loss of one or more elements that affect the power system at least momentarily.

    Contract Path

    Contract Path A specific contiguous electrical path from a Point of Receipt to a Point of Delivery for which transfer rights have been contracted.

    Control Area (Balancing Authority)

    An electric power system or combination of electric power systems bounded by interconnection metering and telemetry to which a common generation control scheme is applied. RTO operates as one control area.

    Control Zone

    One or more transmission zones or multiple contiguous Zones as defined in RTO manuals.


    Any device for changing alternating current to direct current, or direct current to alternating current.

    Coordinated Transaction Scheduling (CTS)

    CTS transactions are interchange transactions between neighboring RTOs/ISOs designed to increase scheduling efficiencies across the seam using forward pricing information. Transactions leverage the differences in price projections, thereby resulting in price convergence and efficiency in the flow direction.

    Cost of New Entry

    Averaged revenue required ($/MW-year) to build a reference combustion turbine in a specific area of RTO.

    Cost-Based Offers

    Offers that shall not exceed the variable cost of producing such energy or another service, as determined in accordance with the Cost Development Guidelines. Cost-based offers are used by RTO to schedule generation in cases in which structural market power is found to exist.

    Critical Energy Infrastructure Information (CEII)

    The Federal Energy Regulatory Commission (FERC) defines Critical Energy Infrastructure Information (CEII) as specific engineering, vulnerability, or detailed design information about proposed or existing critical infrastructure (physical or virtual) that relates details about the production, generation, transmission, or distribution of energy; could be useful to a person planning an attack on critical infrastructure; is exempt from mandatory disclosure under the Freedom of Information Act, and gives strategic information beyond the location of the critical infrastructure.


    Current An electric current is the movement of an electric charge.


    Curtailment A reduction in transmission service or generation as a result of system reliability conditions.

  • D

    Day-Ahead Demand

    The fixed and/or price-sensitive demand bids cleared in the RTO Day-Ahead Energy Market (financial hedge).

    Day-Ahead Energy Market

    A day-ahead hourly forward market in which RTO market participants may submit offers to sell and bids to buy energy. The results of the Day-Ahead Energy Market are posted daily by 1:30 p.m. and are financially binding. The Day-Ahead Energy Market is based on the concept of Locational Marginal Pricing and is cleared using least price security-constrained unit commitment and dispatch programs.

    Delivery Year

    The 12 months beginning June 1 and extending through May 31 of the following year. Delivery Year may also be referred to as Planning Year.

    Demand (Load)

    Demand is the usage or consumption of electricity on a power system. Demand is generally expressed in kilowatt-hours or megawatt-hours.

    Demand Resource

    A resource with a demonstrated capability to provide a reduction in demand or otherwise control the load. A Demand Resource may be an existing or planned resource.

    Demand Response

    A program that allows end-user customers to reduce their electricity usage during periods of higher power prices. In exchange, end-use (retail) customers are compensated through RTO members known as Curtailment Service Provider for decreasing their electricity use when requested by RTO.

    Demand Side Management

    Demand Response and Energy Efficiency measures by end-use (retail) customers

    Demand Side Response

    A change in electricity usage by a customer in response to price or an emergency event affecting grid reliability.

    Direct Current

    A direct current is the movement of an electric charge from negative to positive that flows in only one direction. This is compared to an alternating current, which periodically reverses direction.

    Dispatchable Generation

    The generation that can follow dispatch instructions between the economic minimum and economic maximum.


    Distribution is the final stage of delivering electricity to an end-user. A distribution system steps down electricity from the higher voltage levels on the transmission system to deliver it directly to homes or businesses.

    Distribution Factor

    The term is generally applied to the percentage of power flowing on Element A that will be picked up (or backed down) on Element B as a result of an outage on Element A or a shift in generation.

  • E

    Eastern Interconnect Data Sharing Network (EIDSN)

    A network for the sharing of operating reliability data, including both Supervisory Control and Data Acquisition (SCADA) and synchrophasor data, among appropriate entities to promote the reliable and efficient operation of the Eastern and Quebec Interconnections.

    Economic Demand Response

    The ability for end-use customers to participate in the wholesale energy and ancillary service markets through a Curtailment Service Provider which is economic for them to participate in the market(s).

    Economic Dispatch

    Economic Dispatch The short-term determination of the optimal output of generation facilities, to meet the system load, at the lowest possible cost, subject to transmission and operational constraints.

    Economic Generation

    Units producing energy at an offer price less than, or equal to, LMP.

    Economic Maximum Generation

    The highest incremental MW output level a unit can achieve while following economic dispatch.

    Economic Minimum Generation

    The lowest MW output level a unit can achieve while following economic dispatch.

    Electric Cooperative (REMCs)

    Often found in rural areas, a business jointly owned by its customers and operated as a pooled resource; engaged in the generation, transmission, and/or distribution of electric energy.

    Electric Utility

    An electric utility is an entity involved in the generation, transmission, or distribution of electricity for sale and for use by the general public. An electric utility can be investor-owned, cooperatively owned or government owned such as a municipal system.

    Electrical Energy

    The generation or use of electric power by a device over a period of time, expressed in kilowatt-hours (kWh), megawatt-hours (MWh), or gigawatt-hours (GWh).

    Emergency Demand Response

    A commitment to reduce the load or consume electricity only up to a certain level when RTO needs assistance under expected emergency conditions (also called Load Management).

    Emergency Maximum Generation Limit

    The maximum output of energy a generating unit can produce and still maintain a stable level of operation.

    Emergency Minimum Generation Limit

    The least amount of energy a unit can produce and still maintain a stable level of operation.


    Broadly defined, energy is the ability to do work. Electrical energy is produced by a generator, which converts other forms of energy into electrical energy that is then transmitted through the electric transmission and distribution systems. It is measured in kilowatt-hours and megawatt-hours.

    Energy Management System

    Energy Management System (EMS) provides real-time monitoring of operational information for all critical electrical equipment - information that is central to the reliable operation of the bulk power system.

    Energy Management System (EMS)

    Energy Management System

    Energy Market

    An energy market is a type of spot market in which energy is sold or purchased for immediate delivery. Because electricity is a commodity that is consumed the same moment it is produced, by its nature, energy is delivered immediately upon sale or purchase. RTO's energy market functions at a wholesale level. These energy markets operate every day and participants in the market establish a price for electricity by matching supply (what generators want to sell) and demand (what utilities and customers want to buy). Utilities and competitive retailers that purchase energy from a wholesale market resell it to final consumers at retail rates or prices.

    Equivalent Demand Forced Outage Rate (EFORd)

    A measure of the probability that generating units will not be available due to forced outages or forced deratings when there is a demand on the unit to generate.

    Event Analysis

    Utilization of a systematic approach to analyzing an event which had negative consequences, with the goal of finding the causal factors of the event and develop recommendations to prevent a recurrence of the event.


    The sum of all external transactions where RTO is the Point of Receipt.

    External Resource

    A generation resource located outside the metered boundaries of the RTO- from MISO to PJM, or SPP to MISO, etc.

    External Transaction

    An energy transaction between two parties in which the path of the energy crosses an RTO border.

    Extra-High Voltage (EHV)

    This refers to 345kV and above on the RTO system.

  • F


    A physical condition that results in the failure of a component or facility of the transmission system to transmit electrical power in a manner for which it was designed.

    Federal Energy Regulatory Commission

    The Federal Energy Regulatory Commission (FERC) is an independent regulatory agency within the U.S. Department of Energy. The FERC regulates the transmission and wholesale sales of electricity in interstate commerce. The FERC also administers accounting and financial reporting regulations and conduct of jurisdictional companies.

    Financial Transmission Right

    A Financial Transmission Right (FTR) is a financial instrument awarded to bidders in the FTR Auctions that entitle the holder to a stream of revenues (or charges) based on an hourly Day Ahead congestion price differences across the path.

    Firm Transmission Service

    A transmission service that is intended to be available at all times to the maximum extent practicable, subject to an emergency, an unanticipated failure of a facility, or another event beyond the control of the owner or operator of the facility or of RTO.

    Fixed Resource Adequacy Plan (FRAP)

    An alternative method for an eligible load-serving entity to meet a fixed resource requirement with its own capacity resources as opposed to procuring capacity resources on the in capacity auctions.

    Forced Transmission Outage

    Forced Transmission Outage An immediate removal from service of a Designated Transmission Facility.

    Frequency Bias

    The Balancing Authority’s obligation to provide or absorb energy to assist in stabilizing frequency. If frequency goes low, each Balancing Authority is asked to contribute a small amount of extra generation in proportion to its system’s established bias value.

    Frequency Disturbance

    A system frequency deviation from normal as a result of a generation/load imbalance.

    FTR Auction

    An RTO-administered market for FTRs in which RTO market participants may submit offers to sell and bids to buy on-peak, off-peak, or 24-hour FTRs. FTRs awarded in these auctions can have a term of one calendar month, three calendar months, one year, or three years.

    Fuel Cost

    The cost of the fuel used by each unit expressed in $/MBTU. When multiplied by the incremental heat rate (MBTU/MWh), the incremental fuel cost ($/MWh) results.

    Full Requirements Service

    Full Requirements Service This is a term used by EDCs that typically entails a commitment to supply all the customer's wholesale load requirements.

  • G


    Generation describes both the process of producing electrical energy from other forms of energy (e.g., a power plant burning coal or a windmill turning moving air into energy) as well as the amount of electrical energy produced, which is usually expressed in kilowatt-hours (kWh) or megawatt-hours (MWh).

    Generation Dispatcher

    Member personnel who participate in the real-time operations of the RTO system by dispatching generation and performing other generation-related real-time duties as found on the RTO Generation Dispatcher Task List

    Generation Offer

    Generation Offer Schedules of MW offered and the corresponding offer price.

    Generation Owner

    One of RTO's defined sectors for voting purposes. See Operating Agreement for qualifications.


    A machine that converts different forms of energy into electrical energy. A generator or power plant might burn coal, capture the sun's energy through solar panels, convert moving air into electricity through windmills, or transform the movement of water into energy like hydroelectric power. RTO has a diverse generation fuel mix that includes nuclear power, natural gas, fossil fuels coal, and renewable generation such as wind and solar.

    Generator Operator

    The entity that operates generating Facility(ies) and performs the functions of supplying energy and Interconnected Operating Services. (NERC definition)


    A gigawatt is a unit of power that is equal to one billion watts or 1,000 megawatts. One gigawatt of electricity generated would power between 800,000 and one million homes.


    A gigawatt-hour is a unit of measurement used to describe the amount of electricity produced or consumed. One gigawatt-hour is equal to one billion watt-hours or 1,000-megawatt-hours.


    An electrical grid is an interconnected network of generation, transmission, and distribution elements that delivers electricity from suppliers to consumers.

  • H

    Hertz (Hz)

    Electricity system frequency is measured in Hertz (Hz). Frequency measures 60 Hz in U.S. electric markets and 50 Hz in those in Europe.


    Hub A group of more than one individual bus into a regional pricing node (pnode) developed to produce a stable price signal in the Energy Market and other various systems and Markets within an RTO.

  • I

    Immature Unit

    A unit having between zero and five full calendar years of operating experience for reliability calculations.


    The sum of all external transactions where RTO is the Point of Delivery. Capacity imports from external units must be certified as deliverable using firm transmission and non-recallable by any external party.

    Installed Capacity (ICAP)

    An MW value based on the summer net dependable capability of a unit and within the capacity interconnection right limits of the bus to which it is connected.

    Interconnection Reliability Operating Limit (IROL)

    A System Operating Limit that, if violated, could lead to instability, uncontrolled separation, or cascading outages that adversely impact the reliability of the Bulk Electric System.


    A group of more than one individual bus into a proxy pricing node (pnode) developed for transactions into or out of the RTO in the Energy Market and other various systems and Markets within RTO.

  • J

    Joint and Common

    MISO and RTO Interconnection have developed complementing system operations and a robust, non-discriminatory wholesale electricity market to meet the needs of all customers and stakeholders within both regions. The market was developed through an open stakeholder process, designed to serve residents regardless of whether they reside in states with bundled or unbundled retail rates.

    Joint-Owned Unit

    A generating unit owned by two or more member systems whose output is dispatched as a pool resource, with each owner receiving a share of output for billing purposes on the percentage of ownership.

  • K


    A kilowatt is a unit of power that is equal to 1,000 watts. The power output of many electric motors or heaters is typically expressed in kilowatts.


    Monthly electricity bills for residential consumer shows the kilowatt-hours that were used. One-thousand kilowatt-hours equals one megawatt-hour.

  • L

    Limited Demand Resources

    Demand Resources which can be called on during weekdays (other than NERC holidays) from noon to 8 p.m. up to 10 times from June through September.

    Load (Demand)

    The load is the overall usage or consumption of electricity on a power supply. The load is generally expressed in kilowatt-hours or megawatt-hours.

    Load Curtailment

    Completely or partially reducing consumer electricity consumption.

    Load Management

    A resource with a capacity commitment to reduce load when dispatched by RTO. A demand response resource may be an existing or planned resource.

    Load Serving Entity

    A Load Serving Entity (LSE) is any entity (or the duly designated agent of such an entity), including a load aggregator or power marketer that (a) serves end-users within the RTO Control Area, and (b) is granted the authority or has an obligation pursuant to state or local law, regulation or franchise to sell electric energy to end-users located within the RTO Control Area.

    Locational Marginal Price (LMP)

    Locational Marginal Price (LMP) is defined as the marginal price for energy at the location where the energy is delivered or received. For accounting purposes, LMP is expressed in dollars per megawatt-hour ($/MWh). LMP is a pricing approach that addresses Transmission System congestion and loss costs, as well as energy costs.


    The power is lost as dissipated heat when power flows in transmission lines and transformers.

    Loss-of-Load expectation (LOLE)

    Loss-of-load expectation (LOLE) defines the adequacy of capacity for the entire RTO footprint based on load exceeding available capacity, on average, only once in 10 years.

  • M

    Market-Clearing Price (MCP)

    The price that is paid by all load and paid to all suppliers for the service received or provided.


    An entity that has the authority to take title to electrical power generated by itself or another entity and re-market that power at a market-based price.


    A megawatt is a unit of power equaling one million watts (1 MW = 1,000,000 watts) or one thousand kilowatts (1 MW = 1,000 KW). To put it in perspective, under non-severe weather conditions, one MW could power roughly 800 to 1,000 average-sized American homes.

    Megawatt-hour (MWh)

    A megawatt-hour is a unit of measurement used to describe the amount of electricity produced or consumed. It is equal to 1 million watt-hours or 1,000 kilowatt-hours.


    Any entity that has completed an application and satisfies the requirements of the RTO Operating Agreement to conduct business with RTO including Transmission Owners, Generating Entities, Load Serving Entities, and Marketers.


    Metered Refers to facilities or market entities that are within the RTO RTO.

    Minimum Offer Price Rule (MOPR)

    The provision imposes a minimum offer screening process to determine whether an offer from a new resource is competitive and prevents market participants from submitting uncompetitive, low new entry offers in RPM Auctions to depress auction clearing prices artificially.

    Must-Run Generation

    Generation designated to operate at a specific level and not available for economical dispatch. Also referred to as a fixed generation.

  • N

    Non-Coincident Peak

    Non-coincident Peak is a transmission zone's, load-serving entity's, or end-use customer's peak load during a stated period of time, whether or not it occurs at the same time as the overall system peak.

    Non-economic Generation

    Non-economic Generation Units producing energy at an offer price greater than the LMP.

    Non-Firm Point-to-Point Transmission Service

    Point-to-Point Transmission Service under the Tariff that is reserved and scheduled on an as-available basis and is subject to curtailment or interruption. Non-Firm Point-to-Point Transmission Service is available on a stand-alone basis for periods ranging from one hour to one month.

    Non-RTO-Designated Transmission Facilities

    The transmission facilities within the RTO RTO that are not designated for RTO operation. These are also referred to as Local Non-designated Transmission Facilities.

    North American Electric Reliability Corporation

    The North American Electric Reliability Corporation (NERC) operates as an electric reliability organization to improve the reliability and security of the bulk power system in North America. To achieve that, NERC develops and enforces reliability standards; monitors the bulk power system; assesses future adequacy; audits owners, operators, and users for preparedness; and educates and trains industry personnel. As the Electric Reliability Organization, NERC is subject to audit by the U.S. Federal Energy Regulatory Commission and governmental authorities in Canada.

  • O


    Off-peak is a period of time when consumers typically use less electricity: normally weekends, holidays, or times of the day when many businesses are not operating. RTO typically considers New Year's Day, Memorial Day, Independence Day, Labor Day, Thanksgiving Day, and Christmas Day off-peak; as well as weekend hours and weekdays from 11 p.m. to 7 a.m.

    Offer Data

    Generator data including availability, operational limits, cost data, etc. specified for submission to the RTO Interchange Energy Market that is necessary to schedule and dispatch generation resources to meet the reliability and security of the Transmission System in the RTO RTO.


    On-peak is a period of time when consumers typically use more electricity -- normally on weekdays when many businesses are operating. RTO typically considers weekdays from 7 a.m. to 11 p.m. on-peak, except for the following holidays: New Year's Day, Memorial Day, Independence Day, Labor Day, Thanksgiving Day, and Christmas Day.

    Operating Day

    The daily 24-hour period beginning at midnight EPT for which transactions on the RTO Interchange Energy Market are scheduled.


    An outage has multiple meanings in RTO. First, an outage is a short- or long-term loss of electric power to an area. Planned intervals of time when either transmission lines or power plants are temporarily brought out of service for maintenance are also known as outages.

  • P

    Peak Demand

    An end-user customer's contribution to the zone's weather normalized summer peak load, as determined by the zone's Electric Distribution Company.

    Peak Season

    Peak Season is defined to be those weeks containing the 24th through 36th Wednesdays of the calendar year. Each such week begins on a Monday and ends on the following Sunday, except for the week containing the 36th Wednesday, which ends on the following Friday.

    Peak Season Maintenance

    Planned outages and maintenance outages during the Peak Season.

    Phase Angle Regulator (PAR)

    A power system transformer that has tap changing capability and can change the phase angle across the transformer and thereby increase or decrease power flow.

    Phasor Measurement Unit

    A phasor measurement unit (PMU) measures the electrical waves on an electricity grid to determine the health of the system. In power engineering, these are also commonly referred to as synchrophasors and are considered one of the most important measuring devices in the future of power systems.

    Planned Outage

    The scheduled removal from service, in whole or in part, of a generating unit for inspection, maintenance, or repair with approval of RTO.

    Planned Transmission Outage

    Any transmission outage scheduled for the performance of maintenance or repairs or the implementation of a system enhancement which is planned in advance for a pre-determined duration and which meets the notification requirements for such outages as specified by RTO.

    Planning Period

    The 12 months beginning June 1 and extending through May 31 of the following year. The planning Period may also be referred to as the Planning Year or Delivery Year.

    Planning Year

    The 12 months beginning June 1 and extending through May 31 of the following year. Planning Year may also be referred to as the Planning Period or Delivery Year.

    Point(s) of Delivery (POD)

    Point(s) on the transmission provider's transmission system where capacity and energy transmitted by the transmission provider is made available to the receiving party;

    Point-to-Point Transmission Service

    The reservation and transmission of capacity and energy on either a firm or non-firm basis from the Point(s) of Receipt to the Point(s) of Delivery.


    Power is the rate at which energy is transferred, used, or transformed. It is measured in watts.

    Price Node (Pnodes)

    A single point or a subset of points where a physical injection or withdrawal of energy is modeled and for which a locational marginal price (LMP) is calculated and used for financial settlements.

  • R

    Ramp Rate

    The rate, expressed in megawatts per minute, at which a generating unit can change output level.

    Reactive Power

    The product of voltage and the out-of-phase component of alternating current. Reactive power, usually measured in VARs, is produced by capacitors and overexcited generators and absorbed by reactors and other inductive devices.

    Reactive Service

    Reactive Service maintains transmission voltages within acceptable limits. Generators whose active energy output is altered at the request of RTO for the purpose of maintaining reactive reliability are credited hourly for lost opportunity costs if their output is reduced or suspended and credited in accordance with balancing operating reserve credit calculations if their output is increased. Generators operating as synchronous condensers for the purpose of maintaining reactive reliability at the request of RTO are credited for each hour (or partial hour) of condensing.

    Real-Time Energy Market

    The real-time energy market is a balancing market in which the clearing prices are calculated every five minutes based on the actual system operations security-constrained economic dispatch. The Real-Time Energy Market is based on the concept of Locational Marginal Pricing and is settled based on actual hourly (integrated) quantity deviations from day-ahead scheduled quantities and on real-time prices integrated over the hour.


    The right of a transmission provider to interrupt all or part of transmission service for any reason, including economic, is consistent with Federal Energy Regulatory Commission policy and the transmission provider’s transmission service tariffs or contract provisions.

    Redispatch Cost

    The cost to increase and/or decrease output from generation to manage transmission congestion.


    The capability of a specific resource with appropriate telecommunications, control, and response capability to increase or decrease its output in response to a regulating control signal to control for frequency deviations.

    Regulation Signals

    Signals generated by the RTO control center and sent to controllable entities to adjust generation or consumption quickly to keep RTO’s Area Control Error within allowable limits.

    Reliability Requirement

    The target level of capacity resources (in megawatts) required to meet Reliability standards and principles.

    Renewable Portfolio Standard

    A renewable portfolio standard is a regulation or law that requires a defined amount of energy to be delivered from renewable resources. Many states within the RTO service area have renewable portfolio standards.


    The capacity that currently is not being used but that can be quickly available for the unexpected loss of generation.

    Retail Customer

    The end-user customer purchases electricity from a state-licensed distribution company or a state-licensed alternate supplier at a retail rate.

    Retail Market

    End-use customers purchase electricity through a retail market. In some retail markets, there may be only one choice of an electric distribution company in an area through which customers can purchase electricity, while other markets may have multiple choices.

    Right of First Refusal (ROFR)

    Right of First Refusal (ROFR) means that incumbent transmission owners have the right to construct, own, and propose cost recovery for any new transmission project that is located within their service territory and approved for inclusion in a transmission plan developed through FERC guidelines. The FERC has stated in Order 1000 that it is unjust and unreasonable to grant incumbent transmission providers a federal right of first refusal with respect to certain transmission projects because doing so may result in the failure to consider more efficient or cost-effective solutions to regional needs and, in turn, result in the inclusion of higher-cost solutions in the regional plan.

    RTO Control Center

    The equipment, facilities, and personnel used by RTO to coordinate and direct the operation of the RTO RTO and to administer the RTO Interchange Energy Market, including facilities and equipment used to communicate and coordinate with the Market Participants in connection with transactions in the RTO Interchange Energy Market or the operation of the RTO.

    RTO Monitored Facilities

    Those facilities above 100kV are both monitored in the RTO EMS and included in the LMP calculations for congestion management.

    RTO Region

    RTO Region represents the aggregate of all the RTO transmission zones.

    RTO Reliability Facilities

    Those facilities above 100kV are monitored as part of the NERC BES set of facilities but are not included in the LMP calculations for congestion management.


    The control area recognized by NERC coordinates the movement of wholesale electricity in MISO and PJM.

  • S

    Self-Scheduled Resource

    A generating resource that is turned on by the operating company and committed into the energy market by the operating company. Self-scheduled resources are also known as "running for company."

    Solar Magnetic Disturbance

    Events that occur on the earth as a result of solar activity. The sun emits a stream of charged particles that flow to Earth and disturb Earth’s magnetic field causing unwanted flows and possible damage in electrical transmission systems.


    The balancing authority (BA) in which the generation is located for an interchange transaction. (This will also be a sending balancing authority for the resulting interchange schedule.)

    Spot Market Energy

    Energy bought or sold by Market Participants through the RTO Interchange Energy Market at Locational Marginal Prices.

    Static Var Compensator (SVC)

    A static Var compensator is an electrical device for providing fast-acting, reactive power compensation on high voltage electricity transmission networks.


    A substation changes energy from one amount of voltage to another, often in the direction of a higher voltage to a lower voltage. A high-voltage transmission line will connect to a substation to move electricity into a low-voltage distribution system on its way to consumers.

    Summer Peaking Zone

    A system whose maximum one-hour load during the period of June through September exceeds its winter peak.


    A transient variation of current, voltage, or power flow in an electric circuit.

    System Operating Limit (SOL)

    The value (such as MW, MVAR, amperes, frequency, or volts) that satisfies the most limiting of the prescribed operating criteria for a specified system configuration to ensure operation within acceptable reliability criteria. System Operating Limits are based upon certain operating criteria.

  • T


    The process by which measurable electrical quantities from substations and generating stations are instantaneously transmitted using telecommunication techniques.

    Tie Line

    A circuit connecting two or more Control Areas or systems of an electric system.


    An electromagnetic device for transforming energy from one circuit to another of different voltage levels as in an alternating current system.

    Transmission Constraints

    Limitations on a transmission line or element that may be reached during normal or contingency system operations.

    Transmission Facilities

    Facilities within the RTO Region that have been approved by or meet the definition of transmission facilities established by FERC; or have been demonstrated to the satisfaction of the Office of Interconnection to be integrated with the RTO Region transmission system and integrated into the planning and operation of the RTO Region to serve all of the power and transmission customers within the RTO Region.

    Transmission Loading Relief

    A NERC procedure developed for the Eastern Interconnection to mitigate overloads on the transmission system by allowing reliability coordinators to request the curtailment of transactions that are causing parallel flows through their system.

    Transmission Owner

    A member that owns or leases, with rights equivalent to ownership, Transmission Facilities. Taking transmission service is not sufficient to qualify a Member as a Transmission Owner.

    Transmission System

    The facilities owned, controlled or operated by the transmission provider within the RTO are used to provide Transmission Service.

  • U, V, W, & Z

    Unforced Capacity (UCAP)

    The MW value of a capacity resource in the RTO Capacity Market. For generating units, the unforced capacity value is equal to the installed capacity of the unit multiplied by (1- unit's EFORd). For demand resources and energy efficiency resources, the unforced capacity value is equal to demand reduction multiplied by Forecast Pool Requirement.


    If the flow of electricity through a wire was like the flow of water through a pipe, voltage is akin to the difference in water pressure between two points in the pipeline. It is measured in volts.

    Voltage Reduction

    A means to reduce customer demand by lowering the voltage on the distribution side of the system.


    A watt is a unit of power that measures the rate at which energy is transferred or converted. A 100 watt light bulb, for example, is rated to consume 100 watts of power when turned on.

    Wholesale Customer

    An entity that purchases electric energy for resale, or uses transmission service for such transactions, within the RTO RTO.

    Wholesale Market

    Like other commodities, electricity is bought and resold multiple times before being delivered to the end-use customer. These transactions form the wholesale electricity market. Suppliers that sell electricity to retail consumers or other large-scale consumers purchase energy through the wholesale market. RTO operates a competitive wholesale market for electricity in the region RTO serves.


    A transmission owner's area within the RTO Region.